HARRY HUGHES, Governor

1375

be kept in a book on the surface of the mine and is open for
inspection by any interested person.

(e) (1) Separate Openings. The main intake and main
return air currents in slope mines shall be in separate
openings.

(2)  Liquid-Filled Transformers. Underground
stables, battery charging stations, and transformer stations
containing liquid-filled transformers shall be well
ventilated by separate splits of air conducted through vents
to the return air courses and returning directly to the
surface.

(3)  Changes in Ventilation. Changes in
ventilation that may affect the safety of the workers shall
be made when the mine is idle, when no workers other than
those engaged in changing the ventilation are in the mine.

(f) (1) Deficiency of Oxygen and Excess of Carbon
Dioxide.— Air in mines in which workers work or travel
shall be improved if it contains less than 19.5 percent
oxygen, more than 0.75 percent carbon dioxide, or is
contaminated with any noxious or poisonous gas.

(2)  Excess Methane — Generally.— If the air
immediately returning from a split that ventilates any group
of active workings contains more than 1 percent methane, as
determined with a permissible flame safety lamp, by air
analysis or by other recognized means of accurate detection,
the ventilation shall be improved.

(3)  Same — Returning From a Split.— If the air
immediately returning from a split contains 1.5 percent
methane, a dangerous condition exists and the workers shall
be withdrawn from the mine or its affected portion. Power
shall be cut off from the mine or its affected portion until
the dangerous condition has been corrected.

(4)  Same — Accumulation.— Blasting may not be
done at any working face or other place where methane has
accumulated and is likely to attain an explosive mixture.
The workers shall be removed from each working face or place
until the condition has been corrected.

(5)  Same — Face Operations.— If the methane
content of air in any face operation exceeds 1 percent at
any point not less than 12 inches from the roof, face, or
rib, as determined by a permissible methane detector, a
permissible flame safety lamp, or chemical analysis, the
workers shall be removed from the affected area until the
condition has been corrected by improving the ventilation.

(g)  (1) Generally. Crosscuts between entries and rooms
shall be made at intervals not exceeding 105 feet. However,
this requirement does not apply to recovery work if the
working face is ventilated by a perceptible movement of air