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1
Occupational Exposure Limits
Lectures: based on chapter 4
Instructor:Dr. Ephraim Massawe
Credit: The Occupational Environment -- Its Evaluation and Control
Guidelines to control untoward health effects in the traditional workplace
Protection for workers day after day without adverse health effects Basis for Setting OELs
◦ Human use and experience Epidemiological data Medical case histories Human exposure data vs. adverse effect
◦ Long term animal toxicity studies Best for chronic toxicity and carcinogenicity
◦ Short term animal toxicity studies Dermal data on skin penetration Basis for STEL or Ceiling Limit
2
Goals of OELs
Credit: The Occupational Environment -- Its Evaluation and Control
Special studies in animals ◦ Genotoxicity (use of model animals) evaluations pp66
In vitro and In vivo tests are most desirable Useful for threshold considerations Limitations – false negatives/false positives?
◦ Developmental/reproductive toxicity studies pp67 Teratogens also included in this category Male or female reproductive performance? Behavioral/functions of off-springs or parents? pp67
◦ Metabolism/pharmacokinetics pp66 Absorption (uptake), distribution, fate and elimination
◦ Physical chemical properties
3
Basis for Setting OELs(continued)
Credit: The Occupational Environment -- Its Evaluation and Control
Types of exposure & duration pp66◦ acute? ◦ Subacute/subchronic-pp66?)◦ Chronic?
Species tested (rats/dogs/etc… Chemical factors Test compounds Dose, rate, route factors Route of administration Genetic factors Immunologic and dietary factors Gender, age and emotional status
4
Evaluating Animal Toxicology Studies
Credit: The Occupational Environment -- Its Evaluation and Control
Amount required to produce effects Route of exposure Type of tumors Number of species affected Tumor incidence Time of tumor Metabolism Genetic effects Other: hormonal status, target organ for non-neoplastic lesions
5
Potency of Carcinogens
Credit: The Occupational Environment -- Its Evaluation and Control
The projection, extension, or expansion of known data or experience into an area not known or experienced so as to arrive at a usually conjectured knowledge of the unknown area by inferences based on an assumed continuity, correspondence, or other parallelism between it and what is known.(WEBSTER'S Dictionary)
6
Extrapolation
Credit: The Occupational Environment -- Its Evaluation and Control
Established for workday exposure frequencies and duration, not for continuous exposures.
Intended to provide protection for healthy, young, white male workers, not for the general populations.
Based on widely different types and severity of health effects, some of which may be irrelevant for the general population.
Based on data that varies widely in accuracy and age. Presumed to provide an adequate margin of safety for the workplace,
an adjustment difficult to quantify.
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Extrapolating OELs to Ambient Environments
Credit: The Occupational Environment -- Its Evaluation and Control
ACGIH TLVs AIHA WEEL Guides NIOSH RELs OSHA PELs Standards-Regulatory EPA’s____?
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Occupational Exposure Limits OELs
Credit: The Occupational Environment -- Its Evaluation and Control
Dose = Concentration x Time
D = C x T
C: You will need to conduct field evaluation to obtain it!
T: Time for the task of a worker
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Dose-Response Relationship
Credit: The Occupational Environment -- Its Evaluation and Control
Exposure Dose◦ That amount of chemical substance to which a given organism
is exposed ◦ Expressed as:
parts per million (ppm) for gases & vapors milligram per cubic meter (mg/m3) for solids i.e. particulates
Absorbed dose:◦ That amount of a chemical substance deposited in or absorbed
by a given organism◦ Expressed as:
mg/kg
10
Dose
Credit: The Occupational Environment -- Its Evaluation and Control
ACGIH formed in 1939 MAK (Maximum Allowable Concentration) Committee established 1941 pp63
◦ 5 years later published list of MAKs◦ Problems with MAK concept
Based on TLVs, not maximum ceiling Implication of “allowable”
1960 TLVs ® substituted for MAKs ACGIH Policy They are not developed for use as legal standards, and the ACGIH does not
advocate their use as such (may protect all people in all cases). The Threshold Limit Values (TLVs ®) and Biological Exposure Indices (BEIs)
are developed as guidelines to assist in the control of health hazards. These recommendations or guidelines are intended for use in the practice of
IH, to be interpreted and applied only by a person trained in this discipline.
