WM. PRESTON LANE, JR., GOVERNOR. 1057

The quantity of air reaching the last open crosscut in
any pair or set of entries shall not be less than 6, 000 cubic
feet a minute. However, the quantity of air reaching the
last open crosscut in any pair or set of entries in pillar
sections may be less than 6, 000 cubic feet a minute, pro-
vided that at least 6, 000 cubic feet of air a minute is being
delivered to the intake end of the pillar line. Mines now
operating without the prescribed quantity of air in the last
open crosscut of each pair or set of entries may continue to
operate in such manner, but prompt action shall be taken
to deliver the required minimum volume of air in the last
open crosscut of each pair or set of entries in the mine.

(b) The air current at working faces shall under any
condition have a sufficient volume and velocity to dilute
and carry away smoke from blasting and any flammable
or harmful gases.

(c) At least once each week, the mine foreman, his
assistants, or other competent persons designated by the
mine foreman, shall measure the volume of air near the
main intake or main return, the amount passing through
the last open crosscuts of entries, and the volume of air in
each split. A record of these measurements shall be kept
in a book on the surface and shall be open for inspection
by interested persons.

102. (a) Coursing of Air. The main-intake and main-
return air currents in slope mines driven after the effective
date of this Act shall be in separate openings.

(b) Underground stables, battery-charging stations,
and transformer stations containing liquid-filled trans-
formers shall be well ventilated by separate splits of air
conducted through vents to the return air courses and
returning direct to the surface.

(c) Changes in ventilation that may affect the safety
of the men shall be made when the mine is idle and with
no men in the mine, other than those engaged in changing
the ventilation.

103. (a) Quality of Air. Air in which men work or
travel in mines shall be improved when it contains less
than 19. 5 per cent oxygen, more than 0. 75 per cent carbon
dioxide, or is contaminated with noxious or poisonous
gases.

(b) If the air immediately returning from a split that
ventilates any group of active workings contains more

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