WM. PRESTON LANE, JR., GOVERNOR. 1059

(e) 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 so as
to make the use of concrete, concrete blocks, brick, or tile
impracticable, timbers laid longitudinally "skin to skin"
may be used, provided, however, this sub-section shall not
apply to recovery work.

104A. Doors and Overcasts (a) Doors used on main-
entry or cross-entry (entries from which room entries
are turned) haulage roads, which when open would con-
nect intake and return air courses ventilating the mine
inby such doors shall be in pairs to provide an air lock
large enough to contain an entire trip; provided however,
when only a single door is installed, such single door shall
be attended except in the case of panel or room entries in
process of development. Where air-lock doors are pro-
vided, there shall be sufficient leakage to prevent accumu-
lations of methane between the doors.

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

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

104B. Line Brattice (a) Substantially constructed line
brattice shall be used from the last open crosscut of an
entry or room, when necessary to remove gasses, explosives
fumes, and smoke. When damaged by falls or otherwise
they shall be repaired promptly.

(b) The space between the line brattice and the rib
shall be large enough to permit the flow of a sufficient
volume of air to keep the working face clear of flam-
mable and noxious gases.

Flame-resistive material shall be used in the construc-
tion of line brattice.

104C. Old Workings (a) The entrance to abandoned
workings shall be posted to warn unauthorized persons
against entering the territory.

Abandoned workings shall be sealed or ventilated.