Using real-time portable atmospheric monitors

Transcription

1 Using real-time portable atmospheric monitors Bob Henderson, BS, MBA GFG Instrumentation Inc. Ann Arbor, MI (Electron States) August, 2012 Using real-time portable atmospheric monitors Slide 1 Requirements for use of portable real-time gas detectors Common uses for real-time portable gas detectors: Hazard assessment Exposure assessment Indoor-air quality General atmospheric monitoring Non-permit spaces Permit spaces which have been reclassified as nonpermit spaces Permit-required confined spaces (per 29CFR ) August, 2012 Using real-time portable atmospheric monitors Slide 2 AIHCe 2012 PDC 411 Page 1 of 98

2 Oxygen deficiency and enrichment: Many technologies are available for use in portable real-time instruments Fuel cell oxygen sensors Solid polymer ( oxygen pump ) sensors Combustible gases and vapors: Catalytic % LEL ( Wheatstone bridge ) sensors Non-dispersive infrared (NDIR) % LEL and % volume sensors Thermal conductivity (TC) sensors Toxic gases and vapors: Electrochemical sensors Photoionization detectors Non-dispersive infrared (NDIR) Flame ionization (FID) Ion Mobility Spectroscopy (IMS) The most commonly used technologies are highlighted in red Each type of detection has capabilities and limitations which must be understood for safe use August, 2012 Using real-time portable atmospheric monitors Slide 3 Common Atmospheric Hazards Oxygen Deficiency Oxygen Enrichment Presence of Toxic Gases Presence of Combustible Gases August, 2012 Using real-time portable atmospheric monitors Slide 4 AIHCe 2012 PDC 411 Page 2 of 98

3 Composition of fresh air 78.1 % Nitrogen 20.9 % Oxygen 0.9 % Argon 0.1 % All other gases Water vapor CO2 Other trace gases August, 2012 Using real-time portable atmospheric monitors Slide 5 Oxygen Deficiency Any area that has an oxygen level of less then 19.5% by volume is considered to be oxygen deficient August, 2012 Using real-time portable atmospheric monitors Slide 6 AIHCe 2012 PDC 411 Page 3 of 98

4 Causes of Oxygen Deficiency Combustion Welding and cutting torches Internal combustion engines Decomposing of organic matter Rotting foods, plant life and fermentation Oxidation of metals Rusting Inerting Displacement Absorption August, 2012 Using real-time portable atmospheric monitors Slide 7 Argon Oxygen displacement in an open topped confined space Open-topped pits and spaces potentially very dangerous from standpoint of trapping or containing dangerous atmospheres August, 2012 Using real-time portable atmospheric monitors Slide 8 AIHCe 2012 PDC 411 Page 4 of 98

5 Deliberate displacement of oxygen (inertion) in a fully enclosed vessel For every 5% total volume displaced, O2 concentration drops by about 1% If 5% of the fresh air in a closed vessel is displaced by methane, the O2 concentration would be about 19.9% The atmosphere would be fully explosive while the O2 concentration would still be above the normal alarm setting! N 2 O N 2 2 N 2 O 2 N 2 N 2 N 2 O 2 N N 2 2 O N 2 2 Methane CH 4 N N N N 2 N N 2 2 N N 2 2 N N 2 2 CH 4 N 2 O 2 & N 2 N 2 N 2 N N 2 2 O 2 O 2 O 2 N 2 N N 2 2 CH 4 CH N 2 N 2 4 August, 2012 Using real-time portable atmospheric monitors Slide 9 Oxygen Enrichment Proportionally increases rate of many chemical reactions Can cause ordinary combustible materials to become flammable or explosive Any area with an O 2 level of more than 23.0% is dangerously enriched August, 2012 Using real-time portable atmospheric monitors Slide 10 AIHCe 2012 PDC 411 Page 5 of 98

6 Concentration Effect > 23% Oxygen enrichment 20.90% Normal air concentration 19.50% Minimum safe level 16% First sign of anoxia appears 16 12% 14 10% 10 6% < 6% Effects of oxygen at various concentrations Breathing and pulse rate increase, muscular co-ordination is slightly impaired Behavioral changes, impaired mental ability, abnormal fatigue upon exertion, disturbed respiration Nausea and vomiting, inability to move freely and loss of consciousness may occur Convulsive movements and gasping occurs, respiration stops August, 2012 Using real-time portable atmospheric monitors Slide 11 Measuring Oxygen (Deficiency and Enrichment) August, 2012 Using real-time portable atmospheric monitors Slide 12 AIHCe 2012 PDC 411 Page 6 of 98

7 Fuel Cell Oxygen Sensors Sensor generates electrical current proportional to the O2 concentration Sensor used up over time (one to three years) Oxygen reduced to hydroxyl ions at cathode: O 2 + 2H 2 O + 4e - 4OH - Hydroxyl ions oxidize lead (anode): 2Pb + 4OH - 2PbO + 2H 2 O + 4e - Overall cell reaction: 2Pb + O 2 2PbO August, 2012 Using real-time portable atmospheric monitors Slide 13 Oxygen Sensor Major Components of an Oxygen Sensor August, 2012 Using real-time portable atmospheric monitors Slide 14 AIHCe 2012 PDC 411 Page 7 of 98

8 Height Atm. Pressure PO 2 Partial Pressure O 2 vs. % Vol at Varying Altitudes Con. feet meters mmhg mmhg kpa % Vol 16,000 4, ,000 3, ,000 1, , , % O 2 at sea level = 18 kpa August, 2012 Using real-time portable atmospheric monitors Slide 15 Most O 2 sensors have a capillary pore used to allow sensor to self-stabilize at new pressure O 2 sensors with capillary pore are true percent by volume measurement devices Are able to self stabilize to changes in pressure due to: Barometric pressure Pressurized buildings Capillary pore (located under external moisture barrier filter) Altitude Stabilization at new pressure is not instantaneous, may take 30 seconds or longer August, 2012 Using real-time portable atmospheric monitors Slide 16 AIHCe 2012 PDC 411 Page 8 of 98

9 Output % relative to output at 20 C O 2 sensor output is affected by temperature Increasing temperature increases rate of detection reaction Readings automatically corrected by instrument Correction may not be fully linear outside manufacturer s stated operating temperature range Stabilization at new temperature is not instantaneous, may take 30 seconds or longer Temperature August, 2012 Using real-time portable atmospheric monitors Slide 17 While temperature dropping O 2 readings slightly high Once stabilized at 20, readings return to 20.9% As chamber returned to room temperature O 2 readings slightly depressed Once stabilized at room temperature, O 2 readings return to 20.9% Other sensor readings (LEL, CO, H 2 S) unaffected by temperature Actual readings of instrument cycled from +20 C to 20 C then back to +20 C August, 2012 Using real-time portable atmospheric monitors Slide 18 AIHCe 2012 PDC 411 Page 9 of 98

10 O 2 sensor response to 100% N 2 Instruments used to measure very low O 2 concentrations should be calibrated at Zero Percent O 2 as well as 20.9% Fresh Air concentration O 2 sensors can take two minutes or longer to stabilize completely in very low oxygen Make sure to wait until sensor completely stabilized before noting reading! Two point O 2 sensor calibration evaluates performance both at 20.9% and 0% oxygen August, 2012 Using real-time portable atmospheric monitors Slide 19 O 2 sensor response to 25% CO 2 and 75% N 2 August, 2012 Using real-time portable atmospheric monitors Slide 20 AIHCe 2012 PDC 411 Page 10 of 98

11 O 2 sensor response to 18% O 2, 4% CO 2 and 78% N 2 August, 2012 Using real-time portable atmospheric monitors Slide 21 O2 sensor response to 5% O2, 77% CO2 and 18% N2 August, 2012 Using real-time portable atmospheric monitors Slide 22 AIHCe 2012 PDC 411 Page 11 of 98

12 O 2 sensor response to 6% O 2 in CO 2 August, 2012 Using real-time portable atmospheric monitors Slide 23 O 2 Sensor Failure Mechanisms Lower current output: All available surface of Pb anode converted to PbO 2 Electrolyte poisoned by exposure to contaminants Electrolyte leakage Desiccation Blockage of capillary pore Higher current output: Short-term upward ramping readings due to cracks, tears or leaks allowing O 2 direct access to anode Contraction of bubbles in electrolyte due to rapid temp change Readings do not change: Loss (reduction) in platinum content in current collector and / or sensing electrode Partial occlusion of capillary pore Test sensor before each day s use! August, 2012 Using real-time portable atmospheric monitors Slide 24 AIHCe 2012 PDC 411 Page 12 of 98

