n
operation a sufficient length of time after the appointed time for
such employes to leave their working places, for all persons to be
out of the mine. (Sec. 922, 923, 952; Penalty, Sec. 976.)

[=Pressure gauges.=] At each mine generating fire-damp so as to be
detected by a safety lamp, and wherein twenty or more persons are
employed, a recording pressure gauge for the purpose of recording
the pressure or vacuum of the main air current, shall be provided
and maintained, which shall be kept in constant use, and records
preserved for ninety days, subject to the inspection of the chief
inspector of mines and the district inspector of mines. (Penalty,
Sec. 976.)

Sec. 925. [=Competent person or persons shall be designated as
fire-boss.=] The owner, lessee or agent of a mine generating
fire-damp so as to be detected by a safety lamp, shall designate a
competent person or persons as fire boss or fire bosses, who shall
make a thorough examination of each working place in the mine every
morning with a standard safety lamp, not more than three hours prior
to the appointed time for the employes to enter the mine. As
evidence of such examination, the fire boss shall mark with chalk
upon the face of the coal, or in some other conspicuous place, his
initials and date of the month upon which the examination is made.
If there is any standing gas discovered, he must leave a danger
signal across every entrance to such place.

[=Examination of other than working places.=] Each mine generating
fire-damp so as to be detected by a safety lamp, shall be kept free
from standing gas. All traveling ways, entrances to old workings,
and places not in the actual course of working, shall be carefully
examined with a safety lamp by the fire boss not more than three
hours before the appointed time for persons employed therein to
enter. Parts of the mine not in the actual course of working and
available, shall be examined not less than once each three days, and
shall be so fenced as to prevent persons from inadvertently entering
therein. (Sec. 955, 959; Penalty, Sec. 976.)

Sec. 926. [=Breakthroughs and brattices.=] From a point where the
seam is reached in the opening of a mine, to a point not exceeding a
distance of four hundred feet therefrom, breakthroughs shall be made
between main entries, where there are no rooms worked, not more than
one hundred feet apart, provided such entries are not advanced
beyond the point where the breakt