Arrive Alive

Airbags and Vehicle Occupant Safety

Wearing seatbelts is the Law for all vehicle occupants! Buckling up is simply the best way to protect both drivers and passengers. This is a message we will continue to emphasise in every road safety campaign across all the possible mediums available.

Safety inside the vehicle is also increased through the latest in safety technology such as various airbags developed by vehicle manufacturers. It is important that we understand airbags, how they work, what their limitations are and how they assist in protecting vehicle occupants.

We raised several questions with road crash investigator Stan Bezuidenhout to gain a better understanding of these safety mechanisms.

Does the South African motorist know enough about airbags and would you agree that there is often a false sense of security when the vehicle has airbags?

What are the most important things drivers and passengers should know about airbags then?

To answer this on behalf of everyone would be irresponsible but, in general, people know only three things about airbags: They know that their car has them, they know they’ll deploy in a collision and they know they come out with a bang… But there is a lot more to know than just that.

Most general road users never consider the presence of an airbag until it affects them (by deploying or not deploying or when they are considering the purchase of that shiny new car).

We get regular contacts from clients wanting us to examine their vehicles with an interest in product failure “because they were involved in an accident and the airbags did not come out.” In all the years we have worked on airbag non-deployment cases, we have had so many of the same results that we can almost predict it, based on the (type of) manufacturer involved.

In one case (as in many others), we were still busy with our investigation when the settlement was reached and the record sealed. No one would ever know that airbags from those particular brand might be a concern. The risk is simply too great and manufacturers in the very sensitive South African market simply cannot afford the impact of negative publicity around something as vital as an airbag.

In other cases, we had the manufacturer actually telling the client that airbags are designed to save lives. Since the client survived and did not die, the airbag is essentially irrelevant and therefore they will not entertain any airbag non-deployment discussions or efforts to claim product failure. In that case, we pretty much had proof that the airbag should have deployed (there were six airbags fitted) yet the manufacturer dared the client to go to court. Regrettably, the client did not have big enough pockets to take on the case and attorneys in the matter were loathed to get involved. That case remains un-investigated to this day.

What are the most important facts drivers and passengers should know about airbags?

One of the most important messages I can share, regarding airbags, is that they are not a guaranteed life-saver. While they work with almost 100% success in relatively lower speed collisions, there are no guarantees by the time you are exceeding the 80 Km/h mark. Airbags are designed to reduce the risk of serious injury or death but do not come with a results guarantee. People need to understand that fatalities can come from a wide array of possible causes, including penetration (puncture) wounds, pre-existing heart conditions, shock, internal bleeding and even unattended bleeding from relatively smaller wounds.

I would also wish to remind people that - in some vehicles - the airbags will deploy, even if they are not wearing a seatbelt (think of an unrestrained child). In these cases, the collision could result in the occupant projecting forward (in a frontal collision) at up to 100 Km/h while the front layer of the airbag, during deployment, can travel at several hundred kilometres per hour in the opposite direction. If a relatively soft body encounters an airbag and decelerated relatively aggressively, serious injury or even death might occur.

I would also give parents very serious warnings regarding children standing on seats or up against the dashboard at the front seat, while the vehicle is driven. If a child falls forwards during the braking cycle and the airbag deploys when the child is already striking the dashboard or standing up against it, the “explosion” is essentially happening with direct contact to the child. This alone can lead to serious injury or death.

People also need to realise that - in some vehicles, those fitted with shackle sensors that sense if an occupant is wearing a seatbelt, or not - the airbags might not deploy at all, even where a frontal collision occurs. This can result in the airbags being perceived as faulty or the vehicle restraint systems being considered defective. But this would be because the systems rely on a number of conditions for deployment. Seatbelt engagement might be one of those conditions.

Other vehicles have occupant sensors. They are essentially tactile or pressure switches built into the seat. If an occupant is present, the switch is activated. If the switch is activated and the seatbelt is engaged, the airbag at that position could be deployed. If not - it simply will not. For this reason, children standing in seats might be particularly exposed if enough criteria are met for deployment.

