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A sympathetic detonation (SD, or SYDET), also called flash over or secondary/secondaries (explosion), is a detonation, usually unintended, of an explosive charge by a nearby explosion.
A sympathetic detonation is caused by a shock wave, or impact of primary or secondary blast fragments.
The initiating explosive is called the donor explosive, the initiated one is known as the receptor explosive. In case of a chain detonation, a receptor explosive can become a donor one.
The shock sensitivity, also called gap sensitivity, which influences the susceptibility to sympathetic detonations, can be measured by gap tests.
If detonators with primary explosives are used, the shock wave of the initiating blast may set off the detonator and the attached charge. However even relatively insensitive explosives can be set off if their shock sensitivity is sufficient. Depending on the location, the shock wave can be transported by air, ground, or water. The process is probabilistic, a radius with 50% probability of sympathetic detonation often being used for quantifying the distances involved.
Sympathetic detonation presents problems in storage and transport of explosives and ordnance. Sufficient spacing between adjacent stacks of explosive materials has to be maintained. [1] In case of an accidental detonation of one charge, other ones in the same container or dump can be detonated as well, but the explosion should not spread to other storage units. Special containers attenuating the shock wave can be used to prevent the sympathetic detonations; epoxy-bonded pumice liners were successfully tested. [2] Blow-off panels may be used in structures, e.g. tank ammunition compartments, to channel the explosion overpressure in a desired direction to prevent a catastrophic failure.
Other factors causing unintended detonations are e.g. flame spread, heat radiation, and impact of fragmentation.
A related term is cooking off, setting off an explosive by subjecting it to sustained heat of e.g. a fire or a hot gun barrel. A cooked-off explosive may cause sympathetic detonation of adjacent explosives.
Sympathetic detonations may occur in munitions stored in e.g. vehicles, ships (called a Magazine Explosion), gun mounts, or ammunition depot, by a sufficiently close explosion of a projectile or a bomb. Such detonations after receiving a hit have caused many catastrophic losses of vehicles. [3]
To prevent sympathetic detonations, minimal distances (specific for a given type of the mine) have to be maintained between mines when laying a minefield.
Spallation of materials after an impact on the opposite side may create fragments capable of causing sympathetic detonations of stored explosives on the opposite side of an armour plate or a concrete wall. [4] Transfer of the shock wave through the wall or armour may also be possible cause of a sympathetic detonation.
Class 1.1 solid rocket fuels are susceptible to sympathetic detonation. Conversely, class 1.3 fuels can be ignited by a nearby fire or explosion, but are generally not susceptible to sympathetic detonation. Class 1.1 fuels, however, tend to have slightly higher specific impulses, and therefore are used in those military applications where weight and/or size is at a premium, e.g. on ballistic and cruise missile submarines. [5]
Sympathetic detonation can be used for the destruction of unexploded ordnance, improvised explosive devices, land mines, or naval mines by an adjacent bulk charge.
Special insensitive explosives, such as TATB, are used in certain military applications to avoid sympathetic detonations.
During the Attack of Pearl Harbor, the USS Arizona was struck with an armor-piercing bomb which penetrated the upper deck and stopped inside the forward magazine. The bomb triggered an explosion which was powerful enough to cut the Arizona in half and is considered a sympathetic detonation as there was an apparent delay between the detonation of the bomb and the contents of the forward magazine.
Sympathetic detonation killed 320 sailors and injured 390 others in the Port Chicago Disaster of July 17, 1944 at the Port Chicago Naval Magazine in Port Chicago, California. [6] [7]
During the 1967 USS Forrestal fire, eight old Composition B based iron bombs cooked off. The last one caused a sympathetic detonation of a ninth bomb, a more modern and less cookoff-susceptible Composition H6 based one.
The Russian submarine Kursk explosion was probably caused by a sympathetic explosion of several torpedo warheads. A single dummy torpedo VA-111 Shkval exploded; 135 seconds later a number of warheads simultaneously exploded and sank the submarine.
