Air bags: How they work and why it’s deadly when they don’t work

Car Accidents,Our Blog | May 13, 2015

One of the biggest news stories of 2014 was the General Motors recall scandal. A congressional inquiry and independent investigation revealed that certain GM employees had known about defective ignition switches for more than a decade, but never made substantive efforts to report that knowledge or correct the problem.

So far, the vehicle defect has been tied to 100 car accident fatalities and even more serious injuries. Perhaps the most dangerous result of the defect is that when jostled, the ignition switch could turn to the off position and kill power to the engine – which in turn disabled the vehicle’s air bags.

We often take air bags for granted, even though they literally save lives. And from an engineering standpoint, air bags are incredible devices. A 2011 article in “Car and Driver” (linked below) explains just how precise air bags must be in order to be effective.

First of all, calling them air bags is inaccurate. They are actually filled with nitrogen gas, which is produced by a chemical reaction triggered by igniting chemicals in a small compartment. As of 2011, a driver’s side air bag could fully inflate within about 20 to 30 milliseconds. This is crucial, because there is obviously very little time between the onset of the crash and the life-threatening impact the driver feels.

During a crash at 30 mph, a driver who wasn’t wearing a seatbelt would travel through the space between his chest and the steering wheel in about 23 milliseconds. Even a short air bag delay of maybe 10 milliseconds could mean the difference between life and death.

To sum up, air bags must work incredibly quickly and flawlessly in order to save lives. Small flaws in the operation of air bags could cause serious injury or death. And if the air bags are disabled entirely (as they were in the GM recall scandal), drivers and passengers stand little chance of survival.

Source: Car and Driver, “The Physics Of: Airbags,” John Pearley Huffman, June 2011