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Pascal Hayek
TOP STORIES 
 

AIRBAGS: LIFE SAVERS OR KILLERS?

Airbags are air cushions that are deployed in a fraction of a second after an accident in order to prevent the occupants from striking the interior of the vehicle.

Airbags are passive safety systems, therefore they help minimize the risk of injuries after an impact but they do not prevent an accident from happening. 

Nowadays almost all cars are equipped with at least two airbags, one for the driver and the other for the co-driver.

The driver's airbag is located inside the steering wheel pad, while the co-driver's airbag is installed in the dashboard.

More cars are being equipped with head and thorax airbags. A specially adapted thorax airbag can now be integrated in both the driverís and passengerís seat to provide optimum protection for the upper body in a side impact.

In addition to the thorax airbags, there can be also a separate head airbag in each

door. In the event of a side impact it unfolds from the upper section of the

door trim panel in the shape of a flat cushion. 

More recent innovations include the knee airbag, brought in 2003 by the Mercedes-Benz SLR McLaren, the rear curtain airbag, introduced by the Toyota IQ in 2008 and the rear center airbag, developed by the same Toyota in 2009 to protect rear passengers in case of side collisions.


How it works 

The design is conceptually simple. 

A central Airbag control unit (ACU) (a specific type of ECU) monitors a number of related sensors within the vehicle, including accelerometers, impact sensors, side (door) pressure sensors, wheel speed sensors, gyroscopes, brake pressure sensors, and seat occupancy sensors. When the requisite 'threshold' has been reached or exceeded, the airbag control unit will trigger the ignition of a gas generator propellant to rapidly inflate a nylon fabric bag. 

The job of the different type of sensors is to detect the impact as well as other variables and send a signal to the control unit ECU which is considered the system's brain. As the ECU receives the signal it decides if it is necessary to inflate the airbags. All depends of the strength of the impact and its location and angle.

If the ECU decides to deploy an airbag, it sends a signal to the inflator. An igniter starts a rapid chemical reaction generating primarily nitrogen gas (N2) to fill the airbag making it deploy. 

Each airbag incorporates a pyrotechnic device, known as an initiator or electric match, consisting of an electrical conductor cocooned in combustible material. A current pulse heats up the conductor, which in turn ignites the combustible material. This igniter triggers the chemical reaction that actually fills the nylon fabric airbag with gas. 

                   

 

Advanced systems

 

 Advanced airbag technologies are being developed to tailor airbag deployment to the severity of the crash, the size and posture of the vehicle occupant, belt usage, and how close that person is to the actual airbag. Many of these systems use multi-stage inflators that deploy less forcefully in stages in moderate crashes than in very severe crashes.

 

Occupant sensing devices let the airbag control unit know if someone is occupying a seat adjacent to an airbag, the mass/weight of the person, whether a seat belt or child restraint is being used, and whether the person is forward in the seat and close to the airbag. Based on this information and crash severity information, the airbag is deployed at either a high force level, a less forceful level, or not at all.

 

Adaptive airbag systems may utilize multi-stage airbags to adjust the pressure within the airbag. The greater the pressure within the airbag, the more force the airbag will exert on the occupants as they come in contact with it. These adjustments allow the system to deploy the airbag with a moderate force for most collisions; reserving the maximum force airbag only for the severest of collisions. Additional sensors to determine the location, weight or relative size of the occupants may also be used. Information regarding the occupants and the severity of the crash are used by the airbag control unit, to determine whether airbags should be suppressed or deployed, and if so, at various output levels.

 

A new airbag control system called SeatSentry that automatically identifies whether a front seat passenger is an adult or child and allows or disables the passenger seat airbag accordingly. SeatSentry also detects mass, shape and weight to determine if the "passenger" is a sack of groceries or a person. It is sturdy enough to last the life of the seat. Some cars are equipped with a switch that can enable or disable the passenger airbag.

If we take Porsche for example, in the driver's manual it is clearly mentioned that if a child weighs up to 27 kg is going to be transported in a child restraint system on the passenger's seat, the passenger airbag should be switched off.

After deployment

 

A chemical reaction produces a burst of nitrogen to inflate the bag. Once an airbag deploys, deflation begins immediately as the gas escapes through vent(s) in the fabric (or, as it's sometimes called, the cushion) and cools. Deployment is frequently accompanied by the release of dust-like particles, and gases in the vehicle's interior (called effluent).

