Episode 119: Exploding Bumper

Air Date: May 13, 2009

A car bumper can explode in a car fire and fly across 50 feet (15 m) to knee-cap a person.

busted

Adam and Jamie set fire to a car with gasoline and measured the temperature with a thermographic camera, eventually determining that the blaze reached 1,400 °C (2,600 °F), enough to melt the aluminum bumper but surprisingly unable to make the bumper shock explode. Suspecting that unfocused flames might have caused the explosion to fail, back in the shop they subjected several bumper shocks to directional heat from an oxyacetylene torch at various spots. However, all shocks lost pressure in one way or another before they could explode. During the episode, the MythBusters interviewed an Oakland firewoman who indeed suffered bumper knee-capping. But in her accident, the bumper flew only 15 feet (4.6 m) instead of 50 feet as alleged in the myth. Finally, Adam and Jamie simulated a 50-foot bumper blast using a delicately engineered rig consisting of two pistons packed with gunpowder and wet sand and an electric ignition system, which demonstrated the improbability of such a blast under normal conditions.

Hungarian archers got twice the penetration shooting a bow from a galloping horse than from shooting stationary.

busted

The Build Team first attempted to test the myth by having trained horse archers firing at a foam target at varying speeds. However, they were unable to get consistent data because the three archers they tested all rode at different speeds, fired their arrows at different distances, and had varying arrow velocities. For a more conclusive test, the Build Team obtained a Jeep and mounted a crossbow on the top. They then fired arrows at a large foam target while stationary and then while the Jeep was driving at 40 miles per hour (64 km/h), in both cases from a fixed distance of 60 feet (18 m). While the arrows fired while the Jeep was moving did penetrate deeper into the target, they did not penetrate twice the distance of the arrows fired while stationary, busting the myth.

21 Comments

  1. paco says:

    why didn’t they seal the safety valve in the bumper piston and heat it homogeneously or at least slowly, of course its gonna cut it its a torch

  2. Parry says:

    Watching the episode the Lady Fireman.(Excuse the political incorrectness) Did she not say she turned the nozzel onto the wheelwells before it exploded? Now if there was water thrown on to the bumper struts when extremely hot would it maybe cause some kind of kaboom? Just curious.

    • Jonathan Niles says:

      Yeah, I was wondering the same thing, maybe they can revisit this one?

  3. Grant says:

    Good point Parry.

    I didn’t agree with them busting this myth. We know it can happen, it happened to that firefighter. Just because they could not make it happen, does not mean it is busted.

    They should have said plausible really. I think they need to revisit the myth, but it was kind of a boring one so I don’t really care.

    • MSpears says:

      The myth was busted because it specifically states that the bumper flew FIFTY feet. When it happened to that firefighter, it only flew FIFTEEN feet.

      Simply put, they could not confirm the myth because, by duplicating the conditions of the myth, they were not able to duplicate the results.

      • CBVicious says:

        The problem with the 15 feet part is that the 15 feet including hitting her. I’m sure if she received enough force to shatter both bones in one leg, she ate up a lot of the momentum.

  4. Dragonfyre says:

    Busting it was probably premature…plausible, but highly unlikely has been used before…the situation for this one, however, was incredibly slim…almost no chance, since the bumpers are designed not to fail.

  5. Karen says:

    I was just watching this episode and realized that most car fires are due to an accident so use a perfectly good bumper and not a damaged one would create a different result. If there is no damage to the bumper then the safety mechanisms would work but may not work properly if damaged. so i agree it should have been plausible not busted

  6. Michael says:

    just was the episode and the comments of the firefighter. when she put the water in the right side and stop because of the tire she move around to the front side. the fire was the beginning source but the steam from the water is what set off the cylander. that why all the exmaples failed do to continous fire burning when steam heats just short of pinateration. i believe this be the cuase. thank you for your time.

  7. Bill says:

    By increasing the velocity of the arrow, you double it Ke. Two things. 1.The standing archer shot normal to the target, the horseman shot at an angle resulting in the arrow trying to penetrate the target with a side force component. Friction is the big problem as it is not linear for a cylindrical shaft into the foam. This can be demenstrated by driving a tube into the ground with a constant force, it will eventually stop. Mu of the foam would also be much higher than that of a human body which would change the entire outcome of the test. I think that the test should be run again with human bodies, any takers?

  8. Jeff says:

    As a fire dept. training instructor captain, I train our dept to be aware and avoid these area’s of the vehicle during a fire. Although I personally have never experienced this, I have seen several training video’s and pictures of bumper, hood and hatch shocks taking flight during vehicle fires. Just a comment!!! In my opinion-you were at the wrong place at the wrong time. You have real life proof that this does happen. Just because the distance didn’t meet your criteria, it doesn’t mean that it can’t happen.

