Do you know the chemistry behind airbags ?

Airbags in car as safety equipment inflates within one-twenty-fifth of a second! Have you ever wondered from where does this amount of gas comes in such short interval of time? Where is this gas stored? What makes airbag to inflate? Do the money spend on it really worth? In this article I will discuss the mechanism behind inflation of airbag and the chemistry behind its quick reaction.

The aim of an airbag is to slow the passenger's forward motion as evenly as possible in a fraction of a second. This increases survival chances of the passenger in automobile accidents. In my opinion airbags should be compulsory as car insurances. Slight addition in your car loan can be your invaluable expenditure. There are three parts to an airbag :

1. The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.

2. The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip.

3. The airbag's inflation system reacts sodium azide (NaN3) with potassium nitrate (KNO3) to producenitrogen gas. Hot blasts of the nitrogen inflate the airbag.

Older airbag systems contained a mixture of sodium azide (NaN₃), KNO₃, and SiO₂. A typical driver-side airbag contains approximately 50-80 g of NaN₃, with the larger passenger-side airbag containing about 250 g. Within about 40 milliseconds of impact, all these components react in three separate reactions that produce nitrogen gas. The reaction involved is :

1. 2 NaN₃ → 2 Na + 3 N₂ (g)

2. 10 Na + 2 KNO₃ → K₂O + 5 Na₂O + N₂ (g)

3. K₂O + Na₂O + 2 SiO₂ → K₂O₃Si + Na₂O₃Si (silicate glass)

The inflation system is not unlike a solid rocket booster (see How Rocket Engines Work for details). The airbag system ignites a solid propellant, which burns extremely rapidly to create a large volume of gas to inflate the bag. The bag then literally bursts from its storage site at up to 200 mph (322 kph) -- faster than the blink of an eye! A second later, the gas quickly dissipates through tiny holes in the bag, thusdeflating the bag so you can move.