13 Oxygen Pump (Lead Free) O 2 Sensors European Union (EU) Reduction of Hazardous Substances (ROHS) directive restricts use of certain substances in new electronic equipment Pb, Cd, Hg, hexavalent chromium, polybrominated biphenyls (PBB's), and polybrominated diphenyl ethers (PBDE's) Lead containing fuel cell sensors specifically excluded (for the time being) Oxygen pump sensors are lead-free alternative to fuel cell sensors August, 2012 Using real-time portable atmospheric monitors Slide 25 Oxygen Pump Detection Principle Oxygen passively diffuses into polymer (catalyst) substrate Power from instrument battery used to pump the oxygen back out Reactions: Oxidation / Reduction of target gas by catalyst Sensing: O 2 + 4H + + 4e - 2 H 2 O Counter: 2 H 2 O O 2 + 4H + + 4e - Oxygen generated on counter electrode Amount electricity required to remove reaction product and return sensor to ground state (by generating O 2 at counter electrode) proportional to concentration of oxygen present August, 2012 Using real-time portable atmospheric monitors Slide 26 AIHCe 2012 PDC 411 Page 13 of 98

14 Oxygen Pump Sensor Advantages and disadvantages Advantages: Non-consuming detection technique (sensor does not lose sensitivity or consume itself over time) Disadvantages / concerns: Detection reaction may be influenced by shifts in humidity Sensor is net consumer of electricity (drain on power supply) Important to ensure that reaction product (H 2 O) is removed from sensor August, 2012 Using real-time portable atmospheric monitors Slide 27 Explosive or Flammable Atmospheres August, 2012 Using real-time portable atmospheric monitors Slide 28 AIHCe 2012 PDC 411 Page 14 of 98

15 Fire Tetrahedron Oxygen Fuel Chain reaction Source of ignition August, 2012 Using real-time portable atmospheric monitors Slide 29 Explosive limits Lower Explosive Limit (LEL): Minimum concentration of a combustible gas or vapor in air which will ignite if a source of ignition is present Upper Explosive Limit (UEL): Most but not all combustible gases have an upper explosive limit Maximum concentration in air which will support combustion Concentrations which are above the UEL are too rich to burn Above UEL mixture too rich to burn Flammable range Below LEL mixture too lean to burn August, 2012 Using real-time portable atmospheric monitors Slide 30 AIHCe 2012 PDC 411 Page 15 of 98

16 Flammability Range The range between the LEL and the UEL of a combustible gas or vapor Concentrations within the flammable range will burn or explode if a source of ignition is present Gas Concentration Flammability Range LEL UEL August, 2012 Using real-time portable atmospheric monitors Slide 31 Different gases have different flammability ranges Gas Concentration LEL Flammability Range UEL Fuel Gas LEL (%VOL) UEL (%VOL) Acetylene Ammonia Benzene Butane Carbon Monoxide Ethylene Ethylene oxide Ethyl Alcohol Fuel Oil #1 (Diesel) Hydrogen 4 75 Isobutylene Isopropyl Alcohol 2 12 Gasoline Kerosine Methane 5 15 MEK Hexane Pentane Propane Toluene August, 2012 Using real-time portable atmospheric monitors p-xylene Slide AIHCe 2012 PDC 411 Page 16 of 98

17 Explosive Limits Propane (C 3 H 8 ) Propane Upper Explosive Limit Lower Explosive Limit Flammable range % August, 2012 Using real-time portable atmospheric monitors Slide 33 Explosive Limits Methane (CH 4 ) Methane Upper Explosive Limit Flammable range % Lower Explosive Limit August, 2012 Using real-time portable atmospheric monitors Slide 34 AIHCe 2012 PDC 411 Page 17 of 98

18 Explosive Limits Acetylene (C 2 H 4 ) has no Upper Explosion Limit! Acetylene Flammable range % Lower Explosive Limit August, 2012 Using real-time portable atmospheric monitors Slide 35 Measure of a vapor s weight compared to air Gases lighter than air tend to rise; gases heavier than air tend to sink Lighter than air Vapor density Carbon monoxide Hydrogen Ammonia Methane Propane Hydrogen sulfide Carbon dioxide Gasoline Heavier than air August, 2012 Using real-time portable atmospheric monitors Slide 36 AIHCe 2012 PDC 411 Page 18 of 98

19 Stratification Atmospheric hazards in confined spaces form layers Depending on their weights gases could be at the bottom, middle or top of a given space The only safe way to test the atmosphere of a vessel is to sample all levels at 4 foot intervals with properly calibrated instruments August, 2012 Using real-time portable atmospheric monitors Slide 37 Catalytic Hot Bead Combustible Sensor Detects combustible gas by catalytic oxidation When exposed to gas oxidation reaction causes the active (detector) bead to heat Requires oxygen to detect gas! Signal Detector Compensator +VS Output - + Trimming resistor -VS R1 R2 VR1 + D.C. voltage supply - August, 2012 Using real-time portable atmospheric monitors Slide 38 AIHCe 2012 PDC 411 Page 19 of 98

20 Combustible Gas Sensor The catalyst in the LEL sensor bead can be harmed if it is exposed to certain substances LEL sensor poisons permanently reduce or destroy the sensor s response to gas The most common LEL sensor poisons are silicon containing vapors (like the silicones used in Armour All) Sensors which may have been exposed to a poison must be tested before further use Porous refractory bead with catalyst 0.1 mm Platinum wire coil August, 2012 Using real-time portable atmospheric monitors Slide 39 Traditional LEL sensors are Flame proof devices Flame proof sensors depend on physical barriers such as stainless steel housings and flame arrestors to limit the amount of energy that can ever be released by the sensor The flame arrestor can slow, reduce, or even prevent larger molecules from entering the sensor The larger the molecule, the slower it diffuses through the flame arrestor into the sensor Stainless steel housing Flame arrestor (sinter) August, 2012 Using real-time portable atmospheric monitors Slide 40 AIHCe 2012 PDC 411 Page 20 of 98

21 Catalytic Sensor Structure August, 2012 Using real-time portable atmospheric monitors Slide 41 Typical carbon number distribution in No. 2 Diesel Fuel (liquid) Less than 2% of total diesel molecules small enough to be measured by means of standard LEL sensor August, 2012 Using real-time portable atmospheric monitors Slide 42 AIHCe 2012 PDC 411 Page 21 of 98

22 Vaporization is a function of temperature Vapors are the gaseous state of substances that are either liquids or solids at room temperatures Gasoline evaporates Dry ice (solid carbon dioxide) sublimates Increasing the temperature of the combustible liquid increases the amount of vapor produced August, 2012 Using real-time portable atmospheric monitors Slide 43 Flashpoint Temperature Temperature at which a combustible liquid gives off enough vapor to form an ignitable mixture Gasoline (aviation grade) Acetone Methyl ethyl ketone Ethanol (96 %) Diesel oil Degrees F - 50 F (approx.) 0 F 24 F 62 F F Degrees C - 45 C (approx.) - 18 C - 4 C 17 C C August, 2012 Using real-time portable atmospheric monitors Slide 44 AIHCe 2012 PDC 411 Page 22 of 98

23 Flammable and combustible liquid classifications (OSHA 29 CFR ) Flash Point Temp F Boiling Point F Examples Class IA flammable liquid Below 73 F Below 100 F Methyl ethyl ether Pentane Petroleum ether Class IB flammable liquid Below 73 F Above 100 F Acetone Ethanol Gasoline Methanol Class IC flammable liquid At or above 73 F Below 100 F Styrene Turpentine Xylene Class II combustible liquid At or above 100 F Below 140 F Fuel oil no. 44 (Diesel) Mineral spirits Kerosene Class IIIA combustible liquid Class IIIB combustible liquid At or above 140 F Below 200 F At or above August, 2012 Using real-time 200 portable F atmospheric monitors Slide 45 Aniline Carbolic acid Phenol Naphthalenes Pine oil Typical catalytic LEL sensor relative responses Relative responses of 4P-75 catalytic LEL sensor Relative response Relative response Relative response Combustible gas / vapor when sensor when sensor when sensor calibrated on calibrated on calibrated on pentane propane methane Hydrogen Methane Propane n-butane n-pentane n-hexane n-octane Methanol Ethanol Isopropanol Acetone Ammonia Toluene Gasoline (unleaded) August, 2012 Using real-time portable atmospheric monitors Slide 46 AIHCe 2012 PDC 411 Page 23 of 98

24 Catalytic pellistor combustible gas response curves Reading % LEL True LEL Concentration August, 2012 Using real-time portable atmospheric monitors Slide 47 Correction Factors Correction factor is the reciprocal of the relative response The relative response of 4P-75 LEL sensor (methane scale) to ethanol is 0.8 Multiplying the instrument reading by the correction factor for ethanol provides the true concentration Given a correction factor for ethanol of 1.25, and an instrument reading of 40 per cent LEL, the true concentration would be calculated as: 40 % LEL X 1.25 = 50 % LEL Instrument Correction True Reading Factor Concentration August, 2012 Using real-time portable atmospheric monitors Slide 48 AIHCe 2012 PDC 411 Page 24 of 98

