Airbags: All you need to know!

saket77 · 26th February 2015, 15:40

All that you ever wanted to know about Airbags (but were afraid to ask!)

Airbags: All you need to know!-carairbags.jpg

According to the Ministry of Road Transport and Highways Transport Research Wing, Government of India, about 2.5 lac people in India lost their lives in road accidents in the year 2013. [Secondary Source: Wikipedia]. If you shudder at the thought of losing 2.5 lac lives in a year, then let me tell you that the actual figures could be worse.

India has a poor record and reputation when compared to developed nations in the west when it comes to road fatalities. Hence, it is time and with a reason that we practice safe driving and opt for safer cars. There is no fun without safety as they say and say that quite right. TBHP always advocates safe driving. We have articles highlighting the importance of seat belts. Let’s go a step further and discuss the SRS and particularly the airbags.

SRS means ‘Supplemental Restraint System’ and includes the airbags and seat belt pretensioners. As we already know that most fatal injuries are inflicted on the occupants when the human body strikes or bangs against the interiors of the car like against the steering wheel or the dashboard at the instance of crash.

Airbags are a safety device in your car which inflate much like a balloon in case of a crash/ severe impact and offer effective cushioning to the chest and head of the occupants, hence increasing the chances of their survival. It has to be kept in mind that airbags, a part of SRS, are designed and intended to be used in tandem with seatbelts. Hence, they offer maximum protection when the occupants are properly restraint by seat belts. No prizes for guessing now that seat belts are the PRS- Primary Restraint System. Also, most airbags are designed to be used just once. So, they will need a change once they have seen the action.

The philosophy and concept of efficacy of airbags is simple. Just provide a cushion between the occupant’s body and impact point and hence lessen the injury to critical body parts like the upper torso and the head. Since, it is impossible to trigger the system manually in time as this is a split second affair; it is best left to the system to decide when the airbags would trigger. Hence, the system deploys a number of sensors and algorithms to detect impact and severe deceleration of the car which helps the on board computer (Airbag Control Unit/ integrated ECU) to trigger the airbags in time.

The airbag must be inflated in a split second so as to protect the occupants and to prove their money’s worth, but its split second rapid inflation is not possible by any electronic air pump. So to overcome this problem, the system uses a chemical explosion to inflate the airbags immediately. The chemicals used in most airbag systems are Sodium Azide, Potassium Nitrate and Silicon Di-Oxide, which can react rapidly to form nitrogen. The Nitrogen gas finally inflates the airbags. And, fasten your seat belts ladies and gentlemen, all this happens within 30-40 milliseconds (0.03-0.04 seconds) of impact.

Airbags: All you need to know!-chemical.jpg

After the airbags deploy and serve their use, the vents in the bag allow the nitrogen to escape so as to deflate them. This in turn helps not hamper in the visibility of the driver. The released gases and particles may result in temporary discomfort to the occupants such as irritation in throat and eyes. People with respiratory problems should be taken off the car as soon as it is safe to do so.

Some Do’s / Don’ts and additional useful information:

1. Airbags are part of SRS-Supplemental Restraint System; hence always use the PRS (primary ~) -i.e... the Seatbelts. You have paid for them, so use them. The car will offer the best protection in case of a crash only when both systems work in tandem. Sitting in a car with airbags does not substitute the use of seat belts. Seat belts also keep you in the best possible position in case of airbag deployment. The bottom line is –ALWAYS PUT ON YOUR SEAT BELTS.

2. Placement of the airbags: The driver airbag is housed in the center of the steering wheel while the passenger airbag is placed on the dashboard area of the front passenger. The side airbags are placed in the outer edges of the seats while the curtain airbags are stored in the ceiling area, right above the windows - All marked ‘SRS AIRBAG’.

3. Never ignore the SRS indicator status on your instrument console. Get your SRS system checked at the ASC/competent garage if it comes on or flashes while driving or if it does not come on at all after you turn the ignition on. This may prevent the airbags from deploying when you need them the most.

The SRS Indicator:

4. Keep a good distance between yourself and the dashboard to avoid airbag sustained injuries. Though airbags save lives, but at times the violent inflation may also cause some injuries to people who are not properly restrained; which may even be fatal. So, the best practice is to position your seats as far as possible from the dashboard/steering wheel. A distance of at least 10 inches is recommended between the steering wheel and the chest of the driver but the more this distance, the better.

5. As a driver, position your seating so as that the center of the steering wheel points your chest, not your face or head. This can be done by either tilt adjusting your steering wheel or using the height adjustment of your seats. Also, make sure that you can see all the gauges and warning lights clearly in the console while making these adjustments. If your vehicle is equipped with side and curtain airbags, they will offer better protection to your upper torso and head in case of side impacts.

Adjust tilt to point steering towards chest:

Airbags: All you need to know!-point-chest.jpg

6. Always sit upright and in proper position.

7. Never place any lose stuff on the dashboard, particularly something hard or sharp. An inflating airbag can push the object violently towards you and cause serious injury. While, this may seem obvious, but still many do it inadvertently.