Multiple incidents have been recorded in the more recent GWoT where airstrikes have set off explosives or ammunition caches in insurgent positions. [8] [9] [10] [11] [12]
In rock blasting, sympathetic detonations occur when the blastholes are sufficiently close to each other, usually 24in or less, and especially in rocks that poorly attenuate the shock energy. Ground water in open channels facilitates sympathetic detonation as well. Blasthole spacing of 36in or more is suggested. However, in some ditch blasting cases sympathetic detonations are exploited purposefully. [13] Nitroglycerine-based explosives are especially susceptible. Picric acid is sensitive as well. [14] Water gel explosives, slurry explosives, and emulsion explosives tend to be insensitive to sympathetic detonations. For most industrial explosives, the maximum distances for possible sympathetic detonations are between 2–8 times of the charge diameter. [15] Uncontrolled sympathetic detonations may cause excessive ground vibrations and/or flying rocks.
The spread of shock waves can be hindered by placing relief holes – drilled holes without explosive charges – between the blastholes. [14]
The opposite phenomenon is dynamic desensitization. Some explosives, e.g. ANFO, show reduced sensitivity under pressure. A transient pressure wave from a nearby detonation may compress the explosive sufficiently to make its initiation fail. This can be prevented by introducing sufficient delays into the firing sequence. [14]
A sympathetic detonation during mine blasting may influence the seismic signature of the blast, by boosting the P-wave amplitude without significantly amplifying the surface wave. [16]
An explosive is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material, which may either be composed solely of one ingredient or be a mixture containing at least two substances.
Trinitrotoluene, more commonly known as TNT (and more specifically 2,4,6-trinitrotoluene, and by its preferred IUPAC name 2-methyl-1,3,5-trinitrobenzene), is a chemical compound with the formula C6H2(NO2)3CH3. TNT is occasionally used as a reagent in chemical synthesis, but it is best known as an explosive material with convenient handling properties. The explosive yield of TNT is considered to be the standard comparative convention of bombs and asteroid impacts. In chemistry, TNT is used to generate charge transfer salts.
A warhead is the section of a device that contains the explosive agent or toxic material that is delivered by a missile, rocket, torpedo, or bomb.
A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Different types of shaped charges are used for various purposes such as cutting and forming metal, initiating nuclear weapons, penetrating armor, or perforating wells in the oil and gas industry.
Pentaerythritol tetranitrate (PETN), also known as PENT, pentyl, PENTA, TEN, corpent, or penthrite, is an explosive material. It is the nitrate ester of pentaerythritol, and is structurally very similar to nitroglycerin. Penta refers to the five carbon atoms of the neopentane skeleton. PETN is a very powerful explosive material with a relative effectiveness factor of 1.66. When mixed with a plasticizer, PETN forms a plastic explosive. Along with RDX it is the main ingredient of Semtex.
A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, and explosion-generated effects. Bombs have been utilized since the 11th century starting in East Asia.
C-4 or Composition C-4 is a common variety of the plastic explosive family known as Composition C, which uses RDX as its explosive agent. C-4 is composed of explosives, plastic binder, plasticizer to make it malleable, and usually a marker or odorizing taggant chemical. C-4 has a texture similar to modelling clay and can be molded into any desired shape. C-4 is relatively insensitive and can be detonated only by the shock wave from a detonator or blasting cap.
A depth charge is an anti-submarine warfare (ASW) weapon designed to destroy submarines by detonating in the water near the target and subjecting it to a destructive hydraulic shock. Most depth charges use high explosives with a fuze set to detonate the charge, typically at a specific depth from the surface. Depth charges can be dropped by ships, patrol aircraft and helicopters.
ANFO ( AN-foh) (or AN/FO, for ammonium nitrate/fuel oil) is a widely used bulk industrial high explosive. It consists of 94% porous prilled ammonium nitrate (NH4NO3) (AN), which acts as the oxidizing agent and absorbent for the fuel, and 6% number 2 fuel oil (FO). The use of ANFO originated in the 1950s.
