(a)Quantity of explosive. The sheathed explosive unit shall
contain not more than 1 1/2 pounds of an approved or permissible
explosive.
(b)Chemical composition. The chemical composition of the
sheath shall be within the tolerances furnished by the applicant.
(c)Detonator well. The sheathed explosive unit shall have a
detonator well that--
(1) Is protected by a sealed covering;
(2) Permits an instantaneous detonator to be inserted in
the unit with the detonator completely embedded in the well;
(3) Is provided with a means of securing the detonator in
the well; and
(4) Is clearly marked.
(d)Drop test. The outer covering of the sheathed explosive
unit shall not tear or rupture and the internal components shall not shift
position or be damaged in the drop test.
(1) The drop test is conducted on at least 10 sheathed
explosive units. Each unit is dropped on its top, bottom, and edge from a
height of 6 feet onto a concrete surface. For units with explosives approved
with a minimum product firing temperature, the drop test is performed with
the unit at the minimum product firing temperature established for the
explosive in the unit. For units with explosives approved under regulations
in effect prior to January 17, 1989, the drop test is performed with the unit
at 41 °F.
(2) At least four units which have been drop-tested shall
be cut-open and examined.
(3) At least six units which have been drop-tested shall
be subjected to gallery tests 9 and 10 as provided in paragraphs (e)(1) and
(e)(2) of this section.
(e)Gallery tests. No sheathed explosive unit shall cause an
ignition in gallery tests 9, 10, 11, or 12. Ten trials in each gallery test
shall be conducted and each sheathed explosive unit shall propagate
completely in all tests.
(1) Gallery test 9 is conducted in each trial with three
sheathed explosive units placed in a row 2 feet apart. One of the trials is
conducted with sheathed explosive units which have been subjected to the drop
test as provided in paragraph (d)(3) of this section. The units are placed on
a concrete slab, primed with test detonators and fired in air containing 7.7
to 8.3 percent natural gas or 8.7 to 9.3 percent methane. The air temperature
is between 41 and 86 °F.
(2) Gallery test 10 is conducted in each trial with three
sheathed explosive units placed in a row 2 feet apart. One of the trials is
conducted with sheathed explosive units which have been subjected to the drop
test as provided in paragraph (d)(3) of this section. The units are placed on
a concrete slab, primed with test detonators and fired in air containing 3.8
to 4.2 percent natural gas, or 4.3 to 4.7 percent methane, mixed with 0.2
ounces per cubic foot of predispersed bituminous coal dust. The air
temperature is between 41 and 86 °F.
(3) Gallery test 11 is conducted in each trial with three
sheathed explosive units arranged in a triangular pattern with the units in
contact with each other. The units are placed in a simulated crevice formed
between two square concrete slabs, each measuring 24 inches on a side and 2
inches in thickness. The crevice is formed by placing one slab on top of the
other and raising the edge of the upper slab at least 4 inches. The sheathed
explosive units are primed with test detonators and fired in air containing
7.7 to 8.3 percent natural gas or 8.7 to 9.3 percent methane. The air
temperature is between 41 and 86 °F.
(4) Gallery test 12 is conducted in each trial with three
sheathed explosive units arranged in a triangular pattern with the units in
contact with each other. The units are placed in a corner formed by three
square steel plates, each measuring 24 inches on a side and one inch in
thickness. The sheathed explosive units are primed with test detonators and
fired in air containing 7.7 to 8.3 percent natural gas or 8.7 to 9.3 percent
methane. The air temperature is between 41 and 86 °F.
(f)Detonation test. Each of ten sheathed explosive units
shall propagate completely when fired at the minimum product firing
temperature for the explosive used in the unit or 41 °F for units with
explosives approved under regulations in effect prior to January 17, 1989.
The units are initiated with test detonators.
(g)New technology. MSHA may approve an explosive unit
designed to be fired outside the confines of a borehole that incorporates
technology for which the requirements of this subpart are not applicable if
MSHA determines that such explosive unit is as safe as those which meet the
requirements of this subpart.