25 Catalytic combustible LEL sensor correction factors Correction factors for 4P-75 catalytic LEL sensor Combustible gas / vapor Relative response when sensor Relative response when sensor Relative response when sensor calibrated on pentane calibrated on propane calibrated on methane Hydrogen Methane Propane n-butane n-pentane n-hexane n-octane Methanol Ethanol Isopropanol Acetone Ammonia Toluene Gasoline (unleaded) August, 2012 Using real-time portable atmospheric monitors Slide 49 According to Preamble to OSHA A combustible hazard exists whenever the combustible gas concentration exceeds 10% LEL This is the general hazardous condition threshold, NOT the concentration that should always be used for the LEL alarm set-point According to the original preamble to , if Alternate Entry Procedures are used, the hazard condition threshold is 5% LEL In some cases it may be necessary to use an even lower alarm setting to allow workers adequate time to escape August, 2012 Using real-time portable atmospheric monitors Slide 50 AIHCe 2012 PDC 411 Page 25 of 98

26 Using a lower alarm setting minimizes effect of relative response on readings Instrument Reading CH4 response new sensor Propane response 50% LEL 20% LEL 10% LEL 5% LEL Response to nonane True LEL Concentration August, 2012 Using real-time portable atmospheric monitors Slide 51 Typical catalytic percent LEL sensor response to 50% LEL methane (2.5% vol. CH 4 ) August, 2012 Using real-time portable atmospheric monitors Slide 52 AIHCe 2012 PDC 411 Page 26 of 98

27 Typical catalytic percent LEL sensor response to 50% LEL pentane (0.7% vol. C 5 H 12 ) August, 2012 Using real-time portable atmospheric monitors Slide 53 Catalytic combustible sensor exposed to various gases August, 2012 Using real-time portable atmospheric monitors Slide 54 AIHCe 2012 PDC 411 Page 27 of 98

28 CC Combustible Sensor t90 Response Versus Molecular Weight (g/mol -1 ) of Various Target Gases August, 2012 Using real-time portable atmospheric monitors Slide 55 Catalytic combustible sensor relative response inversely proportional to molecular weight of target gas August, 2012 Using real-time portable atmospheric monitors Slide 56 AIHCe 2012 PDC 411 Page 28 of 98

29 Response to methane over life of sensor CH4 response new sensor Propane response Relative response to methane may change substantially over life of sensor CH4 response partially poisoned sensor August, 2012 Using real-time portable atmospheric monitors Slide 57 Combustible Gas / Vapor Relative response when sensor is calibrated to 2.5% (50% LEL) methane Methane based equivalent calibration gas mixtures Concentration of methane used for equivalent 50% LEL response Hydrogen % CH4 Methane % Vol CH4 Ethanol % Vol CH4 Acetone % Vol CH4 Propane % Vol CH4 n-pentane % Vol CH4 n-hexane % Vol CH4 n-octane % Vol CH4 Toluene % Vol CH4 August, 2012 Using real-time portable atmospheric monitors Slide 58 AIHCe 2012 PDC 411 Page 29 of 98

30 CC LEL sensor response to 50% LEL methane ( 2.5% vol. CH 4 ), 50% LEL pentane (7.0% vol. C 5 H 12 ) and 50% LEL "pentane equivalent" (1.25% vol. CH 4 ) August, 2012 Using real-time portable atmospheric monitors Slide 59 Contaminant LEL (Vol %) Flashpoint Temp (ºF) Acetone 2.5% -4ºF (-20 ºC) Diesel (No.2) vapor 0.6% 125ºF (51.7ºC) Ethanol 3.3% 55ºF (12.8 ºC) Gasoline 1.3% -50ºF (-45.6ºC) n-hexane 1.1% -7ºF (-21.7 ºC) Isopropyl alcohol Kerosene/ Jet Fuels 2.0% 53ºF (11.7ºC) 0.7% ºF ( ºC ) MEK 1.4% 16ºF (-8.9ºC) Turpentine ºF (35ºC) Combustible sensor limitations OSHA PEL NIOSH REL TLV 5% LEL in PPM 1,000 PPM 250 PPM 500 PPM 1250 PPM TWA TWA TWA; 750 PPM STEL None Listed None Listed 15 PPM 300 PPM 1,000 PPM TWA 1000 PPM TWA 1000 PPM TWA None Listed None Listed 300 PPM TWA; 500 PPM STEL 500 PPM TWA 50 PPM TWA 400 PPM TWA None Listed 200 PPM TWA 100 PPM TWA 400 PPM TWA; 500 PPM STEL 100 mg/m3 TWA (approx PPM) 200 PPM TWA; 300 PPM STEL 100 PPM TWA Xylenes (o, m % 81 90ºF 100 PPM 100 PPM 100 PPM & p isomers) ( ºC) TWA TWA; 150 TWA; 150 August, 2012 Using real-time portable atmospheric monitors PPM STEL Slide 60 STEL 1,650 PPM 650 PPM 50 PPM TWA 550 PPM 200 PPM TWA; 400 PPM STEL 200 mg/m3 TWA (approx. 29 PPM) 1000 PPM 350 PPM 200 PPM 700 PPM TWA; 300 PPM STEL 20 PPM TWA 400 PPM PPM AIHCe 2012 PDC 411 Page 30 of 98

31 C1 C4 Aliphatic Hydrocarbon Gases TLV officially adopted in 2004 Specifies toxic exposure limit (8 hour TWA) for methane, ethane, propane and butane of 1,000 ppm Has the force of law in many jurisdictions in the United States and Canada August, 2012 Using real-time portable atmospheric monitors Slide 61 C1 C4 Monitoring Strategy Choosing a pentane level of sensitivity and 4% LEL alarm setting ensures C1 C4 TLV concentration is never exceeded For methane the alarm is activated at exactly at the 1,000 PPM limit For ethane, propane and butane the alarm is activated before the concentration reaches the 1,000 ppm limit The 4% alarm activated by: Approximately 1,000 ppm methane Approximately 816 ppm ethane Approximately 667 ppm propane Approximately 635 ppm butane An added bonus: At 4% the alarm is also activated at the TLV for pentane (600 ppm) August, 2012 Using real-time portable atmospheric monitors Slide 62 AIHCe 2012 PDC 411 Page 31 of 98

32 Effects of O 2 concentration on combustible gas readings Look at O 2 readings first! LEL readings may be affected if levels of O 2 are higher or lower than fresh air Catalytic LEL sensors require a minimum level of 10% oxygen to read LEL If the O 2 concentration is too low the LEL reading should be replaced with question marks Readings in fresh air Readings in O 2 deficient air Readings when O 2 too low for LEL sensor August, 2012 Using real-time portable atmospheric monitors Slide 63 Effects of high concentrations of gas on LEL sensor When doing atmospheric testing we are only concerned with the LEL. Why is that? Work is not permitted in areas where the concentration of gas exceeds safety limits! If the explosive gas concentration is too high there may not be enough oxygen for the LEL sensor to detect properly Concentrations above 100% LEL can damage the LEL sensor Readings in fresh air Initial alarm at 10% LEL High ( Alarm 2 ) at 20% LEL High ( Alarm 3 ) at 50% LEL Over-limit alarm (arrows) at 100% LEL August, 2012 Using real-time portable atmospheric monitors Slide 64 AIHCe 2012 PDC 411 Page 32 of 98

33 Response of electrochemical and LEL sensor to 20,000 ppm hydrogen in nitrogen August, 2012 Using real-time portable atmospheric monitors Slide 65 Combustible sensor poisons Combustible sensor poisons: Silicones (by far the most virulent poison) Hydrogen sulfide Note: The LEL sensor includes an internal filter that is more than sufficient to remove the H 2 S in calibration gas. It takes very high levels of H 2 S to overcome the filter and harm the LEL sensor Other sulfur containing compounds Phosphates and phosphorus containing substances Lead containing compounds (especially tetraethyl lead) High concentrations of flammable gas! Combustible sensor inhibitors: Halogenated hydrocarbons (Freons, trichloroethylene, methylene chloride, etc.) August, 2012 Using real-time portable atmospheric monitors Slide 66 AIHCe 2012 PDC 411 Page 33 of 98

34 Effects of H 2 S on combustible gas sensors H 2 S affects sensor as inhibitor AND as poison Some byproducts of oxidation of H2S left as deposit on active bead that depresses gas readings while inhibitor is present Sensor generally recovers most of original response once it is returned to fresh air H 2 S functions as inhibitor BUT byproducts of catalytic oxidation become very corrosive if they build up on active bead in sensor Corrosive effect can rapidly (and permanently) damage bead if not cooked off fast enough How efficiently bead cooks off contaminants is function of: Temperature at which bead is operated Size of the bead Whether bead under continuous power versus pulsing the power rapidly on and off to save operating energy August, 2012 Using real-time portable atmospheric monitors Slide 67 "Silicone resistant" combustible sensors have an external silicone filter capable of removing most silicone vapor before it can diffuse into the sensor Silicone vapor is the most virulent of all combustible sensor poisons Filter also slows or slightly reduces response to heavier hydrocarbons such as hexane, benzene, toluene, xylene, cumene, etc. The heavier the compound, the greater the effect on response (should not be used on C8 C9 hydrocarbons) Silicone resistant vs. standard pellistor type LEL sensors August, 2012 Using real-time portable atmospheric monitors Slide 68 AIHCe 2012 PDC 411 Page 34 of 98

