1546 LAWS OF MARYLAND. [CH. 727

the percentage of methane in the main return exceeds one
half of one per cent., or in any split, or single return exceeds
three-tenths of one per cent., the mine shall be considered a
gaseous mine. Samples of the mine air shall be taken in
duplicate for testing purposes when the ventilating current
in such mine and mine conditions have been normal for at
least twelve hours; and when a sample is found to exceed the
limits, duplicate samples shall be taken and tested. If the
first results are confirmed the mine shall be rated as gaseous.
Whenever the operator of a mine previously rated as gaseous
shall improve the ventilation thereof until the percentage of
methane in the main return falls below one-half of one per
cent., arid in each individual split falls below three-tenths of
one per cent., as shown by samples taken and duly analyzed,
and such condition has been maintained continuously for a
period of not less than thirty days, the district mine inspector
may by written certificate authorize the rating of such mine,
during maintenance of such condition, as a non-gaseous mine.
"Grounding" means the establishment of an effective electric
connection between the object grounded and the earth, whether
the object grounded be a machine frame, a cable armor or an
electric system.

"Live" or "Alive" applies to any part of an electric system,
circuit, or apparatus or object in contact with or adjacent
thereto, charged with electricity or generating voltage to an
extent that the difference of potential between such system,
circuit, apparatus or object and the earth is measurable by a
voltmeter; or in case of a static charge, by an electrostatic
voltmeter.

"Methane" is a hydrocarbon gas (CH₄) frequently en-
countered in coal mines; when it is diffused through air in cer-
tain proportions of the mixture, 5½ to 14½ per cent., the
mixture will explode in the presence of a flame or hot spark.
"Mine" includes the shafts, slopes, drifts or inclined planes
connected with the excavations penetrating coal and/or fire
clay stratum or strata, which excavations are ventilated by
one general air current, and all appliances and equipment for
hoisting and extracting coal and/or fire clay; and shall em-
brace any and all parts of the mining property and plant on
the surface or underground, which contributes directly or in-
directly to the mining or handling of coal and/or fire clay;
and which is connected by one general system of mine rail-
roads, over which coal and/or fire clay may be delivered to
one or more points outside such mine. The word also includes
a portion of a mine when the sense so requires. The provisions
of this sub-title shall not apply to any mine where less than
five persons are employed or engaged in work inside the mine,
in any one period of twenty-four hours; but any mine inspector