Limits of Exposure to Toxic and Hazardous Substances
In the workplace, an important potential health hazard is
overexposure to airborne toxic and hazardous substances. Thus, health
standards, called Permissible Exposure Limits (PELs) by OSHA, and health
guidelines, called the Threshold Limit Values (TLVs) by the American
Conference of Governmental Industrial Hygienists (ACGIH), have been
established to protect workers from adverse health effects related to
chemical exposure. The following paragraphs are reproduced from the ACGIH
publication, 1994-1995 Threshold Limit Values for Chemical Substances and
Physical Agents, and are included here to give the reader an understanding of
the basis for TLVs.
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"Threshold Limit Values (TLVs) 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. 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 preexisting condition or by development of an occupational illness. Smoking
of tobacco is harmful for several reasons. Smoking may act to enhance the
biological effects of chemicals encountered in the workplace and may reduce
the body's defense mechanisms against toxic substances."
"Individuals may also be hypersusceptible or otherwise
unusually responsive to some industrial chemicals because of genetic factors,
age, personal habits (smoking, alcohol, or other drugs), medication, or
previous exposures. Such workers may not be adequately protected from adverse
health effects from certain chemicals at concentrations at or below the
threshold limits. An occupational physician should evaluate the extent to
which such workers require additional protection."
"TLVs are based on available information from industrial
experience; from experimental human and animal studies; and, when possible,
from a combination of the three. The basis on which the values are established
may differ from substance to substance; protection against impairment or health
may be a guiding factor for some, whereas reasonable freedom from irritation,
narcosis, nuisance, or other forms of stress may form the basis for others.
Health impairments considered include those that shorten life expectancy,
compromise physiological function. impair the capability for resisting other
toxic substances or disease processes, or adversely affect reproductive
function or developmental processes."
"The amount and nature of the information available for
establishing a TLV varies from substance to substance; consequently, the
precision of the estimated TLV is also subject to variation and the latest
TLV Documentation should be consulted in order to asses the extent of the
data available for a given substance."
"These limits are intended for use in the practice of
industrial hygiene as guidelines or recommendations in the control of
potential health hazards and for no other use, e.g., in the evaluation or
control of community air pollution nuisances; in estimating the toxic
potential of continuous, uninterrupted exposures or other extended work
periods; as proof or disproof of an existing disease or physical condition;
or adoption or use by countries whose working conditions or cultures differ
from those in the United States of America and where substances and
processes differ. These limits are not fine lines between safe and
dangerous concentration nor are they a relative index of toxicity.
They should not be used by anyone untrained in the discipline of industrial
hygiene."
"The TLVs, as issued by the American Conference of
Governmental Industrial Hygienists, are recommendations and should be used as
guidelines for good practices. In spite of the fact that serious injury is
not believed likely as a result of exposure to the threshold limit
concentrations, the best practice is to maintain concentrations of all
atmospheric contaminants as low as is practical."
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There are different types of TLVs. The TLV-TWA is a
Time Weighted Average concentration guideline for an 8-hour workday and a
40-hour workweek to which nearly all workers may be repeatedly exposed, day
after day, without adverse effect. Some chemicals have a TLV-STEL, a 15
minute Short-Term Exposure Limit which must not be exceeded either in
concentration or duration, and which must not cause the TWA to be exceeded.
Other chemicals have a TLV-C, a ceiling limit which must not be exceeded
during any part of the workshift. A "skin" notation means that dermal
absorption may contribute significantly to exposure to a given chemical.
Although TLVs are established as guidelines, OSHA has
adopted most of them as regulatory standards, called Permissible Exposure
Limits (PELs). For a few substances, OSHA has developed its own standards
which include not only a PEL, but a comprehensive set of rules governing use,
exposure monitoring, medical surveillance, protective equipment, training,
etc. Some of these substance-specific standards also include an established
Action Level, I.E., an airborne concentration below the PEL at which certain
activities such as exposure and medical monitoring must take place.
TLVs or PELs have been established for approximately 700
chemical substances. For most of these materials, the OSHA Laboratory
Standard requires only that the PEL not be exceeded. For a few materials
that also have action levels, certain requirements for exposure and medical
monitoring go into effect if the action level is exceeded. And for "select
carcinogens, reproductive toxins, and substances with a high degree of acute
toxicity", additional employee protective measures (beyond good laboratory
practice) must be considered (see Section 9 of the Chemical Hygiene Plan).
"Select carcinogen" is defined by OSHA as any substance
which meets one of the following criteria
- It is regulated by OSHA as a carcinogen (designated by an 'x' in the
following table); or
- It is listed under the category "known to be carcinogenic" in the
Annual Report on Carcinogens, published by the National Toxicology Program
(designated NTP Group 1); or
- It is listed under Group 1, "carcinogenic to humans", by the
International Agency for Research on Cancer Monographs; or
- It is listed in either Group 2A or 2B by IARC or under the category
"reasonably anticipated to be carcinogens" by NTP (designated NTP Group 2).
To summarize, "select carcinogens" are either OSHA
designated, IARC 1, 2A or 2B, or NTP Group I or 2.
"Reproductive toxins" have been defined by OSHA as
chemicals which affect the reproductive capabilities including chromosomal
damage (mutations) and effects on fetuses (teratogenesis). OSHA does not
provide a list of specific chemicals to fit its definition. Therefore, in
this Chemical Hygiene Plan, reproductive toxins are considered to be those
materials identified as "female, male, or developmental reproductive toxins"
in the State of California Proposition 65 list of toxic materials. They are
designated on the following table as FREP, MREP, or DTOX.
"Substance with a high degree of acute toxicity" is
completely undefined in the laboratory standard. Therefore, this Chemical
Hygiene Plan adopts OSHA's definition of "highly toxic" as specified in the
Hazard Communication Standard. Under this standard, highly toxic chemicals
are those with an oral-rat median-lethal dose (LD50) of 50 mg or less per kg
of body weight. For a further discussion of acute toxicity measurement, see
Appendix H.
The following list of chemicals combines all of the
above information in one comprehensive table. This table is updated annually
when the Chemical Hygiene Plan is reviewed. A list of definitions of column
headings is provided at the end of the table, along with health hazard
definitions from Appendix A of OSHA's Hazard Communication Standard.
Definitions Used in "Limits of Exposure to Toxic and Hazardous
Substances"
| ACGIH: | The American Conference of Governmental Industrial
Hygienists |
| California List: | California Proposition 65 List which designates
chemicals as female reproductive, male reproductive, or fetal developmental
toxicants. |
| Cancer EPA: | The Environmental Protection Agency (EPA) has six
categories for confirmed and suspected carcinogens: Category A - Substances
that are human carcinogens; Category B1 - Substances that show limited
evidence of carcinogenicity in humans; Category B2 Substances that show
sufficient evidence of carcinogenicity in animals with inadequate or lack of
evidence in humans; Category C - Substances that show limited evidence of
carcinogenicity in animals and inadequate or lack of human data; Category D
Substances that are not classifiable as a human carcinogen; and Category E -
Substances that show no carcinogenicity for humans. |
| Cancer IARC: | The International Agency for Research on Cancer
(IARC) has four categories for confirmed and suspected carcinogens: Category
1 - Those for which sufficient evidence exists to establish a causal
relationship between the chemical and human cancer; Category 2A - Those
for which there is at least limited evidence of human carcinogenicity;
Category 2B - Those for which there is sufficient evidence for
carcinogenicity in animals but inadequate data for humans; and Category 3 -
Those that cannot be classified as to human carcinogenicity. |
| Cancer NTP: | The National Toxicology Program (NTP) listing of
carcinogens contains two categories: 1 - Substances that are known to be
human carcinogens; and 2 - Substances that may reasonably be anticipated to
be human carcinogens. |
| Cancer OSHA: | An "X" under the OSHA column denotes an OSHA
regulated carcinogen. |
| Cancer TLV: | ACGIH lists carcinogens in the TLV columns as either
A1 - a confirmed human carcinogen or A2 - a suspected human carcinogen. |
| CEIL (C): | A Ceiling limit is a concentration that should not be
exceeded during any part of the working exposure. Ceiling limits are
designated in the table using a capital "C" followed by a number. |
| DTOX: | Developmental Toxin. A "+" in this column indicates that
the chemical may have adverse effects on a developing fetus or human being.
The effects may result from exposure to chemical or physical agents prior to
conception (either parent), during prenatal development, or postnatally until
the time of puberty. |
| FREP: | Female Reproductive Toxin. A "+" in this column indicates
that the chemical may have adverse effects on the female reproductive
system. |
| IDLH: | Immediately Dangerous to Life and Health as published by the
National Institute for Occupational Safety and Health (NIOSH). This is the
concentration from which one could escape within 30 minutes without a
respirator and without experiencing any escape-impairing (e.g., severe eye
irritation) or irreversible health effects. Units are in parts per million
(ppm) atmosphere concentration. |
| LD50: | Lethal dose of a toxic material required to kill 50% of a
population of test animals. Dose is reported in terms of milligrams per
kilogram of body weight of test animal. The lower the LD50, the
more toxic the material. |
| MREP: | Male Reproductive Toxin. A "+" in this column indicates
that the chemical may have adverse effects on the male reproductive
system. |
| NFPA 704: | National fire Protection Association (NFPA) Section 704
designations identify the degree of health (blue), flammability (red),
reactivity (yellow) and special hazards (white). A chemical label has a
colored diamond area which can be numbered in the NFPA 704 Hazard Rating
System of 0 to 4, with "O" considered nonhazardous and "4" extremely
hazardous. White section (special hazards) uses letters or symbols to denote
hazard. |
| NIC: | Notice of Intended Change, as promulgated by ACGIH. |
| ODOR: | Odor Threshold: the concentration or range of
concentrations at which the chemical can first be detected by sense of
smell. |
| OSHA: | The Occupational Safety and Health Administration |
| PEL: | Permissible Exposure Limit. Airborne chemical exposure
concentrations set by OSHA and enforceable by law. |
| RESP: | Respirator. Abbreviations in this column indicate the type
of respiratory protection required when working with concentrations of the
chemical above the PEL.
Abbreviations used under Respirator category:
| AM | Ammonia filter |
| AG | Acid gas filter |
| DFM | Dust fume mist filter |
| DM | Dust mist filter |
| (F) | Full face mask |
| HE | High Efficiency Particulate Air (HEPA) filter |
| OV | Organic vapor filter |
| SA | Supplied air mask |
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| Skin: | A "+" in this column indicates that the substance is known
to be absorbed through the skin. In these cases, appropriate measures must
be taken to prevent skin and eye contact with the chemical. |
| STEL: | Short-Term Exposure Limit. A STEL is a 15-minute
time-weighted average exposure concentration which should not be exceeded at
any time during a workday. Numbers in the STEL columns without a "C"
designation are STELs. |
| TLV: | Threshold Limit Value. TLVs are airborne concentrations of
substances to which it is believed that nearly all workers may be repeatedly
exposed day after day without adverse health effects. TLVs are guidelines
set by the ACGIH, and unlike the PELs are not enforceable by law. |
| TWA: | Time Weighted Average. A TWA is a time-weighted average
concentration for a normal 8-hour workday and a 40-hour workweek, to which
nearly all workers may be repeatedly exposed, day after day, without adverse
effect. |
| ?: | There is no CAS# available. |
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