Proposed Revision of Guideline , Managing the Risk of Legionellosis Associated with Building Water Systems

Transcription

1 ASHRAE Guideline R Public Review Draft Proposed Revision of Guideline , Managing the Risk of Legionellosis Associated with Building Water Systems Second Public Review (February 2018) (Complete Draft for Full Review) This draft has been recommended for public review by the responsible project committee. To submit a comment on this proposed guideline, go to the ASHRAE website at and access the online comment database. The draft is subject to modification until it is approved for publication by the Board of Directors and ANSI. Until this time, the current edition of the guideline (as modified by any published addenda on the ASHRAE website) remains in effect. The current edition of any standard may be purchased from the ASHRAE Online Store at or by calling or (for orders in the U.S. or Canada). The appearance of any technical data or editorial material in this public review document does not constitute endorsement, warranty, or guaranty by ASHRAE of any product, service, process, procedure, or design, and ASHRAE expressly disclaims such ASHRAE. This draft is covered under ASHRAE copyright. Permission to reproduce or redistribute all or any part of this document must be obtained from the ASHRAE Manager of Standards, 1791 Tullie Circle, NE, Atlanta, GA Phone: , Ext Fax: standards.section@ashrae.org. ASHRAE, 1791 Tullie Circle, NE, Atlanta GA

2 CONTENTS ASHRAE Guideline R Managing the Risk of Legionellosis Associated With Building Water Systems FOREWORD PURPOSE SCOPE DEFINITIONS OF TERMS LEGIONELLOSIS AND LEGIONELLA POTABLE WATER SYSTEMS ORNAMENTAL WATER FEATURES HEATED WHIRLPOOL SPAS/HOT TUBS OPEN-CIRCUIT COOLING TOWERS, CLOSED-CIRCUIT COOLING TOWERS AND EVAPORATIVE CONDENSERS DIRECT EVAPORATIVE AIR COOLERS, MISTERS (ATOMIZERS), AIR WASHERS, AND HUMIDIFIERS INDIRECT EVAPORATIVE AIR COOLERS AIR HANDLING EQUIPMENT OTHER BUILDING WATER SYSTEMS WHERE LEGIONELLA MAY GROW...39 ANNEX A BIBLIOGRAPHY...42 ANNEX B GUIDANCE FOR US REGULATIONS ON DRINKING WATER TREATMENT AND ON CHEMICALS USED FOR POTABLE AND NON-POTABLE WATER TREATMENT...45 ANNEX C TESTING FOR LEGIONELLA...46 ANNEX D GUIDANCE ON PERSONAL PROTECTIVE EQUIPMENT FOR USE WHEN THERE IS RISK OF EXPOSURE TO CONTAMINATED AEROSOLS...52

3 (This foreword is not part of this guideline. The informative material it contains has not been processed according to the ASHRAE requirements for a guideline and may contain material that has not been subject to public review or a consensus process. Unresolved objectors on informative material are not offered the right to appeal at ASHRAE.) FOREWORD The purpose of ASHRAE Guideline 12 is to provide information and guidance to assist in control of legionellosis associated with building water systems. It is also intended to provide guidance useful in the implementation of ASHRAE Standard 188, Legionellosis: Risk Management for Building Water Systems. Guideline 12 does not recommend or rely on users of the guideline having training or certification in any hazard analysis, risk assessment or risk management methodologies. Legionellosis refers to two distinct clinical illnesses. When the bacterium Legionella causes pneumonia, the disease is referred to as Legionnaires disease (LD). The Centers for Disease Control and Prevention (CDC) estimates that each year there are between 8,000 and 18,000 cases of LD in the United States and that more than 10% of these cases are fatal. Legionella can also cause a less-severe influenza-like illness known as Pontiac fever. Most cases of legionellosis are the result of exposure to Legionella associated with building water systems. This guideline is intended for use by building owners of human-occupied buildings and those involved in the design, construction, installation, commissioning, management, operation, maintenance, and service of centralized building water systems and components, as well as by manufacturers of associated equipment. The presence of Legionella bacteria in building water systems is not by itself sufficient to cause LD. Other factors necessary for LD to occur include environmental conditions that promote the growth of Legionella, a means of transmitting the bacteria to people in the building, such as aerosol generation, and exposure of susceptible persons to water colonized by Legionella and that is inhaled or aspirated into the lungs. Legionella bacteria are not transmitted person-to-person or by normal consumption of contaminated water. Persons who are more susceptible than the general population to developing legionellosis include but are not limited persons receiving treatment for burns, solid organ transplantation or bone marrow transplantation or chemotherapy for cancer, and to persons that smoke or are elderly, have renal disease, or that have diabetes or chronic lung disease. Guideline 12 consists of numbered informative sections and annexes. The sections and annexes include information and guidance that may be helpful to assist in the control of legionellosis in building water systems. Building water systems vary substantially in their design, use and operation and in their capability for transmission of Legionella. Scientific evidence is either lacking or inconclusive in certain aspects of Legionella control. Therefore, the references and bibliography in Guideline 12 provide sources for additional information about Legionella and legionellosis. ASHRAE Standing Standard Project Committee (SSPC) 188 is responsible for Guideline 12, and has devoted a considerable amount of time and thought to resolving the concerns of affected and interested parties. The committee thanks everyone who participated in the development of the guideline, especially those who have made or make public review comments. Since changes to improve the guideline are anticipated, Guideline 12 is anticipated to be on continuous maintenance, permitting it to be updated through the publication of approved addenda. The planned schedule for republication with approved addenda and errata is anticipated to be every third year. Comments to documents under continuous maintenance may be made through the following link: technology/standards--guidelines/continuous-maintenance. PURPOSE The purpose of this guideline is to provide information and guidance for control of legionellosis associated with building water systems. SCOPE 2.1. This guideline applies to new and existing centralized cold and hot potable building water systems and to nonpotable building water systems in human-occupied commercial, institutional, multi-unit-residential and industrial buildings, including, but not limited to, hotels, office buildings, hospitals and other health care 1 ASHRAE Guideline R

4 facilities, assisted living facilities, schools, universities, commercial buildings, industrial buildings, and centralized systems in multifamily residential buildings. While buildings with non-centralized building water systems and single-family residential buildings are not included, some of the information may be useful for such building water systems This guideline is intended for use by building owners and those involved in the design, construction, installation, commissioning, management, operation, maintenance and service of centralized building water systems as well as by manufacturers of associated equipment This guideline is also intended for use in the implementation of ANSI/ASHRAE Standard 188, Legionellosis: Risk Management for Building Water Systems, and does not recommend or rely on users of the guideline having training or certification in any hazard analysis, risk assessment or risk management methodologies. DEFINITIONS OF TERMS aerosol: a fine spray of microscopic water droplets that may contain Legionella bacteria, which can be deeply inhaled into the lungs. AHJ: see authority having jurisdiction (AHJ). analysis of building water systems: the systematic evaluation of potentially hazardous conditions associated with each step in the process flow diagrams. aspiration: the unintended entry of liquids into the lungs, generally while eating or drinking. at-risk individual: any person who is more susceptible than the general population to developing legionellosis because of factors such as age, health, medication, occupation, or smoking. authority having jurisdiction (AHJ): an organization or office or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure. backflow: unwanted flow of water in the direction opposite from that intended. biocide: see disinfectant. biodispersants: chemicals added to water that are intended to penetrate, loosen and disperse microbial masses or deposits. biofilm: a group of microorganisms, embedded in slime, that adhere to a moist surface. bleed: see blow-down. blow-down (bleed): the intentional discharge of system water and typically replacing it with supply water. building water systems: potable hot and cold water systems and non-potable water systems, in the building or on the site. CDC: United States Centers for Disease Control and Prevention. centralized building water system: any system that distributes water to multiple uses or multiple locations within the building or site. concentration ratio: see cycles of concentration. control: to manage the conditions of an operation in order to maintain compliance with established criteria. control limit: a maximum value, a minimum value or a range of values to which a chemical or physical parameter associated with a control measure must be monitored and maintained in order to reduce the occurrence of a hazardous condition to an acceptable level. control location: a point where a physical, mechanical, operational or chemical control measure is required. control measure: a disinfectant, heating, cooling, filtering, flushing or other means, methods, or procedures used to maintain the physical or chemical conditions of water to within control limits. 2 ASHRAE Guideline R

5 corrective action: action to be taken to return control values to within established limits, when monitoring or measurement indicates the control values are outside the established control limits. cross connection: a physical connection between potable and non-potable water systems or between hot and cold potable water systems. cycles of concentration (concentration ratio): the ratio of the concentration of dissolved solids in the evaporative cooling system to the concentration of dissolved solids in the make-up water. dead leg: a section of pipe, a component, or a vessel that contains water but has no flow or is infrequently used. disinfectant (biocide): chemical agent or physical treatments used to kill or inactivate microorganisms. disinfectant (disinfection) byproduct: chemical, organic, and inorganic substances that can form during a reaction of a disinfectant with materials in the water, such as organic matter. disinfectant residual (free disinfectant residual, residual): the net amount of a chemical disinfectant remaining in treated water after chemical demand exerted by the water is satisfied. disinfection: the process of killing or inactivating pathogens. disinfection, secondary: application of a disinfectant to water leaving a drinking water treatment plant and intended to provide continuing disinfection as water moves through the water utility water distribution system. disinfection, supplemental: on-site application of a means of disinfection to water in the building water system. drift: water mist or small droplets carried by the air, part of which may be an aerosol. ecosystem: a biological community of interacting organisms and their physical environment. free disinfectant residual: see disinfectant residual. growth: (amplification) a significant increase in the numbers of Legionella. hazard: Legionella bacteria in a building water system that, in the absence of control, can cause harm to humans. hazardous condition: a condition that contributes to the potential for harmful human exposure to Legionella. HVAC: heating, ventilation and air conditioning immunocompromised: a condition describing an individual who has increased susceptibility to infections due to existing human disease, medication regimens or other types of medical treatment. (See: at-risk) Legionella: the name of the genus of bacteria that was subsequently identified as the causative pathogen associated with the 1976 outbreak of disease at the American Legion convention in Philadelphia. Legionella are common aquatic bacteria found in natural and building water systems, as well as in some soils. legionellosis: the term used to describe Legionnaires disease, Pontiac fever and any illness caused by exposure to Legionella bacteria. mains (water utility distribution piping): water utility transmission pipes that carry water from a water treatment plant to the building water service entrance point. microbial: having to do with very small single celled organisms, including bacteria, protozoa, viruses and some algae and fungi, especially those harmful to humans. monitoring: conducting a planned sequence of observations or measurements of the physical and chemical characteristics of control measures. non-oxidizing biocides: agents that can kill or inhibit growth of microorganisms by a mechanism other than causing them to lose electrons (oxidation). non-potable: water that is not fit for drinking or for personal culinary use and that has the potential to cause harmful human exposure to Legionella. outbreak: two or more occurrences of legionellosis linked to the same site occurring at about the same time. 3 ASHRAE Guideline R

6 OSHA: the US Occupational Safety and Health Administration. oxidizing biocides: agents, such as chlorine, that can cause microorganisms to lose electrons (oxidation), resulting in damage or death. points of use: see water use end points. potable water system: a building water distribution system that provides hot or cold water intended for direct and indirect human contact or consumption. process flow diagram: a step-by-step drawing of a building water system that includes the location of all water processing steps, including, but not limited to, conditioning, storing, heating, cooling, recirculation, and distribution that are part of the building water systems. Program: the water management program. residual: see disinfectant residual. risk: the potential for harm to humans resulting from exposure to Legionella. risk management: systematic practices to reduce risk. secondary disinfection: see disinfection, secondary. siphoning: unwanted reverse water flow and mixing of one liquid into another, due to atmospheric pressure, applied system pressure or induced system pressure. supplemental disinfection: see disinfection, supplemental. taps: see water use end points. testing: conducting a planned sequence of observations or measurements of physical, chemical or microbial characteristics of water to assess whether conditions throughout building water systems meet the goals set by the group or individual responsible for developing, implementing and maintaining the water management program. turbid: see turbidity. turbidity (turbid): the loss of water transparency due to the presence of suspended particulates making the water appear discolored. validation: initial and ongoing confirmation that the Program, when implemented as designed, effectively controls the hazardous conditions throughout the building water systems. verification: initial and ongoing confirmation that the Program is being implemented as designed. water age: the residence time of the water in one or more locations in the building water system. water management program (Program): the risk management plan for the prevention and control of legionellosis associated with building water systems, including documentation of the plan s implementation and operation. water service disruption: planned or unplanned events that reduce water delivery pressure below 20 psi (140 kpa) and that are caused by, but not limited to, new construction tie-ins; replacement of valves, hydrants, or meters; pumping failures; pipeline breaks; and other system repairs or emergency conditions. water use end points (points of use, taps): the points at which water exits from all potable and non-potable building water systems, fixtures and equipment. water utility: entity that provides potable water to buildings for use in building water systems. water utility distribution piping: see mains. LEGIONELLOSIS AND LEGIONELLA This section contains information on Legionella and legionellosis intended to provide context for the practical information and guidance contained in Sections 5 12 and Annex C and D of this guideline. 4 ASHRAE Guideline R

