exposure limits

8/12/2019 Exposure Limits

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Objectives Become familiar with exposure limits,

their basis, and application in theworkplace.

Be able to understand the various

acronyms, their basis and application Understand the regulatory structure as it

relates to exposure limits. Develop the ability to perform exposure

calculations through examples


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ACGIH(Post Litigation Statements

Bold added by JHS)

ACGIH is a n o t - f o r - p r o f i t sc ie n t i f i c a s so c i a t i o n .

ACGIHproposes guidelines known as TLVs a n d B EI s f o r u s e b yi n d u s t r i a l h y g i e n i s t s in making decisions regarding safe levels of exposureto various hazards found in the workplace.

ACGIH is n o t a s t a n d a r d s se t t i n g b o d y . Regulatory bodies should viewTLVs and BEIs as an expression of scientific opinion. TLVs and BEIs arenot consensus standards

. ACGIH TLVs and BEIs are b a s e d s o le l y o n h e a l t h f a c t o r s ; there isno consideration given to economic or technical feasibility. Regulatoryagencies should not assume that it is economically or technically feasible tomeet established TLVs or BEIs.

ACGIH believes that TLVs and BEIs s h o u l d N O T b e a d o p t e d a s

s t a n d a r d s w i t h o u t a n a n a l y s i s of other factors necessary to makeappropriate risk management decisions. TLVs and BEIs can providevaluable input into the risk characterization process.

Reg u l a t o r y a g e n c i e s dealing with hazards addressed by a TLV or BEI

should review the full written documentation for the numerical TLV orBEI.


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TLV- Threshold Limit Value

Refer to airborne concentrations of substances andrepresent conditions under which it is believed that nearly

all workers may be repeatedly exposed day after daywithout adverse health effects

Because of wide variation in individual susceptibility,however, a small percentage of workers may experience

discomfort from some substances at concentrations at orbelow the threshold limit; a smaller percentage may beaffected more seriously by aggravation of a pre-existingillness.

Notice of intended changes - proposed actions for thecoming year. The proposed TLVs are to be used duringthat year.


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TLVs- Threshold Limit Values

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 withoutsuffering from irritation, chronic or irreversible

damage, narcosis sufficient to increase likelihood ofinjury PROVIDED that the TLV-TWA is not exceeded. Itsupplements the TLV-TWA not a separate exposurelimit.


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TLVs- Threshold Limit Values

TLV-C TLV-Ceiling is the concentration that should not be

exceeded during any part of the workday. May bemeasured instantaneously Direct reading instrument,e.g., colorimetric tubes, or more often sampling over a15 minute period.

Some materials only have a TLV-C, e.g., HCl, HBr andglutaraldehyde 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 thatthe time weighted average is less than or equal to theTLV-TWA.

No excursions above the TLV-C are allowed.


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TLVs (continued) 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 60minutes 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 takesprecedence if available.

ppm

TLV-STEL

TLV-TWA

Time

TLV-C


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TLVs (continued) 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. Otherfactors such as MW also impact the skin PermeabilityConstant (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 dermalabsorption.

If a chemical has a high octanol water partition coefficient andhas a low dermal LD50 , e.g., 1000 mg/Kg a skin notation isconsidered.


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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

Must know the number of hours worked per 24 hour day.

A simple calculation and is the most conservative model. No detailed knowledge about the substance isneeded.

Formula:

Adjusted (TWA) = 8 x (24 - h) x Exposure Standard (8-hour TWA)

16 x h

where h = hours worked/day

What is the adjusted TWA for Ethyl alcohol if the 8 -hour TWA is 1000 ppm and the actual workshift is 12hours?

Adjusted TWA = 8 x (24 - 12) x 1000 ppm

16 x 12

= 500 ppm (12-hour TWA)

No adjustment of the exposure standard is made for substances assigned with a Peak Limitation, e.g.,chlorine or hydrogen chloride


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Unusual Workshifts,

Weekly Adjustments:

Brief and Scala ModelBrief R, Scala R. Occupational Exposure Limits for Novel Work Schedules. American Industrial Hygiene Association

Journal. 36:467-469, 1975

Must know the number of hours worked per week.

Weekly Reduction Factor = (40/h) x (168-h)

128

where h = hours worked per day

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 theactual workweek is 10 hours, 5 days a week?

Adjusted TWA = 1000 ppm x (40/50) x (168-50)

128

= 738 ppm

No adjustment of the exposure standard is made for substances assigned with a Peak Limitation, e.g., chlorine orhydrogen chloride


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Calculations TWA for one substance

[T1(C1)+T2(C2)+Tn(Cn)]----------------------------- = TWA

Ttotal

TWA for a mixture (Additive)C1 C2 Cn----- + --------- + ------- = ?TLV1 TLV2 TLVn..

If the result exceeds 1, above TLV TWA for a mixture (Independent)

C1 C2---- or -----

T1 T2

Result of either one cannot exceed 1.


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Calculations A worker is exposed to 4 ppm of hydrogen chloride

gas (TLV-C 5 ppm) and simultaneously to 2 ppmof hydrogen bromide (TLV-C 3 ppm). Assumingadditivity (based on irritant effects) does theexposure exceed the TLV?

C1 C2 Cn----- + --------- +------- =TLV1 TLV2 TLVn

4 ppm 2 ppm----- + --------- = 1.47 = 1.55 ppm 3 ppm

Therefore, TLV for mixture is exceeded.


