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-   -   Frontal Crash - Airbags didn't deploy. Why? (https://www.team-bhp.com/forum/road-safety/157842-frontal-crash-airbags-didnt-deploy-why.html)

A close family friend of ours bought a Honda Brio Automatic. Automatic was new to the driver although the driver had no issues maneuvering through the difficult Bangalore traffic. While parking, instead of hitting the break, since they are new with automatic, they hit the accelerator. The car picked up in no time and sped on to a concrete pole.



This resulted in the front of the car to face quite a bit of damage. The service engineer suggested the repairs to be done for the bonnet while the radiator and bumper to be changed.

The driver hit the face on the steering column due to the impact and was injured. Now the question is, should'nt the airbag have deployed in this case ?

The impact does not look severe enough to trigger an airbag. Was the driver wearing a seat belt?

Since you have mentioned that the driver was parking, was the driver / passenger wearing the seat belt?

Yes he was wearing the seat belt and it happened in a matter of seconds and the seat belt did not hold enough to hold him back from hitting the steering. Probably due to his posture where he was a little front biased to look at the pole in front. The seat belt might have refrained from a bigger damage but it sure did not to hold enough for a impact leading to the lips swelling up and the gum to bleed lightly.

I was curious, what are the triggers for an airbag to inflate cause in this case the damage went all the way till the radiator grill.

abhisheksircar, Did you friend get injured or did he hit the steering? Do you think deployment of airbags would have made the crash any safer?

There has to be a minimum impact speed for the airbags to deploy. Below that sped they may not deploy. The damage seems to be at slow speeds and not one that would trigger the airbags.

I dont think thats an impact severe enough to trigger the airbag. Its just that since the bumper of the brio has a less overhang, the impact reached the bonnet and it caved in. Maybe it was close to triggering the airbag thats it.

As I searched the net, I found that there has to be certain speed above which Airbags should be deployed. It seems the car didn't attain that speed.
The damage looks bigger due to the fact that Honda cars are designed to absorb the maximum impact so as to assure the maximum pedestrian safety, thats what I have understood from the T-BHP.
One more thing I would like to point out that had Airbags been deployed, it would have been resulted in a very costly repair bill to your friend.

Even I think airbags didn't deploy as speed was not much. Just imagine for slow speed crashes if airbags start deploying; it will be very expensive and dangerous affair.

Looking at the picture one doubt came to mind. In case of a frontal impact why both the airbags always deploy? I mean if it's an offset impact say only driver's side is hit; then why passenger airbag also gets deployed? There are airbag sensors. Are these connected in series so that if any one gets hit; all trigger and deploy both the airbags? Instead can't we have a 'passenger present' sensor? The passenger airbag would deploy only when there is a passenger present in above mentioned case? It will save airbag repairing cost also.

I agree with the assessment that the speed was too low for the airbags to deploy, and that is for good in this case since the airbags may end up causing more damage (by hurting the passangers who are relatively safe when a frontal impact occurs at such low speeds). Generally airbags may not deploy betweek 8-14 MPH. The details depend on the weight, vehicle stiffness, Crush (in inches), and Velocity of the vehicle.

Generally, the acceleration (deceleration, actually) sensors work with a combination of various parameters: change in velocity (delta V), acceleration, displacement, jert (which is rate of change of acceleration), etc.). Most technologies use a combination of these above parameters to bring the system from a "stand-by" stage to a "wake-up" stage, and based on the time duration between successive impulses of the monitored parameters, either go in to the "fire" stage, or return to the "stand-by" stage.

Airbags are triggered by impact sensors near the front corners, usually located behind the bumper frame and about 8" off the ground.

The collision force has to be

• severe enough,
• involving either or both sides and
• low enough to deform the chassis section where the sensors are located

for airbags to deploy.

A look at the Honda City's airbag sensors. Going under a truck or hitting a pole with the middle of the bumper causes no effect on these sensors - and therefore no airbag deployment.


Please understand that airbags don't deploy every time there is an impact on the front of the car. How the sensors are located matters. In the pic above, the sensors are located behind the bumper frame - so the frame has to substantially deform for the sensors to trigger. Mild fender benders won't trigger airbags, even at 20 kmph.

He was injured on hitting the steering.

I thought of this as well but was wondering if a car is stagnant and a car comes from behind and hits hard, will the airbag not deploy ? The seat belt, I presume, in this case will not hold anyway.

[Edit] I guess that's one of a case and it will not since anyway they will not have sensors all around but in the front only.

This makes sense which makes me believe that Airbag definitely helps, but it's definitely not the last solution cause there are scenarios where the airbag will not deploy even if it effects the driver.

Analysing the pictures from another thread, let's see where approximately the airbag sensors are located (red circles), and where the bulk of the impact happened (green boxes) (photographs downloaded from FB and suitably edited).


We can't expect airbags to deploy in this situation, nor is it the car or manufacturer's fault. If a service centre guy said, “It’s because you did not collide properly”, there's possibly a modicum of truth in it!

Maybe manufacturers need to relocate their airbag sensors for airbags to deploy more easily - but then there would be so many airbag deployments in mild shunts, that we'll need another section, not a thread, to report all those cases!

Since the impact was strong enough ,by which he had hit the steering wheel despite wearing a seat belt,the airbag should have been deployed.The vehicle may be in a very slow speed ,which would have stopped airbag from deflating.

Thank you. This was enlightening enough. This thread can now be closed as it's clear that it's the position and the speed which resulted in the airbags to not deploy. Scary but that's the truth that you need a technically proper hit for the airbags to deploy.