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 https://www.osha.gov.

February 25, 1988

The Honorable John D. Dingell
Subcommittee on Oversight and Investigations
Committee on Energy and Commerce
House of Representatives
Washington, D.C. 20515

Dear Mr. Chairman:

This responds to your request for information dated January 20, concerning the Occupational Safety and Health Administration's (OSHA) standard for carbon monoxide (CO).

The relevant OSHA standard for carbon monoxide is promulgated in 29 CFR 1910.1000, Table Z-1. The permissible exposure limit (PEL) is currently listed as 50 parts per million (ppm) in air. This level was adopted from the Walsh-Heasley Act, which had previously adopted the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) of 1968. The ACGIH continues to list a TLV of 50 ppm in their 1987-1988 publication. They maintain that "for the great majority of workers,... exposure to carbon monoxide at concentrations below 50 ppm, under a wide range of working conditions, should no result in either mild temporary stress or permanent impairment of health." (See enclosure Documentation of TLV.)

The 35 ppm exposure limit for CO, referenced in your letter, is the exposure level recommended by the National Institute for Occupational Safety and Health (NIOSH) in its 1972 criteria document for CO (copy of pertinent sections enclosed.) This level was based on studies of cigarette smokers and took into consideration the effect of CO exposure on workers with heart disease.

OSHA has initiated rulemaking activity on updating the PEL's for the air contaminants in Table Z-1 and is in the process of drafting a proposal. We anticipate that the proposal will be published in early spring of this year. OSHA is reviewing the ACGIH documentation and NIOSH data on CO, and will determine on the merit of these and other data what action to take.

With reference to the jurisdictional question raised in the second paragraph of your letter, the Occupational Safety and Health Act (PL 91-596) excludes employees of States and their political subdivisions. Accordingly, OSHA does not have enforcement authority over State employed bridge and tunnel workers. Their protection is afforded under laws established and overseen by the states.

Please feel free to contact us again for further assistance.


John A. Pendergrass
Assistant Secretary