12
History of ACGIH & ACGIH Policy
Credit: The Occupational Environment -- Its Evaluation and Control
“Threshold limit values refer to airborne concentrations of chemical substances and represents conditions under which it is believed that nearly all workers may be repeatedly exposed, day after day, over a working lifetime, without adverse effects.”
Susceptible Person “TLVs® will not adequately protect all persons. Some individuals may experience discomfort or even more serious adverse health effects when exposed to a chemical at the TLV ® or even at concentrations below the TLV ®. There are numerous possible reasons for increased susceptibility to a chemical substance, including age, gender, ethnicity, genetic factors (predisposition), lifestyle choices (e.g., diet, smoking, abuse of alcohol or other drugs), medications, and pre-existing medical conditions (e.g., aggravation of asthma or cardiovascular disease). “
13
TLV Definition
Credit: The Occupational Environment -- Its Evaluation and Control
Air Contaminants Time-weighted average (TWA) Ceiling value (C) Short-term exposure limit (STEL)
Range of TLVsHighest
◦ Carbon dioxide - 5000 ppmLowest
◦ Strontium chromate - 0.0005 mg/cu.m.
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Types of TLVs ®
Credit: The Occupational Environment -- Its Evaluation and Control
TLVs are established in terms of ppm mg/m3 values are determined by calculation conversion based upon
760 mm Hg and 25oC (77oF) If samples are taken at P and T conditions different from TLV NTP
conditions and results are in mg and m3, results must be corrected prior to comparison
Converting Concentration
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Comparison & Converting Concentration
45.24))((
)()45.24)(3/()(
)3/(weightmoleculargramppmTLV
weightmoleculargrammmgTLVppmTLV
mmgTLV
Credit: The Occupational Environment -- Its Evaluation and Control
TLV Limitations◦ Not a relative index of toxicity◦ Not a community allowable limit◦ Not for exposures >8 hr/day; or >40 hr/wk◦ Not to be used as proof of hazard (absence of hazard or
protective of all people at all times in all cases)
Changes in TLVs®
◦ Documentation produced◦ Submitted to committee◦ Notice of intended change
After January committee meeting
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TLV® Limitations & Changes in TLVs®
Credit: The Occupational Environment -- Its Evaluation and Control
Sensory irritation e.g. NH3
Lower respiratory irritation e.g. O3
Physical irritation e.g. CaCO3, PNOC Neuropathic effects e.g. n-Hexane Metabolic effects e.g. CO, HCN General systemic toxicity e.g. hexafluoroacetone Hepatotoxicity e.g. ethylene dichloride Cancer (carcinogenic) e.g. benzene Narcosis butane, CFC-12 Sensitization e.g. TDI, MDI Odor e.g. isopropyl ether Analogy e.g. aniline derivatives, methemaglobin anaemia Others e.g. cardiovascular (CS2), ocular (methanol)
428 PELs for which changes were considered by OSHA, 29CFR Part 1910 Air Contaminants; Final Rule
17
Establishing TLVs
Credit: The Occupational Environment -- Its Evaluation and Control
ACGIH Carcinogen A1 Confirmed human carcinogen
◦ human data A2 Suspected human carcinogen
◦ animal data due to conflicting or insufficient human data A3 Animal carcinogen
◦ not relevant for extrapolation to humans A4 Not classified as a human carcinogen
◦ inadequate data A5 Not suspected as a human carcinogen
◦ good negative human◦ considers animal data
Note: If no data exists, compounds remains unclassified
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Classification Schemes for carcinogens pp 69/70
Credit: The Occupational Environment -- Its Evaluation and Control
Average exposure for an individual over a working period of time as determined by taking one or more samples during the working period
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Time Weighted Average TWA
TLV - TWA = ———————————C1T1 + C2T2 + … + CNTN
T1 + T2 + … + TN
Credit: The Occupational Environment -- Its Evaluation and Control
Average exposure for an individual over an 8-hr working period of time as determined by taking one or more samples during the 8-hr working period
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8-Hr Time Weighted Average
81 1 2 2
8TLV TWA
C T C T C TN N
hrs
. . .
