How Do Airbags Work? Everything You Need To Know

Modern vehicles have numerous safety features built-in, from seatbelts and traction control to antilock brakes and adjustable headrests. These features...

Modern vehicles have numerous safety features built-in, from seatbelts and traction control to antilock brakes and adjustable headrests. These features are all designed to reduce the physical effects of a collision or other driving incident. Another modern safety feature in many vehicles is the airbag.

Airbags are designed to reduce instances of head injury by cushioning the head and neck during the forward movement that is often experienced as the result of a collision. The airbag prevents the head from making contact with the dashboard of the vehicle. It can also reduce instances of neck injury by preventing the jolting effect that can occur when the head is repelled forward and then sharply backward after contact with a hard or fast moving surface.

But, how does an air-filled bag that fits inside the dash of your vehicle achieve these and other feats of safety? It all relies on a small explosive charge and the right timing. Before we delve into the workings of the airbag it is important to understand why collisions cause the injuries that they do and the role that momentum plays in this.

safety airbag in a car

Understanding the Energy Involved in a Collision

Energy plays a role in pretty much everything we do and that includes driving a vehicle. And, energy, like most things, is controlled by the laws of physics. More specifically, the energy involved in a moving vehicle is controlled by the laws of motion. To understand why this is so important, we need to look at mass and velocity.

Any moving object has mass; the amount of stuff the object contains. It is a measure that is closely related to how much an object weighs. A moving object also has velocity; speed focused on a specific direction. When an object has both mass and velocity, it also has kinetic energy. The great the mass and velocity of an object, the great the amount of kinetic energy it has.

That does not become a problem until the object stops moving, either because you want to stop or because it has collided with an object. In either case, the kinetic energy that has been built up needs to go somewhere, it does not simply disappear. So, the faster you are moving, the more difficult it is to stop and the more damage that is done to the vehicle. Most cars are now designed to absorb much of this energy during a collision.

While this reduces some of the danger, it does not account for the fact that the driver and passengers are also objects that have their own mass and during the stopping motion of a vehicle, also have their own velocity. Before airbags, the only things stopping the driver and passengers from being carried forward with continuing momentum were their seat belts.

While seat belts have, without question, saved lives, they do not protect the head and neck. The seat belt stops your torso from further forward motion and pulls you back into the seat. During this motion the head and neck are pushed forward and snapped back at speed, often causing damage to the muscles and joints of the neck. Additionally, the speed at which this occurs depends on the speed the vehicle was traveling. At faster speeds, the forward motion can still carry the head into the dash of the car. The airbag cushions the head and neck and stops then from colliding at full force with the dash.

This is only possible because of the very unique way that airbags work.

exploded airbag in the car

How Do Airbags Work?

Airbags work by inflating as soon as the vehicle starts to slow down as the result of an accident. They then begin to deflate as soon as the driver or passenger’s head makes contact with them. If the airbag was not designed to deflate, then it would not solve the problem of the sudden backward movement of the head and neck, as your head would simply bounce off it.

All of this is possible because of a range of sensors and a small explosion. The airbag includes an accelerometer that detects changes in speed. If it detects deceleration above a preset speed, which is greater than normal braking speeds, it triggers the airbag circuit.

The circuit passes an electrical current through a heating element, which in turn ignites a chemical explosive. This generates a large amount of harmless gas that rushes into a nylon bag. The bag, which is packed into a space behind the steering wheel or on the passenger side dash, inflates. When the driver or passenger’s head makes contact with the bag, it begins to deflate with the gas escaping through small holes around the edges of the bag. By the time the vehicle has come to a full stop, the bag should have completely deflated.

Are Airbags Effective?

Airbags are a supplementary restraint system, meaning they are intended to work alongside seatbelts and not be relied on instead of them. When used correctly airbags have been found to reduce head-on vehicle collision fatalities by up to 24%. As airbag design and general vehicle safety improvements, this percentage should only rise.

However, care does need to be taken in the use of airbags. The violent explosion that makes an airbag work carries with it a small risk of eye injury and hearing loss. There are also dangers associated with the use of airbags in vehicles carrying small children. While modern airbags inflate with less force than older models, it is still recommended that rear-facing child seats are not placed in the front seats of vehicles where there is an active airbag. Accidental deaths from the use of airbags have reduced thanks to changes in the design of the airbag and improved driver education on their use.

Understanding more about how airbags work helps you to understand why they are installed as standard in many modern vehicles. It also helps you understand why they do not deploy every time you brake or stop at a signal.  They are just one example of how modern technologies are making driving safer for everyone.

Sources:

  1. Airbags, Explain That Stuff
  2. How Airbags Work, HowStuffWorks
  3. The Basic Facts and How to Stay Safe, Road & Travel