Small Car Rescue Challenges - Part 1

July 1, 2008
SUBJECT: Small Car Rescue Challenges -- Part 1

Topic: 2008 Smart Fortwo

OBJECTIVE: Given information about the 2008 Smart Fortwo vehicle, rescuers will be able to explain the safety features of the vehicle and how they influence medical and rescue activities at a crash scene.

TASK: The rescue team shall list and describe the design features and safety systems of the Smart Fortwo and explain the influence each feature or design has on anticipated fire, safety, medical, or extrication procedures at a Smart car incident.

The challenges presented by small vehicles involved in collisions have always been with us as rescuers. A new trend to market small, fuel-efficient vehicles in the U.S. warrants a new look at small car rescue challenges.

In this first part of our series, we will examine the 2008 DaimlerChrysler Smart Fortwo; the smallest vehicle sold in the U.S. The Fortwo is classified as a microcar, meaning it's even smaller than minicars such as the BMW Mini Cooper. Besides the Mini Cooper, this vehicle will compete against several other new subcompacts recently introduced into the U.S. market; the Honda Fit and Toyota Yaris, for example.

The Smart Fortwo arrived in the U.S. in January 2008. It is available as a hardtop or a convertible. The hardtop may sport an optional, fixed-glass sunroof.

The tiny 1,800-pound Smart For-two is manufactured in France. Around 20,000 Smarts a year will be sold in the U.S. At eight feet, 10 inches (106 inches) in length and only five feet, one inch (61.4 inches) in height, it's more than three feet shorter and almost 700 pounds lighter than the BMW Mini Cooper. It only takes up half of a parking space.

The Fortwo's 1.0-liter, three-cylinder engine is mounted under the trunk floor, just in front of the rear axle. It provides power for the rear wheel-drive vehicle.

Smart Safety Features

All Smart Fortwo models are equipped with driver and passenger dual-stage frontal airbags, seat-mounted side airbags and padded knee protectors. The side airbags are the larger, head-thorax design. The passenger side-impact airbag will not deploy if that seat is unoccupied. A section of the steering column shaft near the instrument panel will collapse in the event of a serious frontal collision.

The car has a seating capacity of two people, both in bucket seats. The passenger seat has the occupant-sensing deactivation feature that turns the passenger frontal airbag off when the seat is unoccupied. The passenger seat is mounted to the floorboard slightly more rearward than the driver's seat to optimize shoulder room. The passenger seat is also a fold-flat design.

Both seatbelts are equipped with pretensioners and have a special force-limiting design. As a frontal crash occurs for example, the pretensioners fire and pull slack out of the seatbelt system. As the deceleration continues, the force-limiting seatbelt feature carefully releases the snug belt before too much pressure is exerted on the occupant's chest. EMS responders might see a ragged or fuzzy section of the seatbelt indicating that the patient has undergone high-impact force energy, enough to activate the force-limiting feature. With such a short front end and minimal crumple zone distance, occupant protection through frontal airbags and the seatbelt force-limiting feature are very important.

Hazard Control

When the decision is made to shut down the vehicle's 12-volt electrical system, you need to already know where the battery is located. You'd never find it within a realistic timeframe if you had to blindly search for it. The 12-volt battery is essentially hidden beneath the floorpan under the front passenger's feet. The carpet has to be moved to reveal the trap door that covers the battery. The top of the battery sits just below floor level. Consider this: You have to be inside the vehicle before you're actually able to shut down the electrical system. Add a jammed door and a trapped front passenger and you can see how complex something as fundamental as electrical-system shutdown will be with this vehicle.

The nine-gallon fuel tank is mounted under the vehicle and occupies most of the center floorpan area. An inertia switch stops the fuel supply in the event of a crash and the electric door locks automatically unlock as the collision occurs.

Tridion Safety Cell

Although real-world crash experience is still very limited with this new vehicle, crash testing has revealed a very significant design strategy that will influence what responders find as they arrive at a Smart car crash incident. The occupants ride within a steel cage that DaimlerChrysler calls the Fortwo's tridion safety cell. The structural steel components of this protective cage distribute impact energy evenly over the car's entire body during a collision. Portions of the special tridion safety cell consist of ultra high-strength steel. This metal is the toughest we can encounter during extrication incidents and includes the A-pillar on both the hardtop and the convertible and the rollbar on the convertible model.

At the rear of the car, a rear "crash box" of aluminum will crumple upon impact. The wheels and axles also take on the function of crumple zones for both frontal and rear collisions.

During recent frontal crash testing conducted at the Insurance Institute for Highway Safety's research facility in Virginia, engineers documented a test result for the Smart Fortwo that is significant enough for responders to be aware of. In the 40-mile-per-hour frontal collision into a stationary barrier, Institute President Adrian Lund stated "We recorded a high head acceleration when the driver dummy's head hit the steering wheel through the frontal airbag." For responders, this indicates that the Institute's test dummy used up all of the available ride down room in the Smart's seatbelt system and interior space as the crash occurred. EMS responders: take note.

The crash-test engineers also noted that during the collision, the driver's door unlatched. This also occurred during side-impact crash testing conducted by the National Highway Traffic Safety Administration. At the Institute, researchers report that the opening of the door did not appear to affect dummy movement during their test. The challenge of having a door latch system that releases unintentionally during frontal or side collisions is that it could allow partial or complete occupant ejection, especially if the occupant is unrestrained.

Side Impacts

For side-impact collision management, each door has a collision beam installed. When another vehicle is colliding with the For-two, due to the Smart's short 73.5-inch wheelbase, the other car will very likely hit an axle. That wheel, tire and axle being struck is another aspect of the vehicle's crashworthiness because these items are connected to structural members that help absorb the impact.

Responders should also note that all Smart Fortwo models are equipped with an electronic recording device; what we commonly refer to as the "Black Box." The device will record data that can help diagnose vehicle systems after a collision. One of the criteria under which the manufacturer is willing to access the information and share it with others is in response to an official request by law enforcement or other government agency. Just something to think about.

TASK: The rescue team shall list and describe the design features and safety systems of the Fortwo and explain the influence each feature or design has on anticipated fire, safety, medical, or extrication procedures at a Smart car incident.

RON MOORE, a Firehouse® contributing editor, is a battalion chief and the training officer for the McKinney, TX, Fire Department. He also authors a monthly online article in the "MembersZone" and serves as the Forum Moderator for the extrication section of the website. Moore can be contacted directly at [email protected].

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