Sympathetic detonation
Encyclopedia
A sympathetic detonation (SD, or SYDET), also called flash over, is a detonation
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...

, usually unintended, of an explosive charge by a nearby explosion
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...

. Sympathetic detonation is caused by a shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...

, or impact of primary or secondary blast fragments
Fragmentation (weaponry)
Fragmentation is the process by which the casing of an artillery shell, bomb, grenade, etc. is shattered by the detonating high explosive filling. The correct technical terminology for these casing pieces is fragments , although shards or splinters can be used for non-preformed fragments...

.

The initiating explosive is called donor explosive, the initiated one is known as receptor explosive. In case of a chain detonation, a receptor explosive can become a donor one.

The shock sensitivity
Shock sensitivity
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...

, also called gap sensitivity, which influences the susceptibility to sympathetic detonations, can be measured by gap tests.

If 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....

s with primary explosives are used, the shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...

 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
Shock sensitivity
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...

 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
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...

. Sufficient spacing between adjacent stacks of explosive materials has to be maintained. 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
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....

-bonded pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

 liners were successfully tested. Blow-off panels may be used in structures, e.g. tank
Tank
A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...

 ammunition
Ammunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...

 compartments, to channel the explosion overpressure in a desired direction to prevent a catastrophic failure
Catastrophic failure
A catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems failure....

.

Other factors causing unintended detonations are e.g. flame spread
Flame spread
Flame spread or surface burning characteristics rating is a ranking derived by laboratory standard test methodology of a material's propensity to burn rapidly and spread flames...

, heat radiation, and impact of shrapnel
Fragmentation (weaponry)
Fragmentation is the process by which the casing of an artillery shell, bomb, grenade, etc. is shattered by the detonating high explosive filling. The correct technical terminology for these casing pieces is fragments , although shards or splinters can be used for non-preformed fragments...

s.

A related term is cooking off
Cooking off
Cooking off refers to ammunition exploding prematurely due to heat in the surrounding environment. It can also refer to a technique used when throwing grenades to achieve a controlled, predictable explosion....

, setting off an explosive by subjecting it to sustained heat of e.g. a fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

 or a hot gun barrel
Gun barrel
A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....

. A cooked-off explosive may cause sympathetic detonation of adjacent explosives.

Military

Sympathetic detonations may occur in munitions stored in e.g. vehicles, ships, gun mounts, or storage depots, by a sufficiently close explosion of a projectile or a bomb. Such detonations after receiving a hit caused many catastrophic losses
Catastrophic kill
A catastrophic kill, K-Kill or complete kill refers to damage inflicted on a vehicle by a weapon that renders it both unusable and unrepairable whereas a "knocked out" vehicle is completely inoperable but not beyond repair...

.

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
Spallation
In general, spallation is a process in which fragments of material are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection or vaporization of material from a target during impact by a projectile...

 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
Armour
Armour or armor is protective covering used to prevent damage from being inflicted to an object, individual or a vehicle through use of direct contact weapons or projectiles, usually during combat, or from damage caused by a potentially dangerous environment or action...

 plate or a concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 wall. Transfer of the shock wave through the wall or armour may also be possible cause of a sympathetic detonation.

Solid rocket fuels of the class 1.1
Dangerous goods
Dangerous goods are solids, liquids, or gases that can harm people, other living organisms, property, or the environment. They are often subject to chemical regulations. "HazMat teams" are personnel specially trained to handle dangerous goods...

 are susceptible to sympathetic detonation. Conversely, fuels of the class 1.3 can be ignited by a nearby fire or explosion but aren't likely to detonate. The 1.1 fuels however tend to have slightly higher specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

, and therefore are used in those military applications where weight and/or size is at premium, e.g. on ballistic
Ballistic missile submarine
A ballistic missile submarine is a submarine equipped to launch ballistic missiles .-Description:Ballistic missile submarines are larger than any other type of submarine, in order to accommodate SLBMs such as the Russian R-29 or the American Trident...

 and cruise missile submarines.