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Calculations A worker is exposed to 4 ppm of hydrogen

chloride gas (TLV-C 5 ppm) andsimultaneously to 2 ppm of hydrogen bromide(TLV-C 3ppm). Assuming INDEPENDENCE of

effects does the exposure exceed the TLV?

C1 C2Is ----- or --------- > 1TLV

1

TLV24 ppm 2 ppm

----- = 0.8 , --------- = 0.675 ppm 3 ppm

How does this compare when additivity isassumed for this set of exposures?


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Calculations TLV of a mixture of liquids 35% toluene, 35%

xylene and 30% hexane. (Units MUST BEmg/m3)

n

n

2

2

1

1

mix

TLV

F..TLV

F

TLV

F

1TLV

++

=

333

mix

mg/m176

0.30

mg/m434

0.35

mg/m188

0.35

1TLV

++

=

3mix

3mix

mg/m230TLV

mg/m0.00437

1TLV

=

=


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Other Topics Covered in

TLV Booklet 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 (


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Biomonitoring (Continued) When the sample is taken, strictly adhere

to the method. These are examples ofdifferent sample collection times for theACGIH 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)


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BEIs (Continued):

Issues on Interpretation Interindividual variability Intraindividual variability

Background levels (B) Susceptible groups (Sc)

What do you do when the biomonitoring data do not

support the air monitoring data? May be due to:

Physiological/health status of worker Exposure by other routes, e.g. dermal, ingestion

Environmental sources (outside work) life style (afterwork activities)

Sample collection, handling etc.


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BEIs Documentation of TLVs and BEIs is a very valuable

resource

Metabolic pathways, metabolites, percentage of total byeach 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)


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TLVs for

Physical Agents 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 ofwavelengths)


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UVA 400 nm - 320 nm

UVB 320 nm - 290 nm

UVC 290 nm - 100 nm


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OSHA Exposure Limits PEL Permissible Exposure Levels Legally enforceable Contained in the following tables:

1910.1000+ Table Z-1 Table Z-2 Table Z-3

Derived from 1968 ACGIH TLVs and ANSI consensus standards.

PELs are TWAs calculated for an eight hour exposure

2hr(100 ppm) +4hr(200ppm)+2hr(200ppm) = TWA= 175 ppm

Denominator in OSHA PEL calculation is always 8 hours regardless of how long the

sample was taken.

Action Level is usually but not always 50% of PEL (e.g., lead). If Action Level isexceeded certain actions are triggered, e.g., medical monitoring, air sampling etc.

Newer OSHA standards include provisions for: medical monitoring, required exposure

monitoring, training, recordkeeping, housekeeping procedures....etc (see asbestosand arsenic standards for examples)

8 hr


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Individual Standards Under OSHA: Lead

Standard 1910.1025(Not Complete) 1910.1025(a)

Scope and application.

1910.1025(a)(1)

This section applies to all occupational exposure to lead, except as provided in paragraph (a)(2).

1910.1025(a)(2)

This section does not apply to the construction industry or to agricultural operations covered by 29 CFR Part 1928.

1910.1025(b)

Definitions.

"Action level" means employee exposure, without regard to the use of respirators, to an airborne concentration of lead of 30micrograms per cubic meter of air (30 ug/m(3)) averaged over an 8-hour period.

"Assistant Secretary" means the Assistant Secretary of Labor for Occupational Safety and Health, U.S. Department of Labor, ordesignee.

"Director" means the Director, National Institute for Occupational Safety and Health (NIOSH), U.S. Department of Health, Education,and Welfare, or designee.

"Lead" means metallic lead, all inorganic lead compounds, and organic lead soaps. Excluded from this definition are all other organiclead compounds.

1910.1025(c)

Permissible exposure limit (PEL).

1910.1025(c)(1)

The employer shall assure that no employee is exposed to lead at concentrations greater than fifty micrograms per cubic meterof air (50 ug/m(3)) averaged over an 8-hour period.

OSHA PEL


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OSHA PELs

Table Z-1 (1910.1000)

OSHA PEL


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OSHA PELs

Table Z-2 (1910.1000)

OSHA PEL


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OSHA PELs

Table Z-3 (1910.1000)


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Silica Calculation Sample collected with a personal cyclone placed in the

breathing zone of the worker. The lab analyzed thesample by x-ray diffraction. The lab reported that thesample contained 23% quartz (a form of silica) and thetotal mass collected in your 8 hour sample collected by a

cyclone sampler operating at 1.7 liter/min was 4 mg. Isthe exposure in compliance with the OSHA PEL forrespirable Silica dust?


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Silica Calculation OSHA PEL for respirable silica (quartz) is calculated as follows:

10 mg/m3

10 mg/m3

------------------ = PEL, -------------------- = 0.4 mg/m3

% 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 mgConcentration in sample = --------------- = 4.9 mg/m3

0.816 m3

Very significant over exposure to respirable crystalline silica


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NIOSH RELs REL Recommended Exposure Limit Not Legally Enforceable

Based on the health related data, does not considerfeasibility.

REL can be expressed as a TWA, STEL or Ceiling Applies to situations with up to 10 hour workday and 40

hour week.


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WEELs and ERPGs 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


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Occupational Exposure Limits

(OEL) Australia China EU Germany Japan Norway Portugal Russia Singapore many others

In Alphabetical order


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Global Samples of OELs

AcrylamidePRIME NAME: ACRYLAMIDECAS: 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 [1999]: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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