# Air Bag Deployment **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [February 7, 2008, 1:42am UTC](https://community.cartalk.com/t/air-bag-deployment/10314 "2008-02-07T01:42:36Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![teta1972](https://avatars.discourse-cdn.com/v4/letter/t/85f322/32.png) [@teta1972](https://community.cartalk.com/u/teta1972)\ **Post date:** [February 7, 2008, 1:42am UTC](https://community.cartalk.com/t/air-bag-deployment/10314/1 "2008-02-07T01:42:36Z")
My husband’s 2005 Ford Escape was hit by a semi truck while his vehicle was parked and off. His steering wheel air bag deployed. How can an air bag deploy if the vehicle is not running and is parked? ---
**Author:** ![Roadrunner](https://avatars.discourse-cdn.com/v4/letter/r/d2c977/32.png) [@Roadrunner](https://community.cartalk.com/u/Roadrunner)\ **Post date:** [February 7, 2008, 2:16am UTC](https://community.cartalk.com/t/air-bag-deployment/10314/2 "2008-02-07T02:16:28Z")
Sensors in the bumpers set it off if they are hit over a certain speed. Whether your vehicle connects with something or another hits it. ---
**Author:** ![bing](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bing/32/4619_2.png) [@bing](https://community.cartalk.com/u/bing)\ **Post date:** [February 7, 2008, 2:37am UTC](https://community.cartalk.com/t/air-bag-deployment/10314/3 "2008-02-07T02:37:19Z")
That’s why they are so dangerous. They use a capacitor to store the current necessary to deploy them-just like a battery. Car doesn’t have to be running. Been people seriously injured removing or carrying air bags without properly disconnecting them. Like they say, the only safe air bag is one that has been deployed. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [February 7, 2008, 2:45am UTC](https://community.cartalk.com/t/air-bag-deployment/10314/4 "2008-02-07T02:45:21Z")
The air bag system has a backup power system. This can be a capacitor or a battery. This is in the event the vehicle is in an accident where the impact doesn’t cause the air bag to deploy but destroys the battery, but if there’s a secondary impact even with the destroyed battery, the air bag will still deploy. Tester ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [February 7, 2008, 11:31am UTC](https://community.cartalk.com/t/air-bag-deployment/10314/5 "2008-02-07T11:31:46Z")
They are designed that way. You would not want the bag not to deploy because the battery was damaged before the bag had triggered. They are designed to operate independent of any other system. ---
**Author:** ![art1966](https://avatars.discourse-cdn.com/v4/letter/a/77aa72/32.png) [@art1966](https://community.cartalk.com/u/art1966)\ **Post date:** [February 7, 2008, 2:26pm UTC](https://community.cartalk.com/t/air-bag-deployment/10314/6 "2008-02-07T14:26:41Z")
I think there is another reason to have the air bag function in the parked car: to protect a person sitting in the car when some bozo smashes into it. Yes, there is always the risk trade-off between protection for rare cases and damage/cost from (rare, we hope) false deployment. However, I’m inclined to trust the automobile Safety Engineers in balacing those risks, just as we are inclined to trust the Internal Combustion Engineers not to miss “miracle” techniques to boost power and efficiency. And there will be a bit of muddling in the design and trade-offs as the technology matures.