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Using the BMS Micro-Blaster for Trail Work

Recreation Tech Tip logo   United States Department of Agriculture Forest Service Technology & Development Program
November 2005 2300/6700 0567-2338-MTDC

Bob Beckley, Project Leader

Closeup image of BMS Micro-Blaster with release plate, safety latch, and actuator tube.
Figure 1--The BMS Micro-Blaster shown in fully cocked position with the safety locked in place and a 25-foot lanyard attached.

Closeup view of BMS Micro-Blaster cartridge showing the primer.
Figure 2--The BMS Micro-Blaster cartridge is about the same diameter as a .32-caliber shell but has explosive properties similar to those of a cartridge as large as a shotgun shell. The brass cap on one end of the cartridge is the primer.

Closeup view of a hole in a rock with a tape measure held under the hole to display the diameter.
Figure 3--The size of the hole in the rock is important. Holes must be drilled straight using a carbide-tipped, 5/16-inch masonry bit.

Closeup of a bore brush, hand-pumped bulb blower, and a can of compressed air that can be used to clean a drilled hole.
Figure 4--It is important to clean the hole thoroughly to prevent misfires. The BMS Micro-Blaster comes with a bore brush and hand-pumped bulb blower. A can of compressed air also works well.

The BMS Micro-Blaster (figure 1) is a low-energy demolition device that breaks rocks using expanding gases from a cartridge containing a small explosive charge. Because the BMS Micro-Blaster does not use high explosives, it can be operated by persons who are not licensed or certified blasters.

No special qualifications or certifications are needed to use the Micro-Blaster. The cartridge (figure 2) resembles a rifle shell about 2¼ inches long. The explosive properties of the cartridge are similar to those of a shotgun shell.

Cartridges for the BMS Micro-Blaster are hazardous materials. All employees involved in the use, storage, and disposal of hazardous materials shall receive specialized training (FSH 6709.11, 61.11). At a minimum, this training will include general safety awareness for handling hazardous materials, and the safe handling and use of these cartridges. Talk to your purchasing agent if you wish to purchase them.

Originally, the BMS Micro-Blaster was designed to open narrow passages for exploration and rescue in caves. However, it also is useful for breaking rocks that are too big to move in one piece.

With support from the U.S. Department of Transportation Federal Highway Administration's Recreational Trails Program, the Missoula Technology and Development Center (MTDC) purchased two BMS Micro-Blasters to evaluate their usefulness for trail construction and maintenance. The BMS Micro-Blaster is similar to the more familiar Boulder Buster, but the BMS Micro-Blaster works only for smaller rocks and uses a different principle to break rocks. For information on the Boulder Buster, see Boulder Buster: Breaking Rocks Without Explosives (9867-2840-MTDC). The BMS Micro-Blaster may be an acceptable alternative to the Boulder Buster for work with a variety of small- to medium-size rocks. The BMS Micro-Blaster also can be used to start cracks in larger rocks, making them easier to break.

Preparing the Hole

The powder cartridge needs to be placed in a 5/16-inch hole (figure 3) that is about 9 inches deep. MTDC drilled the hole with a Milwaukee rotary hammer drill with a 5/16-inch, carbide-tipped masonry bit powered by a portable Honda generator. If the hole is too shallow, the BMS Micro-Blaster could be damaged during the shot. If the hole is too deep, the firing pin might not strike the charge. Two charges can be placed in the hole, one on top of the other, for a four-fold increase in power. The hole should be 12 inches deep when two charges are used.

Allow the drill and bit to do the work. Applying too much pressure to the drill can cause the bit to flex, producing a crooked hole. The hole must be straight for proper placement of the BMS Micro-Blaster and the charge. Place the BMS Micro-Blaster in the hole to check its alignment and fit. If the actuator tube does not slide into the hole easily, the hole may be crooked. Drill a new hole nearby.

The hole must be cleaned thoroughly. The BMS Micro-Blaster comes with a bore brush and hand-pumped bulb cleaner (figure 4) for blowing dirt and dust from the hole. A can of compressed air also works well. Use the bore brush to remove caked dust that blowing won't remove. Blow the hole out again after brushing. The hole must be cleaned thoroughly before the charge is placed because dirt and dust could interfere with detonation, leading to a misfire.

Hole Diameter and Drilling

The hole's diameter is important. If the hole is larger than 5/16 inch, gas from the explosive charge will escape around the actuator tube and the rock will not break. Options for drilling the hole include:

Some mountaineering stores have bit holders for 5/16-inch, carbide-tipped masonry bits, allowing the bits to be used for hand drilling. These bit holders also are referred to as SDS (slotted drive shaft) bit holders. Bits tend to wobble when a hand-drilled hole is being started, making the opening of the hole larger than 5/16 inch. After several inches of hand drilling, the hole should regain the proper size.


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