35 Effects of hexamethyldisiloxane (HMDS) on pellistor sensor August, 2012 Using real-time portable atmospheric monitors Slide 69 Low-power pellistor issues Volume of pellistor bead (a sphere): V = 4/3 π r 3 Since most catalyst sites are within the bead (not on the surface of the bead), when you decease the radius of the bead by x, you reduce the volume of the bead (and number of catalyst sites) by x to the third power ( x 3 ) So, smaller low power LEL sensors are much easier to poison. August, 2012 Using real-time portable atmospheric monitors Slide 70 AIHCe 2012 PDC 411 Page 35 of 98

36 Allow enough time for full stabilization prior to performing fresh air zero DO NOT PERFORM AUTO ZERO AS PART OF AUTOMATIC START-UP SEQUENCE Perform functional test before each day s use! Use methane based test gas mixture OR if you use a different gas (e.g. propane or pentane) challenge the sensor with methane periodically to verify whether the sensor has disproportionately lost sensitivity to methane Low-power pellistor advice August, 2012 Using real-time portable atmospheric monitors Slide 71 Non-dispersive infrared (NDIR) sensors Many gases absorb infrared light at a unique wavelength (color) In NDIR sensors the amount of IR light absorbed is proportional to the amount of target gas present The longer the optical path through the sensor the better the resolution August, 2012 Using real-time portable atmospheric monitors Slide 72 AIHCe 2012 PDC 411 Page 36 of 98

37 Transmission Transmission Transmission Infrared Detectors When infra-red radiation passes through a sensing chamber containing a specific contaminant, only those frequencies that match one of the vibration modes are absorbed The rest of the light is transmitted through the chamber without hindrance The presence of a particular chemical group within a molecule thus gives rise to characteristic absorption bands August, 2012 Using real-time portable atmospheric monitors Slide 73 Infrared absorption spectra for several gases 1,2 1,1 1,1 11 0,9 0,9 Gas absorption spectra 0,8 0,8 0,7 0,7 0,7 Methane CH 4 0,6 0,6 0,6 T 0,5 0,5 0,5 Propane C 3 H 8 Water H 2 O 0,4 0,4 0,4 Carbon dioxide CO 2 0,3 0,3 0,3 0,2 0,2 0,2 0,1 0,1 0, Wellenlänge [nm] Wellenlänge [nm] Wellenlänge [nm] l [nm] August, 2012 Using real-time portable atmospheric monitors Slide 74 AIHCe 2012 PDC 411 Page 37 of 98

38 Infrared Detectors NDIR sensors measure absorbance at specific wavelength to determine concentration of target gas NDIR sensor consists of: Infrared emitter Optical filters that limit IR source to specific infrared wavelength range Optical chamber Pyroelectric detectors (active and reference) August, 2012 Using real-time portable atmospheric monitors Slide 75 Light path through NDIR sensor Optical path can be longer than it looks from the outside of sensor Optimal pathlength may be different for different gases August, 2012 Using real-time portable atmospheric monitors Slide 76 AIHCe 2012 PDC 411 Page 38 of 98

39 Transmission 1,1 Wavelengths typically used for NDIR measurement 1 0,9 0,8 0,7 LEL: 3.3 μm CO 2 : 4.3μm Ref: 4.0μm 0,6 T 0,5 0,4 0,3 0,2 0,1 0 l [nm] Wellenlänge [nm] 3.3μm 4.0 μm 4.3 μm August, 2012 Using real-time portable atmospheric monitors Slide 77 Requirements for IR Absorption CO 2 and CH 4 as well as most other combustible gases absorb IR Hydrogen gas ( H 2 ) DOES NOT absorb IR While acetylene absorbs IR, it is also effectively undetectable at 3.3 μm Also IR-transparent: N 2 O 2 F 2 Cl 2 Hg 2 Ar August, 2012 Using real-time portable atmospheric monitors Slide 78 AIHCe 2012 PDC 411 Page 39 of 98

40 Energy Absorbed by Bond Stretching and Bending Vibration Must have a COVALENT CHEMICAL BOND Symmetric Asymmetric Bend Stretch Stretch O S Nonlinear Molecules Linear molecules: SO August, 2012 Using real-time portable atmospheric monitors Slide 79 Infrared Spectroscopy Geometry of molecule and absorbance of light by specific bonds gives rise to a characteristic IR absorbance fingerprint of molecule August, 2012 Using real-time portable atmospheric monitors Slide 80 AIHCe 2012 PDC 411 Page 40 of 98

41 Relative response of pellistor and infrared sensors to n-hexane Both sensors were calibrated to 50% LEL methane Uncorrected readings for the pellistor LEL sensor much lower than the true concentration 50% LEL n-hexane Uncorrected readings for the IR sensor more than twice as high as the true concentration August, 2012 Using real-time portable atmospheric monitors Slide 81 Response of calibrated pellistor and IR sensors to 50% LEL n-hexane Both sensors were calibrated to 50% LEL n-hexane 50% LEL n-hexane Readings for both sensors are now very close to the true 50% LEL concentration Initial response of IR sensor is slightly quicker than the pellistor sensor However, the time to the final stable response (T100) is virtually identical for both sensors, (about 150 seconds) August, 2012 Using real-time portable atmospheric monitors Slide 82 AIHCe 2012 PDC 411 Page 41 of 98

42 Linearized NDIR combustible gas response curves August, 2012 Using real-time portable atmospheric monitors Slide 83 Response of NDIR LEL sensor (3.33 μm, 44 mm path) to various target gases Shape of raw NDIR CH 4 curve (at 3.33 μm) is less linear than other detectable gases CH 4 curve can be mathematically corrected (normalized) against the response curves of other gases of interest August, 2012 Using real-time portable atmospheric monitors Slide 84 AIHCe 2012 PDC 411 Page 42 of 98

43 Display [ %LEL C3H8 ] Display [ %LEL CH4 ] NDIR sensor performance When CH 4 is present, direct calibration to methane is the most conservative approach MK231-5 CH4-Range and C3H8-Response Calibration to CH 4 generally overestimates uncorrected readings for other aliphatic hydrocarbons; the higher the concentration the greater the overestimation Calibration to other aliphatic hydrocarbons (such as propane or hexane) underestimates uncorrected readings for methane; 20 Cal-Gas CH4 Testgas Concentration [%LEL] MK231-5 C3H8-Range and CH4-Response However, readings can be automatically 80 corrected by choosing response curve from 70 on-board library When other aliphatics are present, 30 calibration to propane provides the most 20 accurate response Cal-gas C3H8 10 Testgas CH Concentration [%UEG] August, 2012 Using real-time portable atmospheric monitors Slide Toxic Gases and Vapors August, 2012 Using real-time portable atmospheric monitors Slide 86 AIHCe 2012 PDC 411 Page 43 of 98

44 Common causes of toxic gases Materials or chemicals stored in the work area or space Compounds absorbed or present in structures or soils of work area or space Contents being disturbed upon entry Work being performed Decomposing materials Adjacent areas PDC 411: Exposure Assessment Chemical Detection in Real Time Slide 87 Toxic Exposure Limits Toxic exposure limits are defined by means of: 8-hour TWA 15-minute STEL Ceiling The exposure limit for a particular contaminant may include more than one part August, 2012 Using real-time portable atmospheric monitors Slide 88 AIHCe 2012 PDC 411 Page 44 of 98

45 Meaning of parts-per-million (ppm) 100% by volume = 1,000,000 ppm 1% by volume = 10,000 ppm 1.0 ppm the same as: One centimeter in 10 kilometers One minute in two years One cent in $10,000 August, 2012 Using real-time portable atmospheric monitors Slide 89 USA Permissible Exposure Limit (PEL) Determined by the United States Occupational Safety and Health Administration (OSHA) Sets limits for legal unprotected worker exposure to a listed toxic substance Force of law in USA! Individual states free to enact stricter, but never less conservative limits Given in Parts-per-Million (ppm) concentrations 1 % = 10,000 ppm August, 2012 Using real-time portable atmospheric monitors Slide 90 AIHCe 2012 PDC 411 Page 45 of 98

46 NIOSH Recommended Exposure Limit (REL) Determined by USA National Institute of Occupational Safety and Health (NIOSH) Guidelines for control of potential health hazards Usually more conservative than Federal OSHA exposure limits Intended as recommendation but incorporated by adoption in many states with OSHA approved safety and health plans Force of law in these states August, 2012 Using real-time portable atmospheric monitors Slide 91 TLV Toxic Exposure Limits Threshold Limit Values (TLVs ) are published by the American Conference of Governmental Industrial Hygienists (ACGIH) TLVs are the maximum concentrations to which workers may be repeatedly exposed, day after day, over a working lifetime, without adverse health effects TLVs are usually more conservative than USA OSHA Permissible Exposure Limits (PELs) or NIOSH Recommended Exposure Limits (RELs) August, 2012 Using real-time portable atmospheric monitors Slide 92 AIHCe 2012 PDC 411 Page 46 of 98

47 Toxic Exposure Limit Terms: TWA TWA: The Time Weighted Average (TWA) is the exposure averaged over a full 8-hour shift When the monitoring session is less than eight hours, the TWA is projected for the full 8-hour shift When monitoring session more than 8 hours, the TWA limit is calculated on an equivalent 8-hour shift basis August, 2012 Using real-time portable atmospheric monitors Slide 93 TWA is Projected Value According to OSHA cumulative TWA exposures for an eight hour work shift are calculated as follows: E = (C a T a + C b T b +... C n T n ) / 8 Where: E is the equivalent exposure for the eight hour working shift C is the concentration during any period of time T where the concentration remains constant T is the duration in hours of the exposure at concentration C August, 2012 Using real-time portable atmospheric monitors Slide 94 AIHCe 2012 PDC 411 Page 47 of 98

48 Toxic Exposure Limit Terms: STEL Some gases and vapors (like CO and H 2 S) have an allowable maximum Short Term Exposure Limit (STEL) which is higher than the 8-hour TWA The STEL is the maximum average concentration to which an unprotected worker may be exposed during any 15-minute interval The average concentration may never exceed the STEL during any 15-minute interval Any 15-minute interval where the average concentration is higher than the TWA (but less than the STEL) must be separated by at least 1-hour from the next, with a maximum of 4 times a shift August, 2012 Using real-time portable atmospheric monitors Slide 95 Ceiling Limit Ceiling is the maximum concentration to which an unprotected worker may be exposed Ceiling concentration should never be exceeded even for an instant The Low Peak and High Peak alarms in most portable instruments are activated whenever the concentration exceeds the alarm setting for even a moment August, 2012 Using real-time portable atmospheric monitors Slide 96 AIHCe 2012 PDC 411 Page 48 of 98

49 Immediately Dangerous to Life and Health IDLH is not part of PEL IDLH is maximum concentration from which it is possible for an unprotected worker to escape without suffering injury or irreversible health effects during a maximum 30-minute exposure Primarily used to define the level and type of respiratory protection required Unprotected workers may NEVER be deliberately exposed to IDLH or ANY concentrations which exceed the PEL August, 2012 Using real-time portable atmospheric monitors Slide 97 Exposure limits for ammonia 8-Hr TWA STEL Ceiling Federal USA OSHA PEL 50 NA NA State OSHA (1989) PEL (NIOSH REL) 25 ppm 35 ppm NA TLV 25 ppm 35 ppm NA August, 2012 Using real-time portable atmospheric monitors Slide 98 AIHCe 2012 PDC 411 Page 49 of 98

50 How are these calculations affected by the choice of datalogging interval? They re not! PEL calculations are continuously updated by the instrument The datalogging interval simply specifies how often the instrument stores a snap shot of the current readings for the purposes of generating a printed report or database file of test results August, 2012 Using real-time portable atmospheric monitors Slide 99 Substance-specific electrochemical (EC) sensors More types of sensors available every year, both for individual toxic gases as well as sensors designed to detect a range of toxic or combustible gases August, 2012 Using real-time portable atmospheric monitors Slide 100 AIHCe 2012 PDC 411 Page 50 of 98

51 Substance-specific electrochemical sensors Gas diffusing into sensor reacts at surface of the sensing electrode Sensing electrode made to catalyze a specific reaction Use of selective external filters further limits cross sensitivity August, 2012 Using real-time portable atmospheric monitors Slide 101 Typical Electrochemical Detection Mechanism H 2 S Sensor: Hydrogen sulfide is oxidized at the sensing electrode: H 2 S + 4H 2 O H 2 SO 4 + 8H + + 8e- The counter electrode acts to balance out the reaction at the sensing electrode by reducing oxygen present in the air to water: 2O 2 + 8H + + 8e- 4H 2 O And the overall reaction is: H 2 S + 2O 2 H 2 SO 4 4HS Signal Output: 0.7 A / ppm H2S August, 2012 Using real-time portable atmospheric monitors Slide 102 AIHCe 2012 PDC 411 Page 51 of 98

52 Electrochemical Sensor Performance August, 2012 Using real-time portable atmospheric monitors Slide 103 Effects of humidity on EC sensors Sudden changes in humidity can cause "transientys" in readings Sensor generally stabilizes rapidly Avoid breathing into sensor or touching with sweaty hand August, 2012 Using real-time portable atmospheric monitors Slide 104 AIHCe 2012 PDC 411 Page 52 of 98

53 Major Components of Electrochemical H2S Sensor August, 2012 Using real-time portable atmospheric monitors Slide 105 Cross sensitivities of Sensoric HCN 2E 30 F hydrogen cyanide sensor at 20 C Relative responses of Sensoric HCN 2E-30F hydrogen cyanide (HCN) sensor at 20 C Gas Concentration Reading (ppm) Alcohols 1000 ppm 0 Ammonia 100 ppm 0 Arsine 0.2 ppm 1 Carbon dioxide 5000 ppm 0 Carbon monoxide 100 ppm 1 Chlorine 1.0 ppm 0 Diborane 0.25 ppm 0.4 Hydrocarbons 1000 ppm 0 Hydrochloric acid 5 ppm 0 Hydrogen ppm 0 Hydrogen sulfide 10 ppm 0¹ Nitric oxide 100 ppm 0 Nitrogen 100% 0 Nitrogen dioxide 10 ppm -19 Ozone 0.25 ppm 0 Sulfur dioxide 20 ppm ) Short gas exposure in minute range; after filter saturation: ca. 40 ppm reading. August, 2012 Using real-time portable atmospheric monitors Slide 106 AIHCe 2012 PDC 411 Page 53 of 98

54 Concentration (% LEL) PID, CC LEL, IR LEL and CO sensors exposed to 50% LEL acetylene (1.25% volume) August, 2012 Using real-time portable atmospheric monitors Slide 107 CO and LEL sensor response to 500 ppm (2.0% LEL) acetylene in air Important notes: ppm acetylene = 2.0% LEL 2. Sensitivity of LEL sensor set to hexane scale August, 2012 Using real-time portable atmospheric monitors Slide 108 AIHCe 2012 PDC 411 Page 54 of 98

55 Response of PID and CO channel of COSH sensor to 100 ppm isobutylene (C 4 H 8 ) August, 2012 Using real-time portable atmospheric monitors Slide 109 Effects of hydrogen on CO sensor readings August, 2012 Using real-time portable atmospheric monitors Slide 110 AIHCe 2012 PDC 411 Page 55 of 98

56 Effects of hydrogen on CO sensor readings August, 2012 Using real-time portable atmospheric monitors Slide 111 Characteristics of Hydrogen Sulfide Colorless Smells like rotten eggs (at low concentrations) Heavier than air Corrosive Flammable (LEL is 4.3%) Soluble in water High concentrations kill sense of smell Extremely toxic! August, 2012 Using real-time portable atmospheric monitors Slide 112 AIHCe 2012 PDC 411 Page 56 of 98

57 Hydrogen Sulfide Produced by anaerobic sulfate-reducing bacteria Especially associated with: Raw sewage Crude oil Marine sediments Tanneries Pulp and paper industry August, 2012 Using real-time portable atmospheric monitors Slide 113 Toxic effects of H2S Toxic effects of H 2 S Concentration Symptoms 0.13 ppm Minimal detectable odor 4.6 ppm Easily detectable, moderate odour 10.0 ppm Beginning eye irritation. 27 ppm Strong unpleasant odor but not intolerable 100 ppm Coughing, eye irritation, loss of smell after 2-5 min ppm Marked eye inflammation, rapid loss of smell, respiratory tract irritation, unconsciousness with prolonged exposure ppm Loss of consciousness and possible death in 30 to 60 min 700 1,000 ppm Rapid unconsciousness, stopping or pausing of respiration and death 1,000 2,000 ppm Immediate unconsciousness, death in a few minutes. Death may occur even if person is moved to fresh air August, 2012 Using real-time portable atmospheric monitors Slide 114 AIHCe 2012 PDC 411 Page 57 of 98

58 Federal USA OSHA PEL 8-Hour TWA STEL Acceptable Ceiling Concentration Exposure limits for H2S Acceptable Max Peak Above Ceiling for an 8-Hour Shift Concentration Maximum Duration NA NA 20 ppm 50 ppm 10-minutes once only if no other measurable exposure occurs during shift REL 10 ppm 15 ppm NA NA NA TLV (2010) 1.0 ppm 5.0 ppm NA NA NA UK OEL 10 ppm 15 ppm NA NA NA FR VL 5 ppm 10 ppm NA NA NA DFG MAK 10 ppm NA 20 ppm peak in any 10-min period, (as momentary ceiling value), maximum 4 per shift August, 2012 Using real-time portable atmospheric monitors Slide 115 The answer is Yes BUT with qualifications.. Some H2S sensors easily capable of providing readings with 0.1 or 0.2 ppm resolution Are H2S sensors capable of measuring at the new TLV limits? Instrument programming (firmware) must permit setting the alarms at the desired concentration May be necessary to update firmware or replace older instrument with a newer model Dual channel COSH sensors used to measure both CO and H2S have a smaller measurement signal Depends on the manufacturer whether or not the instrument can be used with alarms set to the new TLV August, 2012 Using real-time portable atmospheric monitors Slide 116 AIHCe 2012 PDC 411 Page 58 of 98

