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.

November 1, 1995

Mr. Thomas N. Cooper
Certified Safety Professional
Fire Safety Specialist
Purdue University
1666 L.J. Freehafer
Hall of Administrative Services
West Lafayette, Indiana 47907-1666

Dear Mr. Cooper:

This is in response to your letter dated September 13, concerning the interpretation of the Occupational Safety and Health Administration's (OSHA) standards 1910.134 and 1910.156 which address the requirement for workers who are actively conducting operations in atmospheres that are immediately dangerous to life and health (IDLH). Specifically you were concerned about an alert that was distributed on August 1, by the Indiana Public Safety Training Institute (PSTI) to all Indiana fire fighters, regarding it interpretation of IDLH atmospheres.

In response to several inquires, OSHA issued an interpretation on requirements for the number of workers required to be present when conducting operations in atmospheres that are IDLH. Because the interpretation covers several issues relating to IDLH atmospheres, this letter will address those provisions regarding the application of OSHA standards to fire fighting operations. As you will note, OSHA does not consider all fires to constitute IDLH situations. Incipient fires which do not create IDLH situations, or external fire fighting efforts at a major interior structural fire, are not covered by our interpretation. The interpretation does not mandate the number of personal necessary to staff a fire apparatus leaving a station.

The interpretation covers the number of persons who must be on the scene before fire fighting personnel may begin the interior attack on an interior structural fire. An interior structural fire (an advanced fire that has spread inside of the building where high temperatures, "heat" and dense smoke are normally occurring) would present an IDLH atmosphere and therefore, require the use of respirators. In those cases, at least two "outside" (standby) persons (in addition to the minimum of two persons inside needed to fight the fire) must be present before fire fighters may enter the building. This would allow one of the standby personnel to enter the building if an emergency arises requiring rescue of the fire fighters. (The incident commander may be one of the two outside.) Until those persons arrive on the scene, fire fighters may fight the blaze from outside the structure and carry out rescue activities.

Under the National Fire Protection Association standards relating to fire fighter safety and health, the incident commander may make exceptions to these rules if necessary to save lives. OSHA recognizes that the incident commander has the training and experience to recognize when the nature and extent of the fire would call for such exceptions.

With regards to the Indiana PSTI Alert, we contacted Mr. David Bear, Deputy Commissioner, Indiana Department of Labor, regarding the Indiana Public Safety Training Institute's interpretation of OSHA's requirements for IDLH or potential IDLH atmospheres and specifically, its Alert which was sent to all Indiana Firefighters on August 1, 1995. Deputy Commissioner Bear assured us that the Indiana Occupational Safety and Health Administration's (IOSHA) interpretation is identical to Federal OSHA's interpretation. The Deputy Commissioner also indicated that he has personally contacted the Indiana Public Safety Training Institute to clarify IOSHA's interpretation of the requirements for IDLH atmospheres and, the application of the OSHA standard to fire fighting operations.

I hope this information is helpful to you, and will clarify both Federal OSHA's interpretation and the State of Indiana's interpretation.


Paula O. White, Director
Federal-State Operations