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 [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.