Credit: The Occupational Environment -- Its Evaluation and Control
A degreaser operator is monitored for exposure to Stoddard solvent. The monitoring data is:
TIME PERIOD(NUMBER)
CONCENTRATION(PPM)
TIME(HOUR)
1 80 22 110 43 55 2
Example
Where: C = airborne concentration t = time
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TLV-TWA Calculation
81 1 2 2
8TLV TWA
C T C T C TN N
hrs
. . .
81 1 2 2
8TLV TWA
C T C T C TN N
hrs
. . ..
Eight Hr TLV-TWA = 88.75 ppmSolution to the Example
Credit: The Occupational Environment -- Its Evaluation and Control
Excursions in worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a workday, and under no circumstances should they exceed 5 times the TLV-TWA, provided the TLV-TWA is not exceeded
Applicable to TLV-TWAs that do not have STELs
22
Excursion Limit pp60
Credit: The Occupational Environment -- Its Evaluation and Control
Short Term Exposure Limit (STEL) A 15 minute TWA exposure that should not be exceeded anytime during the workday even if 8-hour TWA is within TLV-TWA
The concentration to which workers can be exposed continuously for a short period of time without suffering from:
irritationchronic or irreversible tissue damagenarcosis of sufficient degree to increase the likelihood of accidental injury, impaired self-rescue or materially reduce work efficiencyExposures above TLV-TWA up to STEL:Should not be longer than 15 minutesShould not occur more than 4 times a dayShould be at least 60 minutes between successive exposures in this range
Ceiling Value Concentration that should not be exceeded during any part of the
working exposure Designated by “C” preceding substance listing
Ceiling Value Determination◦ In conventional industrial hygiene practice if instantaneous
monitoring is not feasible, then the TLV-C can be assessed by sampling over a 15-minute period except for those substances that may cause irritation when exposures are short.
23
Ceiling Value pp61
Credit: The Occupational Environment -- Its Evaluation and Control
Substances followed by the designation “Skin” refer to the potential significant contribution to the overall exposure by the cutaneous route, including mucous membranes and the eyes, either by contact with vapors, by direct skin contact with the substance.
Air sampling alone may be insufficient to accurately quantify exposure and measures to prevent significant cutaneous absorption may be required.
24
Skin Notation pp61
Credit: The Occupational Environment -- Its Evaluation and Control
If the biological effects of mixture components are additive:
Where CN = Measured TWA concentration
TN = TLV for a substances
If ratio is < 1, combined exposure is less than TLV (in compliance)If ratio is > 1, combined exposure exceeds TLV (out of compliance
If biological effects of mixture components are: Synergistic or potentates toxicity; Hazard must be determined
individually; and/or Antagonistic No guidelines are presented
25
Mixtures
1
1
2
2
C
T
C
T
C
TK
N
N
. . .
Credit: The Occupational Environment -- Its Evaluation and Control
Adjustments to the TLVs may be needed to apply the TLVs when work schedules are markedly different from the 8-hour day, 40-hour week.Adjustments are not generally necessary if:
◦ The goal of the exposure limit is to avoid excessive irritation or odor, or
◦ the biological half-life of the toxicant is less than 3 hours or more than 400 hours.
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Unusual Work Schedules
Credit: The Occupational Environment -- Its Evaluation and Control
If the goal of the OEL is to minimize the likelihood of a systemic effect, the concentration to which persons can be exposed should be less than the TLV if: ◦ they work more than 8 hr/day or more than 40 hr/wk, and ◦ the chemical has a half-life between 4 and 400 hours.
