Side airbags and advanced restraint systems don't have to be a complete mystery. We'll walk you through the evolution of these systems and prepare you for future repairs.
Being part of the collision repair industry caused me to marvel when Sylvester Stallone (John Spartan) wrecked a futuristic police vehicle in the 1993 movie, "Demolition Man." Upon impact the vehicle completely filled with a fast reacting Styrofoam-like "Insta-foam" material that encased the occupants for protection. Wow! Wouldn't that be cool compared to the airbags we only had at the time!Today, we may not be getting closer to Insta-foam, but we have certainly improved occupant safety many times over since 1993. Today we have dual-stage airbags for both driver and front seat passengers that can sense the severity of the crash and location of the occupants to make better deployment decisions automatically at the time of the crash. We have knee and even foot airbags to lessen the impact force to these body parts. We also have begun to address other crash types, such as side impacts, whiplash and rollovers. Let's focus on side airbags, their evolution and how they will impact future repairs.
What's all the fuss?
When safety systems began, their primary aim was to reduce frontal impact injuries. Seat belts are not effective by themselves in reducing life-threatening head and chest injuries caused by crashes that exceeded 30-35 mph. Hence the introduction of driver and passenger front airbag systems.Frontal impacts account for a majority of collision related damages, but accounted for just 39 percent of the crash fatalities in 2002. Rollover and side-impact crashes combined for 56 percent of the 2002 fatalities. Now that frontal airbags have reduced life-threatening injuries, it is time to concentrate on side-impact fatalities (23 percent) and rollover fatalities (33 percent).
In addition the vehicle mismatch is increasing each year. Collisions of passenger vehicles with light truck vehicles (LTV) has increased from 26 percent in 1991 to 36 percent in 1999, while passenger-car-to-passenger-car crashes decreased from 29 percent to 21 percent in the same time frame.Since safety now sells, the rating system for vehicles has become more important, not only for frontal impacts but also for side impacts.
It is 3.5 times more likely to become a fatal accident for the occupants of a standard unibody vehicle when hit by an LTV than another unibody passenger vehicle.
Side Airbag Types
There are four basic categories for side airbag systems. They are:
- Torso-only
- Inflatable Tubes
- Torso and head combination
- Side curtain
Torso-only
Torso-only systems are mounted normally in the seat or door panel. They provide a cushion to the torso (thorax) and/or chest in the event of a side impact. In 1994, Volvo introduced the first side airbag in its 850 model. This unit was mounted into the seat and provided basic torso protection and minimal head protection. Mercedes and BMW followed in 1996; Ford, General Motors and Audi in 1997. Torso-only airbags are estimated to reduce the serious chest injuries in side-impact collisions by approximately 25 percent.
Since the distance from impact to the occupant is much shorter than a frontal collision, the timing is very critical for proper operation. Special side-impact sensors are used and the inflation time of the airbags is much quicker. Seat mounted bags inflate within 0.0012th of a second, which is four times as fast as a frontal airbag. The bag is inflated at a specific crash severity, usually corresponding to a speed of the impacting vehicle of approximately 25-30 mph.Inflatable Tubes
Inflatable Tubes are mounted in the A-pillar and roof rail areas to protect specific head areas.
In 1997, BMW offered the tubular head protection system designed by Autoliv, an international provider of safety systems. In this period it was realized that adding head with torso protection was one of the next steps for occupant safety.
Inflatable tubes consist of a special nylon tube, installed in the head-liner above the frontal doors, that inflates to a diameter of about 5 inches. This system was a precursor to side curtains and other head protection systems.Torso and head combination
Torso and head combination systems are mounted normally in the seat or door panel and have the ability to protect the head from injury. Head and torso systems were introduced in 1998 for Ford and Renault. These systems initially were seat units that inflated to a size that would protect the occupants' heads in side impacts.
Today there are several variations of this seat type system. One includes a multiple airbag unit that deploys both a head and torso protective bag along with a pelvis bag to protect the lower torso. All of these advancements were a major step for safety since NHTSA determined that six out 10 side-impact fatalities was a result of brain injury. Protecting the head rather than just the torso is critical for safety.Still these torso and head systems do not protect passengers during rollover crashes or rear seat passenger side impacts.
