by Jim Kerr
Airbag technology continues to improve with every new vehicle introduced. From its beginnings with only driver’s side airbags, airbag technology has expanded to include passenger front airbags, side airbags, knee airbags, side curtains, and seat belt pretensioners. Here is what’s new and how they work.
Most airbags still use pyrotechnic charges to trigger inflation. A small igniter starts sodium azide burning, which produces nitrogen gas. The nitrogen gas inflates the airbag. A white powder created by the chemical reaction may irritate skin but most powder after an air bag deployment is just corn starch or talcum powder packed with the airbag to lubricate it as it opens up.
Some airbags are inflated by a compressed gas cylinder. An explosive charge punctures the end of the cylinder allowing the gas into the airbag. Heat from the charge helps the gases expand so the airbag deploys quicker.
From the instant crash sensors detect an impact until the airbag is inflated takes only thousandths of a second. High-speed cameras are needed to catch an airbag inflating. It occurs so quickly that even our eyes cannot see it happening.
Vehicle occupants can be hurt by airbags. One of the most common injuries is friction burns from the high speed of the airbag material rubbing against a person as it deploys. If there are objects between the airbag and the passenger when the airbag deploys, these objects can strike the passenger with tremendous speed. Drivers should place their hands on the steering wheel in the 3 and 9 o’clock positions to reduce the possibility of their hands striking them in the face. Passengers should be sitting in a comfortable upright position. I shudder when I see passengers riding with their feet on the dash. Their knees could pack a horrific punch!
To reduce the possibility of injury from front airbags, manufacturers have “de-powered” them in the last few years. Less forceful inflation rates are still designed to protect in most situations, but some manufacturers chose to use two-stage airbags that will inflate with less force or more force depending upon sensor inputs and accident conditions. One result of two stage airbags is that the airbag may still be charged after an accident although it has already inflated. Even inflated airbags should be handled as if they could go off.
Side air bags are usually located in the sides of the seats although some are located in the side doors. Some manufacturers use special sensors on side airbag systems. Honda has position sensors in the side of the passenger bucket seat that will prevent the side airbag from deploying if the passenger is in the wrong position. Jaguar uses ultra-sonic sensors to help determine passenger position before deploying airbags. Seat track position sensors are also used in some vehicles to determine air bag deployment force.
Side curtain air bags are becoming common in many vehicles. BMW, Mercedes, Volvo, and Ford are but a few manufacturers using airbags that cover the side windows, protecting occupant’s heads during side impacts and roll over. SUV’s such as the Ford Explorer and Volvo XC90 keep the side curtains deployed for up to 6 seconds if a roll occurs, compared to only a fraction of a second for front air bags.
Seat belts are an integral part of air bag systems. They hold us in the proper position for air bags to work. Some manufacturers are using seatbelt pre-tensioners, which are explosive charges that pull the seatbelts tight around the occupant just before the airbag is deployed. This seat belt must be replaced after the pre-tensioner has been activated.
The newest innovation in airbag systems has to be Mercedes Pre-Safe. Studies show that most impacts are preceded by a few seconds of reaction by drivers. The Pre-Safe system senses the driver’s reaction and vehicle movement to predict an impact. It then closes the sunroof, moves the passenger seat to the optimum position, and tensions the seatbelts with re-useable pre-tensioners to hold occupants in position before the impact occurs.
Some airbags use seat sensors to deactivate the system if nobody is siting in the seat. This reduces repair costs if there are no passengers in the vehicle.
Airbags are not the perfect answer. They are designed to help protect us during life-threatening accidents. Seat belts, alert drivers, and good vehicle condition are still the best safety features we have.