Airbags are perhaps the most popular car safety system. Yet, airbags are not well understood. The most common question regarding airbags is “Why did my car’s airbag not deploy?”
This question will be more frequent once every car has six airbags. I would like to clarify some points and burst some myths regarding airbag deployment in this article.
Jump to:
- What is an airbag
- Different airbag types and configurations
- Airbag deployment myths
- Why airbags should not deploy in every crash
- Why did your car’s airbag not deploy?
What is an Airbag
An airbag is a passive safety system that provides restraint and cushioning to a car’s occupant in a crash. The primary purpose of an airbag is to create a protective layer between the occupant and the car’s harder interior components such as the steering, instrument panel, pillars, windows, etc.
Here is how an airbag protects you:
- The air “bag” and inflation system are concealed inside a component such as the steering wheel, instrument panel, seats, etc.
- An Airbag Control Unit (ACU) controls the system. The ACU is nothing but a computer with the primary role of detecting the crash severity. The ACU monitors different crash parameters such as impact speed, angle of impact, collision type, etc.
- Once the ACU detects a severe enough collision, a signal is sent to the bag inflation system that contains the combustible material.
- The combustible material is burnt and it releases gas.
- This gas fills up inside a nylon bag causing the bag to inflate and “pop out” of its concealment.
- The inflated bag provides cushioning to the occupant for a brief moment before deflating instantly.
The whole process of an airbag deployment only takes about a tenth of a second!
Different types of airbags
Although all airbags have the same mechanism, their functionality is different depending on where they are located.
- Front-occupant Airbags: These airbags are located in the instrument panel and steering wheel. They are also separately called “Driver” and “Front passenger” airbags. Front airbags cushion impact forces directed from the front.
- Side-torso Airbags: These airbags are located at the outer edge of the seats, close to the doors. The primary purpose of these airbags is to protect the occupant’s chest and abdomen from side impacts.
- Side-curtain Airbags: The side-torso airbags only protect the torso from side impacts. The side-curtain airbag protects the head from side impacts. These airbags are located in the side roof rail and deploy downwards like a curtain in a theatre (hence the name).
- Knee Airbags: The standard frontal airbags primarily protect the head, face, thorax, and abdomen of the occupants. Knee airbags protect the legs. These airbags are located under the instrument panel.
- Rollover Airbags: Side-curtain airbags are useful in a single side impact. However, they are not useful for longer impacts such as rollovers. Rollover airbags are designed to stay deployed for a longer duration.
- Pedestrian Airbags: These airbags are designed to protect the pedestrians that hit the car’s bonnet. These airbags are located at the base of the windshield on the vehicle’s exterior.
Airbag configurations
If you come across a car’s specification, you may have seen options of 2, 6, or 8 airbags. Here is what each option means:
- A 2-airbag system only has frontal airbags for the driver and front passenger.
- A 6-airbag system has 2 frontal airbags plus 2 side-torso and 2 side-curtain airbags. The side-torso airbags are for the front occupants whereas the curtain airbags are for both the front and rear occupants. The recent government notification proposes this system.
- A car with 7 or 8 airbags has the knee airbags included in addition to the 6-airbag system.
Now that we have understood what an airbag is and how it works, let us move on to understand some myths that have been unfortunately created around them.
Airbag Deployment Myths
Although the airbag system is easy to understand, a lot of misinformation has led to the creation of some myths. It is time to bust these myths.
Myth 1: I don’t need to wear a seat belt if my car has airbags.
Many people get hurt because of this misconception. If you check the airbag badge, you will notice that the badge says “SRS Airbags”. The SRS stands for “Supplementary Restraint System”. The SRS indicates that the airbags are designed to supplement or help the primary restraint system, the seat belt.
The airbag is not a pillow. It is a controlled explosion and hits like a wall. The airbag will hurt you if you do not wear a seat belt. An airbag alone will not save you from getting injured. Always wear a seat belt to get the benefits of an airbag.
A special note for those who use some trick or “jugaad” to fool the seat belt sensor: In the unfortunate event of a crash, the ACU will assume that you are wearing a belt and deploy the airbag at full force. You may fool the sensor, but not the laws of physics.
Myth 2: Airbags will only deploy if I am wearing a seat belt.
Airbags are designed to deploy if the car’s ACU decides that a crash impact is severe. The ACU decides which airbag to deploy depending on the impact force’s direction and severity. It doesn’t matter if you are belted or not. The only exception to this is the ACU in luxury cars. Luxury cars have occupancy sensors and deploy airbags based on seat occupancy.
Myth 3: Airbags will deploy in all crashes
This is more of an expectation than a myth. In recent years, airbags have gained a lot of popularity. This has led to a general belief that having airbags will guarantee safety. Car owners expect the airbag to deploy in every crash. However, this is simply not true. Airbags only deploy in specific crashes.
