The heat from this ignition starts the decomposition of the sodium azide and the generation of nitrogen gas to fill the air bag. What is particularly amazing is that from the time the sensor detects the collision to the time the air bag is fully inflated is only 30 milliseconds, or 0.03 second.
An airbag can deploy in about 55 milliseconds, according to engineering study. This is about the same amount of time it takes you to blink your eyes or sneeze. In other words, airbag deployment is very quick. Authorities have noted that if you are out of position when an airbag deploys, you can be injured.
The answer would be found in a fascinating chemical called sodium azide, NaN3. When this substance is ignited by a spark it releases nitrogen gas which can instantly inflate an airbag.
Because of the small space between an occupant and the side of the vehicle, side airbags must deploy very quickly, typically within the first 10-20 milliseconds of a side crash.
When the car undergoes a head-on collision, a series of three chemical reactions inside the gas generator produce gas (N2) to fill the airbag and convert NaN3, which is highly toxic (The maximum concentration of NaN3 allowed in the workplace is 0.2 mg/m3 air.), to harmless glass (Table 1).
Current is passed through a heating element, which in turn ignites an explosive (a chemical explosive, to be more specific). A large amount of harmless gas instantly fills the nylon bag installed behind the steering wheel as the explosive burns.
In fact, the maximum pressure in an airbag is less than 5 psi—even in the middle of a crash event. Advanced airbags are multistage devices capable of adjusting inflation speed and pressure according to the size of the occupant requiring protection.
SAFETY BELTS MUST BE USED WITH AIR BAGS!
As mentioned above, air bags explode at speeds of 200 MPH for 12 to 18 inches. This is a violent reaction, necessary to have the bag deployed and beginning to slowly deflate when the occupant contacts the bag.
Generally, air bags are designed to deploy when the severity of a crash reaches a preset threshold value. Depending on the specific vehicle model, this threshold is normally equivalent to a vehicle crashing into a solid wall at 13-23 km/h .
When the crash sensor deploys the airbags too late, it can cause serious harm due to the fact that the passengers' heads or bodies are now too close to the airbag when it deploys. This means that someone's body or head is impacted by a 200-mile-per-hour airbag with up to 2,000 pounds of force.
The main chemicals contained in airbags are sodium hydroxide and sodium azide. When a crash happens and an airbag deploys, dust particles from the chemicals are released.
It also spreads the impact over a larger area of the body. That way, no single area (forehead, chin, neck) bears the brunt of it. That's why airbags inflate and then quickly deflate—to gradually bring the driver's momentum from 60 mph to zero.
When the sensors detect a collision, they trigger the deployment of the corresponding airbags (front, side or head curtain airbags). When the airbags deploy the do so very suddenly to reach full inflation before passengers come into contact with them.
Many drivers have endured broken bones in their chest, and damage to soft tissue. Burn and Laceration Injuries – The speed at which airbag deploys can cause abrasions or burns. The face and arms are particularly vulnerable to getting burned.
However, in many vehicles, the airbags will still deploy whether or not an occupant is fastened by a safety belt. Unfortunately for the occupant, not wearing a seat belt and crashing into an airbag can yield much more serious injuries than if a seat belt were worn.
An average airbag replacement cost for the driver side will be between $200 - $700. An average airbag replacement cost for the passenger side will be between $400 - $1,000. An average airbag replacement cost for the side curtain will be between $200 - $700.
The heating element ignites a chemical explosive. Older airbags used sodium azide as their explosive; newer ones use different chemicals. As the explosive burns, it generates a massive amount of harmless gas (typically either nitrogen or argon) that floods into a nylon bag packed behind the steering wheel.
For an airbag to adequately protect a driver from contact with the steering wheel, it must detect a collision, signal the airbag, and ignite the chemical to explode the bag.
Air bags in cars are designed with impulse, or momentum change principles. When a driver gets into an accident their momentum carries them forward into the steering wheel. By putting an airbag in the car, a smaller force is exerted over a longer period of time to change the momentum of the driver to a stop.
Breathing the gas that is formed from sodium azide causes the most harm, but ingesting (swallowing) sodium azide can be toxic as well. The gas formed from sodium azide is most dangerous in enclosed places where the gas will be trapped. The toxic gas quickly disperses in open spaces, making it less harmful outdoors.
The powdery substance released from the airbag, by the way, is regular cornstarch or talcum powder, which is used by the airbag manufacturers to keep the bags pliable and lubricated while they're in storage.
The current airbags contain sodium azide and sodium hydroxide, creating high temperature thermal gases to inflate an airbag. When the airbags deflate, these substances can cause a thermal or alkali burn, complicating the friction burns directly related to contact with the rapidly expanding airbag.
Older air bags used sodium azide as their explosive to generate nitrogen gas; new ones use different chemicals. As the explosive burns, it generates a massive amount of gas (typically either nitrogen or argon) that floods into a nylon bag packed behind the steering wheel.
Air bags inflate and deflate in about 25 milliseconds. In fact, they deploy so quickly that they are fully inflated even before the impact of a crash has begun to move the driver or passenger toward the windshield.
Air bags are used in automobiles because they are able to minimize the effect of the force on an object involved in a collision. Air bags accomplish this by extending the time required to stop the momentum of the driver and passenger.