Prior to the 1980s, seat belts were the only form of passive restraint in our cars, and statistics have shown that the use of seat belts has saved thousands of lives.
In the 1980s the first commercial airbags appeared in motor vehicles. Statistics show that airbags reduce the risk of fatality in a head on collision by about 30%. Nowadays, we also have seat mounted and door mounted side airbags – and some cars have six or even eight airbags. The airbags deploy in the event of a crash, and provide cushioning for the driver and passengers in such a situation.
But how do they work? We know that moving objects have momentum, and cars consist of several objects, including the vehicle, loose objects inside the vehicle and of course, the passengers. When a car is stopped by a collision, the vehicle itself may be stopped, but the other objects inside the vehicle will continue to move at whatever speed the car was travelling, until they too are stopped by the body of the car or the windscreen. When a car crashes, the car’s momentum is changed instantly, but the passengers’ momentum has not changed. The goal of the seat belts and also the airbags is to help to stop the passenger’s momentum while doing as little damage as possible.
SRS airbags supplement the restraining action of the seat belt, and provide a barrier that can reduce the severity of head injuries in a crash. These types of airbags are now standard in most new vehicles, and are located in the hub of the steering wheel (driver airbag), in the dashboard above the glove compartment (passenger airbag), and side airbags are located in the door panel or seat. Curtain side airbags are located above the side doors.
During impact, sensors in the vehicle detect the sudden deceleration. A strong enough impact will initiate a flow of electricity to the inflator which will light the gas generator and the airbag will inflate in milliseconds into the space between the driver and the steering wheel, or between the passenger and the dashboard and between the side door and the driver/passenger. The bag will then deflate quickly when the gas escapes through vent holes or through the fabric – absorbing the energy of the driver/passenger when this occurs.
These days some airbags have different levels of inflation depending on the speed of impact and the distance between the driver and the steering wheel.
It is important to know that certain types of collisions, such as a rear-end collision, or if your car should roll without actually colliding with anything, may not cause the airbags to deploy unless your vehicle is fitted with a rather sophisticated sensor system, and specifically rollover sensors to detect the situation where your car rolls. So it is important when purchasing your vehicle, to check not only how many airbags there are and where they are situated – but also how many and what type of sensors the car has.
Also important to note is that the front passenger airbag should be set OFF if you have a child under the age of 13 or a person less than 153 cm tall in the front passenger seat.
For related reading, see our guide to ANCAP safety ratings and tips for getting familiar with a different car.