8. Always keep your hands away from the airbag covers marked as ‘SRS AIRBAG’. If the airbags deploy at the very instance, it may result in injuries and fractures.

9. Kids & short adults stand a greater risk of sustaining airbag injuries in case of deployment. Hence, it is better for the safety of kids to secure them with the seat belts in the rear seats. Very young kids and infants should be always secured in a child seat at the rear.

10. Some cars have dual (or multi)-stage airbags, which means they inflate in stages depending on the severity of crash. In a severe impact/crash, all stages are inflated simultaneously to provide the greatest protection immediately. In case of a less severe impact, the system can inflate the airbags in stages. This means that after the first ignition for inflation, the system will delay the next stage ignition for a split second to prevent airbag sustained injuries to the occupants.

11. In cars with dual-threshold airbags, the airbags can deploy even if the occupants are not wearing the seat belts. In fact, in such conditions, the airbags can deploy at less severe impact because the occupants would then need extra protection as they are not supported by the seatbelts. The dual threshold airbags would deploy at a higher severity impact if all the occupants are wearing the seat belts as they only need to supplement the protection. So, the point again is – always wear your seatbelts. This not only saves life, but also saves you the airbag reinstatement costs in less severe impacts. Since the dashboard, sensors and of course, the airbag modules need to be changed after airbag deployment, often the bills run high. The good news is that your insurer covers the cost of these replacements.

12. In the unfortunate case of a crash & subsequent airbags deployment, occupants may notice ‘smoke’ or dust kind of stuff in the car. Though not harmful, but it is advised that people with respiratory problems are taken out from this environment as soon as possible. Please note that any associated discomfort is only temporary.

13. After deployment, front airbags deflate immediately so that they do not hamper visibility of the driver and hence the ability to steer the vehicle. The total time for deployment and deflation may be even less than 1/10th of a second. Since the time is so insignificant, most times occupants may not even know that the airbags deployed until they see them lying deflated in their laps.

After Deployment:

Airbags: All you need to know!-deflate.jpg

14. Keep in mind that airbags offer no protection in case of rear impacts. Hence, do not remove the head restraints from your seats of the car. They protect you by supporting your head and neck from whiplash injuries.

15. It is possible for just one airbag to deploy. Strange it may seem, but in cars with more than one airbag, it is possible that in a less severe crash which is on the threshold of airbags getting triggered, only one airbag might deploy.

16. Also, in case of less severe crashes, it is possible that only the seatbelt pretensioners can deploy while the airbags do not. These are cases when the system detects that additional restraint is needed, but airbags aren’t.

17. Maintenance of the SRS: The good news is that the airbags, unlike most systems in your car, are maintenance free for life given that the SRS indicator does not indicate a malfunction; and of course, if the airbags are not already deployed.

No car or system can guarantee the survival & safety of the occupants in case of crashes. But what is in our hands is to use the available systems to maximize the chances of survival in case of the unfortunate event. Always keep in mind that prevention is better than cure. Never drive faster than what is safe for the given condition. Practice safe driving rules & maintain your car properly (esp. tires and suspension components) and you cut the chances of a crash by huge margin. No feature, equipment or safety device beats this.

Drive safe folks!

GTO · 27th February 2015, 11:49

Thread moved from the Assembly Line to Tech Stuff. Thanks for sharing!

SS-Traveller · 27th February 2015, 12:55

Thanks for a fairly detailed writeup about airbags, saket77.

One phenomenon being repeatedly discussed on this forum is the non-deployment of airbags in even severe crashes. It would be nice if you could put in some details about the different mechanisms through which airbags are made to deploy, and conditions in which they may not deploy despite high-speed crashes where the vehicle is otherwise severely damaged and occupants injured, sometimes even fatally.

ghodlur · 27th February 2015, 13:34

Good thread Saket.

A few questions from my side for experts and like:
1) What is the material used for making the air bags?
2) What are the pressures with which the air bags inflate?
3) Is there some kind of voting logic used for crash sensors to activate the air bags? I mean if there are lets say 4 crash sensors, at least two must be impacted for the air bags to operate.
4) Is the logic for driver side and passenger side air bags inflation same or deferred/delayed?
5) How do curtain air bags inflate? I mean where are the sensors generally located?

saket77 · 27th February 2015, 13:50

Thank you sir for your kind words and appreciation!

And yes, there are several reports and some even on our forum of airbags not deploying in case of crashes. As far as my understanding goes, sometimes the SRS do not deploy because the crash & the conditions did not 'fulfil' the logic rules of the algorithms designed for deployment and at times the airbags may not deploy when genuinely they are not needed. At times, it can be a case of plain and simple failure of SRS.

Also, the SRS depends on the feed from the sensors to sense a crash. The sensors are placed at strategic locations in the car, mostly near the front bumpers so that they are most likely to be hit in case of a crash and hence send a signal to the control unit to trigger the deployment. But in a real world scenario, accidents like under-running a higher vehicle like a truck (without under-run protection) will not impact the front bumpers (and hence the sensor), but the crash may still be fatal. In such cases, the chances of airbags deployment can be low.