Airbags are described as a “Secondary restraint” - Why is this? Can you provide a description of how the airbags deploy during a road crash?

Airbags are described as a “Secondary restraint”

Airbags are considered secondary because they have no function until after a particular (collision) event is achieved. Until such time, they are passive and will play no role in collision avoidance or mitigation.

For an airbag to deploy, a combination of the following conditions might need to be met. These are not all the case for all vehicles and might vary in some models, but the basic operation will be some combination of some or all of these conditions:

a) Axis of sensory activation

Axis of sensory activation

People do not know this but there are typically three axes of possible influence. These are obviously the linear axis (along with the length of the car), the lateral axis (from side to side) and the vertical axis (up and down). Often, a collision will LOOK like a frontal collision (bumper damaged, for instance) but if you could measure the FORCES, you would see that the collision was actually a “sideways” collision with the front bumper just ripped off.

Before the Airbag Controller Unit would consider deployment, certain thresholds need to be reached along one of these axes. The axes of the applied force will determine which airbags are deployed: Linear for front or knee airbags, lateral for curtain and hip airbags. Often, vertical forces will not result in airbag deployment since there are none above or below the occupants.

b) Impact Severity

Impact Severity

Airbags do not deploy simply when a force is applied and impact sensors do not really measure (or activate under) “force” as much as they trigger events in response to a change in velocity (called Delta V). So, if you apply foot brakes really hard, the airbags will not deploy. But if you hit something and your car slows down by a big enough amount over a short enough period of time, the sensors would be activated.

As an example, you can go from 200 Km/h to a stand-still in 5 seconds (very harsh braking) but the airbags would not deploy but if you went from 40 Km/h to zero in half a second they would.

So the impact severity is a function of the rate of change in speed and not of the speed itself. In spite of this, many vehicle airbag systems would completely disregard all collisions that occur below a minimum speed value - often about 25 Km/h. This allows for bumper bashing and minor bumps - like parking your car in the garage and hitting your wall accidentally - to occur without the deployment of airbags. They also typically present no risk to occupants at these very low speeds.

c) Vehicle Movement

Vehicle Movement

Not all types of collisions result in airbag deployment. People often contact us and try to get us to investigate a non-deployment event with an interest in claiming from manufacturers but our first interest is always the bullet vehicle movement. We need to know the direction in which forces were applied.

As an example, a collision from the rear (another vehicle striking your vehicle from behind) will not result in the deployment of your airbags. This selective deployment is designed to ensure that deployment is not a “wasted” event and - because airbags are pyrotechnic devices and because they do deploy rather aggressively, this also helps to prevent even minor injuries.

d) Occupant Presence

Where a vehicle is fitted with an occupant sensor (a pressure switch in the seat, essentially), the Airbag Controller Unit will be programmed to consider the presence of an occupant a condition for airbag deployment. This means that the airbag at that position will not be deployed if there is no one sitting in that seat.

What becomes dangerous, however, is when smaller children (not heavy enough to activate the sensor) sit in the front seat or where they stand on the seat (not applying pressure in the correct location).

It is therefore also very dangerous to have luggage or cargo on the front seat of your vehicle since this can be misread as an occupant being present and cause deployment. If anything is too close to the airbag position, the bag might propel that item inside the occupant cell, like a launched projectile.

e) Seatbelt Engagement

In most modern vehicles, there is also a Seatbelt Shackle Sensor installed. This is a sensor (like a switch) that detects the presence of the seatbelt shackle inside the buckle. Thus - the vehicle will “know” whether you are wearing a seatbelt or not.

This is typically the case in vehicles that bing or born when the driver is not wearing a seatbelt. Some drivers who refuse to wear seatbelts have become very innovative and would engage the seatbelt being them. This is obviously extremely dangerous and might cause airbag deployment that would strike the person seated in that position since the system is designed on the assumption that a person would wear their seatbelt.

The Airbag Controller Unit would then next be programmed not to deploy the airbag if an occupant is not wearing a seatbelt, under certain conditions. But, when the collision is severe enough, the airbag might be deployed in any event.

f) Seatbelt Pretensioners

Seatbelt Pretensioners

Some vehicles are designed to include a so-called Seat Belt Pretensioner or Tensioner. This is (often) a pyrotechnic device that will pull the seatbelt tighter at the critical moment during the crash.

This system would ensure that the seatbelt is at optimum tension across the chest of the driver and that the probability of injury is reduced even further. By pre-tensioning the seatbelt by the correct amount, the occupant is essentially “strapped to” the vehicle and would decelerate at a rate as close to vehicle deformation (crumple zone) as possible. The slower an occupant is decelerated, the better the chances for survival.

g) Product Failure

Product Failure

Often, people think that airbags not deploying is an immediate indication of product failure. They think there must be a fault with their vehicle. This is not the case in all instances where airbags do not deploy.

Before you consider the lack of deployment of your airbag an indication of some product fault or failure, consider all the issues above and remember that your airbag will not necessarily deploy during all crashes considered “serious” by you.

If, however, we are appointed in a matter of this kind, we are always interested to know what the vehicle- and model-specific deployment parameters are. We want to know under what exact conditions the airbags are supposed to deploy before we can decide whether the airbags in a particular vehicle in evolved in a particular collision would or should have deployed.

This - the deployment parameters - can vary substantially from vehicle to vehicle and even from model to model.

h) Activity/Error Historical Data

Activity/Error Historical Data

Most modern vehicles are fitted with an Airbag Controller Module that is essentially also a Crash Data Recorder. The devices are often capable of saving several or the last near-deployment and/or deployment events. These devices also constantly monitor and record the performance of the whole vehicle safety system.

This way, if there are any errors, the driver might be alerted via an instrument cluster warning light or message or technicians will see it when they interrogate the vehicle controller unit.

In all cases, this is the best place to start, but there are concerns regarding the possible destruction of evidence if the interrogation is not performed by a qualified person. For this reason, manufacturers often consider any effort by anyone other than their trainer technicians to be tantamount to “tampering” and might declare the evidence gathered in this way as contaminated or moot.

Where possible, it is better to have the manufacturer interrogate vehicle electronic systems.

i) Near-deployment Events

Near-deployment Events

There are often events that are recorded in the Airbag Controller Unit that might approach or come near the deployment thresholds but short of being serious enough to actually cause deployment. These are often recorded as so-called “near-deployment’ events. These might be stored for days, weeks or even months, if the data is not overwritten by another similar event.

j) Head Restraints

Head Restraints

As technologies advance, so do vehicle restraint and injury risk mitigation equipment. Another system that might be deployed in (for example) a rear-end collision are self-actuating head restraints. These deploy during a rear-end collision by “jumping” forward, closer to the seat occupant’s head, to reduce the distance travelled by the occupants head, before it strikes the headrest.

But this also means that - if the occupant seating position is wrong - the system could aggravate or even cause risk of injury. Imagine a driver with a seat in an unnaturally upright position, with the rear of the seat very close to the rear of the driver’s head and the driver very close to the steering wheel, wearing a seatbelt. now - if the airbag deployed, the seatbelt retracted and the headrest deployed, the driver would be struck in the face by the airbag while the head restraint would strike against the back of the driver’s head.

For this reason and in reference to all the deployment considerations outlined above, the occupant seating positions and the proper use of safety equipment are essential components in injury risk mitigation.

What are the types of airbags found in modern vehicle - are there major differences between the various airbags or is there significant standardisation in the industry?

What are the types of airbags found in modern vehicle?

