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AUTO TECH: Airbag tech improves, but not perfect

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General Motors introduced the first front centre airbag last year.

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General Motors introduced the first front centre airbag last year.

Airbag technology continues to improve with every new vehicle introduced. Since the introduction of driver's side airbags, automakers have added passenger front airbags, side airbags, knee airbags, side curtains and seat-belt pre-tensioners.

Here's what's new and how the technology works.

Most airbags still use pyrotechnic charges to trigger inflation. A small igniter starts sodium azide burning, which produces nitrogen gas. This gas inflates the airbag. A white powder created by the chemical reaction may irritate skin, but most powder after an airbag 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.

The time from when crash sensors detect an impact until the airbag is inflated is measured in 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 a 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 6 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 airbags 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 has used ultrasonic sensors to help determine passenger position before deploying airbags. Seat-track position sensors are also used in some vehicles to determine airbag deployment force.

Side curtain airbags are common in many vehicles, especially SUVs, CUVs and crew-cab pickups. BMW, Mercedes, Volvo and Ford are just a few of the manufacturers using airbags that cover the side windows, protecting he heads of occupants during side impacts and rollovers. SUVs such as the Ford Explorer and Volvo XC90 keep the side curtains deployed for up to six seconds if a rollover occurs, compared to only a fraction of a second for front airbags.

Seatbelts are an integral part of airbag systems. They hold us in the proper position for airbags to work. Some manufacturers are using seatbelt pre-tensioners, which are explosive charges that pull the seatbelts tight around the occupant just before an airbag is deployed. This seatbelt must be replaced after the pre-tensioner has been activated.

Manufacturers are beginning to build "anticipation" into their systems such as the 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 designed to help protect us during life-threatening accidents, but they're not the perfect answer. Seatbelts, alert drivers, and good vehicle condition are still the best safety features we have.

Jim Kerr is a mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.

kerr.jim@sasktel.net

Republished from the Winnipeg Free Press print edition November 15, 2013 F4

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