In short, the complex algorithms for SRS activation is something which each manufacturer tunes differently according to their research. For eg. in some cars, airbags won't deploy in a crash unless the occupants were properly belted up where as some manufacturers opine that in such cases, the occupants would need extra protection, hence airbags not only deploy, but also deploy at a lower threshold of severity.

Also, many cars use co-passenger seat sensor so as to sense if there is a passenger present in the navigator's side. If the car senses that there is no co-passenger in the front seat, it automatically turns off the passenger airbag. So, in case of failure of this sensor, the passenger airbag may not deploy. And in a case where the co-passenger is a kid or weighs less than the threshold weight of the sensor to sense positive, the airbags may not deploy despite a passenger being present. For eg. Honda has tuned some of its cars internationally to sense a passenger only when he/she weighs more than 29 kgs.

In my opinion, the system is still developing and will keep on improving in accuracy as manufacturers include and design more complex algorithms to mimic the varied real world scenarios. But still at this point of time they are a huge success and are bringing down mortality rates. The chances of airbags not deploying is small even in today's world.

Thanks!

Quote:

Originally Posted by ghodlur

Good thread Saket.

A few questions from my side for experts and like:
1) What is the material used for making the air bags?
2) What are the pressures with which the air bags inflate?
3) Is there some kind of voting logic used for crash sensors to activate the air bags? I mean if there are lets say 4 crash sensors, at least two must be impacted for the air bags to operate.
4) Is the logic for driver side and passenger side air bags inflation same or deferred/delayed?
5) How do curtain air bags inflate? I mean where are the sensors generally located?

Thanks Girish!

Airbags are normally made of stretchable fabric - mostly nylon or polyamide. More specifically it is nylon 6-6. They tend to absorb impact energies better and characteristics like high mechanical strength, rigidity, and ability to withstand heat make then the material of choice for fabricating airbags. Also the high shelf life helps the purpose as they are intended not to deteriorate in quality during the entire life of the car (for at least 15-17 years) as they are stored in the steering wheel/dashboards/ceiling/seat backs for all this time.

There are tiny holes working as vents in them so that the airbags can deflate in time after deployment.

Coming to sensors, cars not only use impact sensors for the SRS, but also sensors like accelerators, gyroscopes etc. which can detect not only crashes but also rollovers which enable curtain airbags to deploy. Also there are door pressure sensors to detect side impacts.

Logic for both front airbags are mostly same, except if the car is equipped with a co-passenger sensor as I stated in the previous post. Many cars switch off the passenger airbag if it senses that there is no co-passenger present in the car. This saves reinstatement costs. Also, the intensity of deployment is regulated by how far or close the passenger seat is to the dashboard by sensing the sliding mechanism.

I am sure people with more knowledge will chip in with some more useful information.

Thanks!

rr_zen · 27th February 2015, 15:00

@saket77: Thanks for the detalied write-up. While we have read and heard about airbags being/not being deployed etc., I have always wondered how effective will an airbag be upon replacement? Besides, the cost of replacing an airbag is an expensive affair. Of course, most of the times a car with such damage is declared a total loss from what I have seen. Would be good to hear from anyone who has been in this situation.

Ashir · 27th February 2015, 15:06

Very informative! Thanks for sharing.

Quote:

Originally Posted by saket77

...
So, the point again is always wear your seatbelts. This not only saves life, but also saves you the airbag reinstatement costs in less severe impacts. Since the dashboard, sensors and of course, the airbag modules need to be changed after airbag deployment, often the bills run high. The good news is that your insurer covers the cost of these replacements.

Had a few doubt's regarding replacement of deployed airbags.

1. Is it normal that airbags deploy even when minor collisions at stop/go traffic or at speeds of 40-50kmph ? (Rear ending someone)

2. Airbags are fully covered in insurance? If not what is the usual replacement costs?

3. The insurance company does complete analysis of the crash. If it found airbags didn't deploy as PRS (seat belts, etc) were not engaged, does this effect the insurance coverage?

4. Who could be liable if airbags fail to deploy due to unknown reasons? Or also if airbags deploy without any reason? Is the company accountable?

5. In situation mentioned in point 4, what should be the duty of the driver/passenger to keep in mind, so that there is no loss of proof of malfunction. For example, leaving the car as it is (without causing obstruction to the traffic off course) or calling up expert, maybe dealer, for analyzing the situation?

Thanks!
Ash

nareshov · 27th February 2015, 15:23

Nice article!

Questions:
- how heavy are the airbag inflators?
- does each airbag require its own inflator?

I'm curious whether the weight is significant enough to show a difference (for mileage from a manufacturer's point of view, etc.) between a 6-airbag hatchback vs. a 2-airbag hatchback.

saket77 · 27th February 2015, 15:28

Thanks Ashir.

Quote: