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 http://www.osha.gov.

April 19, 1976

Mr. Bernard J. Forquer
Safety Administrator
Raymond - Kiewit - Tidewater
P.O. Box 201
Lusby, Maryland 20657

Dear Mr. Forquer:

This is in response to your letter dated March 30, 1976 regarding use of Mapp gas, oxygen, and acetylene in a tunnel.

In the context of OSHA safety standards and regulations, Mapp is not considered an LPG. This is based on the definition of Liquified Petroleum Gas in 29 CFR 1926.155(j) and the definition of Methylaretylene-Propadiene, Stabilized, in NFPA 51-1969.

In underground construction work, in tunnel work, or in cut and cover construction areas which are temporarily decked over, Mapp gas or acetylene gas may be used for cutting, welding, heating in relations to welding and cutting, and heat treating operations. All such operations must be in compliance with other OSHA regulations and with manufacturer's instructions.

Precautions for handling and storing of acetylene and Mapp gas, shall be not less than for any other fuel gas allowed by OSHA standards in either underground or aboveground operations. Manufacturer's recommendations shall be adhered to, as well or OSHA standards. For underground operations, ventilations must be mechanically supplied in quantities and linear movement sufficient to prevent accumulations of escaped gas above the level allowed in 29 CFR 1926.800(c). In addition, special precautions shall be taken to avoid damage to compressed gas cylinders from vehicles, falling, flying objects, etc.

Additional information covering use of oxygen-fuel gas systems for welding and cutting are:

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

2. NFPA 51-1974, Installation and Operation of Oxygen-Fuel Gas Systems for Welding and Cutting.

3. NFPA 51B-1971, Standards for Fire Prevention in the Use of Cutting and Welding Processes.

Copy of OSHA construction regulations is enclosed as requested.

Sincerely yours,



DAVID H. RHONE
Regional Administrator for
Occupational Safety and Health

Enclosure