Richard Renneboog, Airbags


	Today is

How Do Airbags Work?

Richard M. J. Renneboog
Information Technology Developer / Webmaster
Renaissance Aeronautics Associates Incorporated

Return to Richard's Index Page --> HERE

There is a rule of thumb for life that says 'work expands to fill the time available'. This is a paraphrasing of one of the fundamental properties of gases. All gases expand to fill the space available to them. In so doing, the pressure exerted by the gas is kept uniform throughout. The automobile safety airbag is a rather simple application of this principle. To understand the airbag one could go to any local novelty store that sells helium-filled balloons. There one would find a large tank or canister of compressed helium gas. To get your helium-filled balloon, the attendant will connect an empty balloon to the helium tank, then open a valve to allow the helium gas to expand from the tank into the balloon. When the balloon is as full as it needs to be, the valve is closed and no more helium gas is allowed into the balloon.

An automobile safety airbag functions in essentially the same way as filling up a helium balloon. The difference is in how the filling of the bag is controlled and regulated. An automobile airbag is a safety device: its sole purpose is to prevent an occupant of the vehicle from impacting with the surrounding structure. Typically, in a collision, Newton's laws of motion tend to be obeyed very well. Of particular concern is the law of inertia, which says that objects in motion tend to stay in motion unless acted upon by an external force. A person traveling in a car, even though still inside the car, is nevertheless traveling at the same speed as the car. If the car stops suddenly, the person tends to keep moving with the same direction and speed as before the collision. This has resulted in fatal collisions between the car's occupants and the inside of the car. Seat belts go a long way to prevent such collisions, by effectively making the person a physical part of the car, so that he or she stops when the rest of the car stops. But seatbelts have not proven entirely effective. While the lower part of the person is adequately restrained, the upper portion still tends to fly forward, allowing the person's face and head to impact against the dashboard or windshield with terrible force. Small children may not even be restrained at all by a normal seatbelt. The airbag was designed to provide a protective cushion against such potentially deadly impacts.

In application, there are a number of serious considerations for airbags. The material from which they are made, and their construction, must be strong enough to withstand the pressures generated on impact; the structure must maintain its integrity at all times; and it must itself function both reliably and safely. In its construction, an automobile safety airbag restraint is nothing more than a type of balloon attached to a canister of compressed gas through a valve. An impact sensor opens the valve, releasing the gas into the airbag. The gas pressure is so high that the airbag inflates almost instantaneously, knocking away any protective covers in the process. A pressure relief valve vents excess gas to prevent the bag from rupturing. This maintains a secure impact-absorbing cushion between a person and the vehicle. The effect is rather like throwing a big pillow under someone when they fall so that they hit against something cushioning rather than the hard floor.

Are airbags foolproof? Not at all. As with any mechanical device, there is always a possibility of failure that depends very highly on regular monitoring and maintenance of the system. In a collision, it is also possible that the airbag is damaged so that it can not function. In addition to this, the sudden eruption of an airbag in front of one's face can be likened to having a small bomb go off there. The force of the airbag expansion has been known to blast pieces of the protective coverings away like so much shrapnel. Injuries and deaths have occurred precisely because of this effect, most notably with very small children and infants, whose tiny, delicate bodies are so easily compromised. It is therefore vitally important that proper attention is given to how child and infant car seats are placed in a vehicle. Never place them in the front seat with the little one facing forward, and whenever possible put them in the rear seat.

Image Copyright ScienceMaster.com and its Licensors

To the Top