Questions (and Answers) About Airbag Deployment

[rmoore]

A question received from a west coast firefighter concerns a fire officer reporting to his crew that an airbag can release sodium azide as it deploys.

My response was this;

Dear Firefighter-

What you have been told about airbags is NOT accurate. It is NOT possible for an airbag to 'burst' and release sodium azide or any chemical into the air.

The azide and the potassium nitrate is sealed inside a hockey puck-size container deep inside the airbag inflator module. It is not possible for a rescuer to get into this module and tear the container open. Won't happen.

When a chemical inflator system airbag inflates, it is filled with nitrogen gas, the by-product of the reaction of the sodium azide and other chemicals due to a crash deployment. The bag fills with the gases and deploys in
front of the occupants.

Airbag deployment can cause injuries to occupants who are seated too close
to the bag or who are out of position. Abrasion brush burns, bruising of the
cheeks, even a broken bone is possible. A vehicle occupant or a rescuer will never be exposed to the chemical that generates the airbag gas.

For details on airbag injuries, check out the NHTSA site at <www.nhtsa.dot.gov> and follow the links for airbags and airbag safety.

There is another type of airbag inflator system; used mostly for seat, door and roof-mounted airbag systems. These are called stored gas. They use a pressurized cylinder of argon and helium gas to fill the side impact airbag.

I just wrote an article about this technology in a recent monthly University of Extrication column in Firehouse magazine. Check out the back issues for the story on the Audi A-6 system.

Also, please check out the archive section of the University of Extrication section of our website. My back issues are there. There is a lot of info on safety around undeployed airbags. You should be more concerned with things like staying out of the airbag inflation zones than worrying about contact
with a chemical.

Anyone else have anything additional to add?

[vogelfuer]

I am grateful to you for elaborating on the design in which sodium azide is used. I had read about sodium azide in the Rescue Technician handbook from the University of Maryland and it was scary the way it talked about exposures to a suspected genetic mutant.
I too, wondered how rescuers could get exposed then I heard some departments in an effort to cancel the threat of an airbag will cut the airbag front open with like a utility knife. Ouch!!! The blast has got to go somewhere.

What's next SCBA donning for extrication?

[lutan1]

Your spot on Ron.
Its the same over here in Australia and the airbg systems in use.

A quote from a manual for rescuers states:
" The airbag is triggered by the airbag control unit.
When the triggering limits are exceeded, the integrated accelaeration sensors and the side impact sensors fire the required systems.

In the gas generator, the solid propellant sodioum azide burns completely into nitrogen. The gas flows into the airbag and unfolds it. When the airbag unfolds, the cover (impact ansorber of drivers airbag, cover of passenger airbag, trim of side/head airbags) splits open at the programmed rupture point.

The deposits of talc from the airbag that accumulate in teh passenger compartment do not represent a hazard due to its small concentration."

Another manual, in more technical terms says the following:
" The airbag inflator contains several components:
* An Electro Explosive Device (EED) with:
- An electrical heating elemen(Called an initiator)
- Approximately 100 milligrams of zirconic potassium percolate
* An enhancer pack with approximately 3 grams of barium potassium nitrate.
* A propellant with approximately 114 grams of sodium azide

During deployment, the airbag inflator operates in the following sequence:
The EED recieves current drom the SDM and begins the chemical reaction by igniting the zirconic potassium percolate.
The EED ignites the barium potassium nitrate in the enhancer pack.
The enhancer pack chemical reaction causes the sodium azide to rapidly produce nitrogen gas.
The nitrogen gas pushes the airbag, which seperates the steering wheel horn bar trim cover and inflates.
As the airbag inflates, some of the nitrogen begins to exit into the passenger compartment through vent holes of a calibrated size.
After the deployment, the surface of the cushion may contain a powdery residue. This powder consists primarily of corn starch (used to lubricate the cushion) and by-products of the chemical reaction. Sodium hydroxide dust is produced as a by-product of the deployment reaction.
The sodium hydroxide then quickly reacts with atmospheric moisture and is converted to sodium carbonate and sodium bicarbonate (baking soda).
Therefore it is unlikely that sodium hydroxide will be present after a deployment. As a precaution however, gloves and safety glasses are recommended when handling a deployed airbag to prevent and possible irritation of the skin or eyes."


Sounds pretty involved, but the long and short is- bags are safe....