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 7, 1975

Subject: Clarification of 29 CFR 1926.350(b)(4) to Permit Cylinders Containing Oxygen, Acetylene or Other Fuel Gas to be Taken into Tunnels

This is in response to your memorandums of April 9, and May 19, 1975, regarding the above subject. Addressing our rationale to 29 CFR 1926, Construction Standards, the following is offered:

  1. 29 CFR 1926.350(b)(4) states: "Cylinders containing oxygen or acetylene or other fuel gas shall not be taken into confined spaces." 29 CFR 1926.350(j) adopts and references ANSI Z49.1-1967, Safety in Welding and Cutting. Section 7.4.1 states that a confined space is intended to mean a relatively small or restricted space such as a tank, boiler, pressure vessel or small compartment of a ship. Section 7.4.3 states that when welding or cutting is being performed in any confined space, the gas cylinders and welding machine shall be left on the outside.
  2. 29 CFR 1926.800(e)(1)(v) states: "Gasoline or liquefied petroleum gases shall not be taken, stored, or used underground."
  3. 29 CFR 1926.21(b)(6)(ii) states: "Confined or enclosed spaces include, but are not limited to, ...sewers, underground utility vaults, tunnels, pipelines, and..."

The definition of confined space is: "...any space having a limited means of egress, which is subject to the accumulation of toxic or flammable contaminants or has an oxygen deficient atmosphere." When welding or cutting is being performed in any confined spaces, the gas cylinders shall be left on the outside. Fuel gases that are liquefied petroleum gases shall not be used underground in tunnel construction.

In conclusion, a tunnel can be a confined space or an enclosed space or have a confined space in it based on 29 CFR 1926.21(b)(6)(ii) and the evaluation of the CSHO. When a tunnel, due to its size and means of egress is considered an enclosed space, cylinders contained oxygen or fuel gas (except LP) may be taken into this enclosed space. However, under these conditions other applicable tunnel standards would be considered.

A proposed change to 29 CFR 1926.21(b)(6)(ii) will include a deletion of the word "tunnels". In addition, an amendment to the construction standards, Subpart S, Tunnels, is being finalized and will be published in the Federal Register shortly. This amendment will cover the taking of compressed gas cylinders into tunnels.

Barry J. White
Associate Assistant Secretary for
Regional Programs