Shock sensitivity
Encyclopedia
Shock sensitivity is a comparative measure of the sensitivity to sudden compression (by impact or blast) of an explosive chemical compound
. Determination of the shock sensitivity of a material intended for practical use is one important aspect of safety testing of explosives
. A variety of tests and indices are in use, of which one of the more common is the Rotter Impact Test with results expressed as FoI (Figure of Insensitivity
.) At least four other impact tests are in common use, while various "gap tests" are used to measure sensitivity to blast shock. Julius-Peters KG is a notable German company which manufactures testing apparatus for these tests.
cannot be touched at all without detonating
, and so are of purely academic interest. Some other compounds with a high sensitivity to shock, such as nitroglycerin and acetone peroxide
, may detonate from a firm jolt and so cannot be legally transported in pure form. Acetone peroxide is often used by amateurs and terrorists as a means to detonate other explosives as well as acting as the main blasting agent, often resulting in injuries or death to those who underestimate its sensitivity. A number of methods are known to desensitize nitroglycerine so that it can be transported for medical uses, and it is also incorporated into other less sensitive explosives, such as dynamite
s and gelignite
s.
Many practical commercial materials of intermediate sensitivity, such as gelignites and water gel explosive
s, can be safely handled as they will not explode from casual shocks such as being dropped or lightly knocked by a tool. However they may explode if struck forcefully by a metal tool, and would certainly explode in the barrel if they were used in an artillery shell
. Reliable initiation of such materials requires the small explosion of a detonator
.
Still less sensitive materials such as blasting agents like ANFO
, or shell fillings like Composition B
, are so insensitive that the impulse from the detonator must be amplified by an explosive booster
charge to secure reliable detonation. Some polymer bonded explosives — especially those based on TATB
— are designed for use in insensitive munitions
, which are unlikely to detonate even if struck by another explosive weapon.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
. Determination of the shock sensitivity of a material intended for practical use is one important aspect of safety testing of explosives
Safety Testing of Explosives
The safety testing of explosives involves the determination of various properties of the different energetic materials that are used in commercial, mining, and military applications...
. A variety of tests and indices are in use, of which one of the more common is the Rotter Impact Test with results expressed as FoI (Figure of Insensitivity
Figure of Insensitivity
Figure of Insensitivity is an inverse scale of measure of the impact sensitivity of an explosive substance. In this particular context the term 'Insensitivity' refers to the likelihood of initiation/detonation by accidental means e.g. impact, friction, electrostatic discharge, application of...
.) At least four other impact tests are in common use, while various "gap tests" are used to measure sensitivity to blast shock. Julius-Peters KG is a notable German company which manufactures testing apparatus for these tests.
Sensitivities vary widely
A few materials such as nitrogen triiodideNitrogen triiodide
Nitrogen triiodide is the inorganic compound with the formula NI3. It is an extremely sensitive contact explosive: small quantities explode with a gunpowder-like snap when touched even lightly, releasing a purple cloud of iodine vapor...
cannot be touched at all without detonating
Detonation
Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives, as well as in reactive gases...
, and so are of purely academic interest. Some other compounds with a high sensitivity to shock, such as nitroglycerin and acetone peroxide
Acetone peroxide
Acetone peroxide is an organic peroxide and a primary high explosive. It takes the form of a white crystalline powder with a distinctive bleach-like odor....
, may detonate from a firm jolt and so cannot be legally transported in pure form. Acetone peroxide is often used by amateurs and terrorists as a means to detonate other explosives as well as acting as the main blasting agent, often resulting in injuries or death to those who underestimate its sensitivity. A number of methods are known to desensitize nitroglycerine so that it can be transported for medical uses, and it is also incorporated into other less sensitive explosives, such as dynamite
Dynamite
Dynamite is an explosive material based on nitroglycerin, initially using diatomaceous earth , or another absorbent substance such as powdered shells, clay, sawdust, or wood pulp. Dynamites using organic materials such as sawdust are less stable and such use has been generally discontinued...
s and gelignite
Gelignite
Gelignite, also known as blasting gelatin or simply jelly, is an explosive material consisting of collodion-cotton dissolved in either nitroglycerine or nitroglycol and mixed with wood pulp and saltpetre .It was invented in 1875 by Alfred Nobel, who had earlier invented dynamite...
s.
Many practical commercial materials of intermediate sensitivity, such as gelignites and water gel explosive
Water gel explosive
A water-gel is a fuel sensitized explosive mixture that consisting of an aqueous ammonium nitrate solution that acts as the oxidizer. Water gels that are cap-insensitive are not strictly explosives and are referred to as blasting agents....
s, can be safely handled as they will not explode from casual shocks such as being dropped or lightly knocked by a tool. However they may explode if struck forcefully by a metal tool, and would certainly explode in the barrel if they were used in an artillery shell
Shell (projectile)
A shell is a payload-carrying projectile, which, as opposed to shot, contains an explosive or other filling, though modern usage sometimes includes large solid projectiles properly termed shot . Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used...
. Reliable initiation of such materials requires the small explosion of a detonator
Detonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....
.
Still less sensitive materials such as blasting agents like ANFO
ANFO
ANFO is a widely used bulk industrial explosive mixture. It consists of 94 percent porous prilled ammonium nitrate , that acts as the oxidizing agent and absorbent for the fuel — six percent Number 2 Fuel Oil...
, or shell fillings like Composition B
Composition B
Composition B, colloquially "comp B", is an explosive consisting of castable mixtures of RDX and TNT. It is used as the main explosive filling in artillery projectiles, rockets, land mines, hand grenades, sticky bombs and various other munitions...
, are so insensitive that the impulse from the detonator must be amplified by an explosive booster
Explosive booster
An explosive booster acts as a bridge between a low energy explosive and a low sensitivity explosive such as TNT. It increases the explosive shockwave from an initiating explosive to the degree sufficient to detonate the secondary charge.Unlike C4 plastic explosive, not all explosives can be...
charge to secure reliable detonation. Some polymer bonded explosives — especially those based on TATB
TATB
TATB, or triaminotrinitrobenzene, is an aromatic explosive, based on the basic six-carbon benzene ring structure with three nitro functional groups and three amine groups attached, alternating around the ring....
— are designed for use in insensitive munitions
Insensitive munitions
Insensitive munitions are munitions that are chemically stable enough to withstand mechanical shocks, fire, and impact by shrapnel, but that can still explode as intended to destroy their targets.-Description:...
, which are unlikely to detonate even if struck by another explosive weapon.