716 LAWS OF MARYLAND. [CH. 307

when required by regulation, reversible at the will oi the
operator, which shall not be located directly over the entrance
to a shaft, the air passage from which into the mine shall be
strongly built and kept tight, and which shall be provided with
a self-registering pressure gauge, the record whereof, duly
dated, shall be accessibly filed at the mine office and there pre-
served for one year for reference. Such fan shall be kept con-
tinuously in operation while the mine is working, and during
such further periods as the Bureau may prescribe, unless writ-
ten permission to stop such fan shall be given by the district
mine inspector; and before stopping such fan after such per-
mission given, notice thereof shall be given every employee of
the hours during which stoppage is intended to continue, and
work shall not be resumed until such fan has run two hours
continuously. Provided, that should it at any time become
emergently necessary to stop the fan because of mechanical
failure or other unavoidable cause, it shall first be the duty of
the mine foreman to provide for the safety of persons within
such mine, either by removing them or by furnishing tempor-
ary ventilation; but no ventilating furnace shall be employed
in such temporary emergency in a gaseous mine. No principal
fan shall be placed inside any mine; nor shall an auxiliary
fan be placed in any mine except under regulation of the
Bureau.

SEC. 103. The operator shall, by the mine foreman or other
competent person, at least once every week in non-gaseous
mines, and daily or as required by the district mine inspector,
in gaseous mines, when the men are working, measure the
air current with a correct anemometer at or near the main
intake and outlet, and also in the last cut-through in the last
room and in the entry beyond the last room turned in each
entry; and the air traveling through pillars being drawn; and
enter in a book kept for that purpose a true report of all such
air measurements, designating the place, the area of each cut-
through and entry separately, the velocity of the air in each
cut-through and entry and the number of men employed in
each separate split or district at the time the measurement
was taken, with the date; signed by the person taking the
same; which record shall be kept in the office at the mine, open
to examination by the Bureau or by any person employed
in such mine. Once each month a report of the air pressure
average as shown by the pressure gauge upon the ventilating
fan, the daily air pressure during the principal shift, the air
pressure by districts and number of men and animals working