59 Exposure limits for H2S Old TLV: TWA = 10 ppm STEL = 15 ppm New TLV: TWA = 1.0 ppm STEL = 5.0 ppm Many instruments now provide readings in 0.1 or 0.2 ppm increments Often possible to update firmware in existing instruments to increase resolution August, 2012 Using real-time portable atmospheric monitors Slide 117 Toxic effects H2S August, 2012 Using real-time portable atmospheric monitors Slide 118 AIHCe 2012 PDC 411 Page 59 of 98

60 Where should practitioners who care about the TLV set the alarms? TLV only includes STEL and TWA limits; does not include a Ceiling or Peak limit GfG instruments have 4 user settable alarms (Low, High, STEL and TWA) Many practitioners use the following approach: Low: 5.0 ppm High: 10.0 ppm STEL: 5.0 ppm TWA: 1.0 ppm August, 2012 Using real-time portable atmospheric monitors Slide 119 Characteristics of Carbon Monoxide Colorless Odorless Slightly lighter than air By-product of combustion Flammable (LEL is 12.5%) Toxic! August, 2012 Using real-time portable atmospheric monitors Slide 120 AIHCe 2012 PDC 411 Page 60 of 98

61 Carbon Monoxide Bonds to hemoglobin in red blood cells Contaminated cells can t transport O2 Chronic exposure at even low levels harmful August, 2012 Using real-time portable atmospheric monitors Slide 121 Toxic Effects CO Concentration of only 1,600 ppm fatal within hours Even lower level exposures can result in death if there are underlying medical conditions, or when there are additional factors (such as heat stress) August, 2012 Using real-time portable atmospheric monitors Slide 122 AIHCe 2012 PDC 411 Page 61 of 98

62 Toxic effects of CO Toxic effects of carbon monoxide 25 ppm TLV exposure limit for 8 hours (TWA) 200 ppm Possible mild frontal headaches in 2-3 hours 400 ppm Frontal headaches and nausea after 1-2 hours. 800 ppm Headache, dizziness and nausea in 45 min. Collapse and possibly death in 2 hours 1,600 ppm 3,200 ppm 6,400 ppm 12,800 ppm Headache and dizziness in 20 min. Unconsciousness and danger of death in 2 hours Headache and dizziness in 5-10 min. Unconsciousness and danger of death 30 min. Headache and dizziness in 1-2 min. Unconsciousness and danger of death min Unconsciousness immediately, danger of death in 1-3 min. August, 2012 Using real-time portable atmospheric monitors Slide 123 Exposure Limits for Carbon Monoxide OSHA PEL: 50 ppm 8-hr. TWA NIOSH REL: TLV: 35 ppm 8-hr. TWA 200 ppm Ceiling ppm 8-Hr. TWA August, 2012 Using real-time portable atmospheric monitors Slide 124 AIHCe 2012 PDC 411 Page 62 of 98

63 Characteristics of SO 2 Colorless gas Irritating, pungent odor Heavier than air Reacts with H 2 O to form sulfurous acid Respiratory irritant Toxic! August, 2012 Using real-time portable atmospheric monitors Slide 125 Exposure limits for SO 2 OSHA PEL: TWA = 5.0 ppm NIOSH REL: TWA = 2.0 ppm STEL = 5.0 ppm Old TLV : TWA = 2 ppm STEL = 5 ppm New (2009) TLV: STEL = 0.25 ppm August, 2012 Using real-time portable atmospheric monitors Slide 126 AIHCe 2012 PDC 411 Page 63 of 98

64 Exposure limits for SO 2 Suggested alarms: Low: 2.0 ppm High: 5.0 ppm STEL: 0.25 TWA: 0.25 ppm August, 2012 Using real-time portable atmospheric monitors Slide 127 Exposure limits for NO 2 Old TLV: 8 hr. TWA = 3 ppm 5 min. STEL = 5 ppm New 2012 TLV 8 hr. TWA = 0.2 ppm US OSHA PEL: Ceiling = 5 ppm OX US NIOSH REL: 15 min. STEL = 1 ppm August, 2012 Using real-time portable atmospheric monitors Slide 128 AIHCe 2012 PDC 411 Page 64 of 98

65 Suggested alarm settings for NO 2 Suggested GfG alarms: Low: 3.0 ppm High: 5.0 ppm STEL: 1.0 ppm TWA: 0.2 ppm OX August, 2012 Using real-time portable atmospheric monitors Slide 129 Exposure limits for HCN US OSHA PEL: TWA = 10 ppm US NIOSH REL: TLV: 15 min. STEL = 4.7 ppm Ceiling = 4.7 ppm August, 2012 Using real-time portable atmospheric monitors Slide 130 AIHCe 2012 PDC 411 Page 65 of 98

66 Exposure limits for NH 3 US OSHA PEL: TWA = 50 ppm US NIOSH REL: TLV: 8 hr. TWA = 25 ppm 15 min. STEL = 35 ppm hr. TWA = 25 ppm 15 min. STEL = 35 ppm August, 2012 Using real-time portable atmospheric monitors Slide 131 Characteristics of Chlorine Dioxide (ClO 2 ) Yellow to reddish gas Strong oxidizer Odor similar to chlorine Heavier than air Used in water treatment and as bleaching agent (pulp and paper) Extremely toxic! OX August, 2012 Using real-time portable atmospheric monitors Slide 132 AIHCe 2012 PDC 411 Page 66 of 98

67 Exposure limits for Chlorine Dioxide (ClO 2 ) OSHA PEL: 0.1 ppm (8-hr. TWA) NIOSH REL: TLV: 0.1 ppm (8-hr. TWA) 0.3 ppm STEL 0.1 ppm (8-hr. TWA) 0.3 ppm STEL Remember: it only takes % by volume to exceed the exposure limit!!! OX August, 2012 Using real-time portable atmospheric monitors Slide 133 Photoionization Detectors Used for measuring solvent, fuel and VOC vapors in the workplace environment August, 2012 Using real-time portable atmospheric monitors Slide 134 AIHCe 2012 PDC 411 Page 67 of 98

68 PID - Operating Principle PIDs use ultraviolet light as source of energy to remove an electron from neutrally charged target molecules creating electrically charged fragments (ions) This produces a flow of electrical current proportional to the concentration of contaminant The amount of energy needed to remove an electron from a particular molecule is the ionization energy (or IE) The energy must be greater than the IE in order for an ionization detector to be able to detect a particular substance August, 2012 Using real-time portable atmospheric monitors Slide 135 LEL vs. PID Sensors Catalytic LEL and photoionization detectors are complementary detection techniques Catalytic LEL sensors excellent for measurement of methane, propane, and other common combustible gases NOT detectable by PID PIDs detect large VOC and hydrocarbon molecules that are undetectable by catalytic sensors Best approach to VOC measurement is to use multi-sensor instrument capable of measuring all atmospheric hazards that may be potentially present August, 2012 Using real-time portable atmospheric monitors Slide 136 AIHCe 2012 PDC 411 Page 68 of 98

69 Operation of PID lamp, sensing and counter electrodes Detection sequence: 1. Neutrally charged molecule diffuses into glow zone Sensing electrode Reading Counter electrode Benzene molecule (neutrally charged) August, 2012 Using real-time portable atmospheric monitors Slide 137 Operation of PID lamp, sensing and counter electrodes Detection sequence: 2. Molecule is ionized Sensing electrode Reading e - + Benzene molecule is ionized Counter electrode August, 2012 Using real-time portable atmospheric monitors Slide 138 AIHCe 2012 PDC 411 Page 69 of 98

70 Operation of PID lamp, sensing and counter electrodes Detection sequence: 3. Free electron is electrostatically accelerated to positively charged sensing electrode where it is counted Sensing electrode e - + Reading Electron counted at sensing electrode Counter electrode August, 2012 Using real-time portable atmospheric monitors Slide 139 Operation of PID lamp, sensing and counter electrodes Detection sequence: Sensing electrode 4. Positively charged fragment (ion) is electrostatically accelerated to counter electrode, where it picks up a replacement electron and regains neutral charge e - Reading Neutrally charged molecule diffuses out of detector Counter electrode August, 2012 Using real-time portable atmospheric monitors Slide 140 AIHCe 2012 PDC 411 Page 70 of 98

71 How does a PID work? August, 2012 Using real-time portable atmospheric monitors Slide 141 Ionization Energy IE determines if the PID can detect the gas If the IE of the gas is less than the ev output of the lamp the PID can detectthe gas Ionization Energy (IE) measures the bond strength of a gas and does not correlate with the Correction Factor Ionization Energies are found in the NIOSH Pocket Guide and many chemical texts August, 2012 Using real-time portable atmospheric monitors Slide 142 AIHCe 2012 PDC 411 Page 71 of 98

72 Ionization Energy Values Ionization energy values Gas / vapor Ionization energy (ev) Carbon monoxide Carbon dioxide Methane Water Oxygen Chlorine Hydrogen sulfide n-hexane Ammonia hexane (mixed isomers) acetone 9.69 benzene 9.25 butadiene 9.07 toluene 8.82 August, 2012 Using real-time portable atmospheric monitors Slide 143 PID Components Detector assembly Electrodes: sensing, counter and (in some designs) fence Lamp: most commonly 10.6EV, 11.7eV or 9.8 ev August, 2012 Using real-time portable atmospheric monitors Slide 144 AIHCe 2012 PDC 411 Page 72 of 98

73 PID lamp characteristics Window material and the filler gas determine output characteristics as well as operational life of lamp PID lamp characteristics Nominal lamp photon energies Primary gas in lamp Major emission lines Relative intensity Window crystal ev λ (nm) 11.7 ev Argon Lithium fluoride (LiF) ev Krypton Magnesium fluoride (MgF2) ev Krypton Calcium fluoride (CaF2) Crystal transmittance λ range (nm) August, 2012 Using real-time portable atmospheric monitors Slide 145 Critical PID Performance Issues: Effects of Humidity and Contamination Condensation and contamination on lamp window and sensor surfaces can create surface conduction paths between sensing and counter electrodes Buildup of contamination provides nucleation points for condensation, leading to surface currents If present, surface currents cause false readings and / or add significant noise that masks intended measurement (sometimes called moisture leakage ) PID designs MAY require periodic cleaning of the lamp and detector to minimize the effects of contaminants and humidity condensation on PID readings August, 2012 Using real-time portable atmospheric monitors Slide 146 AIHCe 2012 PDC 411 Page 73 of 98

74 PID instruments are nonspecific Cannot distinguish between different contaminants they are able to detect Provide single total reading for all detectable substances present PID readings always relative to gas used to calibrate detector August, 2012 Using real-time portable atmospheric monitors Slide 147 PID Correction Factors Correction factors are APPROXIMATE values Correction Factor (CF) is measure of sensitivity of PID to specific gas CFs do not make PID specific to a chemical, only correct the measurement scale to that chemical CFs allow calibration on inexpensive, non-toxic surrogate gas (like isobutylene) Most manufacturers furnish tables, or built-in library of CFs to correct or normalize readings when contaminant is known Instrument able to express readings in parts per million equivalent concentrations for the contaminant measured August, 2012 Using real-time portable atmospheric monitors Slide 148 AIHCe 2012 PDC 411 Page 74 of 98

75 CF measures sensitivity Low CF = high PID sensitivity to a gas More toxic the gas, more desirable to have low correction factor: If Exposure limit is < 10 ppm, CF should be < 1 If chemical less toxic, higher CF may be acceptable If Exposure limit is > 10 ppm, CF < 10 When CF > 10 use PIDs as gross leak detectors only High correction factor magnifies effects of humidity effects, zero drift, and interfering gases and vapors August, 2012 Using real-time portable atmospheric monitors Slide 149 Decision making with a PID Two sensitivities must be understood to make a decision with a PID Human Sensitivity: as defined by AGCIH, NIOSH, OSHA or corporate exposure limits PID Sensitivity: as defined through testing by the manufacturer of your PID ONLY USE A CORRECTION FACTOR FROM THE MANUFACTURER OF YOUR PID! August, 2012 Using real-time portable atmospheric monitors Slide 150 AIHCe 2012 PDC 411 Page 75 of 98

76 Correction Factors (10.6 ev Lamp) Examples of manufacturer PID correction factors (10.6 ev lamp) Gas / vapor RAE BW Ion GfG IE (ev) Acetaldehyde Acetone Ammonia Benzene Butadiene Diesel fuel n/a Ethanol Ethylene Gasoline n/a n-hexane Jet fuel (JP-8) n/a Kerosene n/a n/a 9.53 Methyl-ethyl-ketone (MEK) Naptha (iso-octane) Styrene Toluene Turpentine n/a Vinyl chloride Xylene (mixed isomers) August, 2012 Using real-time portable atmospheric monitors Slide 151 Actual response of 10.6 ev equipped PID isobutylene (C 4 H 8 )scale to 1000 ppm toluene (C 7 H 8 ) August, 2012 Using real-time portable atmospheric monitors Slide 152 AIHCe 2012 PDC 411 Page 76 of 98

77 PID Alarms: Varying Mixtures The Controlling Compound Every mixture of gases and vapors has a compound that is the most toxic and controls the setpoint for the whole mixture Determine that chemical and you can determine a conservative mixture setpoint If we are safe for the worst chemical we will be safe for all chemicals August, 2012 Using real-time portable atmospheric monitors Slide 153 PID Alarms: Varying Mixtures Chemical Name 10.6eV CF NIOSH REL Exposure Limit (8-hr. TWA) Ethanol Turpentine Acetone Ethanol appears to be the safest compound Turpentine appears to be the most toxic This table only provides half of the decision making equation August, 2012 Using real-time portable atmospheric monitors Slide 154 AIHCe 2012 PDC 411 Page 77 of 98

78 PID Alarms: Varying Mixtures Set the PID for the compound with the lowest Exposure Limit (EL) in equivalent units and you are safe for all of the chemicals in the mixture Divide the EL in chemical units by CF to get the EL in isobutylene EL Isobutylene = EL chemical CF chemical August, 2012 Using real-time portable atmospheric monitors Slide 155 PID Alarms: Varying Mixtures Chemical name CF iso (10.6eV) NIOSH REL (8 hr. TWA) EL ISO (PEL) TLV (8hr. TWA) EL ISO (TLV) Ethanol Turpentine Acetone IF you are following the NIOSH REL then ethanol is the controlling compound when the exposure limits are expressed in equivalent Isobutylene Units The equivalent EL iso is a calculation that involves a manufacturer specific Correction Factor (CF) Similar calculations can be done for any PID brand that has a published CF list BE CAREFUL: If you are following the TLV the controlling chemical would be turpentine! August, 2012 Using real-time portable atmospheric monitors Slide 156 AIHCe 2012 PDC 411 Page 78 of 98

79 Choosing the best sensor configuration Multi-sensor instruments can include up to seven channels of real-time measurement Available sensors for combustible gas and VOC measurement:: CC %LEL IR %LEL IR %Vol Thermal Conductivity %Vol Electrochemical toxic PID August, 2012 Using real-time portable atmospheric monitors Slide 157 PID, CC LEL, IR LEL and CO sensors exposed to 50% LEL isobutylene (9,000 ppm) The maximum full-range reading for the PID was 3,000 ppm (= 17.5% LEL Isobutylene). Readings at or above this concentration are logged at the maximum value August, 2012 Using real-time portable atmospheric monitors Slide 158 AIHCe 2012 PDC 411 Page 79 of 98

80 Response of IR LEL, CC LEL, PID and CO sensors to 15% LEL turpentine vapor August, 2012 Using real-time portable atmospheric monitors Slide 159 Test run# 1: PID, CC LEL, IR LEL and CO sensors exposed to diesel vapor August, 2012 Using real-time portable atmospheric monitors Slide 160 AIHCe 2012 PDC 411 Page 80 of 98

81 Test run# 4: PID, CC LEL, IR LEL and CO sensors exposed to diesel vapor August, 2012 Using real-time portable atmospheric monitors Slide 161 Selection matrix for Sensors for measurement of combustible gas and VOCs August, 2012 Using real-time portable atmospheric monitors Slide 162 AIHCe 2012 PDC 411 Page 81 of 98

82 Examples of possible sensor configurations optimized for specific applications* * Note that the listed sensor configurations represent possible solutions for specific applications. The presence of additional conditions or requirements may change the optimal sensor configuration. August, 2012 Using real-time portable atmospheric monitors Slide 163 Case Study Fuel barge explosion and cleanup On February 21, 2003, a fuel barge loaded with gasoline exploded at a fuel loading dock on Staten Island, New York Two workers were killed and another critically burned The explosion was the result of an accident, not terrorism or sabotage The barge had unloaded about half its cargo of 4 million gallons of unleaded gasoline when the explosion occurred USCG photo by PA3 Mike Hvozda August, 2012 Using real-time portable atmospheric monitors Slide 164 AIHCe 2012 PDC 411 Page 82 of 98

