1 lectures: based on chapter 4 instructor: dr. ephraim massawe credit: the occupational environment...

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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

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Goals of OELs


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)


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


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


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)

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Extrapolation


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


ACGIH TLVs AIHA WEEL Guides NIOSH RELs OSHA PELs Standards-Regulatory EPA’s____?

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Occupational Exposure Limits OELs


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


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

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Dose


Dose

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Dose Response

Resp

on

se


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.

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History of ACGIH & ACGIH Policy


“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). “

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TLV Definition


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 ®


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


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®


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

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Establishing TLVs


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


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


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

. . .


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


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

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Excursion Limit pp60


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.

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Ceiling Value pp61


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.

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Skin Notation pp61


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

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Mixtures

1

1

2

2

C

T

C

T

C

TK

N

N

. . .


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


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


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 ..

/


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


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


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


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)


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


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


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)


1 lectures: based on chapter 4 instructor: dr. ephraim massawe credit: the occupational environment...

Documents

occupational environment

field evaluation

chronic toxicity

expansion of known data

workday exposure frequencies

adverse health effectsbasis

workers day

c x t c