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Standard Interpretations - Table of Contents
• Standard Number: 1910.1000 TABLE Z-2

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

September 3, 1996



SUBJECT: PEL for Inorganic Mercury

The purpose of this memorandum is to address the permissible exposure limit (PEL) for mercury. As you may know, Table Z-2 of 29 CFR 1910.1000 incorrectly lists the inorganic mercury PEL as a ceiling value of 1 mg/10m3 (0.1 mg/m3). It has come to our attention that compliance officers may be citing workplace mercury exposure as a ceiling PEL rather than as an 8-hour time weighted average (TWA).

While this error has not been corrected in Table Z-2 of 29 CFR 1910.1000, OSHA originally issued a correction notice in the old Field Operations Manual. Enclosed for your use and information is a [
June 30, 1976 letter of interpretation] and a copy of the October 30, 1978 ["Inorganic Mercury and its Compounds" [CPL 02-02-006 (formerly CPL 2-2.6)] directive] which provides documentation for the 8-hour TWA mercury PEL as opposed to a ceiling value.

Please assure that all field personnel receive a copy of this memorandum and when a mercury over-exposure is cited, it is cited as an 8-hour TWA PEL. If you have any questions please contact the [Office of Health Enforcement at 202 693-2190].

[Corrected 6/2/2005]

Standard Interpretations - Table of Contents

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