When buses and automobiles are involved in a collision or emergency braking, many injuries that may occur can be attributed to passenger impact with unpadded or inadequately padded structures such as steel seat framing and stanchions.
The Australian Design Rules (ADR) provide some guidelines for the prevention of lifethreatening injuries caused by head impact, but neglect to address the problems of "lessserious" head injuries such as fractures and non-fatal facial (disfiguring) injuries.
Although many bus seat manufacturers routinely a pply padding to new seats only potentiallethal head injuries are considered during design and testing. Also there are many older style buses in service that have exposed metal framing around seats and as stanchions. This bareframing is a potential source for serious fractures and disfigurement. Public and private bustransport operators are thus faced with the necessity of applying padding to interior framing,such as seat rails and stanchions, to protect passengers against injury in the advent of a crash or rapid deceleration.
This project was carried out to evaluate the impact attenuation properties of padding material to reduce the severity of those less critical injuries. The impact attenuation properties were evaluated with respect to maximum deceleration (gmax), Severity Index (Sl) and Head Injury Criteria (HIC). Several readily available materials were evaluated and ranked according to those criterion.
It was possible to provide some preliminary ranking using static tests on materials samples and adopting minimum and maximum loads (generated) for some specific penetration. For example, using 50 mm x 50 mm samples, at a loading rate of 25 mm/min could use a minimum load of 0.3 kN (to eliminate materials whlch are too soft) and a maximum load of 1.O kN (to eliminate materials which are too stiff).
It is suggested that upper limits of HIC of 300 and a gmax of 100 be used to control impact performance from some specified (crucial) speed (head impact velocity). A good estimate of the potential of a material to provide protection in low speed impacts is using the headform test from a drop of 0.75 m, representing about 14k/h impact. The impact values at this level should not exceed a HIC value of 300, nor a gmax value of 100, for 30 mm thick materials supported on a rigid test bed.