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.

March 27, 1991

                   Regional Administrator

FROM:               PATRICIA K. CLARK, Director 
                   Directorate of Compliance Programs

SUBJECT:            Interpretation of 29 CFR 1926.800 (h)(1)-(3) and 29 CFR

This is in response to your memorandum of February 12, in which you request a clarification of enforcement policy regarding underground construction, as regulated at 29 CFR 1926.800.

The primary issue you raise is that of reconciling the intent and requirements of the definitions at 29 CFR 1926.800(h)(1) through (h)(3) with those of 29 CFR 1910.7, definitions and requirements for a nationally recognized testing laboratory. Our first observation is to point out that 29 CFR 1910.7 is applicable only to General Industry situations and not to the Construction Industry.

Under the construction standards at 29 CFR 1926, Subpart K, Electrical, accepted, approved, certified or listed equipment is that determined to be suitable for a specific application and use by a qualified testing laboratory. (The construction standard has no requirement that a NRTL be used.) Additionally, the construction standard specifies that, under certain circumstances, testing by the Mine Safety and Health Administration (MSHA) is acceptable to OSHA.

Although OSHA requirements in the construction industry do not require certification by a NRTL, equipment so certified is obviously acceptable to OSHA if it is approved for service in the underground construction environment.

Therefore, in further clarification of the requirements of 29 CFR 1926.800(h)(1) through (h)(3), we offer the following discussion:

Should an underground tunneling face be emitting methane gas into the tunnel, and the ventilation system ducting is used to effectively exhaust the hazardous methane containing atmosphere within the tunnel, the tunnel volume would be considered a Class 1, Division 2 location. (A hazardous atmosphere would not exist under normal operating circumstances.) However, were the ventilation system run in reverse and the tunnel become the conduit for exhausting the methane filled atmosphere, the tunnel would be classified as Class 1, Division 1.

In either case, the area ahead of the forward end of the ventilation ducting (that area from the tunnel face to the ducting) would be classified Class 1, Division 1.

Mobile diesel-powered equipment must be approved in accordance with 30 CFR Part 36 by MSHA or demonstrated by the employer to be fully equivalent. Many countries manufacture acceptable diesel- powered equipment which is used in mines and is equivalent. In situations where an employer has elected to use foreign manufactured diesel-powered equipment, the employer must provide documentation to verify equivalence to the MSHA requirements.

Should you continue to have difficulty interpreting the requirements for underground construction, please contact our staff at the Division of Construction Compliance Assistance, FTS-523-8124.