7 4.1. Infection and Disease Legionellosis is a broad term for illness caused by any of at least 60 species of Legionella bacteria. 1 Legionnaires disease and Pontiac fever are the two most common types of legionellosis. Legionnaires disease is a severe form of pneumonia, which frequently requires hospitalization. While of approximately 9% of Legionnaires disease cases are fatal overall, mortality associated with healthcare-associated Legionnaires disease is higher at 25% (. 2,3) Legionnaires disease occurs when Legionella bacteria invade human immune cells in the deep regions of the lungs. Pontiac fever is a self-limited, influenza-like illness that may often go undetected and is not associated with mortality. People at highest risk for Legionnaires disease are smokers; those receiving treatment for burns or chemotherapy for cancer; those who have undergone solid organ transplantation, or bone marrow transplantation; those with underlying diseases, such as cancer, renal disease, diabetes and chronic lung disease; those who are taking drugs that weaken the immune system; those who are otherwise immunocompromised; and the elderly. 4 However, many cases have been reported in otherwise healthy individuals and in all age groups, including infants. Most cases of Legionnaires disease are sporadic, meaning they are not associated with a known outbreak. 5 Infection is possible in any building environment where people can be exposed to water contaminated with Legionella. In the case of aerosols, the fine spray of microscopic water droplets may not be visible. Infection is also possible by aspiration, where water contaminated with Legionella can unintentionally enter the lungs, after eating or drinking. The Legionella contaminated water is usually associated with human-made water systems, such as plumbing systems, cooling towers, decorative fountains and hot tubs. However, Legionnaires disease is relatively rare, accounting for approximately 2-5% of community-acquired pneumonia cases. Legionnaires disease outbreaks are most often associated with water systems in hotels, hospitals, long-term care facilities, resorts, and cruise ships Legionella There are many different species and species serogroups of Legionella bacteria. The majority of disease is caused by species Legionella pneumophila. There are at least 15 serogroups of Legionella pneumophila, however serogroup 1 is responsible for most reported cases. The distribution in the environment of individual Legionella strains may vary by location and over time. The distribution of strains also varies worldwide. Legionella colonization of individual building water systems is related to site-specific conditions, such as system design, system operation and building water system disruptions. The ability of various Legionella species, serogroups, and subtypes to cause disease in all populations is unknown. Therefore, it is important to consider any Legionella strain potentially disease causing. Microbial testing that indicates the presence of a large quantity of a Legionella strain with low disease-causing potential may represent little or no potential for disease in humans, while the presence of a small quantity of a Legionella strain with high disease-causing potential may represent a relatively higher potential for disease in humans. However, the detection of elevated levels of Legionella, regardless of strain, indicates that conditions in the water system are favorable to the growth of legionellae. Further, the detection of Legionella in a building water system, even strains associated with outbreaks, does not guarantee the occurrence of disease in humans. Likewise, the absence of detectable Legionella in a water system does not guarantee that disease will not occur. When Legionella are present in water, the risk of human infection depends on a number of factors, including but not limited to: physical and chemical conditions favorable for Legionella growth a mechanism for environmental transmission of an aerosol containing Legionella, such as a faucet, shower head, cooling tower, water feature or spa exposure through inhalation or aspiration of water into the lungs the ability of the bacteria to cause disease susceptibility of the human host Habitats Legionella are common freshwater microorganisms, present in both natural and human-made aquatic environments as well as in soils. Legionella spend much of their aquatic life cycle in association with other microorganisms, including bacteria, fungi, and protozoa in biofilms. In biofilms, Legionella are protected from environmental stressors, such as extreme temperatures and disinfectants, and can obtain nutrients they need to multiply. Biofilms may be found on any continually moist substrate, though some materials may be more readily colonized than others. Established biofilms are extremely difficult to remove and may serve for decades as reservoirs 5 ASHRAE Guideline R

8 for Legionella contamination. Even when the Legionella in the biofilm are killed, if the biofilm structure remains it may be recolonized. Protozoa play an important role in Legionella growth, virulence and transmission. 6 Legionella are known to grow within protozoa associated with biofilms. When protozoa are exposed to environmental stressors, such as disinfectants and high temperature, the formation of a protective cyst is triggered. Legionella within the cyst are also protected from these stressors. It is believed that human disease results from Legionella exploiting and replicating within human immune cells in a manner similar to the way they exploit and replicate within their natural protozoan hosts Legionella in Building Water Systems Legionella are present, often in very low or undetectable concentrations, in most natural water sources. Physical and chemical conditions in water utility distribution systems and building water systems may support significant increases in the numbers of Legionella. When treated water leaves a drinking water treatment plant, it typically is dosed with a disinfectant in a process called secondary disinfection. Secondary disinfection is intended to establish and carry a persistent, protective disinfectant residual to reduce the presence of disease-causing organisms. However, treated drinking water is not required to be free of all microorganisms. The treated water flows through the water utility distribution system, including water transmission mains, where it is subject to biofilm formation and microbial colonization. As a result, water entering the building is a source for Legionella in building water systems. Buildings that use untreated groundwater may also have Legionella present from the source. Building water systems also have characteristics that can make them prone to significant biofilm formation, microbial colonization and Legionella growth, such as: Water temperature. Many areas of the building water system contain water within a temperature range that supports the growth of Legionella. Low or no disinfectant residual. After water enters a building, factors such as increased water temperature, some types of water treatment, such as filtering with activated carbon and some conditioning processes, such as water softening, can deplete the disinfectant residual. Water age. The longer the residence time of water in the building water system after it enters a building, the greater the depletion of disinfectant residual and the greater the likelihood that water temperatures will move towards temperatures favorable to Legionella growth. Water age is especially characteristic of buildings with large or complex plumbing systems and variable occupancy rates. Dead legs. Legionella can thrive in locations where there is little or no flow, such as dead legs. Dead legs can provide conditions that favor growth and can be a source for reseeding of Legionella into the rest of the building water system. Cross connections. The plumbing systems in buildings offer numerous opportunities for cross connections between potable and non-potable water, which can introduce Legionella into the potable water. Cross connections between hot and cold water can result in water temperatures favorable for Legionella growth. Plumbing materials. Building water systems are constructed using a greater variety of materials than utility water distribution systems. These materials include copper, brass, galvanized steel and a wide range of plastics and elastomers. These materials may be adversely affected by treatment chemicals, may provide nutrients that can support the growth of Legionella, may reduce disinfectant residuals and may promote biofilm formation. Accumulation of sediment. Building water systems have numerous places where sediment can accumulate. Sediment can provide a home for biofilm and can insulate Legionella from disinfectants and elevated water temperatures. Filters, by design, accumulate sediment and if not maintained properly can provide a substantial growth media for bacteria and diminish disinfectant residual. After it is received, potable water in buildings may be processed in many ways. For example, it may be conditioned, filtered, stored, heated, cooled, tempered, and distributed. The physical, chemical, and biological quality of the water may be changed by each of these processes in ways that can increase the likelihood of microbial growth and biofilm formation Intrusion (Legionella getting into the system) 6 ASHRAE Guideline R

9 Legionella can be introduced into the building water system in a number of ways. Legionella frequently are present in small, sometimes undetectable numbers in water supplied to buildings, even when the water delivered to the building complies with all applicable regulations. Disruptions, such as water main breaks, firefighting use, water line construction and sudden change in water pressure can disturb biofilm and stir up sediment in the water distribution system and mains, mixing these into the water delivered to the building. These disruptions can cause a spike in the number of Legionella, protozoa, and other contaminants in the water supplied to a building and make the water turbid. When this microbe-rich, turbid water enters a building water system, the contaminants may consume chemical disinfectants, provide nutrients for microbial growth and create layers of sediment that can provide protection to Legionella and their hosts. Other points for the intrusion of Legionella include, but are not limited to, crossconnections with fire protection piping or other untreated water and siphoning or backflow from non-potable water through plumbing fixtures Growth Biofilms play an important role in Legionella growth. Biofilms are complex and dynamic microbial ecosystems that form on surfaces within the building water systems. Biofilms impair the effectiveness of physical and chemical control methods, such as maintaining hot water temperatures and applying chemical disinfectants. Legionella are known to invade and replicate within protozoa that are associated with biofilms. While inside these protozoa, the Legionella bacteria are further shielded from disinfectants and temperature extremes. Key factors that contribute to Legionella growth include sediment, temperature, water age, and disinfectant residual. Sediment. The accumulation of sediment, such as scale, dirt, mineral deposits, etc., in a building water system can create an environment that supports Legionella growth. Sediment provides a high-surface area structure on which biofilm can grow. It also acts as a thermal insulator protecting Legionella from high temperatures and as a barrier to chemical disinfectants. 7 Plumbing components that are prone to accumulating sediment include, but are not limited to, expansion tanks, water heater storage, oversized piping, and dead legs. Cooling tower components that are prone to accumulating sediment include, but are not limited to sumps, basins, and dead legs. Temperature. Water temperature is a significant factor that influences the survival and growth of Legionella. In laboratory controlled conditions, Legionella can generally grow at water temperatures between 25 C and 45 C (77 F and 113 F) and may grow very slowly at temperatures as low as 20 C (68 F), temperatures often found in many parts of building water systems. 8 The optimal water temperatures for Legionella growth are generally between 25 C and 42 C (77 F and 108 F). Legionella growth slows and they begin to die at water temperatures between 45 C and 49 C (113 F and 120 F). As water temperature increases, the time for Legionella to die becomes shorter and Legionella will die rapidly at temperatures at or above 70 C (158 F). Maintaining water temperatures that are sufficiently hot or cold throughout the building water system can be practically challenging, especially when the system includes un-insulated pipes, dead legs, long pipe runs, areas where cold water pipes are located near hot water, steam or other heated pipes, and situations where portions of the system may go unused for extended periods. Biofilm, debris, and accumulated sediment may provide thermal insulation sufficient for Legionella to survive, even when the water temperature is outside the optimum temperature range. Temperature controls may help to control the growth of Legionella, though hot water temperature above 49 C (120 F) may be necessary. 8 See Figure ASHRAE Guideline R

10 Figure Temperature Effects on Survival and Growth of Legionella in Laboratory Conditions (See Note 1) Note 1: In building water systems, the temperature below which Legionella is dormant, the temperatures and speed at which Legionella grow and the elevated temperatures and speed at which Legionella die are affected by numerous environmental variables, such as ph, salts and minerals, Legionella species, Legionella growth phase and association with biofilms. Water Age. The residence time of the water in one or more locations in the building water system is an important factor in Legionella growth. The probability of Legionella colonization and proliferation increases with water age. 9 Water age, frequently associated with low flow conditions, can lead to water temperatures favorable to Legionella growth, accumulation of nutrients, and loss of disinfectant residual. System design and component selection can affect water age. Water age also is affected by water use patterns, such as variations in occupancy of individual rooms, floors or sections of buildings and fluctuations in water usage associated with business cycles. Water age also is common in new construction where building water systems are completed, filled with water and tested, but then remain largely unused for extended periods before the building is occupied and normal water usage is established. Repurposing of facilities can also adversely affect water age. For example, a portion of a building that serves as a laundry will use significantly less water after it is repurposed to provide space for file storage, resulting in extended water age within supply pipes designed for the originally intended use. The extent of Legionella colonization and proliferation due to water age can be significant. Disinfectant Residual. Water treatment plants typically add a secondary chemical disinfectant, such as chlorine or monochloramine to the water leaving the treatment plant. The secondary disinfectant is intended to persist and control microbial growth in water throughout the distribution system. The disinfectant residual begins to decline as soon as water leaves the treatment facility. As a result, disinfectant residuals from the utility water system may not be high enough to limit Legionella growth in building water systems. Buildings 8 ASHRAE Guideline R

11 farthest from the water treatment plant may receive water with little or no remaining disinfectant residual. Generally, the lower the concentration of disinfectant residual in the supply water entering the building, the more likely it contains microorganisms, including Legionella. However, even when water entering the building has a high disinfectant residual, this residual may not persist throughout the building water systems all the way to the points of use. Disinfectant residual declines as water ages and water temperature increases, leading to higher levels of contamination. There may be no residual disinfectant remaining after the water is heated for use in the hot water system. Lack of a persistent disinfectant residual throughout the various building water systems may increase the likelihood of Legionella growth. Addition of a supplemental disinfectant may be required to generate a disinfectant residual throughout building water systems Transmission (Legionella Release Such That People Can Be Exposed) There are numerous ways Legionella can be transmitted to and infect humans. There is evidence that inhalation of aerosols by a susceptible host is the primary means of infection. Other means of infection include aspiration of water containing Legionella while drinking, eating or vomiting, or introduction directly into the lungs during certain medical procedures. Legionella transmission from person-to-person contact has been reported only once. A variety of devices can produce aerosols containing Legionella in droplets of respirable size and have been associated with outbreaks of Legionnaires' disease. Such devices include, but are not limited to sink faucets, shower heads, cooling towers, evaporative condensers, decorative fountains, whirlpool spas, humidifiers, misters and respiratory therapy equipment that have been filled or rinsed with tap water. Dental unit water lines have been implicated as a source of Legionella transmission, which may occur by either inhalation of aerosols or aspiration of small volumes of water. 10 Ice machines have also been implicated as the source of transmission by aspiration in cases of Legionnaires disease. Outbreaks of legionellosis from whirlpool spas have occurred among both bathers and non-bathers. Data from a few outbreaks attributed to cooling towers suggest that Legionella-contaminated drift may have been carried beyond the building site. Prior to disease a number of events occur, some of which can be influenced by good engineering and maintenance practices. It is desirable to apply control measures to interrupt multiple steps in the chain of transmission of Legionnaire s disease (see Figure ). Steps 1 5 Factors and Events Leading to Legionnaires Disease Entry (Legionella entering Building Water Systems) Growth (A significant increase in the numbers of Legionella) Transmission (Aerosols from Faucets, Shower Heads, Cooling Towers, Fountains, Spa, Etc.) Exposure of Susceptible Human Host (Multiply in Human Host) Legionnaires Disease Factors: Temperature Disinfectant Residual System Design Dirt/Sediment Nutrients Microbial Associations Factors: Temperature Humidity Aerosol Production Distance from Source Microbial Associations Factors: Ability of bacteria to cause disease Virulence Age Disease Immunodeficiency Figure ASHRAE Guideline R

