of Ballistic Foam
Ballistic foam, a type of polyurethane foam placed in the dry bays of aircraft, prevents fires, adds strength with nominal weight to the structure, slows shrapnel during attacks, and offers cost-effect protection.
Foam is placed in the dry bays of aircraft to provide a barrier between spark and fuel. As bullets or shrapnel penetrate the mold line skin surrounding the outermost portions of the dry bay, the ballistic foam deprives sparks of oxygen. Thus when the article punctures the fuel tank, fire does not arise. Not only does the foam displace oxygen, but all gases, including explosive vapors which could magnify the destructive effects of ballistic attack. Dry bays, voids, may also contain “onboard ignition sources” like hot surfaces and electrical sparks which benefit both from a lack of gases and the fire-retardant nature of the foam.
Ballistic foam strengthens aircraft by protecting it from fire as well as fluid while adding little weight. Fluid protection involves resisting damage by “moisture, hydrocarbon fuels, hydraulic fluids, and most common solvents”. The density of the foam varies with the type being used; Type 2.5 is a white to light amber foam weighing 2.5 pounds for cubic foot, while Type 1.8 is a pale blue to green foam weighing 1.8 pounds per cubic foot.
Chopped fiberglass strands embedded in the foam contribute structural integrity through physical support and shrapnel mitigation. The strata that strengthens the foam in turn strengthens the airframe. The fiberglass also prevents shrapnel and bullets from rupturing and removing parts of the foam. It then allows the damage caused by projectile penetration to heal more effectively.
The passive protection afforded by ballistic foam is inexpensive and simple compared to active protection. One method of active protection, filling large dry bays with inert gases which will not sustain a flame, is very expensive and complex. Active protection only offers a “one time” chance for ballistic protection while the ballistic foam is always available.
|Survival Systems International|