AIR BAGS
What is an Air Bag & How does it Work: When a car is speeding along at 50 Km per hour it has a tendency ('Inertia') to keep moving at the same speed and in the same direction unless some force acts on it. The car accelerates its occupants to its own speed so that they seem to be moving as a single unit. The inertia of the occupants is, however, independent of the inertia of the car. If the car were to crash into a tree, the force of the tree would bring the car to an abrupt halt. The speed of the occupants, however, would remain the same because of their independent inertia and they would bang into the steering wheel, the dashboard or the windshield. The force exerted by the steering wheel or the windshield would then bring the occupants to a stop but may in the process cause injury to vulnerable body parts such as the head and the face. Car manufacturers use 2 different restraint systems to help stop the occupants while doing as little damage to him or her as possible. The oldest and till now the most trusted device for restraining the passengers has been the seatbelt that spreads this stopping force across sturdier parts of the body over a longer period of time to minimize damage. The air bag is the second and a more recently developed system that is used to supplement the slowing down by the seat belt by deploying a rapidly inflating cushion in the space between the passenger and the steering wheel or dash board to prevent crash injuries. The Air Bag typically consists of the following 3 parts:

  • The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.
  • The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). Sensors detect the crash using a mechanical switch that closes when a mass shifts and an electrical contact is made. Electronic sensors use a tiny accelerometer that has been etched on a silicon chip.
  • The air bag's inflation system uses the rapid pulse of hot nitrogen gas from the chemical reaction of sodium azide (nan3) and potassium nitrate (kno3) to inflate the bag.

The inflation system is not unlike a solid rocket booster. The air bag system ignites a solid propellant, which burns extremely rapidly to create a large volume of gas to inflate the bag. The bag then literally bursts from its storage site at up to 200 mph (322 kph) -- faster than the blink of an eye! A second later, the gas quickly dissipates through tiny holes in the bag, thus deflating the bag so you can move. Even though the whole process happens in only one-twenty-fifth of a second, the additional time is enough to help prevent serious injury.

The Air Bag and Inflation System Stored In the Steering Wheel

The Inflation System Uses a Solid Propellant and an Igniter

Safety Concerns: It is important to note that the force of an air bag can hurt those who are too close to it. Researchers have determined that the risk zone for driver air bags is the first 2 to 3 inches (5 to 8 cm) of inflation. So, placing yourself 10 inches (25 cm) from your driver air bag gives you a clear margin of safety. Measure this distance from the center of the steering wheel to your breastbone. If you currently sit less than 10 inches away, you can adjust your driving position in the following ways:

  • Move your seat to the rear as far as possible while still reaching the pedals comfortably.
  • Slightly recline the back of your seat.
  • Point the air bag toward your chest, instead of your head and neck, by tilting your steering wheel down (if your steering wheel is adjustable).

The rules are different for children. An air bag can seriously injure or even kill an unbuckled child who is sitting too close it or is thrown toward the dash during emergency braking. Experts agree that the following safety points are important:

  • Children 12 and under should ride buckled up in a properly installed, age-appropriate rear car seat.
  • Infants in rear-facing child seats (under one year old and weighing less than 20 pounds / 9 kg) should never ride in the front seat of a car that has a passenger-side air bag.
  • If a child over one year old must ride in the front seat with a passenger-side air bag, he or she should be in a front-facing child safety seat, a booster seat or a properly fitting lap/shoulder belt, and the seat should be moved as far back as possible.

It is important to remember that air bags are effective only when used in tandem with a lap/shoulder seat belt. An air bag can actually cause serious injury if used improperly and without the seat belt.

The Future of Air Bags: Until recently, most of the strides made in auto safety were in front and rear impacts, even though 40 percent of all serious injuries from accidents are the result of side impacts, and 30 percent of all accidents are side-impact collisions. Many carmakers have responded to these statistics by beefing up doors, door frames and floor and roof sections. Engineers say that designing effective side air bags is much more difficult than designing front air bags. This is because much of the energy from a front-impact collision is absorbed by the bumper, hood and engine, and it takes almost 30 to 40 milliseconds before it reaches the car's occupant. In a side impact, only a relatively thin door and a few inches separate the occupant from another vehicle. This means that door-mounted side air bags must begin deploying in mere 5 or 6 milliseconds! Also under development is the head air bag that looks a little like a big sausage and, unlike other air bags, is designed to stay inflated for about 5 seconds to offer protection against second or third impacts.