83 Case Study Gasoline was released from the damaged berth area where a section of the aboveground piping ruptured USCG photos by PA3 Mike Hvozda August, 2012 Using real-time portable atmospheric monitors Slide 165 Case Study As the blaze was at its height, officials used tugs to push a nearby barge loaded with 8 million gallons of gasoline to the other side of the waterway, where they covered it with water and foam to ensure that it did not explode. August, 2012 Using real-time portable atmospheric monitors Slide 166 AIHCe 2012 PDC 411 Page 83 of 98

84 Case Study Once the fire was extinguished and the barges cooled, Marine Chemist and Coast Guard personnel conducted structural inspections Exposure to toxic VOCs was a primary concern Chemicals of concern included the remaining gasoline, benzene, total BTEX (benzene, toluene, ethylbenzene, and xylenes) and total polycyclic aromatic hydrocarbons (such as naphthalene) USCG photo by PA3 Mike Hvozda August, 2012 Using real-time portable atmospheric monitors Slide 167 What about benzene? Benzene is almost never present all by its by itself Benzene is usually minor fraction of total VOC present Test for total hydrocarbons (TVOC), especially if the combustible liquid has an established PEL or TLV Diesel Kerosene Jet Fuel (JP-8) Gasoline 15 ppm 30 ppm 30 ppm 300 ppm August, 2012 Using real-time portable atmospheric monitors Slide 168 AIHCe 2012 PDC 411 Page 84 of 98

85 Actual toxicity testing results from gasoline fuel barge #1 Previous Loadings: Cat Feedstock/Crude Oil/Cat Feedstock SPACE % LEL PPM TVOC (iso) PPM Benzene %TVOC from benzene No (1) Port Cargo Tank % No (2) Port Cargo Tank % No (3) Port Cargo Tank % No (4) Port Cargo Tank % No (5) Port Cargo Tank % No (1) Stbd Cargo Tank % No (2) Stbd Cargo Tank % No (3) Stbd Cargo Tank % No (4) Stbd Cargo Tank % No August, (5) StbdCargoTank 2012 Using real-time portable 0 atmospheric 64.8 monitors 0.5 Slide % TVOC alarm setting based on fractional concentration benzene for Barge #1 Worst case (No 1 Port Cargo Tank) TVOC hazardous condition threshold alarm of 172 ppm isobutylene would prevent exceeding the PEL for benzene of 1.0 PPM 41 x.0244 = ppm TVOC Hazardous Condition Threshold Alarm for compliance with: Benzene Exposure Limit 1.0 PPM 0.5 PPM 0.1 PPM TVOC alarm setting 41 PPM 20.5 PPM 4.1 PPM August, 2012 Using real-time portable atmospheric monitors Slide 170 AIHCe 2012 PDC 411 Page 85 of 98

86 Actual toxicity testing results from gasoline fuel barge #2 Previous Loadings: Natural Gasoline (3X) SPACE % LEL PPM TVOC (iso) PPM Benzene %TVOC from benzene No (1) Port Cargo Tank % No (2) Port Cargo Tank % No (3) Port Cargo Tank % No (4) Port Cargo Tank % No (5) Port Cargo Tank % No (1) Stbd Cargo Tank % No (2) Stbd Cargo Tank % No (3) Stbd Cargo Tank % No (4) Stbd Cargo Tank % No (5) StbdCargoTank % August, 2012 Using real-time portable atmospheric monitors Slide 171 TVOC alarm setting based on fractional concentration benzene for Barge #2 Worst case (No 5 Port Cargo Tank) TVOC hazardous condition threshold alarm of 172 ppm isobutylene would prevent exceeding the PEL for benzene of 1.0 PPM 172 x.0058 = ppm TVOC Hazardous Condition Threshold Alarm for compliance with: Benzene Exposure Limit 1.0 PPM 0.5 PPM 0.1 PPM TVOC alarm setting 172 PPM 86 PPM 17.2 PPM August, 2012 Using real-time portable atmospheric monitors Slide 172 AIHCe 2012 PDC 411 Page 86 of 98

87 Diffusion mode: Passively measures contaminants or conditions in atmosphere immediately surrounding the instrument Simple, convenient, continuous Ways of using gas detectors Remote sampling: uses motorized pump or hand-aspirator (squeeze bulb) to draw sample through hose and probe assembly back to instrument Pick-hole sampling: Pre-ventilation Sampling during initial (purge) ventilation Final pre-entry Whatever the sampling method, monitor continuously while the work or entry underway! August, 2012 Using real-time portable atmospheric monitors Slide 173 Sample-Draw vs. Diffusion Drawbacks of diffusion operation: Instrument only able to monitor the atmosphere in the immediate vicinity of sensors Only way to obtain readings from remote location is to lower the instrument by rope or lanyard into the confined space Not possible to use monitor for pick hole sampling (requires additional hand aspirator sample draw kit or motorized pump) August, 2012 Using real-time portable atmospheric monitors Slide 174 AIHCe 2012 PDC 411 Page 87 of 98

88 Hand-aspirated sample-draw kit Available for almost all models of diffusion type multi-gas instruments Make sure to squeeze the bulb the required number of times for sample to reach the sensors Continue to squeeze bulb until readings are stable Make sure to test the system for leakage prior to use: Block end of the sample tubing or probe with finger Squeeze the aspirator bulb Bulb should stay deflated until blockage is removed August, 2012 Using real-time portable atmospheric monitors Slide 175 Drawbacks of sample-draw operation: Sample-Draw vs. Diffusion Sample lag time: instrument cannot detect contaminants until they reach the sensors Always wait long enough for sample to reach sensors PLUS time it takes for sensors to respond fully Potential for leakage in the system: critical to test system for leakage prior to use Potential for pump malfunction: instruments with internal motorized pump only operable as long as pump functions Potential for absorbance: some types of tubing, filters and materials in the squeeze-bulb or pump can absorb or limit some gases and vapors from reaching sensors Make sure type of tubing used (e.g. Tygon, butyl, PTFE, etc.) is compatible or appropriate for type of vapor being measured Potential for vapor condensation in tubing: keep length of sample tubing as short as possible August, 2012 Using real-time portable atmospheric monitors Slide 176 AIHCe 2012 PDC 411 Page 88 of 98

89 Sampling Rules Using motorized sample pump equipped instruments Do not exceed the manufacturer s maximum sampling distance Allow 2 seconds per foot of tubing for sample to reach the sensors (minimum requirement) Allow at least 2 minutes AFTER sample reaches sensors before noting respons Confined Space sampling: Top, Middle, Bottom (at a minimum, sample at every 4 ft. interval August, 2012 Using real-time portable atmospheric monitors Slide 177 Perform proper instrument start up Make sure instrument has been properly bump-tested before use Perform proper pump start up (if applicable) Performing a Gas Test Make sure sample probe assembly is used whenever using the motorized sampling pump Make sure sample probe assembly is equipped with hydrophobic barrier and particulate filters replace if discolored or dirty, or if the flow is being blocked Test all areas as required August, 2012 Using real-time portable atmospheric monitors Slide 178 AIHCe 2012 PDC 411 Page 89 of 98

90 Wait until the sensor readings have completely stabilized! Time required for proper testing Remember that when you use an instrument in diffusion mode you may need up to 2-minutes or even longer for the sensors to finish stabilizing If tubing or a wand is used as well you have to add an additional 2-sec per foot for the gas to reach the sensors So if you are testing a vessel that is 10 feet deep and tubing is used, how long would it take to test the entire vessel (entry level, mid level and bottom): ((120 seconds) + (2 sec. x 10 feet)) x 3 = 420 seconds = 7 minutes The time it takes for the sensors to finish stabilizing after the gas begins to reach the sensors The time it takes for the pump to pull the sample through a 10 foot length of tubing The number of tests required August, 2012 Using real-time portable atmospheric monitors Slide (c)(5)(ii)(C): Before an employee enters the space, the internal atmosphere shall be tested, with a calibrated directreading instrument What does OSHA accept as a "calibrated" direct reading instrument? A testing instrument maintained and calibrated in accordance with the manufacturer's recommendations The best way for an employer to verify calibration is through documentation Mandatory to use a "calibrated" instrument maintained according to "manufacturer requirements" August, 2012 Using real-time portable atmospheric monitors Slide 180 AIHCe 2012 PDC 411 Page 90 of 98

91 The response of gas detecting sensors can change over the life of the sensor The changes may be sudden, or can be gradual Substances or conditions present in the atmosphere can have an adverse effect on the sensors Different types of sensors have different constraints and conditions which can lead to loss of sensitivity or failure Important to know how sensors detect gas to understand conditions that can lead to inaccurate readings Why do instruments need to be tested and / or calibrated? August, 2012 Using real-time portable atmospheric monitors Slide 181 Follow manufacturer recommendations Allow instrument to stabilize after turning on Make sure readings in fresh air are correct Perform fresh air calibration if needed Verify Accuracy Daily! Perform functional bump test before each day s use Perform span calibration if necessary Make sure the instrument has been calibrated! August, 2012 Using real-time portable atmospheric monitors Slide 182 AIHCe 2012 PDC 411 Page 91 of 98