Paradigms of blast protection

Approaches to blast protection can be categorised as active (deployed upon detection of an explosion) or passive (always present). An example of an active mitigation system is the water deluge system used on offshore oil and gas platforms [9]. Upon detection of a gas leak, the entire area is showered with carefiilly sized water droplets in order to prevent ignition and remove the energy from a vapour cloud explosion. An active system can only work if the imminent explosion can be detected and a suitable system deployed in time. These systems work offshore because the gas leak, which accumulates relatively slowly, can be detected easily and the water system deployed. A number of researchers have worked on the detection and deployment of mitigation devices for explosive detonations with military applications [10,11]. Such systems have yet to be deployed in the military, and (at the time of writing) no such detection systems are available for the case of explosive detonation on board an aircraft. For such a system to be viable, it would need to be robust and inexpensive to install and operate. 

Passive mitigation systems are therefore the only viable option for the aircraft industry to consider at present. These can be divided into four blast protection paradigms  

Sacrificial systems these absorb energy and prevent the load from transferring to the stmc-ture that is being protected. The use of cellular metals as cladding materials has been investigated [12,13] with possible application to the hull of a mine-resistant vehicle. However, such systems require a (heavy) protective faceplate and need a thick core in order to be effective. Hence, this type of system is impractical for blast protection on board aircraft, where weight and volume are critical. 

Impedance mismatch it is theoretically possible to pair up materials having different impedances in order to prevent stress wave transmission to the structure to be protected. No practical systems employing this principle exist. 

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