Work Environment EH 262 Objectives Become familiar with exposure limits, their basis, and application in the workplace. y Be able to understand the various acronyms, their basis and application y Understand the regulatory structure as it relates to exposure limits. y Develop the ability to perform exposure calculations through examples y ACGIH (Post Litigation Statements Bold added by JHS) y ACGIH® is a not-for-profit scientific association. y ACGIH® proposes guidelines known as TLVs® and BEIs® for use by industrial hygienists in making decisions regarding safe levels of exposure to various hazards found in the workplace. y ACGIH® is not a standards setting body. Regulatory bodies should view TLVs® and BEIs® as an expression of scientific opinion. TLVs® and BEIs® are not consensus standards y . ACGIH® TLVs® and BEIs® are based solely on health factors; there is no consideration given to economic or technical feasibility. Regulatory agencies should not assume that it is economically or technically feasible to meet established TLVs® or BEIs®. y ACGIH® believes that TLVs® and BEIs® should NOT be adopted as standards without an analysis of other factors necessary to make appropriate risk management decisions. TLVs® and BEIs® can provide valuable input into the risk characterization process. y Regulatory agencies dealing with hazards addressed by a TLV® or BEI® should review the full written documentation for the numerical TLV® or BEI®. TLV- Threshold Limit Value Refer to airborne concentrations of substances and represent conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse health effects y Because of wide variation in individual susceptibility, however, a small percentage of workers may experience discomfort from some substances at concentrations at or below the threshold limit; a smaller percentage may be affected more seriously by aggravation of a pre-existing illness. y Notice of intended changes - proposed actions for the coming year. The proposed TLVs are to be used during that year. y TLVs- Threshold Limit Values y Three types of TLVs TLV-TWA Threshold Limit Value- Time Weighted Average is the time weighted average concentration for an average 8-10 hour day AND 40 hour workweek. TLV-STEL Threshold Limit Value- Short-Term Exposure Limit is the concentration to which workers can be exposed continuously for a short period of time without suffering from irritation, chronic or irreversible damage, narcosis sufficient to increase likelihood of injury PROVIDED that the TLV-TWA is not exceeded. It supplements the TLV-TWA not a separate exposure limit. TLVs- Threshold Limit Values y y TLV-C TLV-Ceiling is the concentration that should not be exceeded during any part of the workday. May be measured instantaneously Direct reading instrument, e.g., colorimetric tubes, or more often sampling over a 15 minute period. Some materials only have a TLV-C, e.g., HCl, HBr and glutaraldehyde often due to irritant properties The difference between the TLV-C and TLV-TWA is that excursions above the TLV-TWA are allowed as long as other periods or exposure are low enough that the time weighted average is less than or equal to the TLV-TWA. y No excursions above the TLV-C are allowed. TLVs (continued) y y y y TLV-STEL is a 15 minute TWA exposure which should not be exceeded at any time during the workday , even if the TLV-TWA is still acceptable. Exposures above the TWA and up to the STEL should be no longer than 15 minutes and not occur more than 4 times per day with at least 60 minutes between successive exposures. What sampling time would you use to assess compliance with a TLV-C? (instantaneous is possible, usually 5-15 minute sample) Excursions above the TLV-TWA should be limited to 5 times