There are largely standard airbag designs by a goal. Most manufacturers offer the most basic types of airbags - front occupant airbags. These are typically fitted in the steering wheel, in front of the driver and in the dashboard in front of the front seat passenger. The goal of this airbag is to prevent injury from contact with in-vehicle surfaces in a frontal collision. When the front occupants make contact with interior surfaces, in a frontal collision, their heads are typically exposed to injury. Since the head is the most vulnerable part of the body, these frontal airbags are designed to reduce these injury risks.

Vehicles might also have what are called knee-impact airbags. These are typically installed at the driver position but can also be installed in the front passenger position. These typically protect the occupants from injuries caused by contact with the lower dashboard area. In many cases, the occupant might be projected forward or the vehicle interior might be forced backwards, encroaching on the occupant position. If the occupant, in a seated position then makes contact with a hard surface with their knees, the forces can be projected rearward and cause pelvic or hip fractures. These airbags are designed to prevent this.

Your vehicle might also have lumbar or hip airbags installed. These would typically deploy out of the sides of the front occupant seats and are designed to reduce the risk of injury to the pelvis and hips, from side impacts. Occupants in side-impact collisions often experience serious injuries to their thigh (femoral fracture) or to their hips or pelvis. Injuries could also extend to include lower back injuries. This kind of airbag is designed to reduce this risk.

Side Curtain Airbags might also be installed. These are like long inflatable curtains that can deploy from above the doors and typically stretch for almost the entire length of the vehicle interior. These typically protect occupants from injuries caused by side-impact collisions at the upper body and/or neck/head area. Occupants often experience serious head injuries as their heads collide with door frames. Because the neck bends as the shoulder impacts first, there is also a very serious risk of neck injury. Therefore, the side curtain airbags are designed to reduce this risk.

Rear Occupant Airbags might also be installed but these are found only in upper market vehicles at present. These are essentially the same as the lunar or hip airbags fitted to front seats.

It is possible to switch off the airbags?

It is possible to switch off the airbags … if this something you would guard/warns against?

Typically, airbags should always be on, seatbelt should always be worn and seats should always be positioned properly.

But - for pregnant ladies, where baby seats are fitted in front seats and/or where small children are involved, the airbags might be turned off - but only under very specific conditions, so I would prefer not to generalise at all.

It has been said that airbags have changed the way many hold the steering wheel from the 10-2 to the 9-3 position - is it really that important to change the positioning of the hands for the possible impact and risk of injury from seatbelt deployment?

It has been said that airbags have changed the way many hold the steering wheel.

No. By the time a collision is serious enough for an airbag to be needed, the relatively minor issue of airbag burns (from the slap) is hardly an issue anymore.

What is more dangerous is the “cool hand luke” method of driving with one hand on the steering wheel in a position where the driver is partially holding the centre mass of the steering wheel - but in most collisions that are evolutionary, people change hand positions or brace and straighten their arms in any event. Airbags do not typically cause injuries that are serious. Sometimes, drivers’ wrists are injured when they brace against the steering wheel and it is mistaken for an airbag injury, but the hand position should not have a significant effect on the injuries suffered, to the hands, during airbag deployment and specifically from airbag deployment.

As someone who has attended many scenes of road crashes - what role does the functioning of airbags play in crashes? What do the airbags tell you?

What role does the functioning of airbags play in crashes?

Airbag deployment tells us an enormous amount about the actions and/or habits of occupants. The valuable conclusions we can draw range from the severity of the collision to the angles of the applied forces. We can also make conclusions about seatbelt use, seat position, occupant size (blood or body fluid deposits) and even the identity of occupants (DNA or blood type analysis).

What do we need to create greater awareness of about airbags in our road safety campaigns and efforts?

What do we need to create greater awareness of about airbags in our road safety campaigns and efforts?

People need to understand exactly what airbags are designed to do and what they are capable of and then their limitations.

People need to read this article carefully.

Stanley S Bezuidenhout
Forensic Road Transport and Risk Expert
Crash Guys International
www.crashguys.info

Also view:

How do Seatbelts Save Lives?

Buckle Up Road Safety Campaign focuses on Seatbelt Safety

Seatbelt Safety

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