Episode 139: Dive to Survive

Air Date: March 31, 2010

Diving underwater can protect you from an explosion.

plausible

During their small scale tests, the Mythbusters discovered that water can diminish the force of a shockwave caused by an explosion, giving credence to this myth. For their full scale test, the Mythbusters hung rupture discs 5 feet above water, 5 feet below water, and 10 feet below water at 5, 10, 20, and 50 foot intervals away from the explosives. They detonated 50 pounds of three different types of explosives above the water: gasoline, ammonium nitrate, and dynamite. While the gasoline could only rupture the closest above water disc, the ammonium nitrate ruptured every single disc and the dynamite ruptured all the discs except for the underwater discs located 50 feet away. With these differing results, the Mythbusters declared that the myth was plausible, depending on the explosive.

Filling the cavities of a car’s doors with phone books will make the car bulletproof.

busted

The Build team filled several car doors with phone books and fired various firearms at it. The phonebooks were able to stop 9mm, .357 magnum, and .45 caliber rounds. However, the more powerful deer slug shotgun rounds and the M14 assault rifle were able to pierce the door and the phonebooks easily. Since the phonebooks could not stop all of the bullets, the myth was declared busted. However, the Build Team continued the experiment to see how many phone books behind the door would be needed to stop a deer slug and rifle round and found that only two phonebooks were needed.

A car completely covered in phone books will be bulletproof.

busted

The Build Team calculated how many phone books would be needed to completely bulletproof the car, which was around 900. However, this may phone books weighed significantly more than the car could carry, so the Build Team was forced to cut back the amount of phone books to 400. They installed a remote control system in the car and placed inflatable dummies inside to simulate people. For their first test, they drove the car around as they fired M14 and deer slug rounds at it. All of the dummies inside the car survived this test. In their second test, the Build Team fired various automatic assault rifles at the car, and all of the dummies still survived. For the third test, the Build Team fired various high powered sniper rifles at the car. Kari managed to disable the car with a .50 caliber round and the combined sniper fire managed to kill all of the dummies. Though the car was highly resistant to bullets, the fact that they could still penetrate the car and harm the people inside led the Build Team to declare the myth busted.

29 Comments

  1. Scruf says:

    For where were the phone books published?

    I assume that two editions of a SF yellow pages would make a world of difference when compared to a book from Eli, MN, Nantucket, MA or Ft. Walton, FL.

  2. briana says:

    i have myth it is if tires on a bike get to hot when going really fast will it burst in to flams

  3. Dave says:

    Since when is an M14 an assault rifle?

    • chris says:

      The M14 is an Enhanced Battle Rifle. capable of automatic fire with a 20 round mag. this alone typically classifies a rifle as an assault rifle.

      The M14 is typically used as a Designated Marksmen personal weapon so rather then carring an M4 or M16, soldiers would carry the M14 as their primary.

      typically “sniper rifles” are either semi-automatic, or bolt action. thought there are known to be a few exceptions.

  4. Greg says:

    Are you guys afraid to do the “diving in a refrigerator to escape an atomic blast” test?

  5. Frank says:

    Briana: Me and my freinds in Norway have tried that test. We found a 300-350 meters long downhill and put our stuntman Sander on a normal city bike (the terrain was packed sand) after about 200 meters the tires popped like a ballon (he also aplied metal brakes to increase the heat) and Sander flew into the side of the road. we did the test again with a mountain bike this time, on the same conditions. The tires did not imeadetly pop but after running the entire course there were significant burn holes on the tires and we had to buy new ones… so il let you guys decide what it is (Busted, confirmed or plausible)

  6. Arch says:

    you mite be able to ezcape the blast and it mite dimm the shock wave but when your underr water the shock wave can ruppture your ear drum and cause way more damage to your inner organs

  7. Sammy says:

    That is interesting, Frank. Way back when I was a little fella, there was a hil we used to ride down all the time. It was at least a quarter mile. Our bikes would go so fast the pedals could not add anymore speed to the bike. None of the 15 or so of us ever had a blown tire, and we rode in all the seasons.

  8. marko says:

    you cannot drive bike fast enough to fire a tyres, it’s simply not possible. Maybe if you make some device, like ultra fast threadmill, that would spin wheels something like 200mph it would give results.

  9. yeah ok says:

    @dave http://world.guns.ru/assault/as15-e.htm

    As for bike tires, depending on the composition they usually melt and disapate the heat long before they would get close to ignition. I have blown tires from heavy breaking, (wears through the tire and pops the inner tube) but I don’t think a rolling tire would create enough friction to overcome the air movement and braking pressures would destroy most tires before they combusted I believe. I think they tried this with a car tire doing ‘burnouts’ and it’s seems very unlikely to get a flame.

  10. Scud says:

    For the phone book myth about being bulletproof….they used a M14 (.308) on the range but when they were testing the door window and phonebooks in the “bunker” they were using a M1 Garand (30-06)…yes both went through..but it would be nice to see them not change variables during the testing….

    • nato says:

      30-06 and .308 have almost identical ballistics

  11. Bill says:

    Your underwater test has a major flaw… Movement of discs 5 ft above water could have caused enough movement of the rig to rupture discs underwater due to water pressure and not shock from explosion. Under water discs should have been rigged up seperately.

  12. Joe says:

    I agree with bill. In addition, the disc 5′ under the water was really more than 5′ from the explosion. It would have been closer to 11′. Assuming an inverse square law would apply, that is a significant difference in distance. Of course, it really isn’t about science, but about blowing stuff up.

  13. Logak says:

    Would there actually be enough force from the movement of the rig to break the discs? I was under the impression that it took quite a bit to actually break them – if water pressure alone could rupture them, would they have used them in the first place?

