21. BLOCKS, DEMOLITIONS, CHAIN, M1

a. General. BLOCKS, demolition, chain, M1, assembly (fig. 16 and 17), consists of eight 2- by 2- by 11-inch blocks of tetrytol strung on a 16-foot length of primacord (par. 20 b) and packed in a haversack. The assembly is provided primarily for demolition purposes and is designed for ease in use and handling. The entire chain, or any part of the chain, may be used laid out in a line, wrapped around an object, or as packed in the haversack.

b. Description. Each block is rectangular in shape and is enclosed in a crinkle kraft paper bag. Printed on the bag in at least one place, is the designation: "DEMOLITION BLOCKS, M1 (TETRYTOL). MUST BE DETONATED BY CORPS OF ENGINEERS, U.S. ARMY, BLASTING CAP. ONE BLOCK - SIX ½ LB. TNT BLOCKS." The blocks are cast in place on the primacord with 8 inches between blocks and 2 feet of primacord free at each end. They consists of tetrytol, which is 75 percent tetryl and 25 percent TNT, with a cylin-drical pellet of tetryl cast in each end of each block. The dimensions of the haversack are approximately 12½ by 9 by 4½ inches, and its weight, packed, is 22.5 pounds.

c. Characteristic. Tetrytol is more powerful and more brisant than TNT: hence these blocks are more effective in cutting steel and in demolition work. If necessary, each block may be broken within its bag, but care should be exercised not to break the prima-cord. The blocks and primacord are comparatively insensitive to shock, but the assembly, that is, with tetryl pellet, is sligthly more sensitive than TNT.

Figure 16 - BLOCKS, Demolition, Chain, M1

Figure 17 - Demolition Blocks

d. Use. It is necessary to detonate the primacord by means of a blasting cap or deto-nator in order to fire the entrie chain. Sympathetic detonation of unconnected blocks can be obtained when they are separated by as much as 10 inches of air.