the TLV but may be exceeded by 3X for a total of 30 minutes. TLV-STEL takes precedence if available. TLV-C TLV-STEL ppm TLV-TWA Time TLVs (continued) y “Skin” notation -- Skin contact can be a major contributor to overall exposure. Chemicals that readily penetrate the skin often have high octanol-water partition coefficients. Other factors such as MW also impact the skin Permeability Constant (Kp in cm/hr). log Kp = -2.72 + 0.71 (log Kow) - 0.0061 (MW) From EPA, 1992, EPA Dermal Exposure Assessment Handbook Note: There are many gaps in our understanding of dermal absorption. y If a chemical has a high octanol water partition coefficient and has a low dermal LD50 , e.g., 1000 mg/Kg a skin notation is considered. Unusual Workshifts: Brief and Scala Model Brief R, Scala R. Occupational Exposure Limits for Novel Work Schedules. American Industrial Hygiene Association Journal. 36:467-469, 1975 y Must know the number of hours worked per 24 hour day. y A simple calculation and is the most conservative model. No detailed knowledge about the substance is needed. y Formula: Adjusted (TWA) = 8 x (24 - h) x Exposure Standard (8-hour TWA) 16 x h where h = hours worked/day y What is the adjusted TWA for Ethyl alcohol if the 8 -hour TWA is 1000 ppm and the actual workshift is 12 hours? Adjusted TWA = 8 x (24 - 12) x 1000 ppm 16 x 12 = 500 ppm (12-hour TWA) y No adjustment of the exposure standard is made for substances assigned with a Peak Limitation, e.g., chlorine or hydrogen chloride Unusual Workshifts, Weekly Adjustments: Brief and Scala Model Brief R, Scala R. Occupational Exposure Limits for Novel Work Schedules. American Industrial Hygiene Association Journal. 36:467-469, 1975 y Must know the number of hours worked per week. y Weekly Reduction Factor = (40/h) x (168-h) 128 where h = hours worked per day y Adjusted Exposure Limit = 8 hr OEL x Weekly Reduction Factor where h = hours worked/day What is the adjusted TWA for Ethyl alcohol if the 8 -hour TWA is 1000 ppm and the actual workweek is 10 hours, 5 days a week? Adjusted TWA = 1000 ppm x (40/50) x (168-50) 128 = 738 ppm y No adjustment of the exposure standard is made for substances assigned with a Peak Limitation, e.g., chlorine or hydrogen chloride Calculations y TWA for one substance [T1(C1)+T2(C2)+…Tn(Cn)] ----------------------------- = TWA Ttotal y TWA for a mixture (Additive) C1 ----- + TLV1 C2 …Cn --------- + ------TLV2 TLVn.. =? If the result exceeds 1, above TLV y TWA for a mixture (Independent) C1 ---T1 or C2 ----T2 Result of either one cannot exceed 1. Calculations y A worker is exposed to 4 ppm of hydrogen chloride gas (TLV-C 5 ppm) and simultaneously to 2 ppm of hydrogen bromide (TLV-C 3 ppm). Assuming additivity (based on irritant effects) does the exposure exceed the TLV? C1 ----- + TLV1 4 ppm ----5 ppm C2 Cn --------- +…------TLV2 TLVn + = 2 ppm --------- = 1.47 = 1.5 3 ppm Therefore, TLV for mixture is exceeded. Calculations y A worker is exposed to 4 ppm of hydrogen chloride gas (TLV-C 5 ppm) and simultaneously to 2 ppm of hydrogen bromide (TLV-C 3ppm). Assuming INDEPENDENCE of effects does the exposure exceed the TLV? C1 C2 Is ----- or --------- > 1 TLV2 TLV1 4 ppm 2 ppm ----= 0.8 , --------- = 0.67 5 ppm 3 ppm How does this compare when additivity is assumed for this set of exposures? Calculations y TLV of a mixture of liquids 35% toluene, 35% xylene and 30% hexane. (Units MUST BE mg/m3) TLV mix TLV 1 = mix F1 TLV = F2 TLV + 1 0.35 188 mg/m 3 + .. 