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.

April 15 1976

Regional Administrator - OSHA
Subject: The Handling, Storing and Use of MAPP Gas in Underground Construction Work

This is in response to the memorandum from your office, dated March 29, 1976, regarding the Washington Metropolitan Area Transit Authority's questions on the above subject.

The four questions that were asked and the Occupational Safety and Health Administration's answers are as follows:

1. Question. In the context of OSHA safety standards and regulations is MAPP gas considered an LPG?

Answer. No. This is based on the definition of Liquefied Petroleum Gas as defined in 29 CFR 1926.155(j) and the definition of Methylacetylene-Propadiene, Stabilized, as defined in NFPA No. 51-1969.

2. Question. Is the use of MAPP gas permitted for cutting purposes in underground construction work, in tunnel work, or in cut and cover construction areas which are temporarily decked-over?

Answer. Yes, while staying in compliance with OSHA standards and manufacturer's instructions.

3. Question. In underground situations as mentioned in No. 2 above, is the use of MAPP gas permitted for purposes other than cutting, and if so what are they?

Answer. Mapp gas may be used for purposes, such as cutting, welding, heating in relation to cutting and welding, and heat-treating operations.

4. Question. Are there any special precautions that should be observed for the handling or storing of MAPP gas either aboveground of in underground facilities?

Answer. No less precautions than for any other fuel gas allowed by the standards in either underground or aboveground operations. Manufacturer's recommendations shall be adhered to, as well as OSHA standards. It is noted for underground operations, that ventilation must be mechanically supplied in quantities and lineal movement sufficient to prevent accumulations of escaped gas above the level allowed in 29 CFR 1926.800(c).

There are several references covering the use of oxygen-fuel gas systems for welding and cutting in addition to applicable OSHA standards. Some appropriate standards are:

1. ANSI Z49.1-1973, Safety in Welding and Cutting Systems.

2. NFPA No. 51-1974, Installation and Operation of Oxygen-Fuel Gas Systems for Welding and Cutting.

3. NFPA No. 51B-1971, Standards for Fire Prevention in the Use of Cutting and Welding Processes.

Barry J. White
Associate Assistant Secretary
for Regional Programs