2792 ARTICLE 89.

minute for each person employed therein, and three hundred cubic feet
of air circulation per minute for each animal employed therein; and in
gaseous mines affording not less than one hundred and fifty cubic feet of
air circulation per minute for each person, and five hundred cubic feet
of air circulation per minute for each animal, employed therein; and as
much more in either case as the district mine inspector may by special
safety order require.

1922, ch. 307, sec. 99.

100. The operator shall direct and see that such air circulation, by
means of passages of sufficient area, shaped and located to minimize fric-
tion and assure equable distribution, is conducted through the last cut-
through to the face of each room and entry in such mine. No room or
entry shall be turned in advance of the ventilating current or of the last
cut-through in the entry, excepting that room-necks may be broken off by
workmen driving entries, when approved by the district mine inspector.
Whenever any working places are driven to destination or to the boundary,
or are stopped, such places shall be connected at the face by cut-throughs.

1922, ch. 307, sec. 100.

101. Every such mine shall be divided into ventilation districts or
splits of not more than 75 men in a district, unless in the judgment of
the district mine inspector such limitation in any particular mine is im-
practicable, when such inspector may by written safety order permit a
larger number, not exceeding 100 men, to work therein. In a gaseous
mine the district mine inspector may by written safety order require a
further subdivision of ventilation districts to include a smaller number
of men than 75. Every such ventilation district shall be supplied with a
separate current of fresh air, and the return air current therefrom shall
be conducted direct or through an overcast or undercast to the main return
airway or outside the mine.

1922, ch. 307, sec. 101.

102. All temporary stoppings necessary during the progress of min-
ing shall be strong and tight, and be replaced by permanent stoppings as
quickly as possible unless otherwise authorized by the district mine in-
spector. All permanent brattices and all permanent air bridges, overcasts
and undercasts shall be substantial, amply strong, of materials approved
by the district mine inspector and kept tight. All doors shall be so hung
and adjusted that they will close of themselves, and on main haulage roads,
wherever possible, a second door shall be hung in the same air current, so
that the opening of one door shall not interrupt the air circulation. Doors
on main haulage roads, not self-closing, shall be served by an attendant
whose constant duty it shall be to open such doors for persons and cars
to pass through and to close it immediately after them. When a door is
used in conducting the main air currents, an extra door shall be provided
and kept standing open, out of reach of accident, but ready for immediate
use in case of any damage to the door regularly in service.