18-Wheelers Have Unprotected Fuel Tanks and That’s a Problem

Michael GrossmanSeptember 15, 2015 8 minutes

Each year, somewhere between several dozen and one hundred truck drivers burn to death. These incidents get reported, the news basically implies that the truck drivers killed themselves, and no one seems to care beyond that. Then it happens again, and again, and again.

But let's get one thing perfectly clear. The majority of these accidents are not ultra high-speed collisions wherein a gas tank rupture was simply unavoidable. On the contrary, most of these fatal incidents involve relatively minor collisions that result in catastrophic fires. The reason this happens, in my estimation, is because of a horrible design flaw present in most modern 18-wheelers: fuel tanks that are fully exposed on the side of the vehicle.

Because big rig manufacturers have decided to take the easy way out when designing the fuel system of large trucks, many truck drivers have met their end in the most horrific way imaginable. I think it's high time for big rig manufacturers to answer for their role in these fatal events.

What Causes This? Why Do Big Trucks Catch on Fire?

You probably know that all vehicles, from passenger cars to city buses, need some sort of power source to propel them down the road. For the overwhelming majority of vehicles, that's liquid fuel. Automakers learned long ago that if you tuck the fuel tank into a location near the center underside of the vehicle, the tank is well-protected. But if the tank resides near the very front, very back, or extreme sides of the vehicle, it's incredibly susceptible to rupturing on impact.

In order to appreciate this issue a little better, you need a basic understanding of how vehicles are constructed. While there are many different variations of car body and frame configurations in the modern world, the two most common are:

  • vehicles that use a unibody chassis
  • vehicles (usually trucks) that use a body-on-frame chassis configuration.

Cars with a unibody chassis are structurally similar to a soda can. They are made by taking a bunch of steel sheetmetal, stamping it into all kinds of complex shapes, and then welding those shapes together to form a single body unit (hence the name "unibody"). Almost every passenger car on the road is a unibody car. There are many advantages to this kind of body configuration, but the main advantage is that you can make basically any shape of car that you want; both the Mazda Miata and Honda Odyssey minivan use this same configuration, as do almost every other car in between. There are very few baked-in limitations in the way you can form the metal and weld it together, so this allows engineers the ability to create metal shapes that owe their strength to clever structural engineering rather than from being a giant hunk of metal.

Pic of unibody chassis
This is a unibody chassis. As you can see, it looks like one solid "thing," yet it is really a complex puzzle made up of hundreds of small pieces of metal welded together.

Vehicles with a body-on-frame chassis do take the giant hunk of metal approach. As the name body-on-frame implies, these vehicles consist of a lower frame upon which sits the body of the vehicle. This is almost like a shoebox sitting on top of a skateboard. The top cabin (the shoebox) is strongish, but it pales in comparison to how beefy the frame is (the skateboard). Almost invariably, the frame part of a body-on-frame vehicle is a type of frame called a "ladder frame." It's called that because it looks like a ladder. The main advantage of the ladder frame chassis is that it is rugged. The frame rails (individual pieces that the ladder frame is made of) are made of metal that is 4 millimeters thick. On the contrary, the thin sheetmetal of a unibody car is perhaps only .06 millimeters thick.

Pic of body-on-frame chassis.
This truck has a body-on-frame configuration. The body (made of stamped steel, similar to the unibody car) sits on top of a very primitive ladder frame chassis.

But here's where things get tricky. In an accident scenario, the unibody vehicle made from thinner metal is usually better at protecting its occupants than body-on-frame vehicle with its big bad ladder frame. Why? Again, engineers have figured out ways to make thin metal do more complex stuff (like crumple just the right way in an accident), while big thick frames on more rugged vehicles don't do anything sophisticated in an accident; they're just big and rugged and the hope for the best.

18-wheelers and other large trucks use an extremely rugged version of a ladder frame chassis, upon which sits a very primitive body. In that sense, large trucks are very much so like scaled-up versions of pickup trucks, except for one huge difference: where the fuel tank is placed. That difference can mean life or death in many accidents

Fuel Tank Placement

The best place to put a fuel tank is in the middle, bottom of the car, outside of the passenger compartment. In the case of unibody cars, this usually means that the bottom of the rear seat that you rest your posterior on is actually the "roof" of the gas tank.

Unibody gas tank location
The fuel tank on this Acura sits in the middle (laterally) below the rear set. It should take one heck of an impact to disturb this tank.