12 4.3. References: 1 Mercante, J.W. & Winchell, J.M. (2015). Current and Emerging Legionella Diagnostics for Laboratory and Outbreak Investigations. Clinical Microbiology Reviews, 28(1), Dooling, K.L. et al. (2015). Active Bacterial Core Surveillance for Legionellosis United States, MMWR. Morbidity and Mortality Weekly Report, 64(42), Soda, E.A. et al. (2017). Vital Signs: Health Care-Associated Legionnaires Disease Surveillance Data from 20 States and a Large Metropolitan Area United States, MMWR. Morbidity and Mortality Weekly Report, 64(22), Phin, N. et al. (2014). Epidemiology and clinical management of Legionnaires' disease. The Lancet Infectious Diseases, 14(10), Garrison, L.E. et al. (2016). Vital Signs: Deficiencies in Environmental Control Identified in Outbreaks of Legionnaires Disease North America, MMWR. Morbidity and Mortality Weekly Report, 65(22), Thomas, J.M., & Ashbolt, N.J. (2011). Do Free-Living Amoebae in Treated Drinking Water Systems Present an Emerging Health Risk? Environmental Science & Technology, 45(3), Lu, J. et al. (2015). Molecular Survey of Occurrence and Quantity of Legionella spp., Mycobacterium spp., Pseudomonas aeruginosa and Amoeba Hosts in Municipal Drinking Water Storage Tank Sediments. Journal of Applied Microbiology, 119(1), Kusnetsov, J. et al. (2003). Colonization of hospital water systems by legionellae, mycobacteria and other heterotrophic bacteria potentially hazardous to risk group patients. APMIS, 111(55), Wang, H. et al. (2014). Effect of Disinfectant, Water Age, and Pipe Materials on Bacterial and Eukaryotic Community Structure in Drinking Water Biofilm. Environmental Science & Technology, 48(3), Ricci, ML., Fontana, S., Pinci F., et al. (2012). Pneumonia Associated with a Dental Unit Waterline. Lancet, 379(9816), 684. POTABLE WATER SYSTEMS Note: Section 4 - Legionellosis and Legionella provides essential context for the practical information and guidance contained in this section. Users of this guideline are encouraged to review the information in Section 4 prior to implementing the guidance in Section 5. Characteristics of both hot and cold potable water systems influence colonization and subsequent growth of Legionella. Potable water systems that have been opened for repair, have experienced turbidity at multiple outlets or are being newly commissioned may be at increased likelihood of colonization. Components of potable water system that generate aerosols, when functioning as designed, include, but are not limited to, showerheads, faucets, aerators, and spray nozzles. Other sources of aerosols include water impingement on surfaces, such as sinks. A report by the US Centers for Disease Control (CDC) 1 states that 66% of all water borne disease outbreaks associated with potable water reported for the period were attributed to Legionella. Information and recommendations in this section apply to every portion of the hot and cold potable water systems, including all components and branches, from intake to taps. Methods for limiting Legionella growth in potable water systems include: keeping the system clean and free of sediment controlling hot-water and cold-water temperatures minimizing water age (the residence time of the water in the system) maintaining a disinfectant residual Maintaining a consistent, measurable disinfection residual throughout the entire potable water system can be an effective means of Legionella control, especially where water temperatures cannot be reliably maintained at target levels throughout the system or where stagnant or low-flow conditions may exist. 10 ASHRAE Guideline R

13 Cases of Legionnaires disease have been linked definitively to both hot and cold potable water systems in all types of facilities. Outbreaks from potable water systems typically are in relatively small clusters (i.e. small numbers of cases), but may also occur in larger clusters associated with water service disruptions. The duration of an outbreak can be relatively short, such as days or weeks, but is often for extended periods, such as months or years System description Potable water systems in buildings include all hot and cold potable water piping and system components, starting at the point where the supply water enters the building and ending where the water exits the piping at a fixture or feeds a non-potable use. Typically, backflow-prevention devices are used to separate the potable building water system from the water supplied to the building and from connected non-potable uses System Design/Engineering, Installation, Commissioning Planning to control the conditions that increase the potential for Legionella growth should start with the architecture, design, and engineering of buildings. Building layout and location of water fixtures will significantly affect the number, length, and complexity of pipe runs, the occurrence of dead legs and the use of water and energy. Process flow diagrams are important. Process flow diagrams for potable water systems, including hot and cold water systems, should be consistent with final system design and should be provided with the contract documents. In addition to relatively simple process flow diagrams, more detailed plans showing pipe sizes, valve and control locations, risers, direction of flow, the location of all points of use (faucets, showers, humidifiers, etc.), points for water treatment (if provided), points for confirmation (verification and validation) (if provided), the location and description of all water system components and other appropriate hot and cold potable water system information should be consistent with the final system design and should be provided with the contract documents. The following system design recommendations apply to every portion of the potable water system, including all components and branches, from the building water system intake to all points of use Piping system design A number of physical, chemical, or operational Legionella control measures can be facilitated by choices made when designing a plumbing system. Insulation. Hot and cold water pipes should be insulated where the possibility of gaining or losing heat may result in water temperatures within the range that supports Legionella growth. Examples of conditions that may increase the temperature of cold water in storage tanks and in pipes include heat exhaust from ice machines, heat exhaust from air conditioning and refrigeration condensers, warm exhaust vents and heat from unconditioned spaces, hot equipment rooms, uninsulated hot water pipes, steam pipes, flues for products of combustion, and pipes exposed to solar heat in or on outside walls and rooftops. Examples of conditions that may decrease the temperature of hot water are hot water storage tanks and pipes located in unheated mechanical rooms or near cold areas, especially in cold weather. Pipe sizing. Cold and hot water pipe runs (building main pipes and branches) should have pipe lengths and diameters that are sized to help increase water velocity and to minimize water age, disinfectant loss, and heat loss or gain. Dead legs. Dead legs should be eliminated or, where unavoidable, be made as short as possible. Where a dead leg cannot be avoided, the plumbing design should consider a means for flushing the dead leg or locating it in line with downstream fixtures. Purge and drain valves; recirculation. The use of pumped recirculation, purge valves, drain valves, and other means for reducing or eliminating stagnant conditions, reducing water age and flushing out sediment in the building water system should be considered. Water Pressure. Significant pressure differentials between hot and cold potable water can result in leakage between the hot and cold water and water temperatures conducive to Legionella growth or to possible cross contamination. Sampling points. The addition of points at appropriate locations throughout the hot and cold potable building water systems to provide access for sampling or measuring parameters (such as chemical, biological, temperature, pressure, ph) and for confirmation (verification and validation) should be considered. 11 ASHRAE Guideline R

14 Plumbing component design, selection, installation, and other considerations A number of physical, chemical, and operational Legionella control measures can be facilitated by choices made when selecting plumbing components: Local or point-of-use temperature mixing valves. Local or point-of-use temperature mixing valves may be used to reduce delivered hot water temperature in order to protect against scalding. If mixing valves are used, they should be installed at or near the point of use to minimize the volume of water remaining after mixing that may result in water temperatures within the range where Legionella can grow. Consider the maintenance requirements of mixing valves. For example, missing or failed check valves may result in conditions favorable to Legionella growth. Water storage tanks. Cold or hot water storage tanks should be correctly sized (not oversized) for the intended use. Circulation through the tank should be used to reduce water age and to help maintain temperatures outside the temperature range that supports Legionella growth (See Section Temperature Control). Design considerations should also include the provision for accessible drain valves, and orientation of storage tank connections to avoid stagnation and temperature stratification. Eye wash and safety showers. Infrequently used components, such as eye wash or safety shower stations, should be located at the beginning or middle of a branch and as near as practical to a commonly used fixture, in order to reduce stagnation and facilitate flushing. Faucets with flow restrictors. Flow restrictors increase water age. Flow restrictors, such as those that reduce flow to 1 gpm or less, can significantly increase water age in uncirculated hot and cold supply piping, particularly where faucets are used infrequently. Electronic or Sensor Faucets. Due to their mechanical complexity, electronic sensor faucets may produce conditions that permit Legionella growth. Floor drains. Floor drains should be located near pipes and components that require draining or flushing, such as emergency showers and eyewashes, water heaters, and other plumbing components and to provide the drainage needed for component cleaning, flushing and maintenance. Expansion tanks. Expansion tanks, including but not limited to pressure tanks, well tanks, and hydropneumatic tanks, should be designed, located, and oriented to minimize dirt accumulation, to minimize retained (stagnant) water, and to allow access for required maintenance. Maintenance access. Plumbing components should be accessible for maintenance and replacement. Examples of plumbing components that should be accessible are water hammer arrestors and all strainers, check valves, backflow preventers, and internal strainers, such as those in electronic faucets and pressure regulating valves. Reduction of stagnant and low flow conditions. In addition to piping system design, plumbing system components should be selected, placed into the plumbing system, and oriented to reduce or eliminate stagnant conditions, reduce water age, and to reduce water retention time in the system. For example: If low-flow fixtures and flow-restriction devices are used, provisions should be made to facilitate manual or automated flushing. When the design includes branches to seldom used hose valves, wall hydrants, or emergency fixtures, provisions should be made to facilitate manual or automated flushing. Where rinse and shower hoses are used, components that do not retain water after use should be specified. When using components such as air-chamber type water hammer arrestors, air bleed or relief valves, expansion tanks that do not have a flow-through design, they should be placed as close as practical to pipe runs that can provide a source for replenishment of disinfectant residual and designed to facilitate manual or automated flushing. When cold water storage tanks are used, the design should consider both water age and potential water temperature. For hot water storage tanks, see Section 5.3.1, Temperature Control (2). Cross Connection/Backflow Prevention. Where cross connection between potable and non-potable water or between hot and cold potable water can occur, such as at mop sinks with chemical mixing stations, supply to fire protection, other non-potable system, electronic faucets, certain types of single handle faucets, and local or point of use mixing valves, the design and installation should include adequate backflow prevention. 12 ASHRAE Guideline R

15 Water processing equipment; potential effects on disinfectant residual. Some potable water system components, such as water softeners, water heaters, carbon filters, and UV devices, may reduce or eliminate disinfectant residual. The plumbing system design and component selection should consider the potential effects on downstream disinfectant residual levels. Nutrients. Some chemicals and equipment used to treat potable water and plumbing systems may provide nutrients, such as phosphates and carbon, that promote microbial growth. The consequences of using chemicals and components that add nutrients should be considered Competing Objectives When implementing energy efficiency measures, water conservation and scalding-prevention initiatives, designers should consider the possible unintended consequences that can result in conditions that support Legionella growth. For example, use of flow restrictors on faucets intended to reduce water use may increase water age and reducing hot water temperatures or turning off hot water circulating pumps, intended to save energy, may result in temperatures favorable to Legionella growth Legionella Control Measures There are multiple physical, chemical, and operational Legionella control measures that can be applied together or individually to manage the physical and chemical conditions that facilitate intrusion, growth, and transmission of Legionella. Multiple control measures are often used in the same system. Available control measures include: temperature control supplemental disinfection/treatment flushing recirculation filtration cleaning and maintenance Building design, use, occupancy, location, and other factors can vary significantly across buildings. The selection of Legionella control measures appropriate for any facility may be unique. Depending on the circumstances, the use of one or more Legionella control measures may be appropriate Temperature Control Legionella survival and growth is temperature dependent. See Section Growth and Table Temperature effects on survival and growth of Legionella in laboratory conditions. Storage water heaters and hot water storage tanks should be adjusted or maintained so they deliver water consistently at or above 140 F (60 C), unless other compensating control measures are used. While the temperature in the storage tank must be maintained at or above 140 F (60 C), measures should be taken to prevent scalding. Note: The temperature set point indicated by the water heater thermostat may be different than the temperature of the water within the heater and exiting the heater. Note: Maintaining outlet water temperature at 140 F (60 C) does not guarantee Legionella control in water heaters or hot water storage tanks, especially if there is significant accumulation of sediment, stratification or long residence time. To counter significant stratification or long residence time, an intra-tank circulator loop can be added to water heaters and storage tanks. If such a loop is needed, a pipe from the inlet of the intratank circulator should connect the hot water supply or outlet location near the top of the water heaters and storage tanks. A pipe from the outlet of the intra-tank circulator should connect to the location specified in the manufacturer s installation instructions for connecting the return from the building hot water recirculation loop, taking care not to affect the building hot water return flow. If there are no such instructions, the outlet of the intra-tank circulator should connect to the lowest point on the water heaters and tanks. The pump and piping should be sized and operated as required to reduce Legionella growth in the water within the intra-tank circulation loop. A size often selected is a pump capable of one or two tank changes per hour. When a single intra-tank circulator is used to provide circulation for multiple water heaters and storage tanks, it should provide the same general water circulation as would be provided by individual intra-tank circulators. 13 ASHRAE Guideline R

16 Unless other compensating control measures] are used, hot water should be maintained consistently at or above 120 F (49 C) throughout the hot water system to the points of use and in the hot water return. Temperatures at or above 120 F (49 C) at fixtures have been used successfully as a Legionella control method, however water temperatures must be consistently maintained above 120 F (49 C) between the water heater and the fixtures to assure a minimum of 120 F (49 C) at the fixture and in the pipes returning to the water heater. Maximum allowable temperatures at the tap may require additional control or adjustment at or near the point of use to prevent scalding. Where thermostatic mixing valves are used to prevent scalding, they should be installed as close as practical to the point of use. Where centralized thermostatic mixing valves are used to reduce water temperature, the blended water temperature should be high enough to maintain a minimum of 120 F (49 C) throughout the distribution system, to the point of use and in the return pipe to the water heater. Maximum allowable temperatures at the tap may require additional control or adjustments at or near the point of use to prevent scalding Supplemental disinfection Maintaining a disinfectant residual throughout the potable water system helps to control Legionella growth. Water received from a water utility may or may not contain a consistent, measurable disinfectant residual. Even when the level of residual disinfectant in the water entering the building is at the intended level and meets regulatory requirements, the building potable water system may be colonized by Legionella and require supplemental disinfection. The building owner should consult with the water utility to determine the intended disinfectant level and should verify the actual level coming into the building. Even if the water received does contain a consistent, measureable disinfectant residual, the residual may dissipate while in the plumbing, before reaching the points of use. The rate at which disinfectants decay varies from one disinfectant to another and is affected by a number of factors, including water quality, time, ph, plumbing materials and water temperature. The higher the water temperature the faster the loss of disinfectant. In most cases, heating water for the hot water distribution system rapidly depletes any disinfectant. Supplemental disinfection is most often applied to heated potable water, but water in the cold water distribution system sometimes requires treatment. Because building design, use, occupancy, location and other factors can vary, the selection of Legionella control measures appropriate for any facility may be unique. No one plan or set of control measures is appropriate for all buildings. The following conditions are examples of circumstances for which supplemental disinfection should be considered as part of an overall water management program: Where there has been a case of legionellosis associated with the building water system Where building water system samples have tested positive for Legionella Facilities where hot and cold water temperatures recommended for Legionella control cannot be maintained reliably throughout the entire potable building water system Facilities where there is not a consistent, measurable disinfectant residual in the water received at the building water service entrance Facilities where there is not a consistent, measurable disinfectant residual at all hot and cold water taps after about one minute of flow Facilities with areas designated for treating or housing persons considered at-risk for Legionnaires disease, such as those receiving treatment for burns, chemotherapy for cancer, solid organ transplantation, bone marrow transplantation, those with underlying diseases, such as cancer, renal disease, diabetes and chronic lung disease, people that are immunocompromised, those taking drugs that weaken the immune system, the elderly, and smokers Supplemental Disinfection Used to Treat Building Water Systems The determination of need for treating potable water, and the selection of any particular treatment is a complex subject. Improper analysis may result in the use of disinfectants or treatments where they are not necessary. Inappropriate selection or improper application of disinfectants and treatments may be ineffective, may be harmful to building occupants, and may be damaging to building piping and to building water system components, controls, equipment, and fixtures. 14 ASHRAE Guideline R

