MSHA - Code of Federal Regulations - 30 CFR 75.341
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MSHA - Title 30 CFR
30 CFR § 75.341
Direct-fired intake air heaters.

(a) If any system used to heat intake air malfunctions, the heaters affected shall switch off automatically.
(b) Thermal overload devices shall protect the blower motor from overheating.
(c) The fuel supply shall turn off automatically if a flame-out occurs.
(d) Each heater shall be located or guarded to prevent contact by persons and shall be equipped with a screen at the inlet to prevent combustible materials from passing over the burner units.
(e) If intake air heaters use liquefied fuel systems--
(1) Hydrostatic relief valves installed on vaporizers and on storage tanks shall be vented; and
(2) Fuel storage tanks shall be located or protected to prevent fuel from leaking into the mine.
(f) Following any period of 8 hours or more during which a heater does not operate, the heater and its associated components shall be examined within its first hour of operation. Additionally, each heater and its components shall be examined at least once each shift that the heater operates. The examination shall include measurement of the carbon monoxide concentration at the bottom of each shaft, slope, or in the drift opening where air is being heated. The measurements shall be taken by a person designated by the operator or by a carbon monoxide sensor that is calibrated with a known concentration of carbon monoxide and air at least once every 31 days. When the carbon monoxide concentration at this location reaches 50 parts per million, the heater causing the elevated carbon monoxide level shall be shut down.