Significant improvements in automobile design and safety in recent years have made it increasingly difficult for rescue personnel to stay current with evaluating vehicle technology. Vehicle manufacturers are continuously improving their products to meet impact regulations, reduce weight with new construction materials, improve chassis design and meet customers' safety requirements.
Most structural and safety design improvements are not obvious to rescue personnel until they attempt extrication at the scene of a vehicle accident. Unfortunately, this is where many rescue teams learn the idiosyncrasies of particular vehicles. Few of us have the luxury of cutting apart new cars in the training environment, so we have to rely on information from vehicle manufacturers, which is often difficult to acquire.
Today's automobile manufacturers spend a great deal of time and money developing better protection for occupants in two areas: active and passive.
Active protection includes the technical features that control the vehicle more safely. Examples include cockpit design, onboard information systems, ABS brakes, suspension, steering, lighting and engine-control systems.
Passive protection refers to the equipment that minimizes the risk of injury, such as bonded occupant restraint systems, stronger windows, defined crumple zones, roof cross members, solid "A" posts and reinforced door sills.
Automotive engineers do their part by keeping the occupants inside the vehicle and dissipating energy from the impact with the use of air bags. It's up to us as rescue and medical personnel to get the occupants out.
By contrast, space frames, which are prevalent today, formerly have been described as a chassis resembling a bird cage; however, many new space frames tend to resemble monocoque chassis. The actual space frame is made from box sheet metal or aluminum, with body panels attached to the shell. Space frames, like many other chassis, have progressive crush zones that make them very rigid. Body panels attached to the structure are often plastic.
These plastic panels, called Bexloy (body exterior alloy), come in three types. K-type polyester is used for fenders and doors on many space-frame cars and vans. In an accident involving a plastic body vehicle, rescue crews tend to use familiar tools like hydraulic spreaders, cutters and rams. Although these tools play an important part in many extrications, cutting plastic panels and even roof removal can be accomplished quickly and efficiently using a reciprocating saw with a good-quality demolition blade. The plastic panels can be stripped away to expose the vehicle's space frame and allow rescuers to select a strong part of the frame if hydraulic tools are required.
An area of concern in space frame and monocoque chassis is the ever-increasing use of microalloy or boron steel--another safety feature used to strengthen automobiles for lateral- and frontal-impact collisions. This metal is extremely strong, due, in part, to its high phosphorous content. It is placed in the subframe cowl and cross member of new vehicles. A major difficulty for rescue personnel is that boron steel also is located in vehicle doors to meet side impact protection standards, which sometimes makes door displacement a very difficult task.
Some hydraulic cutters will not cut through boron steel, and attempting to cut it with a reciprocating saw is futile. Proper technique and spreader placement are important to roll the striker bolt latch and open the door. Inserting the spreader 90 degrees to the door and spreading will only tear the metal around the door and collapse the B-post. The bars in the door will withstand much greater force than a hydraulic spreader can exert.
In some cases, a door containing the side impact rod is attached to the lock mechanism. Certain car manufacturers even use boron steel to tie the A-pillars together to further enhance safety in side-impact accidents. Another added benefit to this configuration is that it holds the steering column and dash components from intruding into the driver's compartment during frontal collisions. Even the roof pillars have been strengthened considerably by sandwiching high-strength/low alloy steel inside the posts. In some cases, the A-pillars are filled with urethane--another material for rescuers to cut. Injecting urethane into the posts serves two purposes: making a stronger pillar and reducing noise inside the vehicle.
In its quest to build lighter, more efficient and safer vehicles, the automotive industry has increased its use of many other lightweight materials. An average U.S.-made vehicle, for example, uses approximately 200 lbs. of aluminum, with some models approaching 500 lbs. Some of it is used in castings for cross members and suspension, but a high percentage is in the body panels. The alloy of choice is AA6111 because of its unique combination of formability and paint bake strengthening. One vehicle manufacturer already has an aluminum space frame chassis on the market. The weight saving on a chassis of this type can be as much as 50%, and it is approximately 40% stiffer than its steel counterpart.
Air bags are getting smarter and safer, too. Current air bag systems trigger on an all-or-nothing mode during a crash. In the future, air bags will activate differently. They will monitor the type of vehicle accident, severity of impact, occupants' positions and even the distance of the occupant from the air bag. Some of this technology is already available in certain vehicles. In some automobiles, the passenger's side air bag deploys after a collision only if there is a passenger present. Other systems deploy in a low-speed collision if they sense the occupants are not wearing seatbelts.
The style and placement of bags also are changing. Air bag manufacturers are using a ventless air bag in place of a bag with four holes at the back that allow the release of gas. The fabric on new bags is permeable, allowing the gas to escape. New-style bags are tethered to limit distance, all in the interest of occupant safety.
In 1997 vehicles, air bags explode out of the seats, front and rear doors, knee bolster and even the roof channel between the A and B posts. All of this new chassis design and air bag technology is attempting and succeeding in reducing occupant injuries.
In studying the biomechanics of impact injury and injury tolerances, it becomes clear that the manufacturers' target is to lower head injury criteria (HIC) to an acceptable level. In many cases, this is being achieved in two ways: first, by new chassis designs that dissipate energy and channel it away from vehicle occupants; and secondly, by new air bag technology like the inflatable tubular structure (ITS) system. This type of air bag is located in the roof channel between the A and B posts and was designed primarily for lateral impact. Resembling a long tube when inflated, it provides significant head protection, reducing HIC to an acceptable level.
The information and knowledge acquired by extrication personnel about new vehicles will be the deciding factor on whether an incident is handled in a safe, efficient and more timely manner. These factors obviously benefit patients and reduce stress on the extrication team.
| Gordon Sweetnam is a training officer for the City of Calgary Fire Department in Calgary, Alberta, Canada. |