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Suppression Systems: Passive
Some vehicles have fire retardant material in the engine compartment sound insulation mounted on the underside of the hood. Plastic mounting clips melt in a fire and drop the blanket to inhibit fire propagation.
A polymeric panel containing dry powder suppressant installed behind fuel systems is an example of a passive design to protect against fuel system crash fires. When a vehicle with the panel installed is struck and crushed in the region of the fuel tank, the panel ruptures and releases the suppression agent to inhibit combustion of spilled gasoline. These panels are currently installed on some police and race vehicles [1].
Limitations of fire retardant polymers
Ignition and propagation can be inhibited by use of fire retardant materials. However, it should be understood that flammability is often not a binary (flammable/ non-flammable) question. Many materials used in vehicle manufacture can be chosen for their flammability properties, as characterized by standard tests [2] that measure degree of resistance to burning.
Full-scale burn tests were used to evaluate the effectiveness of using fire retardant polymers in an A/C system housing [3]. The housing was installed in a test vehicle. The test vehicle and a control vehicle with OEM components were both crashed, and then burned. The fire retardant component did not improve the propagation properties of the test vehicle. For this test, other underhood polymers were of standard composition.
References
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