30 CFR § 75.340
Underground electrical installations.
(a) Underground transformer stations, battery charging stations,
substations, rectifiers, and water pumps shall be housed in noncombustible
structures or areas or be equipped with a fire suppression system meeting the
requirements of §75.1107-3 through
§75.1107-16.
(1) When a noncombustible structure or area is used, these
installations shall be--
(i) Ventilated with intake air that is coursed into a return air
course or to the surface and that is not used to ventilate working places;
or
(ii) Ventilated with intake air that is monitored for carbon
monoxide or smoke by an AMS installed and operated according to
§75.351. Monitoring of intake air ventilating
battery charging stations shall be done with sensors not affected by
hydrogen; or
(iii) Ventilated with intake air and equipped with sensors to
monitor for heat and for carbon monoxide or smoke. Monitoring of intake air
ventilating battery charging stations shall be done with sensors not
affected by hydrogen. The sensors shall deenergize power to the
installation, activate a visual and audible alarm located outside of and on
the intake side of the enclosure, and activate doors that will automatically
close when either of the following occurs:
(A) The temperature in the noncombustible structure reaches
165°F; or
(B) The carbon monoxide concentration reaches 10 parts per
million above the ambient level for the area, or the optical density of smoke
reaches 0.022 per meter. At least every 31 days, sensors installed to monitor
for carbon monoxide shall be calibrated with a known concentration of carbon
monoxide and air sufficient to activate the closing door, or each smoke
sensor shall be tested to determine that it functions correctly.
(2) When a fire suppression system is used, these installations shall
be--
(i) Ventilated with intake air that is coursed into a return air
course or to the surface and that is not used to ventilate working places;
or
(ii) Ventilated with intake air that is monitored for carbon
monoxide or smoke by an AMS installed and operated according to
§75.351. Monitoring of intake air ventilating
battery charging stations shall be done with sensors not affected by
hydrogen.
(b) This section does not apply to--
(1) Rectifiers and power centers with transformers that are either
dry-type or contain nonflammable liquid, if they are located at or near the
section and are moved as the working section advances or retreats;
(2) Submersible pumps;
(3) Permissible pumps and associated permissible switchgear;
(4) Pumps located on or near the section and that are moved as the
working section advances or retreats;
(5) Pumps installed in anthracite mines; and
(6) Small portable pumps.