If the biological half-life is unknown, a “safe” level can be estimated by assuming that the chemical has a biologic half-life of about 20 hours.
This will generally yield the most conservative adjustment factor for typical 10-, 12-, and 14-hr workdays.
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Guidance
Credit: The Occupational Environment -- Its Evaluation and Control
OSHA Model
Brief and Scala Model◦ T is the duration of exposure
Hickey and Reist Model
t1 = hours worked per day on unusual schedule
t2 = 24 times days worked/week on unusual schedule
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Adjusting OELs
Modified PEL PELhours
T hours
T hours
8
8
( )
( )
Modified TLV PELhours
T hours
T hoursTLV
8 24
16
( )
( )
( )
Modified TLV TLV
k
t
ke
t ke
ke
t ke
81
1
1201
11 2
2 0 693
160 04
1 2
ln ..
/
Credit: The Occupational Environment -- Its Evaluation and Control
Assuming that 1,2-trichloroethane has a biologic half-life of 16 hours in people, what modified TLV or PEL would be appropriate for persons who wished to work 3 days, 12 hours per day for the work week.
The present ACGIH TLV and OSHA PEL for 1,2-trichloroethane is 10 ppm.
Solution
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Example
Credit: The Occupational Environment -- Its Evaluation and Control
Modified PEL PEL
hours
T hours
ppm
Modified TLV TLV
hours
T hours
T hours
TLV ppm
Modified TLV TLV
k
e
t k
e
k
e
t k
e
ppm
8
6 66
8 24
16
5 0
8
1
1
1
120
1
2
1
7 5
( )
( )
.
( )
( )
( )
.
.
Type of LimitRecommending Body Legally Binding?
Permissible exposure limit Occupational Safety and Health Administration Yes
Recommended exposure limit National Institute for Occupational Safety and Health No
Threshold limit value American Conference of Governmental Industrial Hygienists No
Workplace Environmental American Industrial Hygiene Association (AIHA) NoExposure Level
New chemical exposure limit Environmental Protection Agency (EPA) Yes
Maximum allowable Deutsche Forschungsgemeinschaft (Commission for the Noconcentration Investigation of Health Hazards of Chemical Compounds(translated) in the Work Area) (Germany)
Occupational exposure limit Health and Safety Commission & NoHealth and Safety Executive (Britain)
Emergency Response AIHA (community-based standard, not an OEL) NoPlanning Guide
Reference concentration EPA (community-based standard, not an OEL) Yes
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Summary of Various Inhalation Exposure Limits pp62
Credit: The Occupational Environment -- Its Evaluation and Control
LD50 Probable
Toxicity Common Single Oral Vapor Exposure LD50 Lethal Dose
Rating Term Dose (Rats) MortalityA Skin (Rabbits) for Humans
1 extremely toxic 1 mg or less/kg <10 ppm 5 mg or less/kg a taste, 1 grain
2 highly toxic 1–50 mg 10–100 5–43 mg/kg 1 teaspoon, 4 cc
3 moderately toxic 50–500 mg 100–1000 44–340 mg/kg 1 ounce, 30 g
4 slightly toxic 0.5–5 g 1000–10,000 0.35–2.81 g/kg 1 pint, 250 g
5 practically nontoxic 5–15 g 10,000–100,000 2.82–22.59 g/kg 1 quart
6 relatively harmless 15 g and more >100,000 22.6 or more g/kg >1 quart
Source: Hodge, H.C. and J.H. Sterner: Tabulation of toxicity classes. Am. Ind. Hyg. Assoc. Q. 10:93 (1949). AInhalation 4 hours, 2/6–4/6 rats
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Combined Tabulation of Toxicity Classes
Credit: The Occupational Environment -- Its Evaluation and Control
Hazard Toxicity Categories
Indicators I II III IV
Oral LD50 up to and including from 50–500 mg/kg from 500–5000 mg/kg >5000 mg/kg
