The purposes of incendiaries are to cause maximum fire damage on flammable materials and objects and to illuminate. Incendiary agents are used to burn supplies, equipment, and structures. Initial action of the incendiary munition may destroy these materials, or the spreading and continuing of fires started by the incendiary may destroy them. Even experienced troops may suffer increased battle fatigue when confronted with a surprise enemy weapon, tactic, or attack. Examples include napalm bombs (Israel against Egypt, US against North Vietnam).
The use of flame weapons, such as Fougasse, the M202A1 Flash, white phosphorous, thermobaric, and other incendiary agents, against military targets is not a violation of current international law. They should not, however, be employed to just cause unnecessary suffering to individuals. The use of flame weapons should be addressed in the ROE. Flame weapons are characterized by both physical (flame and overpressure) and psychological casualty-producing abilities.
Flame does not normally need to be applied with pinpoint accuracy to accomplish its mission. Efforts must be made to ensure that certain types of flame munitions effects do not spread to structures needed by friendly forces. Large fires in urban areas are catastrophic, and these fires can create an impenetrable barrier for hours.
Flame weapons can be used against fortified positions, interior buildings, tunnels (to include subways and sewers), and open areas. They can also be used to control avenues of approach for personal and lightly armored vehicles. When employed properly, even if the round or burst misses, enough flaming material and overpressure enters the position or area to cause casualties and disrupt operations. Thermobaric munitions provide a more effective and selective flame capability that is easier and safer to employ at all levels of tactical operations without the side effect of large area destruction due to uncontrolled fires.
Fire is an effective way of interrupting operations of enemy personnel and in damaging supplies stored in the open. Complaints of smelling something burning is a common symptom among Post-Traumatic Stress Disorder [PTSD] sufferers who were exposed to napalm or burning flesh in various wars.
Incendiaries produce intense, localized heat designed to ignite adjacent combustible target materials. The true incendiary produces no fireball and relatively little flame. The basic damage mechanism of firebomb weapons comes from the fireball and burning residual fuel globules, impact momentum of the fuel and container, and damage from fires started by the weapon. The sharp cutoff of casualty-producing mechanisms outside the incendiary pattern allows delivery close to friendly troops, usually parallel to the forward line of battle, with minimum risk. Munitions have been developed with full fragmentation and penetrating capabilities coupled with reactive incendiary devices. These improved incendiaries are highly effective against fuel and other flammable targets. A drawback, however, in planning for the employment of incendiary weapons is that incendiary/fire effects are not evaluated in current weaponeering methodologies.
As refined models with better capabilities were developed, the concept of propelling a jellied oil of thick fuel that splattered and stuck to targets at ranges over 60 yards endured until the early 1970s, when rocket powered flame weapons provided greater standoff capabilities, such as the 4-barrel M202 rocket launcher, the M72 LAW, and MK 153 SMAW. The most common US flame weapons currently employed are the M202A1 Flash, flame field expedients (Fougasse), and the M14 TH3 incendiary hand grenade. The M202A1 Flash may be replaced by a new shoulder-fired, thermobaric warhead, soft-launched rocket to support soldiers.
The main incendiary agents are thermite (TH), magnesium (MG), WP, and combustible hydrocarbons (including oils and thickened gasoline).
Thermite incendiaries are a mixture of powdered aluminium metal and ferric oxide and are used in bombs for attacks on armoured fighting vehicles. Thermite burns at about 2000°C and scatters molten metal, which may lodge in the skin producing small multiple deep burns.
Magnesium (Mg) burns at about 2000ºC with a scattering effect similar to that of thermite. Its particles produce deep burns.
At ordinary temperatures, white phosphorus (WP) is a solid which can be handled safely under water. When dry, it burns fiercely in air, producing a dense white smoke. Fragments of melted particles of the burning substance may become embedded in the skin of persons close to a bursting projectile, producing burns which are multiple, deep and variable in size. The fragments continue to burn unless oxygen is excluded by flooding or smothering.
Combustible hydrocarbons fall into two categories:
- flame-throwers, oil incendiary bombs. During a flame-thrower attack, as flame and burning fuel fills an enclosed fortification, the oxygen content of the air is reduced and a hot toxic atmosphere containing large amounts of carbon monoxide, unburned hydrocarbons and smoke is produced.
- fire bombs containing thickened gasoline. A fire-bomb is a large tank containing thickened (gelled) gasoline that is air dropped. When it strikes the ground, the fuel is ignited by phosphorus igniters and a large fireball of intense heat is produced, lasting about 4 to 6 seconds. Also, a wide area of ground is covered with burning thickened gasoline, which may continue to burn for as long as 10 to 12 minutes.
The Marine Corps uses flame weapons systems, such thermobaric systems, that belong to a new class of fuel-rich compositions that release energy over a longer period of time (more so than standard explosives). When detonated in confined spaces, a chemical reaction causes a vigorous evolution of heat, pressure, and flame or spattering of burning particles as the warhead cloud expands. The result is a deflagration, a rapid [though sub-sonic] combustion process that gives off heat and light [in contrast to a detonation, which produces a super-sonic shock wave].
Incendiary Munitions - Application
To be effective, incendiary munitions should be used against targets susceptible to fire or heat damage. A considerable part of the target must be flammable, so the fire can spread.
Weather conditions have little influence on incendiary munitions themselves. Wind and precipitation, however, may greatly influence the combustibility of the target and its susceptibility to fire spread. Winds assist in the effectiveness of incendiaries, increase the rate of combustion, and can spread fires downwind more rapidly. Actually, each large fire can create a wind system of its own. This wind system results from the tremendous heat generated and the resulting vertical wind currents. Incoming winds can feed more air to the fire. This increases the rate of combustion, which, in turn, can increase the wind. In extreme cases, this wind is called a fire storm and sometimes exceeds 60 knots.
Smoke, sparks, and flames fly in the direction of the wind. Incendiary strikes (at successive targets) should be planned to begin with the farthest downwind target and proceed upwind. This will prevent aiming points from becoming obscured by smoke traveling downwind of initial fires. Additionally, the position of friendly forces or facilities that must not be damaged must be considered (in relation to the wind direction) when planning incendiary strikes.
Temperature, temperature gradient, and clouds have little if any effect on incendiaries. Humidity also has little effect upon incendiary munitions but may affect combustible material. Wood, vegetation, and similar material absorb some moisture from the air over a period. If relative humidities have been high for some time, as in the tropics, it may be more difficult to achieve combustion from incendiary action.
Rain or snowfall, even when light, can render grass and brush quite incombustible and make a continuing fire unlikely. Heavy timbers are not affected unless they have been exposed to long periods of precipitation. Combustible materials exposed to rain may be susceptible to fire damage, such as in mass incendiary attacks. In these attacks, the heat of combustion may be sufficient to dry combustible materials in the target area. In regions of high humidities, such as the tropics, mass incendiary attacks generate tremendous amounts of heat, causing vertical wind currents. This rising air can cause thunderstorms, counteracting the effects of the incendiaries.
It is difficult to extinguish burning metals with water; a spray actually speeds the burning. Water surrounding the area of burning metals prevents fire spread. Water extinguishes burning phosphorus, but unconsumed particles will burn again when dry.
Three elements of terrain affect the efficient use of incendiaries. These are soil, vegetation, and topography. The type of soil affects the impacting of the munition; combustibility of the vegetation affects the efficiency of the incendiary; and topography influences wind speed and direction.
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