  14. Whirligig says:

    Joe: Of course it’s about blowing stuff up, but it’s the science that makes it fun. Just randomly blowing stuff up wouldn’t make a good show in my opinion.

    That being said, I’m not sure if I buy Bill’s statement, but I do buy Joe’s … sort of. Assuming the explosives were 5′ above water (I’m not sure if they were — correct me if I’m wrong), it’s possible that it was the distance and not the water that had the most effect. Here’s a graph I made using a scale of 1 unit = 5′: http://img708.imageshack.us/img708/9172/divetosurvive.png

    Now in this graph, I’m assuming that there’s some sort of simple relationship between the distance from the source of the explosion and the effect of the shock wave, so that there’s a certain “distance circle” where any discs inside the circle rupture, but any discs outside it don’t. I have graphed possible circles for the three explosives used. The gas circle has a radius of 7′, the ANFO circle has a radius of 60′ (but it could really be any circle big enough to cover all of the discs), and the dynamite circle has a radius of 50’6″. Of course, to “squeeze in” between the 50′ discs, there’s a small range of radii the circle can have, but a) this by no means implies it is impossible for the circle’s radius to be in that range, and b) there are a few other factors I’m not accounting for, which could widen the range.

    Overall, the small range of possible radii on the dynamite leads me to believe that the water must have some effect, but other than that, their results could be explained only by using distance. I would remedy this by using explosives closer to the water and by arranging the heights/depths of the discs symmetrically with respect to the height of the explosives.

  15. Johannes says:

    In one of the first test, they demonstrated that a rupture disc would not rupture if it was submerged at the same distance that a non-submerged disc would rupture at.

    Since it was the only variable, it basically proves that water has a dampening effect for that type of explosion

    But the myth should have looked at how far you can get swimming down versus swimming vertical or a midpoint

  16. J. Michael Looney says:

    For what it’s worth, the phone book thing came from the USA network show “Burn Notice”, where they only said “bullet resistant” not “bullet proof” and the bad guys were using 9mm pistols and submachine guns, which did were stopped in the test. Burn Notice also used real bullet resistant glass to replace the car windows.

  17. Jimmy Moone says:

    @J. Michael Looney
    which is why i was surprised when they called it busted… shenanigans.
    @scruf
    The show takes place in Miami, so I’m guessing they were Miami books

    • Confused.individual says:

      Do some of you just watch the show to find reasons to complain and feel like your smarter then the MBers?

      • Triune says:

        No, though some of us do watch the show and get tired of times when they declare something busted without doing it even remotely close to properly.

        And then there’s the myths they declare confirmed which can literally cause you to die if you tried them…

  18. Joe says:

    The parameters given in the Burn Notice episode were proven to be confirmed by MB yet were still given a busted rating. So, yes, in this instance, I feel I am smarter.

    • AF says:

      Yeah this was absurd. I’m sure they would have procured a BMP 25mm if the .50 BMG failed. Lame.

  19. Kurt says:

    This is one of the best shows in television.

  20. dave berthelet says:

    your recent episode dive to survive left me with a couple of questions about the way the experiment was performed, i think it was a mistake to physically attach the above water sensors to the underwater ones with metal rods allowing the transference of force to travel down the metal rods possibly destroying the underwater sensors, an anchor/buoy system should have been used to secure the underwater sensors, leaving the buoys under water also to protect them from the blast(maybe), sorry but i don’t think the results were without variables if you want to try again I’d watch.

  21. dave berthelet says:

    on a completely different note when i was a kid me and a friend used to make cannons out of 4 soup cans and some duct tape, we figured out a way to amplify the blast by simply shaping the bottoms and tops of the connecting cans by only removing parts of them instead of simply making a tube now it would build up pressure in the three lower cans before shooting out the top, for fuel we used lighter fluid squirting in an ample amount them letting it evaporate a little then ad flame and our tennis ball (which happens to fit perfectly in a soup can) was launched completely over the old paint factory next door and because it was new ball with lots fuzz which catches fire easily turned it into a fireball, which landed across the street from the factory right in a ladies bag of groceries she was carrying home at the time both breaking and burning her groceries, she saw us,we ran, parent’s money was used to reimburse the lady, punishment was doled out, etc. I’d be curious to see the design used on grants air cannon, hmmmmm. Or Jamie’s pop gun, or something with some real oomph. Interested?

  22. Robert says:

    The diving underwater to survive a explosion myth, in the last explosion when dynamite was used I saw something shoot from the right hand side at high speed and appear to hit the dynamite just as it exploded, any one else notice this and if so what was it?

  23. Gridlock says:

    Well, here is not a myth, but a question.
    If you were in scuba gear underwater and spotted an explosive device ready to go boom (assuming time bomb, depth charge, or ship about to trigger an anchored floating mine), then would creating a curtain of air bubbles with your breather tube diffuse the force of the blast enough to save your life?

    The idea is that the compression wave would hit your air bubbles and spread outward away from you like a knife slicing the compression force wave. Ideally it would be a wall of bubbles (not practical under any circumstance for underwater military subs), thus giving a liquid compression hitting air.

    Ideally you would need a compression wave of equal or lesser force (which would kill the person releasing such a wavefront unless they were using a shaped charge with a blast shield) to stop or disrupt the liquid compression wavefront, but diffusing it or splitting it would be an option.

  24. Tim W says:

    RE; Dive to survive.
    The test failed to take into consideration normal water pressure at any given depth. water pressure at 20 ft is 8.7psi, therefore it would only require 4.3 psi to rupture the sensor. a person can easly dive without scuba gear to depths producing constant pressures of far greater than the 13 lbs of impact pressure from the explosion required to rupture the disk. ( even at 50 ft the pressure is 22psi and free divers dive much deeper than this) this being said i would postulate that the water pressure mus be compensated for.

Leave a Reply

(required)