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MSHA - Title 30 CFR
30 CFR § 7.506

Breathable air components.

    (a) Breathable air shall be supplied by compressed air cylinders, compressed breathable-oxygen cylinders, or boreholes with fans installed on the surface or compressors installed on the surface. Only uncontaminated breathable air shall be supplied to the refuge alternative.

    (b) Mechanisms shall be provided and procedures shall be included so that, within the refuge alternative,--

    (1) The breathable air sustains each person for 96 hours,

    (2) The oxygen concentration is maintained at levels between 18.5 and 23 percent, and

    (3) The average carbon dioxide concentration is 1.0 percent or less and excursions do not exceed 2.5 percent.

    (c) Breathable air supplied by compressed air from cylinders, fans, or compressors shall provide a minimum flow rate of 12.5 cubic feet per minute of breathable air for each person.

    (1) Fans or compressors shall meet the following:

    (i) Be equipped with a carbon monoxide detector located at the surface that automatically provides a visual and audible alarm if carbon monoxide in supplied air exceeds 10 parts per million (ppm).

    (ii) Provide in-line air-purifying sorbent beds and filters or other equivalent means to assure the breathing air quality and prevent condensation, and include maintenance instructions that provide specifications for periodic replacement or refurbishment.

    (iii) Provide positive pressure and an automatic means to assure that the pressure is relieved at 0.18 psi, or as specified by the manufacturer, above mine atmospheric pressure in the refuge alternative.

    (iv) Include warnings to assure that only uncontaminated breathable air is supplied to the refuge alternative.

    (v) Include air lines to supply breathable air from the fan or compressor to the refuge alternative.

    (A) Air lines shall be capable of preventing or removing water accumulation.

    (B) Air lines shall be designed and protected to prevent damage during normal mining operations, a flash fire of 300 [deg]F for 3 seconds, a pressure wave of 15 psi overpressure for 0.2 seconds, and ground failure.

    (vi) Assure that harmful or explosive gases, water, and other materials cannot enter the breathable air.

    (2) Redundant fans or compressors and power sources shall be provided to permit prompt re-activation of equipment in the event of failure.

    (d) Compressed breathable oxygen shall--

    (1) Include instructions for deployment and operation;

    (2) Provide oxygen at a minimum flow rate of 1.32 cubic feet per hour per person;

    (3) Include a means to readily regulate the pressure and volume of the compressed oxygen;

    (4) Include an independent regulator as a backup in case of failure; and

    (5) Be used only with regulators, piping, and other equipment that is certified and maintained to prevent ignition or combustion.

    (e) The applicant shall prepare and submit an analysis or study demonstrating that the breathable air component will not cause an ignition.

    (1) The analysis or study shall specifically address oxygen fire hazards and fire hazards from chemicals used for removal of carbon dioxide.

    (2) The analysis or study shall identify the means used to prevent any ignition source.