1376

LAWS OF MARYLAND

Ch. 418

which contains not less than 19.5 percent oxygen and not
more than 0.75 percent carbon dioxide. Crosscuts between
entries shall be closed, except the last one in a pair or
set of entries

(2)  Closing. If necessary to obtain a movement
of air to the face of a room in order to clear the room of
flammable or noxious gas, crosscuts between rooms shall be
closed, except the one nearest the face.

(3)  Abandoned Places. A crosscut shall be
provided at or near the face of each entry or room before
the place is abandoned

(4)  Entries Beyond Last Crosscut. Entries,
rooms, or chutes may not be turned off an entry beyond the
last crosscut This does not apply to driving places to make
a connection at the first crosscut or similar passageway
used as a main airway in connection with an entry. It
applies to extending places beyond the airway before the
main intake and return passageways are connected.

(5)  Construction. On entries other than room
entries, stoppings in crosscuts between intake and return
airways shall be built of substantial, incombustible
material, such as concrete, concrete blocks, brick, or tile.
In mines where physical conditions exist because of heavy or
caving ground which makes use of concrete, concrete blocks,
brick, or tile impracticable, timbers laid longitudinally
"skin to skin" may be used. However, this paragraph does not
apply to recovery work.

(h) (1) Doors in General. Doors used on main-entry or
cross-entry haulage roads, which when open would connect
intake and return air courses ventilating the mine, shall be
in pairs to provide an air lock large enough to contain an
entire trip. When only a single door is installed, it shall
be attended except in the case of panel or room entries in
the process of development. Where air lock doors are
provided, there shall be sufficient leakage to prevent an
accumulation of methane between the doors.

(2)  Closing of Doors. Doors shall  be kept closed
except when men or equipment pass through    the doorways.
Motor crews and other persons who open doors   shall see that
the doors are closed before leaving them.

(3)  Construction of Overcasts. Overcasts shall
be constructed tightly of incombustible material, such as
masonry, concrete, concrete blocks, or prefabricated metal,
of sufficient strength to withstand possible falls from the
roof, and of ample area to pass the required quantity of
air.

(i) (1) When Required Substantially constructed line
brattice shall be used from the last open crosscut of an
entry or room, when necessary to remove gas, explosive