  9. Buster says:

    The myth is that the bumper flew 50 feet, it won’t. Not to mention that the probability of this happening is so astronomically small it is negligible. It’s busted.

  10. Dead Eye says:

    Thank you buster, again argument ignoreing the myth, the myth was not will a bumper fly off in a car fire. We know that happens, it was it can fly fifty feet, no it could not. Myth busted. I swear I read all these comments people post, your like the guys who would argue with your math teacher in school how your answer was right because all the work was correct, but the question was what is two plus two, and you answered whats the square root of fifty seven. As a volunteer fire fighter we are trained not to stand in front of the bumper because they can, but not likely explode in a car fire. The guys proved that to, they can but not likely explode in a car fire the myth was the whole, whole! bumper can fly off, and travel fifty feet. The fire fighter who was hit buy the peice of the bumper was hit by just that a peice. Saying that a fire would cause two seperate peices of somethign to fail, at exactly the same time is completely illogical, She was hit by a peice of the bumper that had melted through the center during the fire, they showed that in the episode. The myth was, can the whole bumper fly off, and travel fifty feet. The answer is no, two explosions happening is unlikely, happening at the same time, is even less likely, happening at exactly the same time is near impossible, and they still does not change the fact the bumper still could not fly fifty feet. Myth busted, they answered the myth, you guys are all hung up on the bumper fly off part, that wasn’t the myth.

  11. Hosehund says:

    With TV and everything else that is out there, many false claimes are made like exploding gas tanks and high velocity flying bumpers.

    With the possibility of this actually happening is minimal. If you look at the ones that would explode, they would have past light collisions and corrosion from age. These would add to the likelyhood of increased pressures to to the bumper cylinders, but the bumper still would not fire off as one unit.

  12. TJ says:

    On the exploding bumper. There was one method people forgot to check.

    Take one of the old ships that used boilers. When a boiler hits water it explodes. The shock on a bumper is the same thing, a mini boiler.

    The firefighter started at the wheels and moved forward in front of the car. Whichever angle allowed the cold water from the fire hose to hit the bumper shocks is what does it. The cold water hits the shock, much like a boiler in a ship when it goes down. The result, depending on how long the fire is going, most likely is what triggers the explosion.

    The question then comes down to physics. How long is the car on fire, the materials involved, the temperature of the water and also the normal temp. If one takes in all of the variables, the water hitting the bumper shocks at the right moment, I would almost guarantee they would blow up with enough force to do the damage.

    It may not happen every time, but yes, this is far from busted and extremely plausible. I would not call it confirmed but it can most definitely happen. It may be rare to hit all of the components into one explosive decompression, but try it 50 times and I will bet you 20 blow.

  13. Dragonlord says:

    My problem with the arrow penetration test is that they are not using the period weapons, or calabrating a modern weapon to the same strength. After all, the momentum of the car will add a consistent amount of force to the arrow, so the modern crossbow with its higher pull would show less difference than a traditionally made Hungarian bow with a period string and period arrows.

  14. Greggerbug says:

    I think this myth needs retesting. TJ’s point about the water thrown on the hot bumper is great. Plus, where the fireman’s bumper shot only 15 feet, it was stopped by her leg. Her leg was broken in 20 places. How much force does that take? Enough for a bumper to travel another 35 feet had it missed her?

  15. Justin Ryan says:

    I think the arrow penetration one was more about relative then it was a straight doubling of penetration. An arrow fired at half the velocity would still penetrate the target. Im not sure about the math around it but couldnt they have done 3 sets with a -40mph, 0mph and +40mph ? im not sure if the penetration would follow a linear patern or if its exponential, and if exponential im not sure if at a certain point the penetration would benefit less with more speed at lower speeds or higher speeds. I just think its possible the penetraition depth difference between -40 and 0 vs 0 and +40 could be double or something as interesting.

  16. Jack Homen says:

    The above comments are correct. As a 30 year career firefighter, the use of water as a cooling agent is the difference in the failure to reproduce the bumper exploding off the test bench. If they and applied water it would have caused the catastrophic failure that has injured many firefighters. Not only is it not busted it is fact giving the application of water during the firefight. It is not the hydraulic fluid releasing, it’s the water rapidly cooling and then causing the release of energy that explodes the bumper forward. Strange not of this occurred during the research prior to filming.

  17. Brent Sumrall says:

    I have been doing vehicle fire investigations for a number of years and di one recently where a similar thing happened. The vehicle was being toed and the driver forgot to release the parking break. The wheel got hot and the tire caught on fire. It was not until the driver hit with a fire extinguisher that the tire blew up. The girl that was talking about this said she hit it with a fire hose?? This could be the difference between busted and plausible.

  18. Body Shop says:

    This infuriates my body shop as bumper shocks are not used on newer cars! The bumpers are bolted on and that’s it! This is on ancient cars that are extinct!

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