 

Most of this dust consists of cornstarch, chalk, or talcum powder, which are used to lubricate the airbag during deployment. Newer designs produce effluent primarily consisting of harmless talcum powder/cornstarch and nitrogen gas. In small amounts this chemical can cause minor irritation to the eyes and/or open wounds; however, with exposure to air, it quickly turns into sodium bicarbonate (baking soda). However, this transformation is not 100% complete, and invariably leaves residual amounts of hydroxide ion from NaOH. Depending on the type of airbag system, potassium chloride (often used as a table salt substitute) may also be present.

 

For most people, the only effect the dust may produce is some minor irritation of the throat and eyes. Generally, minor irritations only occur when the occupant remains in the vehicle for many minutes with the windows closed and no ventilation. However, some people with asthma may develop a potentially lethal asthmatic attack from inhaling the dust.

 

 

When is the airbag fatal?

 

Even though air bags are designed to save lives, they can be harmful or fatal to some people.

Airbags can injure or kill vehicle occupants. Injuries such as abrasion of the skin, hearing damage from the extremely loud 165-175 Db deployment explosion, head injuries, eye damage, and broken nose, fingers, hands or arms can occur as the airbag deploys.

 

Most vehicle airbags are inflated using hot gas generated by a chemical process. Using hot gas allows the required pressure to be obtained with a smaller mass of gas than would be the case using lower temperatures. However, the hot gas can pose a risk of thermal burns if it comes in contact with the skin during deployment and occupant interaction. Burns are most common to the arms, face and chest. These burns are often deep dermal or second-degree burns that take longer to heal and risk scarring.

 

Serious injuries are less common, but severe or fatal injuries can occur to vehicle occupants very near an airbag or in direct contact when it deploys. Such injuries may be sustained by unconscious drivers slumped over the steering wheel, unrestrained or improperly restrained occupants who slide forward in the seat during pre-crash braking, and properly belted drivers sitting very close to the steering wheel.

 

From 1990 to 2008, the U.S. National Highway Traffic Safety Administration identified 175 fatalities caused by air bags. Most of these (104) have been children, while the rest are adults. About 3.3 million air bag deployments have occurred and the agency estimates more than 6,377 lives saved and countless injuries prevented.[35]

 

A rear-facing infant restraint put in the front seat of a vehicle places an infant's head close to the airbag, which can cause severe head injuries, or death if the airbag deploys.

 

 

 

History of the airbag

 

The first steps towards today's airbag were taken by John W. Hetrick, a retired industrial engineering technician, in the early '50s. Following a car accident involving Mr. Hetrick and his wife and daughter, he thought of a device that would prevent passengers from hitting the inside of a car.

He received a patent in 1953 for something called "safety cushion assembly for automotive vehicles." At about the same time, German inventor Walter Linderer received a patent for a similar prototype. Mr. Linderer's product was using a compressed air system, which could be either released by bumper contact or by the driver.


 

Following the two patents, Ford and General Motors started tinkering with inflatable restraints, but they were faced with two big problems. One of them was related to the detection of a collision and the inflation of the airbag, which took too long to work properly. The second issue was that the airbags themselves would cause secondary injuries to passengers.

 

It wasn't until the late 1960's that the airbag development made some real progress. The man responsible for this? A New Jersey mechanical engineer by the name of Allen K. Breed. He invented what is considered the world's first electromechanical automotive airbag system in the form of a crash sensor.

Mr. Breed would later on come up with another important development in the field, namely the airbag that vents air as it inflates, reducing the risk of secondary injuries by reducing the inflated bag's rigidity.

 

                                                      Porsche 911 equipped with airbags.  

Conclusion 

We cannot conclude without mentioning that seat belts are as important as airbags.

Nowadays most cars are equipped with seat belt pretensioners. 

Pre-tensioners preemptively tighten the belt to prevent the occupant from jerking forward in a crash. In the event of a crash, a pre-tensioner will tighten the belt almost instantaneously. This reduces the motion of the occupant in a violent crash. Like airbags, pre-tensioners are triggered by sensors in the car's body, and most pre-tensioners use explosively expanding gas to drive a piston that retracts the belt.  

The driver as well as all the passengers should be wearing the seat belts even if the car is equipped with all sorts of airbags. A combination of airbag-seat belt will minimize the risk of injuries and fatalities during an accident. 

Pascal Johnny Hayek B. Eng. AUB, 1983 Service Manager Porsche Service Centre, Kuwait

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