The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:
Detonation is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with speeds about 1 km/sec and differ from deflagrations which have subsonic flame speeds about 1 m/sec. Detonation is an explosion of fuel-air mixture. Compared to deflagration, detonation doesn't need to have an external oxidizer. Oxidizers and fuel mix when deflagration occurs. Detonation is more destructive than deflagrations. In detonation, the flame front travels through the air-fuel faster than sound; while in deflagration, the flame front travels through the air-fuel slower than sound.
Polymer-bonded explosives, also called PBX or plastic-bonded explosives, are explosive materials in which explosive powder is bound together in a matrix using small quantities of a synthetic polymer. PBXs are normally used for explosive materials that are not easily melted into a casting, or are otherwise difficult to form.
The exploding-bridgewire detonator is a type of detonator used to initiate the detonation reaction in explosive materials, similar to a blasting cap because it is fired using an electric current. EBWs use a different physical mechanism than blasting caps, using more electricity delivered much more rapidly. They explode with more precise timing after the electric current is applied by the process of exploding wire. The precise timing of exploding wire detonators compared with other types of detonators has led to their common use in nuclear weapons.
A triggering sequence, also called an explosive train or a firing train, is a sequence of events that culminates in the detonation of explosives. For safety reasons, most widely used high explosives are difficult to detonate. A primary explosive of higher sensitivity is used to trigger a uniform and predictable detonation of the main body of the explosive. Although the primary explosive itself is generally a more sensitive and expensive compound, it is only used in small quantities and in relatively safely packaged forms. By design there are low explosives and high explosives made such that the low explosives are highly sensitive and high explosives are comparatively insensitive. This not only affords inherent safety to the usage of explosives during handling and transport, but also necessitates an explosive triggering sequence or explosive train. The explosive triggering sequence or the explosive train essentially consists of an 'initiator', an 'intermediary' and the 'high explosive'.
Detonating cord is a thin, flexible plastic tube usually filled with pentaerythritol tetranitrate. With the PETN exploding at a rate of approximately 6,400 m/s (21,000 ft/s), any common length of detonation cord appears to explode instantaneously. It is a high-speed fuse which explodes, rather than burns, and is suitable for detonating high explosives. The detonation velocity is sufficient to use it for synchronizing multiple charges to detonate almost simultaneously even if the charges are placed at different distances from the point of initiation. It is used to reliably and inexpensively chain together multiple explosive charges. Typical uses include mining, drilling, demolitions, and warfare.
Shock sensitivity is a comparative measure of the sensitivity to sudden compression 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 At least four other impact tests are in common use, while various "gap tests" are used to measure sensitivity to blast shock.
An anti-personnel mine or anti-personnel landmine (APL) is a form of mine designed for use against humans, as opposed to an anti-tank mine, which target vehicles. APLs are classified into: blast mines and fragmentation mines; the latter may or may not be a bounding mine.
Operation Sailor Hat was a series of explosives effects tests, conducted by the United States Navy Bureau of Ships under the sponsorship of the Defense Atomic Support Agency. The tests consisted of two underwater explosions at San Clemente Island, California in 1964 and three surface explosions at Kahoʻolawe, Hawaii in 1965. They were non-nuclear tests employing large quantities of conventional explosives to determine the effects of a nuclear weapon blast on naval vessels, and the first major test of this kind since Operation Crossroads in July 1946.
An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated by a slower expansion that would normally not be forceful, but is not allowed to expand, so that when whatever is containing the expansion is broken by the pressure that builds as the matter inside tries to expand, the matter expands forcefully. An example of this is a volcanic eruption created by the expansion of magma in a magma chamber as it rises to the surface. Supersonic explosions created by high explosives are known as detonations and travel through shock waves. Subsonic explosions are created by low explosives through a slower combustion process known as deflagration.
In military munitions, a fuze is the part of the device that initiates its function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fuze designs can be seen in cutaway diagrams.