Airbags deploy when crash sensors located in the vehicle react to certain stimuli. There are several sensors throughout a car; each one relays certain information to and from the vehicle's airbag control unit. The unit then analyzes the data and sends a message to the unit's inflator system to deploy the airbag if needed.
The crash sensors are the most important details of a vehicle's airbag system. They are specifically designed to sense when a vehicle has been damaged in an accident. Each sensor responds to stimuli such as sudden stopping or increased pressure on parts of the vehicle. There are also sensors that measure wheel speed, brake pressure and whether or not someone is sitting in a particular seat. All of the sensors are monitored by the vehicle's airbag control unit, which is located in the front portion of the vehicle's cabin.
The entire process of an airbag deploying relies on the sensors working accurately and very quickly. The entire process, from impact to deployment, happens nearly instantly at about 200 miles per hour, or within 25 to 50 milliseconds.
An airbag can cause significant damage due to the speed and force at which it is deployed. It is important to wear a seat belt and stay at least 10 inches away from the airbag as it deploys.