17 If a decision is made to add a supplemental disinfectant or treatment to the water for Legionella control, the use of a number of commercially available disinfectants and disinfection treatments for this purpose (collectively supplemental disinfection methods) are described in the scientific literature. Examples include, but are not limited to, chlorine, chlorine dioxide, copper-silver ions, monochloramine, peracetic acid, hydrogen peroxide, ozone, and ultraviolet (UV) light. This guideline does not promote or endorse any particular supplemental disinfection method. To evaluate the available options, consult available scientific or technical evidence supporting and challenging the overall impact of the supplemental disinfection method on the building water systems, on the building occupants, and on building operation and personnel. Factors that should be considered when evaluating supplemental disinfection options include, but are not limited to: What is the amount of disinfectant residual in the water supplied to the building? What is the compatibility of the disinfectant in the water supplied to the building with the intended supplemental disinfection method? What is the intended disinfectant concentration for the supplemental disinfection under consideration? Can the intended parameters, such as disinfectant concentration at fixtures, be measured reliably in real time? What is the effectiveness of the supplemental disinfection method under the intended use conditions? Use conditions that should be considered include, but are not limited to, water temperature, water age, and water chemistry parameters, such as alkalinity, hardness, ph, concentration, and type of corrosion inhibitors in the water supplied to the building. What is the available scientific or technical evidence supporting and challenging the reliability and effectiveness of the supplemental disinfection method? What, if any, are the unintended consequences of the supplemental disinfection method, such as the potential for promoting growth of other microorganisms that may cause infection or disease, and the formation of toxic disinfectant byproducts in the building water system? Is the supplemental disinfection method under consideration, when applied appropriately, likely to have a significant adverse impact on plumbing materials, equipment, or components, including metals and nonmetals, such as plastics and elastomers? How and where is the supplemental disinfection method to be applied, controlled, and monitored to maintain the desired treatment level during normal and off peak operating conditions? What is the degree of complexity and technical skill necessary to verify the intended control limits are being met, for example, the measurement of disinfectant concentration or water quality at the fixtures? Does the person responsible for implementing the supplemental disinfection method have the technical skills, capability, and experience to safely and successfully complete the implementation, including pre-installation water chemistry evaluation, planning, installation, start-up, confirmation of post-treatment water chemistry and disinfectant byproducts, training, and support? Do the authorities having jurisdiction have any requirements that pertain to the supplemental disinfection method under consideration, such as maximum allowable disinfectant and disinfection byproduct levels and possible permitting requirements? See Annex B for guidance on US regulations Physical barriers: Screens and Filters Point-of-use devices. A physical barrier to environmental transmission of Legionella from the potable water system is sometimes established by means of point-of-use (POU) filters. Additionally, POU filters are sometimes used for short term intervention in areas intended to serve at-risk individuals, for the purpose of preventing contaminants in the water from exiting the system. POU filters with an effective pore size of 0.2 microns have been shown to prevent transmission of Legionella. POU filters should be replaced following the manufacturer s instructions. If the manufacturer s instructions are not followed, POU filters may become fouled and support microbial growth Point-of-entry devices. Physical removal of some contaminants from incoming water may be accomplished by means of point-of-entry (POE) screens and filters. These devices typically have pore sizes far too large to remove Legionella bacteria, but can be beneficial for removing particulates and nutrients that can deplete disinfectant residuals, contribute to sediment accumulation and create conditions that are favorable for Legionella growth. POE screens are useful in reducing the effects of water supply disruptions and pressure surges that can cause an increase in particulates and turbidity in 15 ASHRAE Guideline R

18 water supplied to the building. Filters may become fouled and support microbial growth. Some filter media, such as activated carbon, consume disinfectants Routine Flushing Routine flushing is the control measure most often used to help reduce water age. Flushing replaces aging water, in which the level of disinfectant residual is declining with residence time, with newer water. Flushing also helps purge accumulated sediment, deposits and turbid water from the water system. Flushing protocols typically include opening all taps and drain valves for the time necessary to purge the old or turbid water from pipes, fixtures, and other areas and components containing old or turbid water. Effective flushing can take from a few minutes to many hours, depending on the size of the system, pipe and component size, flow rates, the total volume of water, accumulated sediment, and deposits to be flushed. When flushing, the practitioner should consider use of auxiliary drain valves to facilitate flow through areas of the building water system or components that are not necessarily flushed by opening taps at normal points-of-use. Auxiliary drain valves also can help speed system flushing, especially where there are flow restrictions Hot Water Recirculation Recirculation is frequently used to maintain consistent water temperatures throughout the building hot water system within a target range (See: Section Growth and Table Temperature effects on survival and growth of Legionella in laboratory conditions ). In addition to maintaining target temperatures, recirculation helps prevent water age relative to uncirculated systems, especially in infrequently or inconsistently used portions of the system Routine Cleaning and Maintenance Routine cleaning and maintenance to remove biofilm, bacteria, scale, accumulated sediment, and other deposits are important Legionella control measures. Examples of building water systems components that should be considered for periodic cleaning and maintenance include faucets, showers, water storage tanks, filters, water softeners, electronic faucets, local and point-of-use mixing valves, water hammer arrestors, and non-flow through expansion tanks. Backflow prevention devices should be installed and maintained in good working order, and should be tested by a qualified technician in compliance with local codes and the authority having jurisdiction. Routine monitoring and repairs should be made in a timely manner to address conditions that may contribute to Legionella colonization of system components. When turbidity at multiple outlets occurs, consider flushing the building water system until water quality is restored. Examples of causes of turbidity include water distribution pressure loss and repressurization, water main breaks, water utility construction, and high water usage events such as hydrant flushing and firefighting. The water utility providing water to the building should be requested to provide notification of any water pressurization event Remedial Treatment Potable water systems colonized by Legionella sometimes require remedial treatment. Even when successful, remedial treatment is only a temporary measure. Re-colonization is very likely to occur unless the underlying reasons for Legionella colonization are addressed, and a proper water management program is implemented. If a decision is made to implement a remedial disinfection method for Legionella control, the use of a number of commercially available disinfectants and disinfection treatments for this purpose are described in the scientific literature. Examples include, but are not limited to chlorine, chlorine dioxide, copper-silver ions, hydrogen peroxide, ozone, and peracetic acid. This guideline does not endorse or promote any particular disinfectant/treatment. To evaluate the available options, consult available scientific or technical evidence supporting and challenging the disinfection s overall impact on the building water systems, on the building occupants and on building operation and personnel. Factors that should be considered when evaluating remedial disinfection/treatment options include, but are not limited to: Which systems require remedial treatment: the hot water system, the cold water system, or both the hot and cold water systems? 16 ASHRAE Guideline R

19 What is the expected extent and duration of disruption of normal operations, including setup and implementation? What is the available scientific or technical evidence supporting and challenging the reliability and effectiveness of the remedial disinfection method? What is the intended disinfectant concentration and contact time (duration) required for the remedial disinfection method under consideration? Can the intended parameters, such as disinfectant concentration at fixtures, be measured reliably in real time? Are there water quality parameters, such as ph, presence of corrosion inhibitors, or alkalinity that may affect the results of the remedial disinfection method under consideration? What, if any, are the unintended consequences of the remedial disinfection method, such as the potential for growth of other microorganisms that may cause infection or disease and the formation of toxic disinfectant byproducts in the building water system? Is the remedial disinfection method under consideration, when applied appropriately, likely to have a significant adverse impact on plumbing materials, including metals and non-metals, such as plastics and elastomers? How and where will the remedial disinfection method be applied, controlled, and monitored to maintain the desired treatment level? What is the degree of complexity and technical skill necessary to verify the intended control limits are being met, for example, the measurement of disinfectant concentration at the fixtures? Are water use restrictions/warning required during remediation? If physical and chemical parameters, such as building water system temperature and chemical concentration, are above the allowable regulatory or code limits, water restrictions may be required. These water restrictions may include a number of precautions, such as clearly posted out-of-service and warning signs and tag-out lockout procedures. If the building water system physical/chemical parameters are within the allowable regulatory code limits, water restrictions may not be required. What are the immediate possible health risks to building occupants, such as scalding or release of toxic fumes? Does the person responsible for implementing the remedial disinfection method have the technical skills, capability, and experience to safely and successfully complete the implementation, including planning, installation, treatment, confirmation of post-treatment water chemistry and disinfectant byproducts, training, and support? Do the authorities having jurisdiction have any requirements that pertain to the remedial disinfection method under consideration, such as maximum allowable disinfectant levels, maximum chemical concentrations, or water temperatures that can be discharged into the sewer system, and possible permitting requirements? See Annex B for guidance on US regulations Chemical Shock Chemical shock is remedial treatment to kill Legionella in hot or cold potable water systems, using chemical disinfectants, such as chlorine or chlorine dioxide for a relatively short period, for example, one to twenty-four hours, frequently at concentrations well above maximum levels permitted for potable water. Typically, the chemical disinfectant is introduced upstream of the area to be treated, which then distributes throughout the potable water system by sequential flushing every fixture until the intended disinfectant residual level is achieved. Because chemical shock typically utilizes chemical concentrations above the maximum levels permitted for potable water, adequate precautions should be taken to prevent occupants from consuming or being exposed to water with higherthan-allowed chemical concentrations. Reducing hot water temperatures supplied to the building hot water system during disinfection may reduce chemical demand. After completion of treatment, the system should be thoroughly flushed before use. Precautions should include advance occupant notification and frequently include warning signs. Some conditions may allow the use of a lower disinfectant concentration applied for a longer period of time. Some building use patterns may allow chemical shock treatment to be scheduled when the building is unoccupied or when occupancy is low. The potential for corrosion and other damage to plumbing system components and piping, including metals and non-metals, increases with disinfectant concentration, contact time, temperature, and the frequency at which such measures are implemented. Disinfection procedures designed for disinfecting water utility distribution systems may not be appropriate for building water systems and may result in significant damage. For example, the AWWA Standard for Disinfecting 17 ASHRAE Guideline R

20 Water Mains (C ) is an aggressive treatment procedure that may cause significant building water system damage and should not be used for this unintended purpose. Component and equipment manufacturers often provide the maximum chemical concentrations to which their products can be exposed. Disinfection with higher concentrations may cause damage and may invalidate the component and equipment manufacturers warranties Thermal Shock Thermal shock is the use of very-high temperature water for remedial treatment of a building hot water system colonized by Legionella. Thermal shock cannot and must not be used to treat cold water systems. Thermal shock is sometimes used for system components that can be isolated, such as hot water storage tanks. A typical thermal shock protocol for system wide treatment involves flushing all fixtures, including all sinks, showers and drain valves, for 20 minutes with water at 70 C (158 F). Thermal shock of system components that can be isolated can be effective. However, thermal shock of the entire potable hot water system has significant shortcomings. Thermal shock is frequently ineffective and often leads to rapid Legionella re-colonization. Legionella re-colonization levels may rebound to levels higher than pre-treatment. After water temperatures are restored, the surviving Legionella are likely to grow because of nutrients released by freshly killed microorganisms. 2 Water heaters that provide hot water to the building water system frequently are not capable of achieving, maintaining and delivering the volume of water at the temperature necessary to kill Legionella throughout the building hot water system. Even if the water heater is capable of providing adequate hot water, it may take extended periods of time and the very-high temperature water may not reach all portions of the system due to factors such as small pipe diameters, system orifices, low flow fixtures and dead legs. There is significant potential for severe scalding associated with the very-high water temperatures required for thermal shock. Damage to plumbing system components is likely. Many electronic faucets, shower mixing valves, plastic pipes and other components have manufacturer specified temperature limits of 140 F or lower, so treatment with higher temperatures may damage these materials and components, and may invalidate the manufacturers warranties. Some temperature limiting devices, such as mixing valves, some shower valves, and some sink faucets must be bypassed, removed, and manually disinfected. Very high water temperatures used for thermal shock may cause failure of elastomeric seals, causing a high probability of leakage across the hot and cold sides of these valves which may result in water temperatures within the range where Legionella can grow. Thermal shock may stress or damage other system components and materials in the building water system. During and after thermal shock, the allowable temperature of the water being flushed to waste must not exceed limits allowed by local codes. If the waste pipes are plastic, such as PVC, significant damage may result from flushing water hotter than 140 F. For these reasons, use of system wide thermal shock for remedial treatment of Legionella-contaminated plumbing systems is not recommended in most circumstances References 1 Beer, K. et al. (2015). Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water United States, MMWR. Morbidity and Mortality Weekly Report, 64(31), Temmerman et al. (2006); Falkinham, J., Hilborn, E., Arduino, M., Pruden, A., & Edwards, M. (2015). Epidemiology and Ecology of Opportunistic Premise Plumbing Pathogens: Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa. Environmental Health Perspectives, 123(8), ORNAMENTAL WATER FEATURES Note: Section 4 - Legionellosis and Legionella provides essential context for the practical information and guidance contained in this section. Users of this guideline are encouraged to review the information in Section 4 prior to implementing the guidance in Section 6. Ornamental or decorative water features ( water features ) are human-made fountains, waterfalls, cascades, sprays and the like that use water for architectural, decorative or aesthetic effects. Water features may be part of a building s water system and may be located indoors or outdoors. This guideline does not include guidance for fish ponds, natural bodies of water, natural waterfalls and water features that are intended for public interaction, such as swimming pools, wading pools, interactive fountains, water parks and the like. Water features that are intended for pubic interaction generally fall under the public health requirements for managing recreational water or swimming 18 ASHRAE Guideline R

