Air-bags – History, function and related laws in Spain

For years, the seat belt provided the sole form of restraint in our cars. Now we have the air-bag, and it has saved many lives! In this article we’d like to take a look at the history, technology and safe usage of the air-bag, and also look at specific legislation concerning air-bags in Spain.

The history of the air-bag

John Hetrick, a retired American industrial engineer, designed the original “safety cushion” for car use in 1952. Air-bags for passenger cars were introduced in the mid ’70s, when seat belt usage rates were quite low. Air-bags were originally marketed as a convenient alternative to seat belts!

In 1987, the Porsche 944 turbo became the first car in the world to have driver and passenger air-bags as standard equipment. By the mid 90s, European car manufacturers such as Vauxhall, Peugeot, Renault and Fiat were including air-bags as optional equipment across their entire model ranges. By the end of the decade, it was very rare to find a mass market car without an air-bag, and some late ’90s products, such as the Volkswagen Golf (Mk IV) also had side air-bags.

How an air-bag works

The function and design is conceptually simple, a central “Air-bag control unit” (ACU) monitors a number of sensors within the vehicle, including impact sensors , accelerometers, side pressure sensors, wheel speed sensors, brake pressure sensors , gyroscopes, and seat occupancy sensors. When the requisite “threshold” has been reached or exceeded, the air-bag control unit will trigger the ignition of a gas generator propellant to rapidly inflate a nylon fabric bag. And it is rapid! An air-bag explodes at 200mph (322 kph) – faster than the blink of an eye! It’s loud too ( 165-175dB) can be measured during the deployment explosion.

As the car’s occupant collides with and squeezes the bag, the gas escapes in a controlled manner through small vent holes. The air-bag’s volume and the size of the vents in the bag are tailored to each vehicle type, to spread out the deceleration of the occupant over time and over the occupant’s body, compared to a seat belt alone.

The goal of an air-bag is to slow the passenger’s forward motion as evenly as possible in a fraction of a second. The bag itself is made of thin nylon, which is folded into the steering wheel or dashboard or, more recently, the seat or door. Inflation happens when there is a collision force equal to running into a brick wall at 10/15 miles per hour.

A mechanical switch is flipped when there is a mass shift strong enough to close an electrical contact. The sensors receive information from a microchip mounted accelerometer. The air-bag’s inflation system combines sodium azide with potassium nitrate to produce nitrogen gas. Hot blasts of the nitrogen inflate the air-bag. The gas then quickly dissipates through tiny holes in the bag, deflating the bag so you can move.

The whole process happens in only 1/25 of a second! The powdery substance released from the air-bag is regular cornstarch or talcum powder, which is used by the air-bag manufacturers to keep the bags pliable and lubricated while they’re in storage.

Specific laws for Spain

In April 1975, the Traffic Safety Administration of Spain implemented a mandatory safety-belt use law for persons who were front-seat passengers travelling outside city limits. On June 15, 1992, the law was expanded to include all front-seat passengers travelling in vehicles in the city limits and passengers in the back seats of vehicles with manufacturer-installed safety belts.

In 1997 the National Highway Traffic Safety Administration (NHTSA) issued a rule to allow car dealers to install on/off switches that allow air-bags to be deactivated. Individuals with medical conditions in which the risks of deploying the air-bag exceed the risk of impact can apply for deactivation of either or both driver and passenger sides. (Every case is personally accessed.)

For the driver side those who cannot position themselves to properly operate their cars at least 10 inches (254 cm) hack from the centre of the driver air-bag cover. Passenger side deactivation for individuals who need to transport a baby in a rear-facing child restraint in the front seat because time car has no rear seat, the rear seat is too small to accommodate a rear-facing child seat or because it’s necessary to monitor a child’s medical condition. (Many vehicles feature a passenger air-bag on/off switch.) They did not, however recommend turning off air-bags for relatively common conditions such as: pacemakers, eye-glasses, angina, emphysema, asthma, mastectomy, previous back/neck surgery, old age, or pregnancy.

Safe usage of your air-bag

Never try to disable the bag yourself, remember, this is not a soft cushion! It’s a powerful device, and can hurt you if you don’t know what you’re doing. To use your air bag correctly, follow these tips: Move the seat at least ten inches from an air-bag and always use your seatbelt. Place children under 12 in the back seat. Drive with both hands on the side of the wheel (10 to 2), not draped or laced, to prevent a broken arm if the air bag deploys. Don’t smoke, drink or eat while driving, And remember to have the air bag professionally inspected every five years.

This article was written on Monday, March 15th, 2010
It's filed under: "Technical guides"

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