The Truth About Explosive Decompression

By on July 7, 2004

Is it true that if you shoot a bullet through the skin of an airliner in flight, everyone would get sucked out the little hole? If not, Hollywood has a lot of explaining to do.

Adam and Jamie from Mythbusters on the Discovery Channel set out the other night to find out if this was true. The myth is based on the fact that an airliner at 35,000 feet is like a ballon flying through the air — the air pressure on the inside (pushing out against the inside of the plane) is much higher than the ambient air pressue at that altitude.

When you pierce the skin of a ballon with a pin, the whole thing pops. The pressurized air inside the ballon rushes out with such force that it “grabs” the edges of the hole as it leaves and tears the ballon apart in an instant. The same should be true for an airliner, right? And everything in the plane should go rushing out the hole, right?

No. Mythbusters proved this wasn’t the case, thus proving wrong several dozen action movies and at least one James Bond film. And, true to Mythbuster’s style, they proved this point with a veritable tidal wave of geekiness.

They went to an airline graveyard in the Mohave Desert and found an old Hawaiian Airlines 737. They sealed it up, then brought in a massive air compressor and pumped the plane full of air until the difference between the interior of the plane and the air at sea level was the same as it would be if the plane was flying at 35,000 feet.

Now the cool part — inside the plane, they had parked their crash-test dummy, Buster, in a window seat. In the aisle, they rigged up a Glock 9mm to a firing mechanism and pointed it at the hull of the plane. Then, with the plane fully pressurized, they fired the gun remotely.

What happened? Nothing. Sure, the air rushed out, but even styrofoam peanuts they had placed in the aisle didn’t move, much less Buster. They did the test a second time, this time firing through the window right next to Buster. Same result — nothing.

Not satisfied (I love it when they’re not satisfied…), they rigged explosive cord around the window to simulate the window blowing out due to structural failure. They pressurized the plane again and blew the window.

The results were much more satisying — Buster got his arm yanked out the window. Crash test dummies aren’t designed to come apart, but if he were a human, I think he would have lost his arm. However, the rest of his body just wasn’t going through the window, no matter what the myth said.

Still not satisifed, Adam and Jamie put a “shaped charge” (whatever that is) against the hull next to Buster’s knee. Plane pressurized once again, they blew the charge.

Now, I don’t know how much damage was from the charge and how much was from the air rushing out, but the entire roof came off the plane. Buster, believe it or not, was still belted in his chair, but there was a 20-foot section of the roof missing. That plane was toast, and it looked eerily similar to Aloha Airlines flight 243 that lost its roof in mid-flight back in 1988.

So, myth busted. However, they didn’t address one thing: the drop in air pressure caused by the velocity of the air outside the plane. You see, the entire concept of flight is based on the fact that air pressure goes down as the speed of the air goes up.

So when a hole gets blown in the side of the plane, even after all the air rushes out and the pressue of the plane is equal to the ambient air pressure at that altitude, you now have 600 m.p.h. air rushing past the hole, which would have a much lower air pressure than the stationary air inside the plane. Does this make sense to anyone else?

That question aside, this segment proved, once and for all, that Mythbusters ranks right up there with Extreme Engineering and Modern Marvels as God’s gift to geeks.

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Comments

  1. Joe says:

    I'll have to catch this one. My favorite so far has been their repeated attempts to determine whether a frozen chicken, when used as a projectile, carries more penetrating force than a thawed chicken. They finally pulled it off a couple of weeks ago, and found that frozen chickens make better bullets.

  2. SL says:

    No. They found out that the energy trasfer time from a frozen or thawed chicken is the same. i.e. there is no difference in that speed.

  3. Yves says:

    The explosive decompression experiment is not complete. When the situation occurs in a jet flying at approximately 500 to 600mph, there is also a tremendous suction that occurs as the air moves along the fuselage. This will likely contribute to sucking out suff and people.

    I have opened the window on a Piper Cheroke (single engine) flying at 2000- 3000 feet and the suction is strong enough to empty a bottle with the opening located in the openend window (20 sq in).

  4. Anonymous says:

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     from Justin
    
  5. Jeff says:

    A shaped charge is an explosive that is shaped so that its explosvie force is directed in a specific direction. A Bazooka's charge from World War II (and most anti-tank weapons) uses a shaped charge so that the force is directed into the armor of the tank instead of going in all directions.