2 1 0.35 + 434 mg/m 1 TLV mix = TLV mix = 230 0.00437 mg/m mg/m 3 3 Fn TLV 3 + n 0.30 176 mg/m 3 Other Topics Covered in TLV Booklet y y y y y y Carcinogens (Appendix A) A1 Confirmed Human A2 Suspected Human A3 Animal A4 Not classifiable as a human carcinogen A5 Not suspected as a human carcinogen Notice of Intended Changes Exposure levels can be changed as well as the classification, e.g., benzene is proposed to change from an A2 carcinogen to A1. Substances Variable Composition Welding fume Polytetrafluoroethylene Decomposition Products Chemical Substances Under Study Particle Size Selective TLVs Inhalable Particulate Mass Deposited anywhere in the respiratory tract (<100 um) Thoracic Particulate Mass (<25 um) Deposited in the lung airways or the gas exchange region Respirable Particulate Mass (<10 um) Deposited in the gas exchange region Example: Silica respirable dust Biomonitoring y BEI - Biological Exposure Indices Complements air monitoring . Useful when there is an advantage over air sampling alone Useful for substantiating air monitoring Evaluating PPE Evaluating skin absorption y Sampling media y Blood (venous, arterial) e.g. mg/100 deciliter of blood Urine (mg/100 ml urine, 5.0 mg/g creatinine) Exhaled air (ppm) Nails, Hair (ppm, mg/g...) Because there is a BEI, it does not imply a necessity for biomonitoring Biomonitoring (Continued) y When the sample is taken, strictly adhere to the method. These are examples of different sample collection times for the ACGIH BEIs. End of shift (Phenol) End of shift at end of workweek (Co, Cr) During or end of shift (Methemoglobin inducers) End of workweek (Perchloroethylene) Prior to next shift (Styrene) Discretionary (organophosphates) Not critical (Pb) BEIs (Continued): Issues on Interpretation y y y y Interindividual variability Intraindividual variability Background levels (B) Susceptible groups (Sc) y What do you do when the biomonitoring data do not support the air monitoring data? y May be due to: Physiological/health status of worker Exposure by other routes, e.g. dermal, ingestion Environmental sources (outside work) life style (after work activities) Sample collection, handling etc. BEIs y Documentation of TLVs and BEIs is a very valuable resource Metabolic pathways, metabolites, percentage of total by each pathway ….. Routes of excretion and relative amounts References Rationale for BEI and how it relates to the TLV-TWA Background exposures, their significance and sources Susceptible groups (high risk groups) Methanol BEI Example Please review the methanol BEI document provided in the class folder. Note the types and depth of data. TLVs for Physical Agents y y y y y y y y y y y y y y Ultrasonics Cold Stress Hand-Arm Vibration Heat Stress Ionizing Radiation Lasers Light and Near Infrared Noise Rf and Microwave Static Magnetic Fields Sub-radiofrequency Magnetic Fields Ultraviolet Light Lifting, Whole Body Vibration are being added Example: Ultraviolet Light (weighting of wavelengths) WL (nm) TLV (mJ/cm2) 200 100 210 40 220 25 230 16 240 10 250 7.0 254 6.0 260 4.6 270 3.0 280 3.4 290 4.7 300 10 305 50 310 200 315 1000 Ultraviolet Light: Exposure Limits by Wavelength UVA 400 nm - 320 nm UVB 320 nm - 290 nm UVC 290 nm - 100 nm OSHA Exposure Limits y y y PEL Permissible Exposure Levels Legally enforceable Contained in the following tables: 1910.1000+ Table Z-1 Table Z-2 Table Z-3 y Derived from 1968 ACGIH TLVs and ANSI consensus standards. y PELs are TWAs calculated for an eight hour exposure 2hr(100 ppm) +4hr(200ppm)+2hr(200ppm) = TWA= 175 ppm 8 hr y Denominator in OSHA PEL calculation is always 8 hours regardless of how long the sample was taken. y Action Level is usually but not always 50% of PEL (e.g., lead). If Action Level is exceeded certain actions are triggered, e.g., medical monitoring, air sampling etc. y Newer OSHA standards include provisions for: medical monitoring, required exposure monitoring, training, recordkeeping, housekeeping procedures....etc (see asbestos and