Chemistry of Airbags in Car

Have you ever wondered that cars can be associated with Chemistry? However, there are various operations in a car that are based on the principles of chemistry such as burning of fuel to run the engine, chemical reactions in the car battery and others. One of the interesting applications of chemistry is the airbags of a car. Yes, you read it right! Airbags are not inflated by compressed air, instead, there is a chemical reaction behind the inflation of airbags. But before that let’s trace the evolution of Airbags in a car.


Evolution of airbags

As we all know that the main purpose of airbags is to protect the automobile driver and passengers in case of an accident. However, the journey of the invention of airbags is full of twists and turns. In the late 1950s, the automobile industry started its research on airbags and how it can act as a safety tool in case of an accident. At the initial stage, there were many difficulties in the development of an airbag. Crash tests revealed that for an airbag to be protective, the bag must be inflated within 40 milliseconds. Also, the system of airbags should be able to distinguish between a major crash and a minor crash during the very short duration of accidental impact. All of these difficulties took 30 years for airbags to be commonly available in the year 1980s.


Mechanism of Airbags: Chemical Reaction and a matter of few milliseconds

The chemical inside the airbag that is responsible for the spontaneous reaction is called Sodium Azide- NaN3. Sodium Azide is stable at room conditions, however, when heated it breaks down. The chemical reaction behind airbags is as follows:

   2NaN3 —–> 2Na + 3N2

In the above reaction, the second product is N2 which is also known as nitrogen gas. As Nitrogen gas occupies a large volume so handful of Sodium Azide (130 grams approx.) will produce enough nitrogen gas required to inflate an airbag.


That is the main chemical mechanism that happens in a span of 30 milliseconds inside an airbag, but it is not the only one. In the reaction, the first product produced is Sodium (Na). It is a highly reactive metal and will immediately react with water to produce Sodium Hydroxide (NaOH). Sodium Hydroxide is a toxic compound, it will be very harmful if it comes in contact with the eyes, nose or mouth. To avoid such a dangerous situation and to minimize its exposure, other chemicals are mixed with Sodium Azide to dilute the reaction of sodium which in return produces lesser toxic compounds during the chemical reaction.


To detect a collision or an impact, there are sensors in the front part of the automobile. These sensors send some electrical signals to the container that contains the Sodium Azide and detonate it, resulting in ignition. The heat generated from this ignition reacts with Sodium Azide and it starts breaking down into Sodium & Nitrogen. In the end, the nitrogen gas fills the airbag. One of the most interesting things is that all of this mechanism, right from the time the sensor detects the collision till the inflation of the airbag, all of this happens in 30 milliseconds which is around 0.03 seconds. So, we can say that after 50 milliseconds of an accident, the airbags are inflated and protects the passengers by absorbing their forward-moving energy.


How does an airbag become inflated by this chemical reaction?


Nitrogen gas molecules in an airbag
Nitrogen gas molecules in an airbag


According to the kinetic theory of gases, gases are ideal and treat each molecule as a physical body that moves continuously in random directions. Nitrogen is a gas and its molecules behave in the same manner inside an airbag. Upon hitting a surface, these molecules exert a tiny force on the surface. A large amount of nitrogen gas is generated from the breakdown of Sodium Azide, resulting in a larger number of molecules exerting force on the surface which results in the inflation of airbags.



Airbags are important and helpful in reducing severe injuries and deaths due to accidents. Airbags safeguard us during the collision by providing a cushion that decreases the force and absorbs the forward-moving energy. This will prevent the passengers from hitting the steering wheel or any hard surface.


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