Airbags: An explosive answer to injury prevention

Federal requirements for the use of air bags in automobiles have been the source of much political and scientific debate for more than 30 years. Recent reports of five known fatalities due to catastrophic airbag failures is the latest controversy to affect a mainstay feature in the constellation of onboard safety systems.

The gory details of these airbag failures ignited a news-media frenzy and federal government intervention. In these fatalities, the airbag safety system’s pyrotechnic inflator detonated so violently that the explosive’s metal container actually ruptured and shot metal shards toward the vehicle occupant. However, these five known incidents attracted much more attention than the larger number of deaths and injuries that are attributable to air bags that function properly.

The case for widespread airbag use derives from utilitarianism’s notion of the “common good”—roughly, “the greatest good for the greatest number.” Statistics show that airbags, especially when coupled with seatbelt use, protect significantly more people than they harm. The National Highway Transportation Safety Administration (NHTSA) estimates the combination of seatbelts and airbags reduces the risk of death by 61% in frontal crashes compared to a 50% risk reduction with seatbelts alone.

Nonetheless, the history of airbag usage reveals that even as they are integral to current onboard safety systems, vehicle occupants need to understand the way airbags operate and identify their onboard locations. Thankfully, minimal numbers of drivers and passengers experience the explosive drama of an airbag blowing up in their faces. It is shocking and probably painful as a body absorbs severe jostling and possibly injuries. It is a to-be-avoided experience, but just in case, an airbag tutorial is a very good idea.

Vehicle airbags 1.0

The basic operating principle of an air bag is to inflate a fabric bag that expands toward a driver or passenger during an automobile collision in order to insulate a vehicle occupant from the effects of an impact. Generating the gas to inflate the airbag within milliseconds of a collision requires a pyrotechnic device to create an explosion releasing hot gas. As the bag inflates, it simultaneously vents some of the gas through calibrated openings in the airbag. This deflation is necessary to prevent the occupant from being bounced backward.

The earliest airbag models (identified in the vehicle by the label SRS—Supplemental Restraint System) were calibrated to a front-facing, unbelted, adult male driver weighing 170 pounds. This turned out to be a dangerously limited perspective when airbags initially joined seatbelts in an effort by automakers and regulators to reduce injuries/death resulting from crashes. With actual use, airbags encountered belted and unbelted vehicle occupants of different shapes, sizes, and ages, eliciting mixed results. Reports of death and injury (23 lives lost between 1993 and 1996) prompted a Department of Transportation educational campaign targeting proper seatbelt usage and airbag dangers. Subsequently, NHTSA allowed automakers to reduce the power of air bags and permitted mechanics to deactivate them.

Evolving airbag safety systems 

Evolving airbag safety systems

New rules addressing the one-size-fits-all logic that had governed airbag activation took effect in late 1998. They required air bags to pass safety tests utilizing crash dummies in large adult, small adult, child, and infant sizes. Meeting those standards posed daunting technical challenges: a vehicle’s sensing system would need to discern the weight of the occupants and whether they were seat-belted in order to ensure the appropriate explosive discharge to inflate the air bag safely in a collision.

In addition, as seatbelt tensioners became more commonplace in vehicles, the air bag control module would also have to detect collision severity so only the seat belt tensioners would trigger in lesser collisions, while in more severe circumstances, both the air bags and the tensioners would activate. Also, if there were no passenger, the system had to avoid deploying that air bag.

And now, with 20 years of federal oversight and automaker compliance, airbags and the other vehicle occupant safety systems components are reaching higher performance levels with smart airbags and more nuanced applications—a recent Volvo innovation is a windshield-guarding airbag to cushion a car-felled pedestrian. That automaker’s innovation is an outlier; typical airbag technology expansions include side-door air bags, head-curtain air bags, and knee-bolster air bags.

There is also discussion of ways to enhance rear-seat occupants’ safety, which could include airbags built into seatbelt harnesses. All of these variants rely on significant advances to function: airbag inflators—dual-stage, multi-stage, and variable inflators—and onboard sensors to detect seat occupant girth, seat position, seatbelt use, and crash severity.

Reality check: Driving with airbags aboard

Even with all of this creative thinking and product development, airbags can still be dangerous to the unwary. The best-case scenario is to avoid collisions by driving safely and the next is to identify the location of all the airbags and their firing paths because vulnerable occupants like infants, children, pregnant women, and the otherwise fragile need some accommodations to avoid harm during airbag deployment.

If the bottom line for preventing airbag-related injuries is to stay out of harm’s way, that notion also applies to the hale and hearty: make appropriate use of age-determined car seats and boosters; grip the outside of the steering wheel when driving, not the center; ban propped legs on dashboards; and avoid leaning on passenger doors while napping. The rest is up to attentive driving and fate—although with the current spate of NHTSA-driven airbag recalls, complying with relevant repairs is another controllable safe-use factor.

Feb 17, 2015 | By Vernell M. Hance, John C.

 

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