Why Don’t Cars Catch Fire When Crash Tested?

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Cars catch fire in real crashes, but not crash tests. Here’s why.

Fire needs three just things; Fuel (gasoline works great), oxygen (plenty of that in testing facilities) and an ignition source (like a shorted battery, or hot manifold). The National Fire Protection Agency says a vehicle fire occurs every two minutes in the United States, so why don’t cars crash-tested by the Insurance Institute for Highway Safety (IIHS) ever burst into flames when they are crashed? The reason, in a nutshell, is preparation.

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IIHS takes measures to prevent fires from happening during crash testing but has an interesting way of predicting if they could have happened. The first thing to know is that IIHS does not actually drive those cars into the crash test barriers (or vice versa). Instead, the institute has a complex track with a device that pulls the car up to speed using hydraulic power and compressed nitrogen. By using this method, as opposed to a car with its engine running, the hot manifold is removed from the equation.

IIHS is also aware that 17 gallons of premium unleaded is more than enough to burn down their state-of-the-art testing facility and injure their workers (and test dummies). So the Institute removes and flushes the gasoline (or diesel) from every test car.

In its place, IIHS puts a liquid similar to paint thinner called Stoddard Solvent mixed with purple dye. This industrial solvent has a similar density to gasoline but is less flammable. Russ Rader of IIHS told BestRide, “We start out knowing how much the fluid in the tank weighs so if there is a leak, we can determine how much of the fluid leaked.” How much leaked is a good indication of whether a fire might have occurred in the real world. IIHS tells us that they have “…seen fuel leaks, although it hasn’t happened in a long time.”

In case you were wondering, the rest of the car’s fluids are also drained. That’s because nobody wants to be the person at IIHS who’s job involves mopping up five gallons of anti-freeze, oil, and brake fluid. In place of brake fluid, IIHS inserts nitrogen that can be pressurized to actuate the rear brakes. This is done to help keep the car from leaving the test hall or hitting the hall barriers after a frontal crash.

There was one fire that happened during a crash test, but it was from an unlikely source. During the test of the 1999 Volkswagen Jetta, the Jetta’s pyrotechnic device in its seat belt pre-tensioner caused a fire in the insulation in the car’s B pillar. To be on the safe side, Volkswagen redesigned the material to be non-flammable on the Jetta and Golf, though a recall on the limited vehicles already built was not conducted.

Back in the 2000 through 2001 model year, IIHS crash testing uncovered dangerous liquid fuel leaks in two models, the Isuzu Trooper and the Dodge Caravan. The fuel leak in the Trooper was called “Major” by IIHS. To its credit, Isuzu jumped into action, requesting that IIHS do more testing to help isolate the root cause of the issue. After three tests, the problem was identified by Isuzu engineers and Isuzu issued an immediate recall to correct the problem.

In the Caravan, it was a coincidental second frontal test done at the request of Dodge that uncovered the defective part. IIHS discovered that “A part on top of the gas tank to which the fuel pump is attached cracked during the impact, allowing fluid to leak from the fuel system.” Dodge redesigned the part for future models and a third test showed that the new part did not leak.

If you were alive during the 1970s, you may remember a famous crash test involving an exploding Ford Pinto. That was not a standard crash test and was staged to demonstrate a problem engineers had already discovered. Rear-impact fire risk tests are still done in some cases, but modern vehicles no longer mount the tanks outboard of the vehicle’s platform, or “frame,” greatly reducing the risk Pinto owners lived with.

Electric vehicles pose their own unique fire threats. Watch for our upcoming focus on EV safety testing.