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.

July 5, 1994



Regional Administrator
Acting Director
Directorate of Technical Support
SUBJECT: Carbon Monoxide or High Temperature Alarm Requirement for Portable Breathing Air Compressors


This is in response to your memorandum of June 7 in which you requested us to determine whether the high temperature or carbon monoxide (CO) alarm requirement applies to the portable breathing air compressors.

You stated that there are two sets of conflicting documents concerning the requirement for the CO or high temperature alarm: an OSHA Health Hazard Information Bulletin with an update issued in 1985, and a letter addressed to Mr. George Horne in 1978. Under normal operating conditions, there is little chance of the generation of CO from oil lubricated air compressors. However, when any malfunction occurs, significant amounts of CO could be produced by lubricant breakdown when the compressor cylinder head reaches a high temperature. The Health Hazard Bulletin permitted the use of portable breathing air compressors such as the Bullard "Free Air Pump" or the Willson "Ambient Air Breathing Apparatus" without their being equipped with either a CO or high temperature alarm because these portable air compressors use carbon vanes as the air mover which do not need lubrication.

The Horne letter addressed only stationary breathing air compressors; it did not address the alarm requirement for portable air compressors since they were not available at that time.

If you have any questions, please contact Ching-tsen Bien of my staff at 202-219-7065.