VEHICLE STABILIZATION: THE FOUNDATION

BY DAVE DALRYMPLE




Let’s consider vehicle stabilization and some new tools and concepts (photo 1). Although not glamorous or high profile, vehicle stabilization is critical at an extrication scene and must be a consideration at all motor vehicle accidents (MVAs). Unwanted vehicle movement is a hazard at an MVA and needs to be addressed like any other scene hazard. Although most vehicles involved in accidents end in an upright position, and it is a very straightforward process to manage them, it is the vehicle that is in an unusual position that pushes the envelope and often causes personnel to become more stressed than they need to be. Vehicle construction also plays a role: Crash damage and our tool evolutions may displace vehicle components and weaken the vehicle’s structural integrity. Weakening the vehicle’s structure may assist us at times, but it is vital today to “capture” the vehicle and secure on a foundation that is rock solid. Many of the tool evolutions we perform today need this solid platform on which to work. How can you displace a dash today if your vehicle is not sitting on a solid platform?

VEHICLES AND CONSTRUCTION

Today’s vehicles and their construction affect all of our extrication efforts, including patient care, tool operations, and stabilization. Unibody construction is the current prevalent method. Basically, the vehicle’s framework is the occupant floorpan with sub-frames off the front and rear of the vehicle. The rest of the vehicle structure, including the glass, rounds out the structural integrity.




In a crash, vehicle components are damaged and displaced, weakening the vehicle’s strength (photo 2). The tool evolutions performed to disentangle a patient can have the same effect. As the vehicle is weakened in this way, it can twist, bend, and contort even if it is sitting on its wheels. Such movement can jam doors that were previously opened; add tension to the glass so that when it is broken during extrication, it shatters explosively; and even further entrap an occupant’s feet or legs by folding the footwell/firewall area. If this movement is managed by placing the vehicle on a platform and securing it there, we minimize the hazard and manage it better and improve our tool evolutions.




Consider vehicle ride height, the distance between the underside of the vehicle and the ground. In the past, we handled most stabilization with step chocks (if the vehicle was upright). Step chocks are purpose-made cribbing blocks, built into a stair step fashion. Two of the most popular vehicle types today are sport utility vehicles (SUVs) (photo 3) and minivans. There are also greater numbers of SUVs and pickups on the road today. These vehicles tend to have a higher ground clearance (and a higher center of gravity). Many times, step chocks alone are not high enough to properly capture and secure a vehicle alone; usually personnel need to build a small box crib under the step chock for it to work well.

On the opposite end, many cars today are much lower to the ground, low enough that many times when we insert a step chock under the vehicle, we get only a few steps in and under the vehicle, leaving most of the step chock sticking outside the vehicle and presenting a trip hazard to us.




In addition, contemporary vehicles readily absorb energy when struck in a crash. This energy absorption principle can affect the vehicle by basically absorbing a certain amount of crash energy or “crush” including the drivetrain and even tires-often we find today that the vehicle ends up sitting on the ground. How do we put a step chock under that? Well, you might say, why bother since the car is sitting on the ground? However, we need to manage it and control it ourselves to ensure it is mitigated properly. Last, consider “run-flat” tires or tires with air monitoring/supplementation. How well can you deflate a “run flat” tire today (photo 4)?

TOOLS AND METHODOLOGY

Cribbing, wedges, and step chocks are the tools in our primary stabilization cache. Cribbing of various sizes is used day in and day out at a wide variety of incidents, wedges fill up gaps and voids, and step chocks are used as discussed above. Today, these may be made of plastic as well as wood. Let’s look at some of the new stabilization concepts and tools and revisit the old ones.

Step chocks evolved from extrication challenges back in the 1980s to assist with rapid stabilization of a vehicle on its wheels. Today it’s the same, although there are some additional options to help us.




One type of chock with teeth appears similar to a step chock but has a unique process to provide quick stabilization. The two-piece plastic device consists of a large chock that has an inclined plane with teeth instead of steps. The other part is a “traveling block” that is an inclined plane with teeth matching those of the large chock. The traveling block has a large flat platform at the top. The teeth of each inclined plane lock together when pressed (photo 5).

The device is placed much like a step chock. The large chock base is placed teeth side up, and the traveling block is placed near the base of the large chock. When the large chock is placed under the vehicle, the “traveling block” is slid upward on the large chock base, wedging the traveling block between the large stair and the underside of the vehicle. This step maximizes contact between the vehicle underbody and the ground. This device makes for rapid setup, stabilization, and securing of the vehicle.