Side Curtain
Side Curtain airbag systems are normally mounted along the roof railing and are designed to protect front and rear occupants from head injury in side-, frontal-and even rollover-crash events. These units include a long tube and inflator unit with a packed narrow airbag. These units typically use a compressed gas container to supply the required air pressure and volume. These units are designed to not only inflate based on several crash criteria, but to even stay inflated longer than frontal airbags to allow for rollovers and secondary impacts. Toyota, Mercedes and Volvo introduced them into production in 1998.There have been several challenges with the design of these systems and the ability to maintain inflation and coverage for occupant impact areas. For this reason most of today's designs include greater pressures and a chamber design where air inflates in "pockets." However, they have not all tested as effective in reducing injuries. During a 2004 IIHS side-impact test the 2004 Saturn L300 with an optional curtain still allowed the occupant's head to make direct contact to the impacting barrier. This demonstrated that limiting air volume reduces occupant safety.
First generation curtain styles typically used 10 to 25 liters of air volume, whereas newer designs exceed 30 liters. The challenge is that larger volumes require larger inflator units, better sensors and larger space for mounting.Since side curtain width or "dropping distance" is also fairly limited, the heads of shorter drivers may not reach the fully inflated curtain. This also may be true for rear-seated occupants. Chambered curtains may allow the head to impact an area between the chambers where little protection is available.
There is no doubt, side curtains are continuing to evolve based on the need to protect occupants in a variety of crash events. Even during frontal impacts, an occupant's head can rebound back toward the side door glass, B-or C-Pillars. Extensive side curtains will assist in preventing injuries as a result of this reaction.TRW has also introduced advancements in side impacts, secondary impacts and rollover crash events. Their new designs have included inflators that are positioned at the B-Pillar rather than the typical C-Pillar location that will simultaneously inflate the side curtain for both front and rear occupants. They have produced seat airbag units that have their own cover and do not destroy the seat in the process of deployment, and advanced side-impact protection with a new advanced side curtain system.
In most of these crash events, ensuring the occupants are properly positioned is also critical. Therefore, pre-tensioning seat belts will become standard so these curtains can be effective. Unrestrained occupants are very difficult to protect since their movement is not controllable and they are not decelerating as a restraint's occupant will be.Child safe or child injury
Once data began to be analyzed, concerns for child safety began to arise. What happens when a child is sleeping in the seat and resting close to the door or side of the seat? Will anyone out of position be seriously injured by a side airbag or curtain system? There have been several studies completed on these concerns by NHTSA. They can be reviewed online at www.safercar.gov and www.hwysafety.org.
Some manufacturers are using a special seat system called an Occupant Detection System (ODS) that senses out of position occupants or light occupants (such as children). These seats can determine if an occupant's weight is equal to a child and whether their body position is an area for safe airbag deployment.The Occupant Detection System (ODS) is made up of a series of flexible fabric sensors embedded in the seatback. The sensors set up a low-level electric field to determine the size and position of the occupant. An electronic control unit sends the appropriate signal to the airbag control to suppress or deploy the airbag in case of an accident. This system is currently available by Honda and Acura.
Working with safety systems
The first and foremost rule for working with any of today's restraint systems is to have the tools and information necessary to safely work around and with the specific system installed in the vehicle being repaired. This is no easy task since the systems are constantly improving and changing.You must be able to obtain vehicle manufacturer information regarding the disabling, removal, replacement and reactivating of each system. You should never work on any safety system that you do not have this information available. This information is critical to prevent accidental deployment and injury while working on the vehicle, and to ensure the system is properly operational when it is completed at your facility. Make sure you follow all the procedures as outlined in the manufacturer's service manual before performing repairs that require the disarmament.
Also keep in mind that side-impact sensors also must be mounted exactly as designed, and remember that mis-positioning these sensors will have an effect on the deployment upon a future crash event. Other replacement requirements and procedures are also provided for in the manufacturers' service manuals.If you have difficulty in obtaining manufacturer information, you can contact a company that can assist you with these needs called Scene of the Accident. They are a not-for-profit organization dedicated to providing timely vehicle-specific information to first responders of the accident scenes, namely fireman, police, paramedics and other emergency medical personnel.
They also have been providing tools for technicians who have been victims of natural disasters that have hit our country in the last several years. These technicians can be a valuable resource for vehicle-specific information. You can contact them through their Web site at www.sceneoftheaccident.com.
What's next to come?
Kia introduced a knee bolster airbag a few years ago to reduce the injury to knees and legs from frontal impacts. Look to see this and other technological advances, such as floor airbags to protect from foot injuries and additional protection in the roof area for rollover protection, coming from vehicle manufacturers.
One thing is for sure...more safety systems will be introduced along with stronger center section designs. This may include additional boron steel, aluminum and other new materials. Who knows... maybe "Insta-Foam" is not as far away as we thought?