21 pools as specified and enforced by the authority having jurisdiction. Design characteristics of water features may influence the colonization, survival and growth of Legionella. Even small water features that become colonized with Legionella can disseminate contaminated aerosols (water droplets and mists) into the air. Legionnaires disease has been linked to water features in facilities, including, but not limited to hospitals, long-term care, hotels and restaurants. Before installing an ornamental water feature, first consider the potential health and liability risks System Description Water features vary greatly in size, configuration and complexity. Water typically is either sprayed into the air or cascades over a medium, and then returns to a sump, basin or pool. Small tabletop water features may have only a water pump, while more complex water features often include an automatic water treatment system, one or more water pumps, water filters, valves, and specialty nozzles and lighting. Large outdoor fountains can be highly complex, consisting of millions of gallons of water, multi-stage water treatment systems, constant and variable speed pumps, computerized controls, specialty lighting systems, valves, specialty piping materials, compressed air injection systems, fixed and variable spray nozzles, solenoid valves, motorized valves and motorized nozzles. Designs can include elaborate performances specifically intended to attract large crowds. In addition, water features may have limited hours of operation which can encourage microbial growth due to water age, heat gain and loss of biocide residual. Sources of heat gain have the potential to increase water temperatures into the range that has been shown to support Legionella growth (25-45 C [ F]). In addition to the potential for solar heat gain, some water feature components can result in significant localized heat gains, such as from submerged incandescent lighting, lights over a large surface area of a water wall and submerged circulation pumps. Indoor water features can also gain heat when part of the system is located in unconditioned areas. Any increase in water temperature speeds the rate at which disinfectant residual is lost. Water features produce aerosols with droplets of various sizes, including sizes smaller than 5 micrometers that can be inhaled deeply into the lungs. Multiple cases and outbreaks of legionellosis have been associated with fountains that appeared to release little or no aerosols, such as small fountains with coarse sprays, cascading features and water walls. However, indoor water features release aerosols to a confined environment, where the aerosols are not readily diluted or dissipated. Outdoor water features release aerosols to an unconfined space, where they can more readily be diluted by fresh air and dissipated by wind. Water features near sources of heat or in warm climates are more likely to contain water at a temperature within the range favorable to Legionella growth (25-45 C [ F]). Intermittent operation may also create situations where water temperature increases in localized parts of the system. If a water feature is not drained and flushed after use, then the water should be circulated at least daily to maintain distribution of water treatment chemicals, even when the water feature is not being used. Water features are subject to contamination from a wide variety of sources, including materials scrubbed from the air and returned to the feature s water by falling water droplets, by organic and inorganic materials dropped, thrown or blown into the fountain and by rust and other materials from the water feature structure, piping and components. Water evaporation concentrates these contaminants and if not cleaned and managed, these contaminants can result in scale accumulation and can support microbial growth, including biofilms. Exposure of surfaces to light can result in increased algae growth. Algae and biofilm can support Legionella growth in water feature pools and basins that are less than 1 meter (3.3 feet) deep and on surfaces that may be wetted but not submerged or that may not be wetted continuously System Design/Engineering, Installation, Commissioning Planning to control the conditions that support Legionella growth in water features should start with design and engineering. System design, layout, piping configuration, pumps, water filters, lighting, system and system component locations, accessibility for maintenance and other design elements can significantly affect growth and transmission of Legionella. The following system design elements are recommended: Cool water temperatures should be maintained by locating indoor water features and all components inside conditioned space and by avoiding submerged heat-generating lighting. Water features using water that is recirculated should be equipped with a filter installed according the 19 ASHRAE Guideline R

22 manufacturer s instructions. Water features using water that is not recirculated should have provisions for routine draining, flushing and cleaning. Pumps and piping should be designed with flow rates sufficient to avoid low flow and poor water turnover. Sufficient water turnover and flow are needed to maintain water treatment applied for microbial control. Water features should not be located in areas with at-risk individuals or where the potential for aerosol exposure to at-risk individuals is known to exist. System design should allow for complete system drainage. Drains and sumps should be situated at the lowest point to allow complete system drainage of the water feature and all associated piping. There should be no points in the water feature, including system piping and components that cannot be completely drained. Pumps, filters and other components requiring cleaning or service should be readily accessible and have proper drainage. Systems should be cleaned and disinfected prior to commissioning. Systems that have been out of service should be cleaned and disinfected prior to startup. Indoor water features should be supplied with make-up water from a potable cold water source. Recycled or other non-potable water sources should not be used for indoor water features. Outdoor water features should be supplied with make-up water from a potable cold water source. Recycled water may contain contaminants and nutrients not present in potable water, however may be acceptable if pre-treated. Acceptability of pre-treated recycled water should be confirmed with the authority having jurisdiction. Supplying human-made water features with make-up water from natural water sources (such as lakes, rivers, ponds, rainwater or the like) or the use of grey water should be avoided. Ventilation and conditioned air should be directed toward an indoor water feature and away from people, where possible. Based on the analysis of hazardous conditions, water features should be designed to include a means for performing continual or manual disinfection while in operation Operation, Maintenance and Legionella Control Measures Proper operation and maintenance of a water feature is essential to managing the potential for Legionella growth and transmission. A water management program (Program), such as the one contained in ANSI/ASHRAE Standard Legionellosis: Risk Management for Building Water Systems, should be implemented. The Program should contain multiple control measures to manage the potential of Legionella growth and transmission. Such measures include operating the water feature to avoid elevated water temperature and to control water age, cleaning to remove accumulated sediments and biofilms and adding biocides on a regular basis to suppress microbial growth. The control measures used should be monitored to confirm they are being maintained within their control limits. Design elements, such as encasing the water feature in glass can help block aerosol transmission. Additional information is available in Guidelines for the Control of Legionella in Ornamental Water Features-2005, published by the South Dakota Department of Health. When used, biocides should be applied in a manner consistent with product s label and comply with the requirements of the authority having jurisdiction. See Annex B for guidance on US regulations. The following operation, maintenance and control measures are recommended for systems with volumes greater than 25 gallons (100 liters): Idle periods should be avoided. Systems should be operated at least daily to maintain water treatments. Accumulation of solids, algae and biofilms should be avoided. A water treatment program for microbial control should be implemented and maintained. Before use, all biocides should be registered or permitted, as required, by the authority having jurisdiction specifically for microbial control in water features. See Annex B for guidance on US regulations. A biocide residual should be maintained for microbial control. The biocide residual should be measured and recorded at a location where residual is expected to be lowest, such as a low flow area or a high temperature area and away from any source that may give non-representative high readings, such as near the chemical feed or make-up water locations. Automated addition and control of biocides is recommended when practical. Commercially available oxidizing biocides include bromine, chlorine, chlorine dioxide, peracetic acid, and bromine-chlorine formulations. 20 ASHRAE Guideline R

23 Systems treated by manual dosing and control should maintain an effective oxidizing biocide residual (at least 0.5 mg/l free chlorine residual is recommended when using a chlorine-based biocide) for 6- hours a day. Systems treated using automated dosing and control should maintain a continuous oxidizing biocide residual (at least 0.5 mg/l free chlorine residual is recommended when using a chlorine-based biocide). An algaecide should be applied, as needed. Slimy surfaces (algae and biofilms) should be spot cleaned and disinfected, as they appear. Water quality should be monitored at least weekly, using automation when possible. Monitoring frequency should be increased as necessary for systems with persistent conditions that favor microbial growth. Water should be maintained at less than ph 8.5 for chlorine-based biocides Water should be maintained at less than ph 9.0 for bromine-based biocides. Water temperature should be monitored. Water temperatures above 25 C (77 F) are favorable for Legionella growth. Systems that operate above 25 C (77 F) may require greater care to reduce the potential for Legionella growth. Heat sources such as incandescent lights should be avoided whenever possible. Water should be maintained visibly clear and have no noticeable odors due to microbial growth or other contaminants. Routine microbial testing of bacteria, such as by the heterotrophic plate count (HPC) method or by a dip slide, is an indicator used to estimate microbial content in the water and should be performed at least monthly. (Note: Heterotrophic bacteria testing does not correlate with the presence or absence of Legionella.) The system should be cleaned and disinfected on a routine basis to remove scale and deposits (See Section 6.3, Operation, Maintenance and Legionella Control Measures). Cleaning and disinfection frequency should be increased as necessary for systems with persistent conditions that favor microbial growth. Recirculate system water that is maintained at the proper biocide level. Water filters should be used and maintained according to the filter manufacturer guidelines, such as routine backwashing, cleaning and disinfection. Water features that do not have a filter system should be routinely drained, cleaned and flushed. The following recommendations are for water features that have a water volume less than 95 Liters (25-gal): An oxidizing biocide should be manually added to the water to achieve an appropriate residual, such as 3 to 5 mg/l free chlorine residual for chlorine-based biocides, for at least one hour per day. The water feature should be cleaned and disinfected at least monthly or as recommended by the manufacturer. Water features of less than 20 Liters (5-gal) water volume should be cleaned and disinfected at least weekly or as recommended by the manufacturer. Water filters should be serviced and replaced following the manufacturer s recommendations or, in the absence of a manufacturer recommendation, at least monthly. The water feature should be taken out of service if potentially affected parties cannot verify systems are being maintained according to the manufacturer s instructions. SPAS Note: Section 4 - Legionellosis and Legionella provides essential context for the practical information and guidance contained in this section. Users of this guideline are encouraged to review the information in Section 4 prior to implementing the guidance in Section 7. Recreational spas open to the public that are not drained between uses have been recognized as a source of infection and disease resulting from waterborne pathogens, including Pseudomonas aeruginosa, non-tuberculous mycobacteria (NTM) and Legionella. Legionellosis outbreaks have frequently been traced to spas. The water temperature in spas, baths, and pools is generally in the range of C ( F), with the maximum temperature based on bather comfort. These water temperatures are within the range most favorable to 21 ASHRAE Guideline R

24 Legionella growth (25-45 C [ F]) and favorable for growth of many other microorganisms. These water temperatures, along with water aeration and a high ratio of the surface area of the bather s body, relative to water volume, accelerate the loss of the biocide residual. Spas operate with high-velocity water recirculation and air injection which create bubbles of varying size that rise to the water surface and then burst, creating a constant aerosol. Microorganisms, such as Legionella can be released from the water into the air, either via bubbles or aerosol. These bubbles and aerosols have water droplets of varying sizes, many less than 5 micrometers, that extend into the air above the water surface to a height of at least 0.5 meters (1.5 ft.), well within the breathing zone of the bathers. The aerosols can then be carried much further distances by airflow. Indoor spas should be located in rooms with isolated air handlers and include dehumidifiers to maintain relative humidity below 60%, in order to reduce the probability of exposure to individuals outside the immediate spa location. Spas have a relatively small volume of water per occupant (approximately 300 liters, compared to 50,000 liters in a typical swimming pool), so the bathing load can quickly introduce a variety of contaminants into the water, such as body oils, skin flakes, bacteria and fungi, suntan lotion, and other organic materials. In addition to serving as microbial nutrients, these organic materials can also increase in biocide demand, which reduces the biocides ability to control microbial growth. In surveys of spas, Legionella has been isolated from as many as 33% of the spas sampled, primarily where the biocide residual levels were not adequately maintained. Therapeutic spas typically are drained, cleaned and filled with fresh potable water between uses and therefore have a lower probability for microbial growth System Descriptions Spas are small baths or pools used for recreational relaxation, hygienic, or therapeutic purposes. Common features include warm water temperatures from 32 C to 40 C (90 F to 104 F), constant water recirculation and agitation of the water through high-velocity jets or injection of air. The differences among the types of baths and pools are related mainly to size, purpose, design and materials of construction. Specific types of spas include: Whirlpool Spas Whirlpool spas are recreational baths or pools holding more than one person and filled with warm turbulent water. The water is not replaced after each use but rather is filtered to remove particulates and is chemically treated (typically with chlorine or bromine based biocides) to provide microbial control. They may be located indoors or outdoors. Most smaller spas are made from molded fiberglass, while larger in-ground varieties are generally made of stone or concrete with a plaster finish. They are generally circular in shape, shallow (less than 1.3 m [52 in.]), and contain seats that allow occupants to submerge up to the chest or neck Hot Tubs Hot tubs are traditionally deeper hot water baths or pools and are typically made of wood. Redwood is common, but they may also be made of cedar, mahogany, white oak, pine, or teak. Otherwise, the features and uses of hot tubs are similar to those of spas Whirlpools This term whirlpool has been traditionally used for the small therapeutic pools (often used in athletics) filled with warm, vigorously moving water and may be small enough for treatment of only a specific joint, such as a knee, ankle, or elbow. These pools are generally made of stainless steel and are emptied between uses Whirlpool Baths Whirlpool baths are small baths often found in bathrooms of hotel rooms or private residences and are used for both recreational and hygienic purposes. Jetted birthing tubs may also be included in this category. Whirlpool baths are fitted with high-velocity water jets or air injection, but unlike whirlpool spas and hot tubs, the water typically is emptied after each use. Designs that allow water to remain in the re-circulation lines when the spa is not in use can create conditions that support the growth of Legionella and other opportunistic premise plumbing pathogens System Design/Engineering, Installation, Commissioning Plumbing should be a simple as possible with the fewest number of connections. System should have no cross connections with other water systems and should have no stagnant flow areas. 22 ASHRAE Guideline R

25 System should have gauges for monitoring temperature and pressure, including pressure differential across filters. For commercial applications, systems should have automatic feed and control system for ph and biocide application and monitoring. Routine draining and filling is required. Draining and filling should be designed to be simple and quick. Sand filters, if used, require routine backwashing; the design should include adequate drainage for sand filter backwashing. All components should be readily accessible for routine maintenance and service. Dehumidification is required to reduce the aerosol concentration in the room where a spa is in use. Locate air handling systems outlets and returns to reduce the potential for transmission of aerosols System Operation and Maintenance (Routine) Health risks associated with spas are significant. In many jurisdictions, public spas are subject to state and local regulations covering public swimming and bathing facilities. In jurisdictions without such regulations, public spas should comply with recommendations of local government agencies providing oversight. In jurisdictions without such regulations or local agencies, public spas should comply with the CDC s Model Aquatic Health Code or the National Swimming Pool Foundation s Pool & Spa Operator Handbook. These guidelines cover all areas of operation, including mechanical specifications and operational parameters such as flow rates, temperature, water chemistry and bacteriology Bather Load The maximum number of occupants should be clearly posted, such as Maximum Load five (5) persons at one time. A common surface area per bather is 0.93 m 2 [10 ft 2 ]. Using this common surface area per bather, applied to a 2.5 meter (8 ft.) diameter circular spa, results in a maximum bather load of five persons at one time Bather Health Restrictions Warnings of the increased health risk to individuals who are immune compromised or who have chronic lung disease should be posted Filter Operation Hygienic maintenance of spa filters generally require more action than is required for swimming pool filters because of the higher ratio of the number of bathers to the volume of water in the pool. Health codes typically include recommended flow rates for different filter types. Filter maintenance should include regular back flushing to remove buildup of organic debris. The required frequency of back flushing is typically determined by manufacturer recommendations (flow-rate requirements) rather than by microbiological criteria. In general, daily back flushing may be required during periods of heavy usage. If back washing is not maintained at the proper frequency, there is increased potential for poor backwashing due to caking of the media or channeling. Filter cartridges should also be cleaned or replaced on a regular basis, typically once or twice weekly. Filters are designed to collect sediment and have the potential for biofilm and bacteria growth. To reduce this potential, water containing the proper level of disinfectant should be circulated across the filter. Commercial spas should have constant water flow across the filter. Non-commercial spas generally have lower bather loading, but still have the potential for biofilm and bacteria growth when disinfectant circulation stops when the spa is not in use. Spa operators should establish and maintain at least minimum levels of disinfectant in accordance with Table 7.4 prior to startup and during use Legionella Control Below is a table showing some typically recommended biocide residual control limits. 23 ASHRAE Guideline R

