All 1998 (model year) and newer automobiles sold in the United States are required via NHTSA / FMVSS to be equipped with a minimum of two airbags (driver and passenger side). Light trucks were required by model year of 1999. Within the next few years, all vehicles will have as standard equipment 6 - 8 Original Equipment Manufacturer (OEM) airbags. Air bag(s) must deploy, before the occupant(s) strike specific component(s) of the interior. Once the bag has been inflated, it slowly deflates by several small rear vent holes. Most air bag systems are made up of three basic components they are as follows:
The Bag: is constructed of a woven material similar to nylon, which is folded like a parachute. They are coated with talc like power that lubricate the air bag material for storage. After deployment, this powdery dust may contain residue from the chemical reaction, which may cause minor irritation. Therefore, the technician should wear protective clothing; gloves, eye goggles, long sleeve shirt and a respirator mask (check the manufacturer for details).
The inflation system: is similar to a solid rocket booster. This solid material ignites which burns extremely hot and rapidly to create gas. This action inflates the nitrogen gas (pulsed) via the chemical reaction of sodium azide (NaN3) and potassium nitrate (KN03). It bears mentioning that the bag can deploy at a forward velocity up to 200 mph.
The sensor: is an electrical and/or mechanical device, which triggers a firing squib, which activate the inflation system and deploys the air bag. The electrical sensor uses tiny accelerometer, which determines certain types of negative acceleration (decelerations). Generally, air bag systems will be deployed at a vehicle that is traveling a minimum speed above 10 mph. Of course, this is subject to many additional factors, such as type of impact, position, delta v (change in speed), and location of the subject vehicle. However, mechanical sensors (switch) close when mass shifts via the vehicle.
Most air bags are located underneath plastic baffles. Debris can accumulate in the general area of these baffles. This so-called debris can act as a projectile and/or prevent and/or rupture the bag, thereby causing additional injuries, which can be a major liability issue. The air bag circuitry remains active even though the battery is disconnected. It bears mentioning that some older vehicles may have mechanical sensors, which may not be easily disabled.
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About the Author Perry J. Zucker, Degreed Engineer (several degrees in engineering as well as technology), provides technical reports, pre-trial preparation, and expert witness testimony concerning vehicle related accidents (reconstruction), traffic violations, general accidents, and product liability cases, for both plaintiffs / defendants and civil / criminal. He is a member of SAE, IEEE, ASME, State Appellate Div. Expert Panel, ASE certified, State vehicle inspector and a certified speed measuring device operator / instructor. His office can be reached at (718) 375-5063 or visit him on the web at trafficdoc.com.