arsenic standards for examples) Individual Standards Under OSHA: Lead Standard 1910.1025 (Not Complete) y 1910.1025(a) y Scope and application. y 1910.1025(a)(1) y This section applies to all occupational exposure to lead, except as provided in paragraph (a)(2). y 1910.1025(a)(2) y This section does not apply to the construction industry or to agricultural operations covered by 29 CFR Part 1928. y 1910.1025(b) y Definitions. y "Action level" means employee exposure, without regard to the use of respirators, to an airborne concentration of lead of 30 micrograms per cubic meter of air (30 ug/m(3)) averaged over an 8-hour period. y "Assistant Secretary" means the Assistant Secretary of Labor for Occupational Safety and Health, U.S. Department of Labor, or designee. y "Director" means the Director, National Institute for Occupational Safety and Health (NIOSH), U.S. Department of Health, Education, and Welfare, or designee. y "Lead" means metallic lead, all inorganic lead compounds, and organic lead soaps. Excluded from this definition are all other organic lead compounds. y 1910.1025(c) y Permissible exposure limit (PEL). y 1910.1025(c)(1) y The employer shall assure that no employee is exposed to lead at concentrations greater than fifty micrograms per cubic meter of air (50 ug/m(3)) averaged over an 8-hour period. OSHA PELs Table Z-1 (1910.1000) OSHA PELs Table Z-2 (1910.1000) OSHA PELs Table Z-3 (1910.1000) Silica Calculation y Sample collected with a personal cyclone placed in the breathing zone of the worker. The lab analyzed the sample by x-ray diffraction. The lab reported that the sample contained 23% quartz (a form of silica) and the total mass collected in your 8 hour sample collected by a cyclone sampler operating at 1.7 liter/min was 4 mg. Is the exposure in compliance with the OSHA PEL for respirable Silica dust? Silica Calculation y OSHA PEL for respirable silica (quartz) is calculated as follows: 10 mg/m3 10 mg/m3 ------------------------------------- = 0.4 mg/m3 = PEL, % Silica + 2 23 + 2 Volume sampled = (1.7 liters/min) x (480 min) = 816 liters (816 liters) x (1 m3/1000 liters) = 0.816 m3 4 mg Concentration in sample = --------------- = 4.9 mg/m3 0.816 m3 Very significant over exposure to respirable crystalline silica NIOSH RELs REL Recommended Exposure Limit Not Legally Enforceable Based on the health related data, does not consider feasibility. y REL can be expressed as a TWA, STEL or Ceiling y Applies to situations with up to 10 hour workday and 40 hour week. y y y WEELs and ERPGs y y y y Work Environmental Exposure Levels (WEEL) Emergency Response Planning Guidelines (ERPG) Both published by the AIHA and contain rationale for selecting the level, background information and user guidance Only 100+ available Occupational Exposure Limits (OEL) In Alphabetical order y y y y y y y y y y Australia China EU Germany Japan Norway Portugal Russia Singapore ……many others Global Samples of OELs Acrylamide PRIME NAME: ACRYLAMIDE CAS: 79-06-1 RTECS NUMBER: AS3325000 INTERNATIONAL OCCUPATIONAL EXPOSURE VALUES -AUSTRALIA:TWA 0.3 mg/m3; Skin; Carcinogen JAN93. -BELGIUM:TWA 0.3 mg/m3; Skin; Carcinogen JAN93. -DENMARK:TWA 0.3 mg/m3; Skin; Carcinogen JAN93. -FINLAND:TWA 0.3 mg/m3; STEL 0.9 mg/m3 JAN93. -FRANCE:TWA 0.3 mg/m3 JAN93. -HUNGARY:STEL 0.3 mg/m3; Skin; Carcinogen JAN93. -IRELAND: TWA 0.3 mg/m3; Skin; Carcinogen JAN-97 -JAPAN (JSOH) [1999-2000]:TWA 0.3 mg/m3; Skin -THE NETHERLANDS :TWA 0.3 mg/m3 JAN93. -THE PHILIPPINES:TWA 0.3 mg/m3; Skin JAN93. -POLAND: TWA 0.1 mg/m3; Skin 1998 -RUSSIA:STEL 0.2 mg/m3; Skin JAN93. -SWEDEN:TWA 0.3 mg/m3; STEL 0.9 mg/m3; Skin JAN93. -SWITZERLAND:TWA 0.3 mg/m3; Skin; Carcinogen JAN93.
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