Shared from a FB friend
People have asked me: “Why did you join the Army/” I replied: “To learn a skill.” Here’s a synopsis –
I finally began my demolition training 0n 11 December. My mathematics skills came in handy. It was easy to think that one needed only place a stick of dynamite or a pound block of TNT on an object to destroy it, but it could mean too much peripheral damage. Also, the stick or pound block might not do the job, due to improper placement of the charge.When used in a military application one had to remember that someone had to carry all those explosives. Therefore, the most effective use of explosives was extremely important. You didn’t want each team member carrying five to ten pounds of explosives, time fuse, detonating cord, blasting caps, etc., when five to ten pounds total would do the job. That said, one of the things we joked about a lot was the use of the letter P (which equaled the amount of explosives to use in the equations). The easy way out was to just say P = Plenty.Contrary to most people’s opinion, explosives were used just as much for constructive purposes as well as destructive. When used for construction, the use of mathematical equations was very common. By constructive purposes I’m talking about quickly digging a deep ditch or foxhole utilizing dynamite or a cratering charge, using the “Monroe effect” of a shape charge to produce a large post-hole, blasting rock or a hillside to make way for a road, using explosives to fell trees, etc.There was a different formula for each different use of explosives, so mathematical expertise was a must in demolition utilization. It was easy to think to oneself that additional explosives would do the job just as well, if not better. Hogwash! An over-abundance of explosives in a charge, or a poorly placed charge, could destroy a project.Safety was highly stressed. Explosives were nothing to fool around with. Procedures were in place for handling and using military explosives. So long as those procedures were followed to the letter, demolition work was generally a safe activity. We were reminded that there were no old, fearless demolition men. You were to always treat explosives carefully and with your mind focused on the job at hand. You were never to take shortcuts and you were to not just double-check, but triple-check everything.The uses of explosives were numerous. Different types of explosives were used for different outcomes. The low explosives were slow burning (called deflagration) and tended to push or shove objects (such as dirt, boulders, etc.). The burning rate for low explosives was 400 meters (1,300 feet) per second or less. Black powder and smokeless powder were examples of low explosives. High explosives were very fast burning (called detonation) used to cut or demolished objects (such as train rails, trees, bridges, etc.). Heat or shock was usually required to detonate high explosives. The burning rate was 1,000 meters (3,300 feet) per second or greater. Examples were TNT and dynamite.
An explosion generally resulted in pressure, accompanied by heat. The main effects were fragmentation (of any container used), blast (aka concussion), and incendiary (fire). Fragmentation would, of course, be best when using a heavy metal container to house the explosive. A good example was a pipe bomb. That was constructed using a piece of metal pipe, into which explosives were packed. The addition of bolts and/or nails (or other suitable metallic fragments) inside the pipe increased the fragmentation significantly.Blast was most noticeable inside a building. The blast effect was caused by expanding gasses, creating a concussion wave. Incendiary action is instantaneous, but would last longer if combustible materials are present, causing a fire.The detonating velocity of different explosive materials was one of the important qualities to consider when selecting the correct explosive for the job at hand. It also determined the classification of the explosive. Velocity was measured in feet per second that the detonation wave travels through a column of the explosive material.As a rule, the slower the velocity, the greater the moving action (such as in ditch digging) of the charge. On the other end of the spectrum, the faster the velocity, the greater the shattering action of the explosive.Explosives were classified as (1) low explosives, (2) primary-initiating explosives, and (3) high explosives. Low explosives burned slowly and were mainly used as propellants. Two examples were smokeless and black powders.
Primary initiating explosives were extremely sensitive and detonated without burning. They included mercury fulminate (an initiating explosive that was extremely sensitive to heat, friction, spark, flame, and impact, and used in detonators and blasting caps) and lead azide (an initiating explosive that was sensitive to flame and impact and used in blasting caps).High explosives had a very fast, or high, detonating rate. Examples were dynamite, nitroglycerin, and TNT. We worked with several basic military explosives, including TNT (21,000 fps detonating velocity), Tetrytol (23,000), Compositions C-3 and C-4 (both 26,000), ammonium nitrate (11,000), and military dynamite (20,000).Black powder was a “low explosive.” It burned rather than detonated. “High explosives” detonated in a highly fast and violent action. The burning speed of black powder was determined by the grain size. Finely granulated black powder burned much faster than larger grain. The chief use of black powder was in quarrying, fireworks, and time fuse. It was one of the first explosives used by man.
There were numerous different commercial dynamites, each having a different purpose. Commercial dynamite came in three types, straight dynamite, ammonia dynamite, and gelatin dynamite. Each type was further broken down by the amount of nitroglycerin content, which determined the strength or force of the resulting explosion. Commercial dynamite varied in detonating velocity from about 9,000 to 19,000 feet per second.
Numerous factors came into play when selecting the correct dynamite for the job at hand. Among those considerations was the material that was targeted, desired fragmentation, and condition of the target (wet or dry). Strength, when used in conjunction with dynamite, referred to the energy, which in turn, determined the power it developed, hence the work it could do.When rating the nitroglycerin or straight dynamites, they were referred to according to the percentage by weight of nitroglycerin. In other words, a 20% straight dynamite contained 20% nitroglycerin by weight. The percent didn’t indicate the relative strength, however. 40% dynamite was not twice as strong as 20%. In fact, a 60% dynamite was only about 1½ times stronger than 20% dynamite.In other types of dynamites, the nitroglycerin was substituted with other powerful ingredients, such as ammonium nitrate. That made for an even larger selection of dynamites and dynamite strengths. Commercial dynamite was initiated by either electric or nonelectric blasting caps. Military dynamite was unlike commercial dynamite in many respects, especially its makeup, moisture retention, and safety factors.
Because military dynamite was destined for use in battlefield conditions and under all possible weather conditions, and it contained no nitroglycerin, it was much safer to transport, store, and handle, than the commercial variety. Military dynamite also did not absorb or retain moisture, making it usable in almost all weather conditions. Its detonating velocity was about 20,000 feet per second. Military dynamite was detonated using electric or nonelectric military blasting caps, or detonating (det) cord.So, there you have it.