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As mentioned in the previous airbag disarming post, non=deployed airbags present a significant risk when extricating casualties from a car following a collision.
This mode of disarmer would be similar to the impact sensitive switches that turn off fuel pumps.
Once an impact occurs, the impact sensor
triggers a time delay (4-5 seconds should be sufficient) and then all the power to the airbag trigger mechanism is cut off. This would have to be in the circuitry after the capicitor that powers the system.
The time delay would still enable any airbag required to deploy during the impact sequence but then to make the remaining ones 'safe'. Ideally some indicator as to whether this has sucessfully occurred would also be useful.
Airbag Disarmer I
Airbag_20Disarmer
[oneoffdave, Jun 03 2005]
Securenet
http://www.holmatro...Id=1185&GroupId=126
One airbag 'catcher'. [oneoffdave, Jun 03 2005]
[link]
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Maybe this sounds strange, but isn't the safest mode when the thing has fired? Should there be a way to make it fire, under control? |
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You'd have to set them all off during the impact phase as the last thing you'd want to subject the occupant to is a series of detonations just as the car came to a halt. This could have the potential to exacerbate injuries as well as being startling. |
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There's also the cost issue as replacing the 5-6+ airbags that a lot of modern cars have would be very expensive. |
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What is the cause of the undesired airbag deployment? Is it a still-active airbag computer that gets a bad signal from a sensor? A damaged airbag computer? Power cross-wired to the charge by a damaged electrical system? Physical pressure or other manipulation of the charge resulting from the rescue efforts? |
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When you say "trigger mechanism", are you referring to the explosive charge itself or the electronics that detect impact and send the power to fire the charge? |
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Though I've never experienced it, I've heard of airbags being deployed when an ohmmeter is errantly used to probe the airbag circuit. |
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If forced to guess, I'd suspect that the problem is most likely the cross-wiring thing. In order to prevent all electrical power from reaching the explosive charge, it seems like it would be necessary to somehow short-circuit the triggering circuit very near the charge itself. |
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Maybe apply a reverse biased diode across the charge with a fusible link downstream from there. When post-impact disabling system goes in to effect it sends a reverse-of-normal polarity charge to the firing circuit thus forward biasing the diode and blowing the fuse. Probably not safe because it might deploy the airbag if the diode fails. Just thinking "out loud". |
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The usual causes for non-deployment is either an impact not quite hard enough to trigger it but enough to injure the occupant or an impact from a direction not relavant to that particular airbag (a frontal collision not setting off the side airbags). |
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The usual cause of undesired deployment is damage to the vehicle during the extrication process by the rescue services. The most common one being the steering wheel one deploying whilst the steering column is being displaced to free the casualty's legs. There are bag restraints available for these but not for the other airbags in a modern car. |
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I should have been clearer, by trigger mechanism I meant the systems that send the signal to detonate the charge. Possibly a relay that is held closed when energised and open when no power is supplied might work. |
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