A sympathetic detonation (SD, or SYDET), also called flash over or secondary/secondaries (explosion), is a

detonation 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 s ...

, usually unintended, of an

explosive charge An explosive (or explosive material) 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 expl ...

by a nearby

explosion An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...

Definition

A sympathetic detonation is caused by a

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

, 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 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 ...

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

detonator A detonator, frequently a blasting cap, is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the last two being the most common. The commercial use of explosives uses electr ...

s with

primary explosive An explosive (or explosive material) 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 ...

s are used, the

of the initiating blast may set off the detonator and the attached charge. However even relatively insensitive explosives can be set off if their

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

explosive An explosive (or explosive material) 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 expl ...

s and

ordnance Ordnance may refer to: Military and defense * Materiel in military logistics, including weapons, ammunition, vehicles, and maintenance tools and equipment. **The military branch responsible for supplying and developing these items, e.g., the Uni ...

. 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 is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also co ...

-bonded

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

liners were successfully tested.

Blow-off panel A rupture disk, also known as a pressure safety disc, burst disc, bursting disc, or burst diaphragm, is a non-reclosing pressure relief safety device that, in most uses, protects a pressure vessel, equipment or system from overpressurization ...

s may be used in structures, e.g.

tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful ...

ammunition Ammunition (informally ammo) is the material fired, scattered, dropped, or detonated from any weapon or weapon system. Ammunition is both expendable weapons (e.g., bombs, missiles, grenades, land mines) and the component parts of other we ...

compartments, to channel the explosion overpressure in a desired direction to prevent a

catastrophic failure A catastrophic failure is a sudden and total failure from which recovery is impossible. Catastrophic failures often lead to cascading systems failure. The term is most commonly used for structural failures, but has often been extended to many oth ...

. Other factors causing unintended detonations are e.g.

flame spread A flame (from Latin '' flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density they ...

heat radiation Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is ...

, and impact of fragmentation. A related term is

cooking off Cooking off (or thermally induced firing) is unfired weapon ammunition exploding prematurely due to heat in the surrounding environment. The term is used both for detonation of ammunition not loaded into a weapon, and unintended firing of a loa ...

, setting off an explosive by subjecting it to sustained heat of e.g. a fire or a hot

gun barrel A gun barrel is a crucial part of gun-type weapons such as small firearms, artillery pieces, and air guns. It is the straight shooting tube, usually made of rigid high-strength metal, through which a contained rapid expansion of high-pres ...

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

Military

Sympathetic detonations may occur in

munition Ammunition (informally ammo) is the material fired, scattered, dropped, or detonated from any weapon or weapon system. Ammunition is both expendable weapons (e.g., bombs, missiles, grenades, land mines) and the component parts of other wea ...

s stored in e.g. vehicles, ships (called a Magazine Explosion), gun mounts, or storage depots, by a sufficiently close explosion of a projectile or a bomb. Such detonations after receiving a hit have caused many catastrophic losses of vehicles. To prevent sympathetic detonations, minimal distances (specific for a given type of the mine) have to be maintained between mines when laying a

minefield A land mine is an explosive device concealed under or on the ground and designed to destroy or disable enemy targets, ranging from combatants to vehicles and tanks, as they pass over or near it. Such a device is typically detonated automati ...

Spallation Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary p ...

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 (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or f ...

plate or a concrete wall. 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 impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse is ...

s, and therefore are used in those military applications where weight and/or size is at a premium, e.g. on ballistic and

cruise missile submarine A cruise missile submarine is a submarine that carries and launches cruise missiles ( SLCMs and anti-ship missiles) as its primary armament. Missiles greatly enhance a vessel's ability to attack surface combatants and strike land targets, and al ...

s. Sympathetic detonation can be used for the destruction of unexploded ordnance,

improvised explosive device An improvised explosive device (IED) is a bomb constructed and deployed in ways other than in conventional military action. It may be constructed of conventional military explosives, such as an artillery shell, attached to a detonating mecha ...

land mine A land mine is an explosive device concealed under or on the ground and designed to destroy or disable enemy targets, ranging from combatants to vehicles and tanks, as they pass over or near it. Such a device is typically detonated automati ...

s, or

naval mine A naval mine is a self-contained explosive device placed in water to damage or 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 ...

s by an adjacent bulk charge. Special

insensitive explosives Insensitive munitions are munitions that are designed to withstand stimuli representative of severe but credible accidents. The current range of stimuli are shock (from bullets, fragments and shaped charge jets), heat (from fires or adjacent ther ...

, such as

TATB TATB, triaminotrinitrobenzene or 2,4,6-triamino-1,3,5-trinitrobenzene is an aromatic explosive, based on the basic six-carbon benzene ring structure with three nitro functional groups (NO2) and three amine (NH2) groups attached, alternating arou ...

, are used in certain military applications to avoid sympathetic detonations.

Examples

During the

Attack of Pearl Harbor The attack on Pearl HarborAlso known as the Battle of Pearl Harbor was a surprise military strike by the Imperial Japanese Navy Air Service upon the United States against the naval base at Pearl Harbor in Honolulu, Territory of Haw ...

, 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 The Port Chicago disaster was a deadly munitions explosion of the ship SS ''E. A. Bryan'' that occurred on July 17, 1944, at the Port Chicago Naval Magazine in Port Chicago, California, United States. Munitions detonated while being loaded ...

of July 17, 1944 at the Port Chicago Naval Magazine in Port Chicago, California. During the 1967 USS ''Forrestal'' fire, eight old

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 and various other munitions. It was also use ...

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 A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, ...

warheads. A single dummy torpedo

VA-111 Shkval The VA-111 ''Shkval'' (from russian: шквал, '' squall'') torpedo and its descendants are supercavitating torpedoes originally developed by the Soviet Union. They are capable of speeds in excess of 200 knots (370 km/h or 230 miles/h). ...

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.

Civilian

rock blasting Drilling and blasting is the controlled use of explosives and other methods, such as gas pressure blasting pyrotechnics, to break rock (geology), rock for earthworks (engineering), excavation. It is practiced most often in mining, quarrying and ...

, 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 Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

in open channels facilitates sympathetic detonation as well. Blasthole spacing of 36in or more is suggested. However, in some

ditch blasting A ditch is a small to moderate divot created to channel water. A ditch can be used for drainage, to drain water from low-lying areas, alongside roadways or fields, or to channel water from a more distant source for plant irrigation. Ditches ...

cases sympathetic detonations are exploited purposefully.

Nitroglycerine Nitroglycerin (NG), (alternative spelling of nitroglycerine) also known as trinitroglycerin (TNG), nitro, glyceryl trinitrate (GTN), or 1,2,3-trinitroxypropane, is a dense, colorless, oily, explosive liquid most commonly produced by nitrating ...

-based explosives are especially susceptible.

Picric acid Picric acid is an organic compound with the formula (O2N)3C6H2OH. Its IUPAC name is 2,4,6-trinitrophenol (TNP). The name "picric" comes from el, πικρός (''pikros''), meaning "bitter", due to its bitter taste. It is one of the most acidic ...

is sensitive as well. Water gel explosives,

slurry explosive A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal pu ...

s, and

emulsion explosive An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althou ...

s 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 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 ( ) (or AN/FO, for ammonium nitrate/fuel oil) is a widely used bulk industrial 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 fue ...

, 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 Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...

of the blast, by boosting the

P-wave A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any ...

amplitude without significantly amplifying the

surface wave In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within liquids, at ...

References

{{reflist, 30em Explosions Explosives engineering

Definition

Military

Examples

Civilian

See also

References