26 TABLE 7.4 Typically Recommended Biocide Residual Control Limits Biocide Control Measures Typical Biocide Residual Control Limits Free chlorine residual (mg/l) Bromine (mg/l) ph Requirements specified by the authority having jurisdiction for the use and application of biocides should be followed. Biocides should be applied in a manner consistent with the product s label. See Annex B for guidance on US regulations. Maintaining the required biocide residual is essential for controlling the growth of Legionella (and other bacteria) in spa water, so the biocide residual level should be measured frequently, as often as hourly during periods of heavy use. The best control is provided by automatic systems that continuously monitor biocide residual and add biocide as needed. Several alternatives for spa treatment are currently available, including copper/silver ionization, ultraviolet light and ozone. While these treatments may control Legionella and other bacteria in pools and spas, there are insufficient data to support their recommendation. Use of alternative biocides in combination with chlorine or bromine may decrease chlorine or bromine demand. Pool and spa health regulations may require the use of chlorine or bromine, even if alternative biocides are used Microbial Testing Regular microbial testing of spas can provide an important record of operating conditions and may alert operators of conditions indicating need for review and possible adjustments to the operation and treatment program. Microbial testing is not usually required by the authorities having jurisdiction. Microbial tests results often require up to 24 hours or longer and should only be used to confirm the effectiveness of disinfection. Microbial testing is not a replacement for frequent testing of the water chemistry, nor is it a replacement for routine maintenance. The most common microbial test to confirm overall control of a spa disinfection program is Heterotrophic Plate Count (HPC), also called Total Heterotrophic Aerobic Bacteria (THAB). (Note: THAB does not directly correlate with the presence or absence of Legionella.) Listed below are some typical bacteria and bacteria limits useful in spa review. Standard agar Total Heterotrophic Aerobic Bacteria plate count (THAB/HPC) (at 35 C) - < 200 CFU per ml (maximum) Total coliforms - 2 organisms per 100 ml (maximum) Fecal coliforms - None allowable Escherichia coli - < 1 CFU per 100 ml Pseudomonas aeruginosa (at 41 C) - None allowable Legionella species See Annex C: Microbial Testing for Legionella Where testing for Legionella, see Annex C: Microbial Testing for Legionella for guidance on proper sampling, handling, and shipping of Legionella test samples. HPC is not considered adequate for confirming levels of Legionella Routine Maintenance Recommendations for routine maintenance include taking the spa out of service at the end of each day to carry out disinfection using higher than normal biocide residual levels. When a chlorine-based biocide is used a free residual of 10 mg/l or 10 times the combined chlorine level, whichever is greater, for at least one to four hours is commonly used. Due to the buildup of total dissolved solids and organic matter in the water, spa water should also be replaced at least once a week (or more often, when the frequency of use is higher). Daily water changes may be necessary if the spa is subject to conditions of continuous high use. The water replacement interval (in days) will vary. According to the CDC s Model Aquatic Health Code, the interval should be calculated by dividing the spa volume (in gallons) by three and then dividing by the average number of users per day. In order to remove buildup of biofilm, the spa should be thoroughly cleaned, including vigorous scrubbing of the spa surface, weirs and skimming devices, each time it is drained to replace the water. Maintaining filters and the proper operation and calibration of automatic biocide feed and control equipment is very important and should be regularly confirmed by checking filter replacement records, 24 ASHRAE Guideline R

27 pressure drop across the filter Training and Record Keeping Maintenance personnel should be trained in all aspects of safe operation of spas and hot tubs. Training should make very clear that spas do not operate the same way as swimming pools and the concentrated number of bathers in a small volume of water places a much higher load on a spa than that seen by swimming pools, so the maintenance requirements for safe operation are different. Maintenance personnel should maintain complete and accurate records of all water chemistry measurements, microbial sample test results, back flushing of filters, water changes, spa cleaning, filter replacement, and service events. All records should be kept for at least three years or the duration required by the authority having jurisdiction, whichever is longer Remedial Treatment (Non-routine) When high bacterial counts occur, remove the spa from service and conduct shock disinfection with a biocide such as chlorine, maintaining 10 ppm free chlorine for 1 hour. When shock disinfection is completed, drain the water, clean spa surfaces, service filters, fill with fresh potable water and return the spa to the routine biocide residual level before use. If an outbreak or illness is suspected 1, remove the spa from service; discuss with the local public health agency; collect water samples as directed by the local public health agency; drain the spa; scrub all spa surfaces; replace filters or filter media; make need repairs; refill the spa; hyper-chlorinate using 20 ppm free chlorine (maintain a minimum of 20 ppm for 10 hours); flush the system, and recollect water samples as directed by the local public health agency. The spa should then be refilled with fresh potable water and the biocide level established in accordance with Table 7.4 prior to use. If an outbreak or illness was suspected, perform Legionella testing after remediation to confirm elimination of Legionella is suggested References 1 CDC. (2017). National Center for Immunization and Respiratory Diseases, Disinfection of Hot Tubs Contaminated with Legionella [ Centers for Disease Control and Prevention, Atlanta, GA. OPEN-CIRCUIT COOLING TOWERS, CLOSED-CIRCUIT COOLING TOWERS, AND EVAPORATIVE CONDENSERS Note: Section 4 - Legionellosis and Legionella provides essential context for the practical information and guidance contained in this section. Users of this guideline are encouraged to review the information in Section 4 prior to implementing the guidance in Section 8. Evaporative heat rejection systems use circulating water to efficiently cool chillers, heat pumps, compressors, condensers, heat exchangers, and other process devices. The heat transferred to the circulating water from process devices is rejected to the atmosphere through evaporation in open-circuit cooling towers, closed-circuit cooling towers, and evaporative condensers. Open-circuit cooling towers, closed-circuit cooling towers, and evaporative condensers are collectively referred to as evaporative heat rejection equipment, or often simply as cooling towers. Other equipment in evaporative heat rejection systems includes pumps, valves, and water treatment devices. Evaporative heat rejection systems have been linked to Legionnaires' disease. Growth and transmission of Legionella in evaporative heat rejection systems have been associated with system design and maintenance, periods of intermittent operation, systems that are idle without draining, periods when water treatment is stopped or is absent, and contamination of supply water Description of Systems Open-Circuit Cooling Tower Systems Principles of Operation. An open-circuit cooling tower cools water by evaporating a part of the water through direct contact with atmospheric air. Air movement through the tower is usually achieved by fans, although some large cooling towers rely on natural draft for air movement. Open-circuit cooling towers associated with building water systems are typically used to reject waste heat from the condenser of chillers providing building air conditioning. Water from the cooling tower is circulated to the chiller where it is heated and then returned to the cooling tower to be cooled (Figure 1). Open-circuit cooling towers commonly use media, referred to as "fill", to improve contact between the water and 25 ASHRAE Guideline R

28 the air. Louvers are often employed at the tower air inlet to keep water from splashing out of the water collection basin. Inertial stripping devices called drift eliminators are installed at the air discharge to minimize the escape of water droplets (drift) from the tower. The effectiveness of these drift eliminators can vary significantly based on design and physical condition. High efficiency drift eliminators designs are recommended. Building potable water is typically used to initially fill the system and as make-up water, although alternate water sources, such as reclaimed water and air conditioning condensate are increasingly used. As cooling tower water evaporates, mineral ions in the remaining water become more concentrated. This concentration of potentially scaleforming or corrosive ions is managed through a controlled bleed. Make-up water is added to replace water lost through evaporation and bleed. Figure Typical open-circuit cooling tower/chiller system Temperature. The temperature of the water in open-circuit cooling systems at typical summer design conditions ranges from 29 C (85 F) to 35 C (95 F) although temperatures can be above 49 C (120 F) and well below 21 C (70 F) depending on system heat load, ambient temperature, and system operating strategy and design. Water System Volume. Open circuit cooling system water is circulated by one or more pumps through pipes from the cooling tower to the chiller/process equipment, where it absorbs heat and is then returned to the tower to again be cooled. System water volumes vary greatly due to variation in the piping size and arrangement, and due to variations in the volume of water contained in the chiller/process equipment, in cooling towers, and in other water-containing parts of the system Closed-Circuit Cooling Tower Systems Principles of Operation. Closed-circuit cooling towers and evaporative condensers contain two separate circuits. One circuit is an open-loop water spray in direct contact with atmospheric air, much like the circulating water in an opencircuit cooling tower. The second circuit is a closed-loop containing the process fluid to be cooled. The process fluid, such as water, a glycol and water mixture, oil, or a condensing refrigerant such as ammonia, is contained inside the coil assembly and does not directly contact the cooling air (Figure 2). Heat is transferred from the process fluid located inside the coil to the open-loop water spray, which is cooled by evaporating a part of the spray water that is in direct contact with atmospheric air. In some ambient conditions, the water spray may be turned off, so that heat is transferred from the coil to the atmospheric air alone. Since the process fluid circulates in a closed-loop, it is easier to keep the associated chillers or compressors free of deposits. Similar to open-circuit cooling towers, closed-circuit cooling towers typically include louvers at the air inlet and drift eliminators at the air discharge to reduce the escape of water droplets from the equipment. Building potable water is typically used to initially fill the closed-circuit system and as make-up water, although alternative water sources, such as reclaimed water and air conditioning condensate, may be used. The concentration of scale-forming or corrosive ions in the open-loop recirculating spray water is managed through a controlled bleed and the addition of make-up water, in the same manner used in open-circuit cooling towers. 26 ASHRAE Guideline R

29 Figure Typical closed-circuit cooling tower or evaporative condenser configuration Temperature. The open-loop water temperature in closed-circuit cooling towers and evaporative condensers is typically slightly lower than in open-circuit cooling towers. The open loop water temperature is variable depending on system heat load, ambient temperature and system operating strategy. Water System Volume. Most commonly, there is no external cooling water piping in these systems. Because the water is totally contained within the closed-circuit cooling tower unit, the volume of water is usually significantly lower than with open-circuit cooling tower systems. The smaller volume of water reduces the amount of treatment chemical required to operate these systems. If the closed-circuit cooling tower system includes external piping, remote sumps, equalizers, headers and other water-containing components, the water volume can be similar to open-circuit cooling towers, from an operating and treatment perspective Guidance This section contains information on preplanning, design, operation, start-up, shut-down, commissioning, and remedial actions related to legionellosis risk management in evaporative heat rejection systems Design Good design practices facilitate proper system maintenance and water treatment. It is important to maximize mass transport and minimize accumulation of water based solids, airborne contaminants and bio-matter. Design guidelines include: Discharge piping and equalizers should be designed to ensure that cooling water moves effectively through all sections of the piping system, to avoid low or no flow locations, commonly known as dead legs. Avoid areas in equalizer piping that are stagnant by design or in operation. Balancing run time between cells on installations with multiple cooling tower cells helps maintain system cleanliness. Drain connections should be added to the low points and in unavoidable dead leg piping to allow for periodic draining. Design system piping to regularly recirculate system water during periods of intermittent operation, to limit stagnation. Access and work platforms should be incorporated to allow inspection and periodic physical cleaning of the evaporative cooling equipment. 27 ASHRAE Guideline R

30 An automated water treatment system should be designed and installed. Successful automated treatment system design requires an understanding of cooling water treatment and experience in sizing and locating automated treatment systems. Individual cooling tower cells should have a means to be isolated for cleaning. When variable speed pumps are incorporated, the system should not be allowed to fall below the minimum flow rate recommended by the equipment manufacturer to maintain cleanliness. The minimum flow rate through heat exchangers, such as the chiller condenser, should not fall below 3 fps for extended periods of time to avoid deposition of contaminants. Make-up water valves should be designed so they do not harbor water in internal hidden cavities and should be operated on a regular basis to avoid creation of stagnant areas. Design make-up piping to include back-flow prevention to prevent cooling water contamination of the potable building water system. Air-gaps and backflow preventers should comply with applicable codes and regulations. If no such regulations exist, air-gaps should comply with the requirements of ASME/ANSI A To control drift, use high-efficiency cooling tower drift eliminators. Cooling tower water collection basins should be designed to minimize sediment accumulation, facilitate cleaning, and allow for complete drainage Cooling Tower Siting Closed-circuit cooling towers, open-circuit cooling towers and evaporative condensers should be located to minimize their exit air and drift from being drawn into building air intakes and to minimize exit air and drift from coming into contact with people. Sufficient space should be provided to enable adequate access for maintenance and inspection. Locate away from fresh air intakes, including windows that can be opened, doors, HVAC system fresh air intakes and truck bays. Cooling tower exhaust should be a minimum of 25 ft. (7.5 m) from all building air intakes, or at a distance to allow a 10:1 dilution of the exhaust with fresh air before reaching a building air intake 1. Consider neighboring structures and public areas, particularly hospitals, nursing homes and other buildings housing at-risk individuals, both as a source of contamination and as a receiver of tower exit air and drift. Avoid locating towers in the immediate area of kitchen or laundry exhaust fans, vegetation, truck bays, or other sources of dirt, debris or organic matter. Consider the direction of prevailing winds and locate the exhaust downwind of highly trafficked and public areas. Consider the impact from future on-site and nearby off-site construction. Consider the addition of separators, side-stream filtration, and/or basin sweeping filtration methods to reduce the concentration of environmental suspended solids in the cooling system, thus minimizing water conditions that foster microbiological activity, and improving heat transfer and water treatment effectiveness. Locate in an area that is adequately accessible for inspection and maintenance. For more information, see ANSI/ASHRAE Standard , Ventilation for Acceptable Indoor Air Quality, Section 5.2, Exhaust Duct Locations and Section 5.13, Access for Inspection, Cleaning and Maintenance, and ANSI/ASHRAE/ASHE , Ventilation of Health Care Facilities, Section 6.3, Outdoor Air Intakes and Exhaust Discharges Temperature Strategies Reducing the water temperature of the system below the range favorable to Legionella growth, C ( F) and other microorganisms is suggested. Reducing system operating water temperatures to the lowest practicable value also improves operating efficiency in most systems. Review system operating strategies for pumps and cooling tower fans and consider steps to reduce circulating water temperatures. It may be possible, after discussion with equipment suppliers and mechanical service contractors, to lower circulating water temperatures by adjusting the system set points. 28 ASHRAE Guideline R

31 Note: The use of strategies to reduce the system water temperature does not eliminate the need for a cooling water treatment program Water Management Program Actions for Legionella control are compatible with the goals of a properly designed and maintained cooling water management program (Program). These goals include: Extending equipment life Minimizing energy consumption Minimizing water consumption Maintaining a safe environment To achieve these goals, the Program should include control of the following interrelated issues: Corrosion of all metallic components in the system Scale formation on heat exchange surfaces Sediment/deposition of solids (organic or inorganic) on system surfaces Microbial growth, including Legionella The objectives of all these goals are interrelated. Failure to control sediment, for example, can lead to corrosion and microbial growth, which in turn can contribute to fouling on heat transfer surfaces. A properly designed Program utilizes both operational and water treatment methods. The Program should consider materials of construction, local water supply chemistry, variations in supply water quality, operating environment, cooling system type, cooling system load, cooling system risk characterization, and industry standard performance metrics. The Program should provide confirmation that it is being implemented as designed (verification) and that it is effectively preventing fouling, controlling corrosion, Legionella and other bacteria, and biofilm growth in the system (validation). Establishing a Program requires an understanding of cooling water treatment and experience in developing such Programs. For further information, refer to 2015 ASHRAE Handbook HVAC Applications, Chapter 49 - Water Treatment; 2016 ASHRAE Handbook HVAC Systems and Equipment, Chapter 40 Cooling Towers; and Annex A Bibliography Operational Methods Blowdown (Bleed-Off) Control: Control of the cycles of concentration is required to achieve water treatment objectives. Automated control systems should be employed. Filtration: Depending on factors such as supply water quality, the location of the tower, the level of maintenance personnel available, and particle load, filtration can be of benefit on some cooling tower installations. Filtration should be properly sized and installed to reduce the level of suspended solids in the water. When selecting the type of filtration, consideration should be given to particle load, particle size as well as manpower availability. Proper maintenance of the filtration system is essential. The filtration system should be installed to ensure proper flow and movement of water in the tower basin to minimize accumulation of deposits in low flow zones. Basin sweepers can improve the effectiveness of the water filtration system. System Cleaning: Keeping the system clean helps reduce microbial populations by preventing the harboring of organisms inside crevices and deposits. The frequency of physical cleaning will vary depending on operational factors Chemical Water Treatment Methods Scale, Corrosion and Sediment Control: Scale control programs are designed to maintain the solubility of scale forming impurities. This can be achieved with careful control of ph and the addition of scaling threshold-inhibitors, crystal modifying polymers, and polymeric dispersants. Corrosion can be reduced by the addition of corrosion inhibitors selected for the site-specific system metallurgies and water quality. Understanding system metallurgy, flow velocity and water chemistry will dictate the type of inhibitors. Use of a synergistic combination of inhibitors will 29 ASHRAE Guideline R

32 provide multi-metal protection of the cooling water system. Dispersant polymers are used to inhibit particulates from adhering on system surfaces. The amount and type of dispersant polymer required is dependent on the amount and type of dirt, oil, or other material that is present. An automated chemical feed system should be used to ensure that these additives are maintained within their target control range Microbial Control: The two primary components for microbiological control are oxidizing biocides and non-oxidizing biocides. Feed strategy should ensure intended biocide levels at all times, including standby periods (see Section System Standby and Shut-down). Oxidizing biocides: Oxidizing biocides control microbial population by their ability to oxidize organic matter. Oxidants break down microbial cell walls, penetrating the cell and oxidizing internal cellular structures. The most commonly used oxidizing biocides for cooling water treatment are chlorine and bromine. Non-oxidizing biocides: Non-oxidizing biocides function in a number of ways, including reacting with intracellular enzymes, solubilizing cell membranes, and precipitating essential proteins in microbial cell walls. These biocides for cooling water application include many organic compounds that are effective at specific concentrations for a specific period of contact time. The most commonly used non-oxidizing biocides include glutaraldehyde, dibromo-nitrilo-propionamide, isothiazolones and various organo sulphur compounds. In addition to microbial control agents (biocides), dispersants are also used to enhance the performance and increase the effectiveness of the biocides by maintaining deposit-free and clean surfaces within the cooling system. Biocides follow requirements for their use and application specified by the authority having jurisdiction. Biocides should be applied in a manner consistent with the product s label. See Annex B for guidance on US regulations. In most jurisdictions, biocide use is regulated and products must be registered. In many jurisdictions, an applicators license or certification is required for the person applying or company supplying the products Non-chemical and Physical Water Treatment Methods & Equipment: Non-chemical and physical water treatment methods and equipment are potential additions or alternatives to chemical programs for water treatment in certain cooling water loops. Integrating these alternative technologies into a water management program requires compliance with manufacturers recommendations and instructions. More detailed information about individual technologies is available in the ASHRAE Handbook - HVAC Applications. Such alternative technologies should be subject to the same confirmation that they effectively control the hazardous conditions (validation) as a chemical water treatment program Miscellaneous Guidelines Supply Water Quality and Disruptions: A significant risk factor for evaporative heat rejection systems is a spike in Legionella concentrations due to supply water quality. In particular, water service disruptions such as water main breaks, hydraulic transients, and other disruptive conditions in the water utility distribution piping can introduce relatively high levels of stirred-up sediment, dirt and microbial contaminants. Building managers should establish communications with their water supplier, and develop plans for responding to such water service disruptions. Cooling Tower Drift Eliminators and Louvers: State of the art, high efficiency drift eliminator designs are recommended. It is critical that drift eliminators are correctly installed (without air gaps) and used within the design air velocity range established by the manufacturer. Frequent inspection of drift eliminators should be performed, cleaning dirt or fouling as necessary, and replacing deteriorated material. Louvers help to contain fine particulate mist occurring due to water splashing into the basin. Correctly installed louvers in good condition and proper fan operation can reduce the amount of mist in the air near the basin. Piping Dead Zones: Avoid piping dead zones. Specifically, free-cooling water loops can be stagnant during the summer and condenser water loops can be stagnant during the winter. Either bypass some portion of the normally circulating flow to the unused water loops or use a timer to periodically open the control valve so 30 ASHRAE Guideline R

33 the stagnant areas can be flushed at least weekly. Equalizers must be flushed periodically, either automatically or manually. When sequencing the operation of multi-cell cooling towers, choose the farthest tower on the branch as the lead (primary) cell in order to promote a flow of cooling water through all cells System Standby and Shut-down Evaporative heat rejection systems may require a shut down, in whole or in part, for a variety of reasons such as; physical cleanings, system maintenance, low cooling load, redundant design or off season operation. Whenever a system is required to be offline, one of the following conditions will apply: Standby (Wet): Whenever the system is shut down or out of service or when portions of the system are nonoperational for less than 5 days, without draining the water, the following actions should be taken: Maintain the system s water treatment program (microbial, corrosion and scale/sediment control), along with normal monitoring practices. When an automated biocide program is in use, adjustments to the feed program may be required to ensure the biocide is added while the system is circulating, and not skipped once the system is in standby. Circulate water daily throughout the open loop of the closed-circuit cooling tower and the entire open-circuit cooling system, including any basin sweeping and filtration systems. This periodic circulation will help restore control of water treatment parameters and help control biological growth. Shutdown (Dry): Whenever the system is expected to be shut down for an extended period of time, the system should be drained of its water and put into a dry, offline position. A dry shutdown is often implemented when the system is not needed for an extended period due to seasonal conditions, such as cold winter temperatures. The following actions should be taken as part of a dry shutdown: Drain and properly dispose of all system water, including water in the cooling tower, system piping, heat exchangers and filtration systems. Open appropriate valves so that the entire system and all dead legs drain. If possible, the system should be air-blown to force water out of low spots in the lines. It is recommended to keep the system closed until it is needed again. Periodically inspect the open-circuit cooling tower, closed-circuit cooling tower or evaporative condenser and clean any debris, such as leaves and dirt, from horizontal collection surfaces of the exposed equipment System Startup Prior to returning an idle or wet stored system to service, the manufacturer s recommendations and instructions for inspection and cleaning should be followed. If filtration or separators are present, the manufacturer s recommendations and instructions should be followed. The following are recommended when starting up the system from a wet standby state: Inspect the cooling tower and/or cooling tower system and clean all accessible solid debris from the cooling tower basin, sump and from any remote storage tank(s) that may be used. Operate the water circulating pumps and adjust valves to bring all parts of the system on-line, including all piping, heat exchangers and filtration equipment. Confirm the appropriate levels of biocides and corrosion inhibitors have been added to the system. Consult a water treatment professional as required. Maintain the maximum biocide label-residual before operating the cooling system fans. If the circulating water system contains multiple pumps, chillers, or heat exchangers, they should be rotated systematically to ensure that all parts of the system are flushed. The following are recommended when starting up the system from a dry shutdown state: Remove any solid dirt and debris from the cooling tower. Inspect the cooling tower and clean surfaces including inlet louvers, drift eliminators and water collection basins as necessary. Consult with a water treatment professional as required to add treatment to bring the system water into compliance with the control limits in the current Program. Operate the water circulating pump(s) and adjust valves to bring all parts of the system on-line, including all piping, heat exchangers and filtration equipment. 31 ASHRAE Guideline R

34 When an oxidizing biocide protocol is used, the fans may be restarted once a sufficient free residual oxidant is present. When a non-oxidizing biocide protocol is used, ensure that sufficient biocide dosage and contact time are achieved according to label recommendations prior to restarting the fans New System Commissioning Equipment and piping should be protected from construction dirt and debris throughout shipping, storage and installation. The cooling equipment should not be filled or operated if the building s potable water system is under hydrostatic testing, or is being disinfected. The mechanical contractor should coordinate with the water treatment professional to ensure that any necessary treatment equipment is properly installed prior to the first introduction of water into the cooling tower system. A visual inspection of the evaporative cooling equipment should be conducted before water is first introduced into the system. A physical cleaning should be undertaken to remove any visible dirt or debris from the system. Pre-cleaning and/or passivation of the new evaporative cooling equipment should be considered as part of a Program prior to filling the system with water. The water treatment professional should be consulted to assist in developing a Program for the responsible parties to follow during construction, commissioning and operation. The Program should consider factors such as sanitization, passivation and on-going water treatment once the system is filled Online Remedial Treatment/ Offline Emergency Cooling Water System Disinfection When remedial online or offline disinfection actions are required, the cooling system should be considered as a whole. Mechanical cleaning of all components of the cooling system may need to be applied as practical Online Remedial Treatment On-line remedial treatment of cooling water systems typically requires use of an oxidizing biocide at higher-thanusual concentrations. The decision to use online disinfection may be driven by microbial testing as described in Section 8.3. In general, on-line remedial treatment should include: Disengaging all water treatment components, including the conductivity sensor, ph sensor, ORP sensor, automated chemical feed systems and any other water treatment control sensor. Confirming that the fill and drift eliminators are clean and in good working condition. Fill should be free of debris. Water should be circulated through all associated system equipment. If significant biomass or fouling is present, all associated system equipment should be physically (mechanically) or chemically cleaned. Lowering the system cycles of concentration to reduce system ph that improves the effectiveness of oxidizing biocide treatment, particularly chlorine. Adding an oxidizing biocide sufficient to achieve >5.0 mg/l of biocide residual and maintaining that level for a minimum of one hour. Blowing down the system until the biocide residual level is 1.0 mg/l or lower. Re-engaging all water treatment components, including the conductivity sensor, ph sensor, ORP sensor, automated chemical feed systems and any other water treatment control sensor. Restoring routine treatment Offline Emergency Cooling Water System Disinfection The following off-line remedial treatment procedure is based on United Kingdom HSG 274 and other governmental recommendations. It is typically used when there is a suspected association of disease with the cooling water system. This procedure may require modification based on system volume, water availability and wastewater treatment capabilities. Remove heat load from the cooling system, if possible. Shut off fans associated with the cooling equipment. Shut off the system blowdown. Keep makeup water valves open and operating. Close building air intake vents in the vicinity of the cooling tower, especially those downwind, until after the cleaning procedure is complete. Continue to operate the recirculating water pumps. Add an oxidizing biocide sufficient to achieve an initial level of >20 mg/l of free halogen residual. Add an appropriate dispersant and antifoam, if needed. 32 ASHRAE Guideline R

35 Maintain a free oxidant residual for the specified time listed in Table Add biocide as needed to maintain the appropriate free oxidant residual for the minimum time listed. Monitor the system ph. Since the rate of oxidizing disinfection often slows at higher ph values, acid may be added, or the cycles of concentration can be reduced to achieve and maintain a ph of less than 8.0 for chlorine-based disinfectants or less than 8.5 for bromine-based disinfectants. Drain the system, following all applicable rules, regulations and permits, to a sanitary sewer. Refill the system and repeat steps 1 through 10, before continuing to step 12. Inspect the system after the second drain-off. If a biofilm is evident, repeat steps 1 through 10 and refill the system until no biofilm is evident. When no biofilm is evident, mechanically clean the tower fill, tower supports, cell partitions, and sump. Workers engaged in tower cleaning should follow the guidance provided in Annex D, Guidance on Personal Protective Equipment for use when there is Risk of Exposure to Contaminated Aerosols. Refill and recharge the system to achieve a 5 mg/l disinfectant residual. Hold this residual for one hour and then drain the system until free of visible turbidity. Drain and refill the system, then add the appropriate corrosion and deposit control chemicals, reestablish normal disinfectant residuals and put the cooling tower back into service. TABLE MINIMUM CONCENTRATION LEVEL PER CIRCULATION TIME 2 Minimum Circulation Time (Hours) Minimum Continuous Free Oxidant Residual (mg/l) Legionella Testing Legionella testing can be used to confirm the Program is controlling Legionella growth. Trending of Legionella bacteria population through testing provides a direct indicator of the effectiveness of Legionella control activities. Testing is not a substitute for a water management program, but can be included as part of an analysis of potential hazardous conditions, and to validate the efficacy of remediation methods. Decisions regarding whether to test for Legionella, determining testing frequency and interpretation of test results vary based on numerous site specific conditions, including, but not limited to supply water quality, equipment type, use patterns, environmental conditions, individuals served and other risk factors. See Annex C: Microbial Testing for Legionella, for guidance on Legionella testing and circumstances where Legionella testing may be appropriate. Based on remedial confirmation, further maintenance, including mechanical cleaning of other points within the system may be required Program Documentation Installation, Operation and Maintenance manuals for the evaporative cooling equipment and the selected water treatment systems should be readily available. Site specific log sheets, test procedures, service reports and test results should be maintained on-site. Additionally, the following records should be maintained on-site: Safety Data Sheets for any chemicals brought on-site As built drawings or documentation of the evaporative cooling and water treatment systems Water system volume, the date of measurements and the method of volume determination Name and contact information for the party or parties responsible for the Program Names and contact information for personnel responsible for system operation and shutdown Water treatment test procedures, including site-specific control ranges for tested variables Water treatment equipment and control parameter test schedules 33 ASHRAE Guideline R

36 Corrective actions for test results which fall outside the site-specific control ranges Written reports showing which routine inspections have been conducted, the inspection findings, the inspection date and the personnel conducting the inspections Written reports showing which routine maintenance has been conducted, a summary of before and after maintenance conditions, the maintenance date and the personnel conducting the routine maintenance. Written reports documenting any repairs or modifications made to the evaporative cooling or water treatment systems, the date the actions were taken and the personnel making the repairs or modifications. Written documentation of the date and duration of any water service disruptions References 1 Petersen, R.L., J.D. Ritter, A.S. Bova, and J.J. Carter. (2015). Simplified procedure for calculating exhaust/intake separation distances. Final Report, ASHRAE 1635-TRP. 2 HSE. (2014). HSE Books, Legionnaire s disease, HSG 274. Health and Safety Executive, London, UK. DIRECT EVAPORATIVE AIR COOLERS, MISTERS (ATOMIZERS), AIR WASHERS, AND HUMIDIFIERS Note: Section 4 - Legionellosis and Legionella provides essential context for the practical information and guidance contained in this section. Users of this guideline are encouraged to review the information in Section 4 prior to implementing the guidance in Section 9. Direct evaporative air-cooling equipment and humidifiers cool and humidify air by direct contact with the water, either by wetted-surface materials such as used in wetted media air coolers or with a series of sprays such as used in air washers and misters. These devices (see Figures 9a and 9b) are used to control the temperature and humidity levels for commercial, industrial, residential and agricultural applications. These systems utilize either once-through or recirculating water. Wetted media systems may include a pump, water distribution piping, and a sump to collect or hold water. A fan may be utilized to move air across the system and distribute evaporatively cooled and humidified air to the location being served. Concentration of contaminants in the water can be reduced by sump bleed off and dilution with fresh water makeup. 34 ASHRAE Guideline R

37 Figure 9a. Direct evaporative air cooler/humidifier System Description Figure 9b. Single bank air washer humidifier. There are many different types and designs of equipment in the category Direct evaporative air-cooling equipment and humidifiers. Some types have been linked to cases Legionnaires disease, while others have not been associated with cases Legionnaires disease Wetted Media Wetted media devices utilize a porous substrate to provide extended surface area for evaporation of water. These devices utilize either once-through potable building water or may be equipped with a recirculating system including a pump, automatic makeup water valve, a bleed-off/purge, and a positive draining reservoir. Water is either circulated over the media or the media is rotated slowly through a water bath. When operating properly, wetted media devices produce no aerosols, since evaporation occurs as air is blown across a wick or media and water vapor is released into the air. Mist eliminators are not usually necessary. However, if a sudden and unintended significant event occurs droplets of less than 5 micrometers may be created (See Transmission Legionella released such that people can be exposed ). Larger droplets may form as a result of improper maintenance and uneven water or air distribution. The exact size of the droplets will vary with factors such as the condition of the wetted media and drift eliminators (where used), air velocity through the unit, and irrigation rate. When operating, the recirculating water temperature in wetted media devices is generally below the range favorable to Legionella growth (25-45 C [ F]), because the water comes close to the wet-bulb temperature of the airstream to which it is exposed, which in most regions where these devices are used is well below 25 C (77 F). Where dirt, scale or biological matter can accumulate and when water remains during periods of shutdown, such as weekends, there is the potential for Legionella growth in areas like media, water storage tanks and collection troughs. Media located inside a large built-up air house may not dry completely during the period of shutdown. To facilitate drying the media, recirculation pumps should be shut down prior to fan shutdown. Smaller systems and those with media located adjacent to inlet louvers may dry sufficiently without assistance. For systems experiencing high contaminant loading, a flush-out cycle that runs fresh water through the pads every 24 hours during a period of time when the system is not in operation may be needed. Media should be cleaned or replaced when necessary. The use of a biocide registered for evaporative air-cooling equipment applications may be applied to control microbial growth with the system in accordance with the AHJ, the manufacturer s recommendations, and the materials of construction. 35 ASHRAE Guideline R

38 Air Washers Air washers utilize high-pressure nozzles to reduce water to small droplets for evaporation. These systems typically have a chamber or casing containing one or more banks of spray nozzles and drift eliminators. Air washers contain a sump for collecting excess spray water. The drift eliminator section removes droplets of entrained water from the air. Air washers utilize either once-through potable building water or are usually equipped with a recirculating system including a pump, automatic makeup water valve, a bleed-off/purge, and a positive draining reservoir. The water may be chilled for additional cooling and/or dehumidification. The major causes of droplets being entrained into the airstream are fouled spray nozzles and damaged or dirty mist eliminators. Air washers can produce droplets of various sizes and have the potential to produce droplets less than 5 micrometers in diameter. When operating, the recirculating water temperature in air washers is generally below the range favorable to Legionella growth (25-45 C [ F]), because the water comes close to the wet-bulb temperature of the airstream to which it is exposed, which in most regions where these devices are used is well below 25 C (77 F). Where dirt, scale or biological matter can accumulate and when water remains during periods of shutdown, such as weekends, there is the potential for Legionella growth in areas like water storage tanks and collection troughs. Use of corrosion inhibitors to prevent metal corrosion and the formation of corrosion byproducts may be needed. The use of a biocide registered for air washer applications may be applied to control microbial growth within the system in accordance with the AHJ, the manufacturer s recommendations, and the materials of construction. Actions to control the level of suspended solids that can supply nutrients and growth areas for Legionella are generally necessary Misters Misters produce an aerosol by use of ultrasonic devices, spinning disks, or spray nozzles. Normally these devices use fresh cold potable water directly from the building water systems, where the water temperature is usually below a temperature favorable to the growth of Legionella (25 C [77 F]), however, some systems contain a reservoir. If the mister is fed from a stagnant reservoir, if the reservoir or mister piping is exposed to heat or it the cold water supply exceeds 25 C (77 F), conditions can become favorable for the growth of Legionella. These systems can produce droplets of varying size, including droplets less than 5 micrometers in diameter. The use of a biocide registered for mister applications may be applied to control microbial growth within the system in accordance with the AHJ, the manufacturer s recommendations, and the materials of construction. Note: Clinical equipment such as nebulation devices and ventilators should be rinsed and filled only with sterile water. Devices should be cleaned between uses as directed by the manufacturer Heated Element and Steam-Type Humidifiers Heated element and vapor-type humidifiers convert water to vapor that is discharged into the space being conditioned. Due to the elevated temperature and the fact that water droplets are usually not generated, these humidifiers are not considered a risk for the growth of Legionella during normal operation. However, if the humidifier is improperly installed, moisture may accumulate in the duct and lead to bacterial growth. During periods when equipment is not in use, all water should be drained from the system to avoid possible bacterial growth. The use of a biocide registered for heated-element and steam-type humidifiers may be applied to control microbial growth within the system in accordance with the AHJ, the manufacturer s recommendations, and the materials of construction Portable Humidifiers Portable Humidifiers are tabletop or larger furniture-style versions of wetted media, air washer, mister, heatedelement or steam-type systems. A multispeed motor on the fan or blower or other means may be provided to adjust output. Portable humidifiers usually require periodic filling with fresh cold potable water from a bucket or filling hose. The water reservoir should be emptied and the tank cleaned at least daily. If water is left standing in the tank, the unit should be thoroughly disinfected before reuse. Proper care and cleaning of portable humidifiers is important for reducing potential exposures to microorganisms including Legionella. Some portable humidifiers have the option to be semi-permanently connected to obtain fresh cold potable water directly from the building water system. When operating, the recirculating water temperature in media type portable humidifiers is generally below the range favorable to Legionella growth (25-45 C [ F]), because the water comes close to the wet-bulb temperature of the airstream to which it is exposed, which in most regions and in most interior spaces where these 36 ASHRAE Guideline R

39 devices are used is below 25 C (77 F). If the portable humidifier uses water from an uncirculated reservoir or if it is water supply rises to 25 C (77 F) or higher, the conditions are favorable for Legionella growth. In addition to the guidance provided in this section, portable humidifiers should be operated, cleaned and maintained in accordance with the equipment manufacturer s instructions. The use of a biocide registered for portable humidifiers may be applied to control microbial growth within the system in accordance with the AHJ, the manufacturer s recommendations, and the materials of construction. Portable humidifiers are not recommended for use in healthcare facilities. Many regulations, codes and standards, such as ANSI/ASHRAE/ASHE , Ventilation of Health Care Facilities, prohibit the use of portable humidifiers in healthcare facilities. Figure Portable Impeller humidifier Portable Impeller Humidifiers Portable impeller humidifiers produce a mist by means of a high-speed rotating disk drawing water up from the basin and discharging a water mist or aerosol into the air stream created by the spinning disk. On some designs room air is constantly drawn into the basin adding even greater potential for bacterial growth. The water in the basin is exposed to the bacteria, nutrients and dirt. Water is at room temperature in the basin and can be exposed to slightly higher temperatures near the impeller. Avoid any condition that could cause water in the basin to exceed 25 C (77 F), which is favorable for Legionella growth. Portable impeller humidifiers have the potential to produce some aerosols as larger droplets that can be reduced by evaporation to a size that can be inhaled into the lungs Portable Ultrasonic Humidifiers Portable Ultrasonic Humidifiers produce a cool mist by vibrating the water at a high frequency. Avoid any condition that could cause water in the basin to exceed 25 C (77 F), which is favorable for Legionella growth. These devices have been linked to cases of Legionnaires disease Portable Evaporative Humidifiers Properly operating portable evaporative humidifiers produce no mist or droplets, as air is blown across a wick or media and water is evaporated into the air. The equipment should be operated and maintained in accordance with the equipment manufacturer s instructions Fixed Equipment Siting Evaporative air coolers/humidifiers should not be located near the outlet of a cooling tower, fluid cooler, evaporative condenser, kitchen exhaust, or any other source of organic contamination. Air filtration upstream of the evaporative air cooler/humidifier is recommended when particulate contamination is expected. If air filtration is located downstream of the equipment it must be a sufficient distance away to allow absorption of moisture into the air stream. For more information, see ANSI/ASHRAE Standard , Ventilation for Acceptable Indoor Air Quality, Section 5.10, Drain Pans and Section 5.13, Access for Inspection Cleaning and Maintenance, and ANSI/ASHRAE/ASHE , Ventilation of Health Care Facilities, sec ASHRAE Guideline R

40 9.3. Fixed Equipment System Operation, Routine Maintenance and Microbial Control Evaporative air coolers/humidifiers, air washers, misters, and ancillary equipment should be regularly cleaned and maintained. Dead-end piping, low spots, and other areas where water may stagnate during shutdown should be eliminated. Water filters and air filters should be cleaned as required. In every case, a regular schedule for cleaning and flushing the entire system should be maintained. For systems with recirculating water, proper sump water level or spray pressure must be maintained. Bleeding off or purging some of the water is the most practical means to minimize scale and nutrient accumulation. The bleed or purge rate depend on water quality (including hardness) and airborne contaminant level. Regular inspections should be made to ensure that the bleed or purge rate is adequate and is being maintained. If additional precaution is indicated, sumps can be automatically drained during shutdown of the fan. When it is impractical to shut down the system for cleaning, it should be provided with a positive draining sump and provided with method for flushing the distribution header during operation. After flushing, a biocide approved by the authority having jurisdiction for use in recirculated cooling water should be applied, following the instructions on the manufacturer s label. The equipment should be operated and maintained in accordance with the equipment manufacturer s instructions. Additional information can be found in the 2016 ASHRAE Handbook - HVAC Systems & Equipment, Chapter 21, Humidifiers. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. See Annex B for guidance on US regulations. INDIRECT EVAPORATIVE AIR COOLERS Note: Section 4 - Legionellosis and Legionella provides essential context for the practical information and guidance contained in this section. Users of this guideline are encouraged to review the information in Section 4 prior to implementing the guidance in Section 10. Indirect evaporative air coolers (IEC) provide a cool airstream through the use of a heat exchanger that is cooled by the evaporation of water. The IEC evaporatively cools one side of a heat exchanger, which transfers heat to the primary airstream as shown in Figures 10a and 10b. Moisture for evaporative cooling is only added to the secondary air side of the heat exchanger. No moisture is added to the primary air stream, since it is physically separated from the secondary air side of the heat exchanger. Good design practices which facilitate proper equipment maintenance and water treatment should be applied to the secondary air side of the heat exchanger and the equipment should be operated and maintained in accordance with the equipment manufacturer s instructions. As of September 2016, the CDC has not published a link between indirect evaporative air coolers and cases of Legionnaires' disease. Indirect Evaporative Air Cooler Figure 10a. Indirect evaporative air coolers 38 ASHRAE Guideline R

41 10.1. System Operation Figure 10b. Indirect evaporative air coolers Indirect evaporative air cooling systems utilize one of several methods of operation to cool the primary airstream: By evaporatively cooling water that directly wets one side of a heat exchanger surface, while the primary air stream is cooled by contacting the other side (dry side) of the heat exchanger surface, or By evaporatively cooling a secondary air stream, which is then passed through an air to air heat exchanger to cool the primary airstream, or By evaporatively cooling water that is passed through a water to air heat exchanger located in the primary air stream. When operating, the recirculating water temperature in IEC systems is generally below the range favorable to Legionella growth (25-45 C [ F]), because the water comes close to the wet-bulb temperature of the airstream to which it is exposed, which in most regions where these devices are used is well below 77 F (25 C). The use of a biocide registered for indirect evaporative air-cooling equipment applications may be applied to control microbial growth within the system in accordance with the AHJ, the manufacturer s recommendations, and the materials of construction. For more information, see the 2016 ASHRAE Handbook HVAC Systems and Equipment Siting Indirect evaporative air coolers should not be located near the outlet of a cooling tower, fluid cooler, evaporative condenser, kitchen exhaust, paint booth, incinerator, or any other source of organic matter. For more information, see ANSI/ASHRAE Standard , Ventilation for Acceptable Indoor Air Quality, Section 5.10, Drain Pans and Section 5.13, Access for Inspection Cleaning and Maintenance and ANSI/ASHRAE/ASHE , Ventilation of Health Care Facilities, sec 6.3. COOLING COILS AND CONDENSATE COLLECTION 39 ASHRAE Guideline R