Naturally, that's a good setup since it puts as much metal between the car that hits you and the gas tank as possible. Although pickup trucks take a slightly different approach, they still place the fuel tank inside the safety of the frame rails.

Fuel tank placement pic.
Even though this Toyota Tundra doesn't have a fancy unibody chassis, Toyota's engineers had the good sense to place the gas tank INSIDE the frame rails where it's protected from side impacts.

The main takeaway is that the more of a vehicle's frame you can put between the gas tank and an object that comes rocketing toward the gas tank, the better chance that the fuel tank will survive the accident, which is obviously a good thing. The manufacturers of large trucks don't do this. Instead, they place the fuel tanks on the OUTSIDE of the vehicle's frame rails.

Here's what we're talking about:

Basic large truck chassis.

Above, you see a side view of a basic semi truck chassis. You see the ladder frame, some wheels, front and rear bumpers, and the trailer hitch, technically known as a "fifth wheel" (yes, I'm aware that I stink at photoshop).

Chassis with cab.

Here, we see the chassis with the addition of the cab. So far so good.

Truck with fuel tank.

Here's where things get a bit nuts. That giant barrel on the side of the truck (usually right below the door) is the fuel tank. That's right, there is literally nothing that stops an oncoming vehicle from careening directly into the a thin-walled barrel that holds 100+ gallons of diesel fuel.

Every time I've ever explained to someone what I just covered above, their response is always, "You mean those shiny metal tubes on the side of the truck are fuel tanks?!?! How does that make sense?" Once you see it, you'll notice them everywhere. Fuel tanks that sit on the outside of a vehicle's frame rails are often referred to as "side-saddle gas tanks."

Fuel tank placement on an 18-wheeler.
How is this so common? Other than using it as the front bumper, is there a worse place to put a fuel tank?

A Minor Accident Can Lead to Major Injuries Because of the Side-Saddle Gas Tank

The dangers of side-saddle gas tanks are nothing new to automakers. Over 10 million GM trucks had this tank design installed between the years of 1973 to 1987, and these trucks suffered record-breaking vehicle fires that caused extensively bad PR and numerous lawsuits. GM knew of the defect and yet continued to build their trucks in this manner. A solution was possible, and yet, they didn't take it - endangering passengers, drivers, and GM's own reputation.

Despite the fact that this is a well-known phenomenon, the manufacturers of 18-wheelers continue to place the fuel tanks outboard of the truck's frame rails. Consequently, when trucks are side-swiped or T-boned by other vehicles, or when they side-swipe guardrails or other barriers, it's likely that fuel tank could be easily punctured and catch fire.

Make no mistake about it, there are some accidents where the forces involved are so severe that it doesn't matter where the fuel tank is placed, there's going to be a problem no matter what. But that's not what we're talking about here. What we're discussing are minor accidents where everyone involved should walk away mostly unharmed, yet someone, usually a truck driver, ends up badly injured or killed. This is due to the poor placement of the side-saddle fuel tank - placing this tank on the side of the vehicle instead of within the frame is lazy manufacturing that leads to a no-win situation.

Manufacturers of 18-wheelers would have you believe that this is the only feasible option for them. Where else are they going to put all that fuel? Well, here's a suggestion. Don't use big metal drums to store fuel. Instead, create a composite (e.g. fiberglass, aramid fibers, etc... the same stuff your bath tun, tennis rackets, and, you guessed it, many fuel tanks are made of) fuel tank that is abnormal in shape and is placed inside the frame rails. There's enough room alright. Don't believe me? Just look to all of the "truck of tomorrow" designs that commercial truck manufacturers are showing at auto shows and guess where they are placing the tanks on these vehicles.

Failing a redesign of the tank itself, install a primitive "roll cage" type structure around the outboard fuel tanks that is skinned in sheetmetal as to stave off punctures. This would be inexpensive, unobtrusive, would be easily removable for service, and, most importantly, it would work. If that's too cost prohibitive (it wouldn't be), forget a welded, bent-tube structure, and just build a simple box from frame rail pieces. I could keep going with suggestions, but the point is that this is something that should be easy to address. The fact that manufacturers of these vehicles, replete with knowledge as to the hundreds of truck drivers who have burned to death, haven't tackled this problem is telling.

Naturally, our attorneys are of the opinion that as technology progresses manufacturers can and should use it. Put simply, there are now alternatives to placing the fuel tanks in harm's way and manufacturers who continue to use the side-saddle fuel tank, just because that's the way it's always been done, are making a risky and bad decision, and they are just asking for the lawsuits that our firm will inevitably file against them.