How do airbags work?

The airbags they are passive safety devices present in most vehicles which – thanks to a gas, a chemical reaction or an explosion – inflate in the event of a collision and act like a cushion, preventing the people inside from suffering serious injuries.

Thousands of people are alive thanks to this amazing invention, but who invented it and how does it work?

How airbags work: here’s what triggers them

Luckily, we might say, not everyone gets to see airbags in action, but the way they work is undoubtedly fascinating.

The operation of this device is extremely delicate: imagine you are driving your car and, while going over a bump, you suddenly find yourself with a huge balloon in front of your nose. It wouldn’t be pleasant, would it? However, the airbag does not deploy for such a short time. This is because inside our cars there are different types of sensors, whose purpose is to monitor the correct functioning of the vehicle, and therefore to guarantee safety for the driver and passengers. The moment a impact with another vehicle or with an obstacle, i acceleration sensors present inside the SRS control unit (Supplemental Restraint Systemmore commonly known as the airbag control unit) ei shock sensors distributed along the body of the vehicle, they allow the control unit to determine the severity of the impact and – if necessary – activate the airbag. Only 0.01 seconds (10 ms) are needed from the start of the collision for the command to reach the control device. inflating the cushion.

Although the intervention by the control unit is very rapid, inflating the cushion also requires considerable speed. Precisely for this reason, the guanidine nitrate which, unlike the sodium azide found in early commercial versions of the airbag, is less toxic and less susceptible to moisture. Ignition usually occurs by means of a heating element operated by the same control unit.

Once the impact has been detected, the trigger device heats the explosive within 2 milliseconds and fills the airbag cushion within 20-30 milliseconds, thus guaranteeing the airbag system an overall intervention time of approximately 0.042 seconds!

Once this contact has occurred, the cushion partially deflates to be able to absorb the energy produced by the impact. This allows you to reduce or even eliminate the possibility of head or chest injuries. After approximately 6 minutes, the pillow will have completely deflated.


A curiosity about the airbag that not everyone knows? The pillow consists of thousands of nylon threads (about 11 thousand) which make the fabric very dense and extremely resistant. To make it even stronger, however, it is covered with a layer of protective silicone. To better cushion the impact, there are cushions behind the cushion ventilation holeswhich allow it to deflate without it being able to stiffen or explode.

In addition to the classic front airbags, there are also side ones, which work following the same mechanism.

The first airbag prototype? Two dentists invented it

It was two students from the University of Birmingham, Harold Round and Arthur Parrott, who developed the first rudimentary version of the airbag, designed to prevent impact fractures of the mandible during the First World War.

The two, who had treated several victims of the war, noticed that many of them suffered various injuries due to bullets and bombs, but also to collisions between vehicles. To minimize this type of injury they designed the “air cushion” which would then be installed on cars and planes driven by soldiers. Although the two creators were English, they decided to apply for the patent in the United States where it was accepted in November 1919.

First airbag prototype

More decades passed before an American, John Hetrick, would bring to light the importance of this device, but in a vehicle intended for civilian use. The idea came one Sunday afternoon, when the man was in the car with his wife and daughter. They were headed into the countryside when a deer crossed his path, and he had to swerve sharply to avoid it. Although Hetrick managed to hit the brakes in time, the vehicle ended up in a ditch, and the three got quite a scare.

He then asked himself what could be done to avoid the impact of the body against the dashboard, and began to design a “safety cushion for automotive vehicles”, patented in August 1952.

The following year it was German Walter Linderer to carry forward Hetrick’s idea, designing a inflatable compressed air cushion. A short time later it was discovered that not even compressed air could inflate the airbags in a reasonable time, making this prototype also ineffective.

1967: The first commercial airbag

Thanks to numerous studies on automotive safety and on the aforementioned airbag prototypes, in 1967 the American mechanical engineer Allen Breed developed a new type of sensor, the “ball in-tube sensor” (a steel ball held in place with the help of a magnet), still considered today as the world’s first electromechanical automotive airbag system. This type of airbag was equipped with a device capable of detecting a collision and activating the cushion within 25 milliseconds.

But how did it work? When the sensor sensed that the vehicle was heading for a collision, the steel ball separated from the magnet, closing the airbag detonator switch and activating the cushion expansion device (located inside the steering wheel) containing sodium azidea powdered substance which – if triggered – gives rise to a large volume of molecular nitrogen, capable of filling the pillow in less than 50 milliseconds.

But unfortunately sodium azide is highly toxic (just as its reaction products can be particularly harmful) and is very sensitive to humidity, which can compromise the functioning of the cushion inflation system. To neutralize the toxicity of azide, airbags were also introduced in later versions silica And potassium nitrate.

Only in the United States in the last thirty years these devices they saved the lives of more than 50 thousand people.

It is important to underline, however, how the seat belts are essential to protect passengers from serious injury. The presence of the Airbag system, in fact, does not make the use of seat belts optional, which remain the main one tool passive safety.

security belt