144
and insert the detonator into it.
The demolition expert is provided with a number of formulae, by means of which he calculates how much explosive is required for any particular job. He has, therefore, to ascertain the exact dimensions of the bridge, wall, ship's side, rail, stone pier, tree, or whatever it is he wishes to cut; and having obtained these, he looks up his formulae, which vary for each type of material to be demolished and each kind of explosive to be used, and works out the correct amount. It is essential that the charge shall be placed in close contact with the surface to be cut. That means in the case of a steel girder of H section for instance, you will require three separate charges, one for each of the three surfaces. The top and bottom faces of the girder are called the top and bottom flanges, and the connecting piece is the web. They will all vary in thickness. If the top flange is 2" thick, the web will probably be 1" thick, and the bottom flange 2½" or 3" thick. A flange 3″ thick and 2 feet wide requires 36 lb of 808 to cut it. You take your 144 × 4 oz. cartridges, remove the wax wrapping, roll them all up together packed in cloth to make one sausage 2 feet long, and apply it to the surface of the flange. If it is the top flange you can hold it in position by resting some bricks or other heavy substance on it; but if it is a bottom flange you must tie your sausage to a board, cut about 2 ft. 6 in. long, lower the board below the girder, and lash it on by passing a rope round the 3" protruding from each side. The simplest type of bridge has one girder on each side; that means 6 charges. In a bridge of any size at all however the girders will themselves be built up of various steel angle-irons and cross pieces, so that to cut the bridge through at one cross section, and drop it, may call for twenty or more charges.
to ensure that the charges shall go off simultaneously - and that is important, because if one charge were to go off even a fraction of a second before the others the blast would blow them off their lashings and they would either drop into the water below, or explode harmlessly in the air - a special detonation fuse is used. Lengths of this are led from the primer placed in each charge to a central point, where they are all tied together and to the detonator. The safety fuse will set off the detonator, the detonator will fire the detonating fuse, which is so fast that it will reach the charges simultaneously and they will all go off as one.
What we were chiefly interested in was the rapid sort of demolition, that might be useful in guerilla work. It meant first reconnoitring your bridge to obtain all the necessary dimensions; no easy feat, if enemy
144
and insert the detonator into it.
The demolition expert is provided with a number of formulae, by means of which he calculates how much explosive is required for any particular job. He has, therefore, to ascertain the exact dimensions of the bridge, wall, ship's side, rail, stone pier, tree, or whatever it is he wishes to cut; and having obtained these, he looks up his formulae, which vary for each type of material to be demolished and each kind of explosive to be used, and works out the correct amount. It is essential that the charge shall be placed in close contact with the surface to be cut. That means in the case of a steel girder of H section for instance, you will require three separate charges, one for each of the three surfaces. The top and bottom faces of the girder are called the top and bottom flanges, and the connecting piece is the web. They will all vary in thickness. If the top flange is 2" thick, the web will probably be 1" thick, and the bottom flange 21⁄2" or 3" thick. A flange 3′′ thick and 2 feet wide requires 36 lb of 808 to cut it. You take your 144 × 4 oz. cartridges, remove the wax wrapping, roll them all up together packed in cloth to make one sausage 2 feet long, and apply it to the surface of the flange. If it is the top flange you can hold it in position by resting some bricks or other heavy substance on it; but if it is a bottom flange you must tie your sausage to a board, cut about 2 ft. 6 in. long, lower the board below the girder, and lash it on by passing a rope round the 3" protruding from each side. The simplest type of bridge has one girder on each side; that means 6 charges. In a bridge of any size at all however the girders will themselves be built up of various steel angle-irons and cross pieces, so that to cut the bridge through at one cross section, and drop it, may call for twenty or more charges. to ensure that the charges shall go off simultaneously - and that is important, because if one charge were to go off even a fraction of a second before the others the blast would blow them off their lashings and they would either drop into the water below, or explode harmlessly in the air - a special detonation fuse is used. Lengths of this are led from the primer placed in each charge to a central point, where they are all tied together and to the detonator. The safety fuse will set off the detonator, the detonator will fire the detonating fuse, which is so fast that it will reach the charges simultaneously and they will all go off as one.
What we were chiefly interested in was the rapid sort of demolition, that might be useful in guerilla work. It meant first reconnoitring your bridge to obtain all the necessary dimensions; no easy feat, if enemy
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