Another type of chock is a “quick chock.” A good friend of mine and fellow Transportation Emergency Rescue Committee (TERC) member, Deputy Chief Murray Smith from Gainesville (FL) Fire and Rescue, introduced this device to me. His department actually has switched from using step chocks to these quick chocks on all apparatus. The quick chock is comprised of two pieces: a platform of three or four 18-inch-long 4 × 4 cribs screwed and glued together with a top plate of 12 inch plywood screwed on top of the platform. The second piece is an approximately 18-inch-long 6 × 6 or 4 × 6 wedge (photo 6). The quick chock is also placed under the vehicle like step chocks, with the platform as the base; the wedge is driven in between the platform and the vehicle underbody. This allows for rapid setup and a flexible approach; depending on ride height and vehicle damage, you can add or subtract components to fill in space to stabilize.

Another idea that deserves a revisit is the lock blocks or Lego® block type of cribbing. Made of plastic and manufactured by a variety of companies, these cribs basically look like square or rectangular Lego® blocks of various heights that nest or lock together. They provide a large contact base, and various heights can be built and slid under the vehicle, placing a column of cribbing under the vehicle. Also, there are wedges that are made to mesh with these blocks. All these adjuncts work well with the design changes in vehicles, the dynamics involved when these vehicles crash and interact with the tool operations we perform today, and provide for a more rapid and complete stabilization of vehicles that are upright on their wheels.

What about those vehicle tires? The extremes we see out on the street today range from ultra high-performance tires that have almost no side wall to the newest “run flat” tires and the large sidewalls of SUV and pickup tires, not to mention aftermarket changes to these as well. When we crib the vehicle, we capture the vehicle and its suspension, spreading that point of contact over a large area of the ground.

However, depending on the vehicle’s tires, we can still generate movement by “flexing” the tires’ sidewalls. Some of these sidewalls may be fairly large; this movement can rock the vehicle off the platform we created with our stabilization evolutions. This unwanted movement can be caused by accessing the vehicle or even tool evolutions. Remember, we need to minimize this unwanted movement in our patient care.

So how do you deflate these tires? There are many options, but we want to strive for a controlled release of air from the tire-stabbing the tire sidewall is not advisable. Unscrewing the valve core from the stem, pulling or cutting valve stems, and using a dedicated tire deflation tool are all good choices.




Now let’s look at stabilizing vehicles other than on their wheels. In the past, besides cribbing, we relied on adjunct tools such as high lift jacks, come-alongs, and even lifting bags to assist in stabilization. Although these items still give us options today, the current trend is to use a technique called “tension buttress cribbing,” which stabilizes vehicles on their sides, overturned, or in an unusual position.

In this concept, one or more “right” triangles are placed against the vehicle. This shape ties a strut or brace with a ratchet strap to the vehicle, and then the strap is tensioned (photos 7, 8, and 9). This action basically extends the base of contact with the vehicle and the ground.




There are many variations of this stabilization principle. From a simple home-made long crib with a ratchet strap, a section of cribbing with a manufactured base and strap combination and a crown or cap or a manufactured strut, to a base and strap combination-all of these use the principle of tension buttress cribbing. This principle allows us to “capture” a vehicle and hold it in place effectively and rapidly and is very simple and straightforward to learn and apply in a variety of situations.




The devices themselves can also be stored on a variety of apparatus; some have extensive accessories to enhance application options. Depending on vehicle orientation, this principle can be applied and the vehicle stabilized in less than two minutes. Depending on the device, as the devices are adjusted, they can also provide a source of controlled lift while stabilizing.

• • •

Although this is by no means a complete list of the new “widgets” on the market, I have highlighted some of the new tools and concepts and even revisited some traditional ones. Some of these items significantly reduce that all-important scene time, making our extrications more rapid. They also add an enhanced margin of safety by making the vehicle we are working on rock solid. We need to save time on the street so we can improve our patient’s chances of a successful outcome. To ensure this, we always want a safe working environment.

Remember, always recheck your cribbing and stabilization after every major action performed on the vehicle (e.g., roof removal, side evolution, and so on) from which the patient is being extricated.

DAVE DALRYMPLE is a career EMS provider for Robert Wood Johnson University Hospital/St. Peter’s University Hospital Emergency Services in New Brunswick, New Jersey. He is also a firefighter/EMT/rescue technician and former rescue services captain of the Clinton (NJ) Rescue Squad. Dalrymple is the education chair of the Transportation Emergency Rescue Committee-US and serves on the Expert Technical Advisory Board of the International Emergency Technical Rescue Institute as the road traffic accident advisor.

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