50 mg/kg
Inhalation LC50 up to and including from 0.2–2 mg/L from 2–20 mg/L >20 mg/L
0.2 mg/L
Dermal LD50 up to and including from 200–2000 mg/kg from 2000–20,000 mg/kg >20,000 mg/kg
200 mg/kg
Eye effects corrosive; corneal corneal opacity no corneal opacity; no irritation
opacity not reversible reversible within 7 irritation reversible
within 7 days days; irrigation within 7 days
persisting for 7 days
Skin effects corrosive severe irritation at 72 hrs moderate irritation at 72 hrs mild or slightirritation at 72 hrs
Source: Code of Federal Regulations Title 40, Part 162.10 (h)
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Warnings and Precautionary Statements — EPA (FIFRA)
Credit: The Occupational Environment -- Its Evaluation and Control
Acute oral LD50 highly toxic; LD50 £ 50 mg/kg toxic; 50 mg/kg < LD50 £ 500 mg/kg
Acute dermal LD50 highly toxic; LD50 £ 200 mg/kg; 24 hrs toxic; 200 mg/kg < LD50 £ 1000 mg/kg
LC50 inhalation highly toxic; LC50 £ 200 ppm toxic; 200 ppm; < LC50 £ 2000 ppm
LC50 £ 2 mg/L; 1 hr 2 mg/L £ LC50 < 20 mg/L
Carcinogen if IARC “carcinogen” or “potential carcinogen”; or if National Toxicology
Program “carcinogen” or “potential carcinogen”; or OSHA regulated
carcinogen
Corrosive visible destruction of, or irreversible alterations in living tissue by contact; 4 hrs
Irritant not corrosive; reversible inflammatory effect on living tissue by contact; 4 hrs;
skin score ³ 5
Sensitizer substantial portion of exposed people or animals develop allergic reaction
Source: Code of Federal Regulations Title 29, 1910.1200. Appendix A
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OSHA Health Hazard Definitions
Credit: The Occupational Environment -- Its Evaluation and Control
Inhalation Gases, Skin EyeAcute OralA Dermal Vapors (ppm) Irritation IrritationToxicity Liquids, Liquids, Dusts, Fumes, Liquids, Liquids,Rating Solids Solids Mists (mg/L) Solids Solids
LD50 Rat (mg/kg) LD50 Rabbit (mg/kg) LC50Rat 4-hr ExposureB
1-hr Exposure
4 0–1 0–20 0–0.2 mg/L not applicable not applicable
3 >1–50 >20–200 >0.2–2 mg/L severely corrosive; irreversible>20–200 ppm irritating and/or corneal opacity>20–200 ppm corrosive
2 >50–500 >200–1000 >2–20 mg/L primary irritant irritating or moderately >200–2,000 ppm sensitizer persisting > 7 days with
reversible corneal opacity
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Acute Toxicity Rating Criteria
Credit: The Occupational Environment -- Its Evaluation and Control
Inhalation Gases, Skin EyeAcute OralA Dermal Vapors (ppm) Irritation IrritationToxicity Liquids, Liquids, Dusts, Fumes, Liquids, Liquids,Rating Solids Solids Mists (mg/L) Solids Solids
1 >500–5000 >1000–5000 >20–200 mg/L slightly irritating slightly irritating but
>2000–10,000 ppm reversible within 7 days
0 >5000 >5000 >200 mg/L essentially nonirritating essentially nonirritating>10,000 ppm
AThe oral route of exposure is highly unlikely in a workplace setting. If situations are encountered through where the oral LD50 value would indicate a significantly different rating, toxicity values for the other routes of entry may be considered more appropriate when assigning the rating. BNote animal species and duration of exposure if different from that recommended.
Source: National Paint & Coatings Association (Hazardous Materials Identification System® HMIS®; Label Master); Washington, DC
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Acute Toxicity Rating Criteria(continued)
Credit: The Occupational Environment -- Its Evaluation and Control