Sympathetic detonation can be used for destroying of e.g. unexploded ordnance
Unexploded ordnance
Unexploded ordnance are explosive weapons that did not explode when they were employed and still pose a risk of detonation, potentially many decades after they were used or discarded.While "UXO" is widely and informally used, munitions and explosives of...

, improvised explosive device
Improvised explosive device
An improvised explosive device , also known as a roadside bomb, is a homemade bomb constructed and deployed in ways other than in conventional military action...

s, land mine
Land mine
A land mine is usually a weight-triggered explosive device which is intended to damage a target—either human or inanimate—by means of a blast and/or fragment impact....

s, or naval mine
Naval mine
A naval mine is a self-contained explosive device placed in water to destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel...

s by an adjacent bulk charge.

Special insensitive explosives, e.g. 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 used in e.g. military applications to prevent the sympathetic detonations.

Examples

During the 1967 USS Forrestal fire
1967 USS Forrestal fire
The 1967 USS Forrestal fire was a devastating fire and series of chain-reaction explosions on 29 July 1967 that killed 134 sailors and injured 161 on the aircraft carrier , after an unusual electrical anomaly discharged a Zuni rocket on the flight deck...

, eight old 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...

 based iron bombs cooked off
Cooking off
Cooking off refers to ammunition exploding prematurely due to heat in the surrounding environment. It can also refer to a technique used when throwing grenades to achieve a controlled, predictable explosion....

. The last one caused a sympathetic detonation of a ninth bomb, a more modern and less cookoff-susceptible Composition H6
Composition H6
Composition H6 is a castable military explosive compound composed of the following percentages by weight:* 45% RDX* 30% TNT* 20% powdered aluminium* 5% paraffin wax as a phlegmatizing agent....

 based one.

The Russian submarine Kursk explosion
Russian submarine Kursk explosion
On 12 August 2000, the Russian Oscar II class submarine Kursk sank in the Barents Sea after an explosion. The investigation showed that a leak of hydrogen peroxide in a torpedo led to explosion of its fuel, causing the submarine to hit the bottom which in turn triggered the detonation of further...

 was probably caused by a sympathetic explosion of several torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

 warheads. A single dummy torpedo VA-111 Shkval
VA-111 Shkval
The VA-111 Shkval torpedo and its descendants are supercavitating torpedoes developed by the Soviet Union. They are capable of speeds in excess of 200 knots .-Design and capabilities:...

 exploded; 135 seconds later a number of warheads simultaneously exploded and sank the submarine.

Civilian

In rock blasting
Rock blasting
Rock blasting is the controlled use of explosives to excavate, break down or remove rock. It is practised most often in mining, quarrying and civil engineering such as dam or road construction...

, sympathetic detonations occur when the blastholes are sufficiently close to each other, usually 57 mm or less, and especially in rocks
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 that poorly attenuate the shock energy. Ground water in open channels facilitates sympathetic detonation as well. Blasthole spacing of 300 or more millimeters is suggested. However, in some ditch blasting cases sympathetic detonations are exploited purposefully. Nitroglycerine-based explosives are especially susceptible. Picric acid
Picric acid
Picric acid is the chemical compound formally called 2,4,6-trinitrophenol . This yellow crystalline solid is one of the most acidic phenols. Like other highly nitrated compounds such as TNT, picric acid is an explosive...

 is sensitive as well. 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, 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. Uncontrolled sympathetic detonations may cause excessive ground vibrations
Ground vibrations
Ground vibrations is a technical term that is being used to describe mostly man-made vibrations of the ground, in contrast to natural vibrations of the Earth studied by seismology. For example, vibrations caused by explosions, construction works, railway and road transport, etc - all belong to...

 and/or flying rocks.

The spread of shock waves can be hindered by placing relief holes – drilled holes without explosive charges – between the blastholes.

The opposite phenomenon is dynamic desensitization. Some explosives, e.g. 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...

, 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.

A sympathetic detonation during mine blasting may influence the seismic signature of the blast, by boosting the P-wave
P-wave
P-waves are a type of elastic wave, also called seismic waves, that can travel through gases , solids and liquids, including the Earth. P-waves are produced by earthquakes and recorded by seismographs...

 amplitude without significantly amplifying the surface wave
Surface wave
In physics, a surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient...

.
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