100. Precautions.—If a tamped hole misses fire it should never be cleared out for recharging. A new hole should be drilled near, but not breaking into it.
Electric fuses or Bickford fuses (with blasting-caps for high explosives) should always be used when they can be obtained.
DEMOLITIONS.
101. Deliberate Demolitions, such as the destruction of walls, casemates, etc., in time of peace, or at a distance from the enemy in time of war, should be so made as to economize powder and work. To accomplish this, the mines and blasts should be located where they will produce the best effects attainable, and the charges should be proportioned to the work required from them.
The table previously given (p. 124) will serve as a guide for computing the first charges used, and from the results of these the charges of subsequent ones may be determined.
Judgment must be used in placing the charges, so that, when possible, they will destroy the supports and allow the superstructure to break up by falling.
The charges will usually be placed in chambers under or hollowed out in the masonry. Sometimes they are more advantageously placed in a trench outside and close to the foot of the walls. They should always be well tamped: when in mine-chambers, by methods previously described; when in trenches, or laid along the exterior of walls, by loading them with earth, etc., until the line of least resistance passes through the wall to be destroyed.
102. Hasty Demolitions are made when the time available for the work is limited.
The structures usually destroyed are houses, walls, stockades, bridges, tunnels, canal-locks, railroads, rolling-stock, etc., etc.
The time does not usually allow the charge to be placed in the most advantageous position or to be properly tamped. For this reason the high explosives are best suited for this kind of work, and large charges are a necessity.