1074 LAWS OF MARYLAND. [CH. 437

4. Boreholes shall be cleaned and checked to see that
they are placed properly and are of correct depth, in re-
lation to the cut, before being charged.

5. To prevent blow-throughs, all portions of the bore-
holes where the height, of the coal permits, shall have a
burden in all directions of at least 18 inches before being
fired.

6. Boreholes shall be stemmed with at least 24 inches
of incombustible material, or at least one-half of the length
of the hole shall be stemmed if the hole is less than 4 feet
in depth.

7. In gassy mines examinations for gas shall be made
immediately before and after firing each shot where on-
shift shooting is done.

(b) Charges exceeding 1 1/2 pounds, but not exceeding 3
pounds, shall be used only if boreholes are 6 feet or more
in depth, and explosives are charged in a continuous train,
with no cartridges deliberately deformed or crushed, with
all cartridges in contact with each other, and with the end
cartridges touching the back of the hole and the stemming
respectively, and Class A or Class B permissible explosives
are used, provided that the 3-pound limit shall not apply to
solid rock work such as solid rock tunnels etc.

(c) Shots shall be fired by certified shot firers in mines
using coal-cutting equipment. The shot firer shall comply
with the requirements of this Act pertaining to blasting.
In mines where charging or shooting is done on shift, each
shot or each group of simultaneous shots shall be fired
immediately after it is charged.

(d) Only wooden tamping bars shall be used when
charging holes. Leg wires of electric detonators shall be
kept shunted or the ends twisted together until ready to
connect to the firing cable. Shots shall not be fired from
the power or signal circuit while any men are in the mine.

(e) Roof and faces of working places shall be tested be-
fore and after blasting.

(f) Ample warning shall be given before shots are fired,
and care shall be taken to ascertain that all persons are
in the clear. Men shall be removed from adjoining work-
ing places when there is danger of a shot blowing through.

(g) Adobe (mudcap) or other open, unconfined shots
shall not be fired in any mine.