2770 ARTICLE 89.

Non-Gaseous Mine is a mine which has not been rated as gaseous; or
a mine which, having been rated as gaseous, has been re-rated as non-gase-
ous as prescribed in the definition of a gaseous mine, elsewhere in this
section.

Operator means any firm, corporation, association or individual operat-
ing any coal mine or part thereof, whether as an owner, lessee or otherwise,
and also includes the representative of such operator.

Panel means a unit, area in a system of mining by which the mine is
divided into large rectangles or panels isolated or surrounded by solid pil-
lars of coal into which pairs of entries are driven for the development of
rooms and the extraction of pillars.

Permissible. Unless the context requires a different sense, "permis-
sible " means the admission of a device, plan, formula, method, machine
or course of action by the United States Bureau of Mines to a list, after
actual test thereof.

Potential and Voltage. These words shall be taken as synonymous, to
mean electric pressure as determined by the voltmeter.

Shaft means an opening, the axis of which is approximately vertical,
extending downwards from the surface; and shall include an underground
shaft driven between two levels.

Slope includes an inclined opening in a dipping coal bed and an inclined
tunnel to a coal bed.

Superintendent means the person who shall, on behalf of the operator,
have immediate supervision of one or more mines.

Tunnel means a level or inclined passageway driven mainly through
barren strata. It may or may not come to the surface.

Ventilating Current means a current of air circulating throughout the
mine excavations, of such purity that it shall contain not less than 19 per
cent, of oxygen nor more than (1 1/4) one and one-fourth per cent, carbon
dioxide. The district mine inspector shall, whenever he has reason to sus-
"pect an excessive proportion of carbon dioxide, or insufficient oxygen in
the atmosphere of any mine, take such tests as the Bureau may prescribe,
and upon disclosure of a ventilating current below or approaching mini-
mum standard, require the operator by written safety order to improve the
ventilation immediately.

Working Place means a room, breast, entry, cross-cut or pillar where
coal is being mined or extracted and where one or more miners per working
shift of the mine are regularly employed until the place is finished or

stopped.

As to mining companies, see art. 23, sec. 180 et seq.

TITLE I—ADMINISTRATION.
CHAPTER I—Supervision.

1922, ch. 307, sec. 17.

18. There is hereby created under the Commissioner of Labor and
Statistics, a department to be known as the " Bureau of Mines," herein-
after referred to as the Bureau.