FACT SHEET ON EXPOSURE LIMITS FOR SARIN (GB)
JULY 1997

Occupational and General Population Exposure Limits to Sarin (GB)
Air Concentrations and Summary of How They Were Derived

The purpose of this fact sheet is to summarize the exposure limits for the chemical nerve agent sarin, which is also called GB. Two different exposure limits are recommended for occupational settings and for the general population. The definitions for these exposure limits are provided, and the underlying data from which the limits were derived are briefly described. In addition, the levels of sarin that can cause mild symptoms, severe symptoms, and death are summarized.
The following three references are cited:

1. Department of the Army. Army Field Manual No 3-9; Potential Military Chemical/Biological Agents and Compounds, p.19-20. Headquarters, Department of the Army, Washington, D.C. December 12, 1990.

2. McNamara, B., and Leitnaker, L. Toxicological Basis for Controlling Emission of GB into the Environment-Edgewood Arsenal Special Publication, U.S. Army, Medical Research Laboratories, Edgewood Arsenal, Aberdeen Proving Grounds, Maryland. March 1971.

3. Department of Health and Human Services, Centers for Disease Control. Final Recommendations for Protecting the Health and Safety Against Potential Adverse Effects of Long-Term Exposure to Low Doses of Agents: GA, GB, VX, Mustard Agent, (H, HD, and T), and Lewisite (L). Federal Register 53: 8504-8507. March 15, 1988.


I. Limits for Occupational Exposure (Workers without Respiratory Protection)

A. Army and CDC Recommendation for Occupational Limit:

Both agencies have the same recommendation: a maximum averaged air concentration of 0.0001 mg/cu.m. (averaged over an eight hour work day). (2,3)

B. Calculated Dose:

If a person was exposed for eight hours at the occupational limit, the calculated dose of sarin would be 0.048 mg-min/cu.m.

C. Definition:

The maximum air concentration allowable in a workplace is 0.0001 milligrams of sarin per cubic meter of air, when averaged over an eight hour work day. (2,3)

Even if a worker was exposed to this maximum allowable concentration for 8 hours per day, for 40 hours per week for a working lifetime (i.e., 40 years), there should not be any adverse effect. (2,3)

The notation "mg-min/cu.m." translates to a cumulative dose over time. This means that the milligrams of sarin per cubic meter of air, are multiplied by the number of minutes of exposure, in order to calculate an individual's dose.

D. How the exposure limit was derived:

The air concentration for the occupational limit was calculated, based on data from experiments with human volunteers. The lowest doses of sarin that could cause miosis and cholinesterase depression were observed in these experiments. (2) The earliest noticeable effect of a low dose of sarin is pinpointing of the pupil of the eye ("miosis"). (2) A decrease in a chemical in the blood, called red blood cell cholinesterase, is detectable with very low level exposures to sarin, before miosis can be observed. (2)

To calculate the occupational limit, a safety factor was applied to the levels of sarin that can cause these earliest health effects. (2) At this occupational limit, even the mildest miosis or cholinesterase depression should not occur. (2) This means that workers should not develop any detectable health effects at or below this limit, including changes in blood chemistry.

CDC reviewed the evidence for this limit in 1988, and concluded that "human health will be adequately protected from long-term exposure" to sarin at the occupational limit. "Even long-term exposure to these concentrations would not create any adverse health effects." (3)


Limits for the General Population

A. Army and CDC Recommendation for General Population Limit:

Both agencies have the same recommendation: a maximum averaged air concentration of 0.000003 mg/cu.m. (averaged over 72 hours). (2,3)

B. Calculated Dose:

If a person was exposed for 72 hours at the general population limit, the calculated dose of sarin would be 0.01296 mg-min/cu.m.

C. Definition:

The maximum air concentration allowable for the general population is 0.000003 milligrams of sarin per cubic meter of air, when averaged over a 72 hour period. (2,3) This exposure limit applies to non-workers, for example, members of communities located near chemical weapon incinerators.

Even if a person was exposed to this maximum allowable concentration for 72 hours, there should not be any adverse effect. (2,3)

The notation "mg-min/cu.m." translates to a cumulative dose over time. This means that the milligrams of sarin per cubic meter of air, are multiplied by the number of minutes of exposure, in order to calculate an individual's dose.

D. How the exposure limit was derived:

The occupational limit for sarin that is recommended for worker exposure was calculated, as described in the previous section. Then, another safety factor was applied to develop the general population limit. (2)

This additional safety factor is warranted, because the general population includes infants, elderly people, and the rare individuals who have genetic variation in their cholinesterase activity. (2) This safety factor should be adequate, so that even if a person is exposed at the general population limit for 72 hours, there should be no miosis or cholinesterase depression.(2)

CDC reviewed the evidence for this limit in 1988 and concluded that "human health will be adequately protected from long-term exposure" to sarin at the general population limit. "Even long-term exposure to these concentrations would not create any adverse health effects." (3)


(First Noticeable Health Effect)

A. Army and CDC Recommendation for Limit: NONE

B. Experimental Dose for Miosis:

1 mg-min/cu.m. (1)

C. Definition:

The first noticeable effect of a low dose of sarin is pinpointing of the pupil of the eye ("miosis"). (2) Also, at about the same low levels of sarin, there are other mild symptoms, including runny nose, tightness of the chest, and eye pain. (2)

The notation "mg-min/cu.m." translates to a cumulative dose over time. This means that the milligrams of sarin per cubic meter of air, are multiplied by the number of minutes of exposure, in order to calculate an individual's dose.

For example, if a person breathed a concentration of 1 milligram of sarin per cubic meter of air for one minute, he or she could develop miosis. Alternatively, if a person breathed a concentration of 2 milligrams of sarin per cubic meter of air for 0.5 minutes, he or she could develop miosis.

Note: At a cumulative dose of 0.5 mg-min/cu.m. or less, fewer than 1% of a human population would be expected to show the mildest symptoms, such as miosis, runny nose, tightness of the chest, and eye pain. (2) This is because the body can eliminate very low doses of sarin over time. (2)

Note: The dose for sarin which causes these mild health effects, such as miosis, is about 100 times lower than the dose of sarin that could be fatal.

D. How the miosis dose was derived:

The dose for miosis was observed in experiments with human volunteers. (2)


IV. Lethal and Incapacitation Levels in Humans

A. Army and CDC Recommendation for Limit: NONE

B. Experimental Dose:

1. Lethal concentration-50% (respiratory): 100 mg-min/cu.m. (resting) (1)
2. Incapacitation concentration-50% (respiratory): 75 mg-min/cu. m. (resting) (1)

C. Definition:

The notation "mg-min/cu.m." translates to a cumulative dose over time. This means that the milligrams of sarin per cubic meter of air, are multiplied by the number of minutes of exposure, in order to calculate an individual's dose.

For example, if a group of people breathed a concentration of 100 milligrams of sarin per cubic meter of air for one minute, this would be a lethal dose for 50% of the group. Alternatively, if the concentration was 50 milligrams of sarin per cubic meter of air, and the group breathed it for 2 minutes, that would also be lethal for 50% of the group.

Death usually results within 15 minutes after absorption of a fatal dose. (1)

The incapacitation dose is also expressed as a cumulative dose, which is a lower level than the lethal dose. (1)

If the group of exposed people were exercising, they would be breathing faster and the lethal or incapacitation dose would be lower. (They would take in more air per minute.) (1)

D. How the lethal and incapacitation doses were derived:

The lethal dose was derived from data from animal experiments, which were extrapolated to humans. (2) The incapacitation dose was derived from experiments with human volunteers and lab animals. (2)

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