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Standard Interpretations - Table of Contents
• Standard Number: 1910.1018; 1910.1018(b)

OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at

December 13, 1978

Charles R. McDuff, Director
Government Technical Affairs Research & Development Dept.
Economics Laboratory, Inc.
Osborn Building
St. Paul, Minnesota 55102

Dear Mr. McDuff:

This is in response to your letter to Mr. Gail Brinkerhoff in which you asked some questions about 29 CFR 1910.1018, the standard for occupational exposure to inorganic arsenic, published in the Federal Register on May 5, 1978. Please accept my apology for the delay.

The standard has no intent of requiring initial monitoring or labelling where there is no realistic possibility of employees being exposed above the action level defined under 29 CFR 1910.1018(b). Of the substances you listed, the sulfuric acid contains the most arsenic contamination. Because of the low quantity of arsenic (.005%) present in this sulfuric acid, a very large amount of the acid would have to be introduced into the air in order to exceed the action level or the 8-hour time-weighted average (TWA) value. So much sulfuric acid would be required; in fact, that laboratory personnel would be unable to tolerate the irritation. The sulfuric acid would, thereby, act as an indicator, because its irritating effect would become intolerable before the arsenic level could become a problem.

Airborne sulfuric acid is very irritating to the respiratory passages at airborne concentrations around 2 milligrams per cubic meter. Therefore, when one considers the warning property of sulfuric acid, it seems very unlikely that the referent sulfuric acid would ever be unwittingly used in such a manner as to expose employees to concentrations of arsenic above the action level. Also, the Occupational Safety and Health Administration has set a permissible exposure limit of 1 milligram per cubic meter (8-hour TWA) for airborne sulfuric acid. Thus, one would expect the permissible exposure limit for sulfuric acid to be the controlling factor and obviate any need to apply the provisions of 29 CFR 1910.1018 when the referent sulfuric acid is used.

However, if there is some use of the referent sulfuric acid which could unwittingly expose employees to concentrations of arsenic above the action level, then labelling of the referent sulfuric acid applied to that use is required. Similarly, initial monitoring is required in that circumstance.

The foregoing type of rationale can be applied to all the other referent substances.

Thank you for your interest in occupational health.


Irving Weisblatt, Acting Director
Federal Compliance and State Programs

[Corrected 4/21/2009]

Standard Interpretations - Table of Contents

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