An unusual mechanism of airbag injury

Abstract

An airbag mounted within the steering column of a car is an increasingly common safety feature in new motor vehicles sold in the UK. Together with the three-point lap-shoulder seatbelt it improves the level of protection for the driver in the event of a frontal collision. An airbag is intended to be a supplemental. It is triggered by a frontal impact within 30 degrees of each side of the head-on position, when an electronic crash sensor detects a sudden deceleration from a speed of over approximately 20 miles/h (32 km/h). If the sensor's crash conditions are satisfied then the inflator is fired. This is a pyrotechnic device containing sodium azide which on ignition produces a large volume of nitrogen gas, which then inflates the airbag up to a volume of 40 l (Eurobag design) or 70 l (full size) within 50 ms. The 'leading edge velocity' of the bag during deployment is between 46 and 184 mph but should be zero at the time of contact with a normally positioned driver. Evidence is accumulating to demonstrate that, with the airbag, overall mortality and serious injuries have been reduced, but there has been a new spectrum of injuries as a result of its deployment. Thermal injuries from the hot gases generated during firing, a chemical keratitis produced by the talcum or corn starch used to lubricate the neoprene surface or by a small amount of sodium hydroxide during sodium azide combustion, and the shearing forces produced by the 'punch out' of the bag are now well described, although uncommon. A case is reported in which the collision dynamics resulted in the driver being in close proximity to the steering column at the time of the bag's deployment.