Not every crash requires Airbag deployment
Airbags are controlled explosions. An unwanted airbag deployment can injure the occupant. For example, in a low-severity frontal crash, where even the seatbelts may be sufficient to provide safety, the deployment of the frontal airbags could cause a face injury to the occupants. Here are some sample scenarios where airbag deployment can cause injuries:
- When you are not wearing a seat belt.
- When you are not seated in an ideal position at the time of the accident. E.g. you are leaning forward, have your hand on the instrument panel, or have reclined the seat for sleeping, etc.
- When you have an object between you and the airbag.
- Children should not be seated in the front seats. The risk is even higher if the child is in the lap. Children should always use a child car seat. Also, the child car seat should be kept in the rear, away from the airbag.
Why did my car’s airbags not deploy?
No car owner complains when the airbags deploy. Usually, most car owners are happy to see that their airbags are working. It is the opposite situation of airbag non-deployment that confuses most car owners.
Two factors play a huge role in airbag deployment. But, to understand these factors, let us look at some basic physics.
If you recall your Physics class in school, you might remember your teacher mentioning that “Force is a vector quantity”. Any force has two components: the force’s severity and the direction in which it is acting.
In simple words, an impact force’s severity in a crash is calculated through:
- The deceleration or “jerk” caused by the force.
- The direction in which the vehicle experiences the deceleration.
The deceleration caused by the impact force
Airbags are programmed to deploy only when the vehicle experiences a sufficient deceleration or “jerk”. In technical terms, this is known as the “Delta-V” or change in velocity caused by the impact. An airbag manufacturer sets a threshold value for the deceleration. This value is captured by the car’s ACU.
Airbags get deployed only if the deceleration exceeds this threshold value. If not, there will not be any airbag deployment.
The direction of the impact force
Each airbag type only protects against impact forces in a certain direction. For example, a side-thorax airbag will only protect you against side forces. Not protect against a frontal force.
That is why the airbag control unit also measures the direction of the impact force along with the impact force severity. Both conditions need to match for the airbag to deploy. An airbag will not deploy if the impact force exceeds the threshold deceleration but does not act in the desired direction.
Airbag deployment is even more uncertain for angular impact forces.
Another important point to note is that the angle of force should be close to the vehicle’s horizontal plane. Airbag sensors do not register non-horizontal forces. Airbags may not deploy if something falls on the vehicle’s top or if the vehicle rolls over an object.
Scenarios where airbags may not deploy
The algorithms behind airbag deployment are highly complex. However, based on my investigation experience I have listed down some crash scenarios where the airbag may not deploy.
- The lighter the collided object, the lower the chance of an airbag deployment. For e.g airbag deployment in impacts with pedestrians is less likely than an impact with a tree or a pole.
- Airbags rarely deploy in pure rollover crashes. This is because a rollover does not create the required deceleration. However, considering the unpredictability of rollover accidents, airbag deployment is observed in some rare cases. But, a frontal or side airbag will not help much in a rollover. Wearing a seat belt is the best way to protect yourself from injuries in a rollover.
- Airbag deployment is not guaranteed in crashes with multiple small objects. In such crashes, the ACU measures the severity and direction of each collision. The airbag will only be deployed if one of the collisions is severe enough to cross the threshold value. So, you may have a crash where your car impacts multiple breakaway poles but the airbags did not deploy.
- An airbag may or may not deploy in underride crashes i.e. crashes in which a car goes under a truck. Airbag deployment depends on the structure of the truck, the presence of underride protection bars, the speed of the car, etc.
- Airbags will not deploy if the car is hit from behind.
- Airbag deployment is not guaranteed in impact with animals or if an object falls on the vehicle.
Airbags are not a magic balloon
Airbags have proven beneficial in reducing road crash injuries and fatalities.
The Ministry of Road Transport and Highways has mandated the installation of six airbags in all passenger cars by Oct 2023. (The rule has now been rescinded with the advent of BharatNCAP).
The announcement has received a mixed response. Some have welcomed the notification, stating that having six airbags will provide an extra layer to car occupants. On the other hand, some contest that the mandatory installation of six airbags will not only increase the price of cars, but six airbags will not provide much benefit if the car’s body is still weak.
However, having an airbag in your car does not guarantee safety in all crashes. Airbags are a supplementary safety system and require the usage of seat belts to provide maximum benefits. That is why I consider seat belts the most important safety feature in a car.
You may feel angry if your car’s airbag does not deploy. However, we should remember, that airbags have limitations just like all systems. It may happen that your car’s airbag did not deploy because the impact force was not severe enough or the impact force direction did not warrant airbag deployment.
You can contact the car’s manufacturer if you still feel that your car’s airbag should have been deployed considering the crash circumstances. An alternate option is to contact a professional crash investigator.
If you have any more questions related to airbags, you can ask them in the comments.
Last Updated on September 26, 2023 by RSG