Basic Characterization and Information Gathering

Transcription

1 Basic Characterization and Information Gathering

2 Walkthrough Survey The basic characterization builds on the walkthrough survey which industrial hygienists have practiced for many years. To assess exposures and evaluate health risks, at a minimum industrial hygienists must answer the following questions: What are the agents in the work environment? What health effects are associated with excessive exposure? What are the occupational exposure limits for each agent? How is the work force organized? What are the significant sources of exposure? What processes and operations, and what tasks and work practices, pose significant potential for worker exposure to the agents? What controls are in place, and how are they used?

3 Gathering Workplace Information Preparation of a schematic diagram or a written description of the processes can be used to adequately describe most workplaces. Process flow diagrams are particularly helpful in characterizing continuous, semicontinuous, and batch operations. The key elements of a process flow diagram are the sources of potential exposure. Sources of potential exposure include equipment and tasks that potentially bring a worker into contact with an environmental agent. Unit operations and associated equipment should be identified. The factors affecting exposure potential, such as ventilation systems, open-top tanks, open sumps and use of personal protective equipment, should be considered. Maintenance and repair activities should be characterized. Most maintenance exposures are associated with specific tasks that can be identified and characterized. Sources of dermal contact should be assessed.

4 Gathering Work Force Information (1) To understand the division of labor and work practices. Detailed knowledge of the routine and nonroutine work assignments, work schedules, and tasks must be acquired. The work force characterization should be based on a variety of resources, including the plant roster, job descriptions, work interviews, management interviews and,most important, careful observation of work practices and the workplace. To identify work groups and link individual workers to the groups. Personnel record keeping systems A brief outline of work duties and task is needed. The percentage of time spent in the general process areas.

5 Gathering Work Force Information (2) A work activity description should be prepared in the form of a time distribution. Showing each major work area and time spent on each task. specific unit operation and tasks potential skin contact dermal absorption As OELs are reduced to smaller and smaller values, the importance of the dermal route of exposure in contributing to the total body burden increases dramatically. Contractors should be included in the exposure assessment process.

6 Gathering Information on Environmental Agents Each potentially hazardous chemical, physical, and biological agent in the workplace should be identified. For each agent, information describing its use, physical properties, routes of exposure, potential health effects, and pertinent OELs should be collected. A site s inventory of hazardous materials and associated material safety data sheets (MSDSs). Raw materials, products, byproducts, additives, solvents, refractories, insulations, lubricants, coating, resins, welding rods, and compressed gases. To link each environmental agent to one or more work groups.

7 Quantities and Physical Properties To understand the approximate quantities and use rates of chemical agents used in the process. Bulk quantities information is often available from warehouse records or production reports. To gather physical property data (e.g., boiling points, vapor pressure, particle size distribution, wavelength of laser radiation), for each agent, under conditions of use.

8 Health Effects Data The health effects data must be sufficient to differentiate acceptable and unacceptable exposure levels. Material safety data sheets are a convenient source of health effects data, but many MSDSs also have inadequate health effects information --- all too often because of a lack of toxicological data.

9 Occupational Exposure Limits (OELs) Regulatory OELs OSHA: permissible exposure limits (PELs) MSHA (US Mine Safety and Health Administration) European Commission (EC) Authoritative OELs ACGIH: threshold limit values (TLVs) AIHA: workplace environmental exposure limits (WEELs) NIOSH: recommended exposure limits (RELs) Internal OELs Some private organizations to device internal OELs for substances with no regulatory or authoritative OELs. Working OELs A working OEL is an informal limit created in the course of performing an exposure assessment. A working OEL will be based on whatever data are available --- including epidemiological or toxicological information.

10 Considerations for Using OELs Why was an existing OEL set at its particular level? What safety factors were used in deriving the OEL? What potentially important health effects were not evaluated? How adequate are the health effects data that support the OEL? Were the health effects data based on animal or human studies? Were the health effects studies acute or chronic? Are the health effects reversible or irreversible? What are the target organs? Do the health effects include reproductive, teratogenic, or carcinogenic effects; immediate death or disability? Does the agent have warning properties at levels less than the exposure limit or only at levels greater than the OEL? Does the agent have warning properties at levels less than the exposure limit or only at levels greater than concentrations that are immediately dangerous to life or health (IDLH)?

11 OEL Averaging Times (1) The averaging time refers to the time span for which an average exposure is estimated. In practice, three averaging times account for the majority of authoritative and regulatory OELs: 8 hours, 15 minutes (for shortterm exposure limits, STELs) and instaneous (for ceiling limits). If the toxic agent acts very quickly, then very short averaging times are appropriate. If the toxic agent acts slowly --- through some combination of accumulation of the toxic agent or metabolites, or accumulation of bodily damage --- then longer averaging times may be appropriate. Acute effect: STELs and ceiling limits Chronic effect: 8-hour TWA TLVs

12 OEL Averaging Times (2) Few regulatory or authoritative long-term average OELs (LTA- OELs) have been developed. Instead, 8-hour TWA OELs have been used to limit cumulative dose for chronic disease agent. Properly implemented, single-shift limits will reduce the true longterm average exposure to a fraction of the 8-hour TWA-OEL. For a wide range of geometric standard deviations the true long-term average exposure will be less than half the 8-hour TWA-OEL when the true 95th percentile of the exposure distribution is less than the OEL. Roach and Rappaport suggested that an LTA-OEL should be 1/10 to 1/4 the single-shift limit. Given the temporal variability in exposure levels, what exceedance of the OEL is permissible? Ceiling limits: can not be exceeded any time. TWA TLV: 5% exceedance Some OELs are defined as a long-term average values.

13 OEL Averaging Times (3) Unfortunately, there are few statistically defined OELs, and each organization must decide how applicable regulatory and authoritative OELs should be applied. NIOSH In statistical term, the employer should try to attain 95% confidence that no more than 5% of employee days are over the standard. To recommend a single-shift limit with the explicit goal of limiting longterm exposure below a specific value.

14 NIOSH Respirable Coal Mine Dust Recommended Exposure Limit (1) In 1995, NIOSH issued an REL of 1 mg/m 3 for respirable coal mine dust. This exposure limit was determined using a target long-term average exposure of 0.5 mg/m 3 and estimates of within-occupation variability for underground coal mining. NIOSH determined that the 95th percentile daily exposure (i.e., single-shift average exposure) for a miner whose long-term average exposure is 0.5 mg/m 3 will be approximately 1 mg/m 3. NIOSH then recommended an upper limit of 1 mg/m 3 for each single-shift average exposure.

15 NIOSH Respirable Coal Mine Dust Recommended Exposure Limit (2)

16 European Long-Term Average OELs Employers must ensure that the exposure of employees to vinyl chloride monomer (VCM) in the air of working areas is as low as is reasonably practicable and that in any event it does not exceed the maximum exposure limits (MELs) for VCM. These are 3 ppm average over a year (the annual limit) and 7 ppm (TWA) averaged over 8-hours.