  6. Steve says:

    You don't need to take into account the movement of the airplane because the air pressure at 30,000 feet is only 4psi. Even if there was a Bernoulli effect that made the outside pressure seem like a perfect vacuum (going from "inside air pressure"->0 instead of "inside air pressure"->4), it would have made little difference in the explosion because it is only a fraction of the total psi difference.

    Besides, the effect is not an important factor in real life. If SL in his Piper really saw an effect from Bernoulli effect from the open window, he would have passed out because the air in his aircraft would have been sucked out. Instead, I am quite sure the air pressure in his aircraft was very close to the air pressure outside it.

    Many pressurized aircraft have been shot up (for example, B-29's over Japan and Korea, and B-52's over Vietnam) and have made it home. Sometimes the people inside don't even know it happened until after they landed.

  7. John says:

    I am a flight attendant and have alot of knowledge with aircraft decompressions. It is true that you would get different results if you had 500mph wind going over the fuselage. MANY people in the past sadly proved this when a flight attendant was sucked out of a 737 over the pacific and 9 passengers in their seats were sucked out also over the pacific on a different airline. Some of these people went into the engine. I am not sure if I would say this is a MYTHBUSTED.

  8. There was a demonstration of decompression in a Convair airliner in the 1960's. It was filled with water to simulate compressed air. A few Convairs had had their roof blow off during flight. Those planes, of course, crashed. After a lot of tests, the roof blew off. The diagnosis was metal fatigue in the skin of the airplane. I forget what precautions have been mandated since then. I suspect that the shaped charge was the 'last straw' , especially since it was the fourth rapid decompression of the cabin of a retired 737.

  9. Anonymous says:

    i was in an explisive decompression and yes the ai rushing past the hole is strong enough to tear a piece of the fuselage off and that is what happened- there was a bomb on board and it went off and the hole wasnt that big but then the air rushed into the cabin and tore a 10 foot section and sucked 2 passengers out

  10. scigeek says:

    I completly agree with steve. If you have a 500 mph rushing past the plane it would change the results darasticly. The pressure of layer of wind rushing by the plane/hole would be less than that of the air pressure of an object sitting still, there for the pressure and according to Bernoulli the rate of decompression would decrese.

  11. scigeek says:

    sry (typo) there for the pressure would be less and according to bernoulli the rate of decompression would increse.

  12. Deane says:

    If you have a 500 mph rushing past the plane it would change the results [drastically].

    I mentioned this in the original post, but everyone seems to have missed it. I said:

    [...] they didn’t address one thing: the drop in air pressure caused by the velocity of the air outside the plane. You see, the entire concept of flight is based on the fact that air pressure goes down as the speed of the air goes up.

    So when a hole gets blown in the side of the plane, even after all the air rushes out and the pressue of the plane is equal to the ambient air pressure at that altitude, you now have 600 m.p.h. air rushing past the hole, which would have a much lower air pressure than the stationary air inside the plane. Does this make sense to anyone else?

  13. Mark says:

    I've been thinking about this question for some time and still can't male up my mind.

    There seem to be real stories about holes in planes that give conflicting evidence: some say people have been sucked through holes; some say it is harldy noticable.

    I wonder whether military aircraft have a different set up - they may have less pressure inside than commercial aircraft. They don't have to be as comfortable as commercial aircraft and they must be prepared get bullet holes from time to time.

  14. Steven says:

    In response to John's point about the 737 that lost alot of it's upper fuselage over the Pacific, that was cause by micro fractures in the skin of the airplane. Which allowed it to open up with a zipper effect. It was NOT a result of a small hole. You also have to take into account True Airspeed and Indicated Airspeed. By this I mean that when your higher up in the air, there is less air. So you can move faster with less drag. An airliner moving at 500 knots is actually true airspeed. The indicated airspeed will vary but will be around 300 knots maybe less, depending on altitude. Indicated airspeed is the measure of actual air moving over the airframe. Speed over the hole, imho, will have a negligible effect in and of itself. Think of the space shuttle, it is in orbit flying at Mach 25, but has zero indicated airspeed.

  15. gggonzalez says:

    People, we are talking about a BULLET hole, not something from an explosion. The person up there reference a hole from an explosive that "wasnt that big ", but I'll bet it was much, much larger, surface area wise, than a bullet hole. We are talking a hole with an area smaller than 1/2 square inch..

  16. Mike Teague says:

    there are already holes in every airliner in the sky. They aren't "air-tight". I guarantee there are tons of leaks in every door. Airliners are designed to still provide decent cabin pressure with SEVERAL windows missing.

    Pressurization works kinda like this on a modern airliner (until they start using the bleedless technology enmasse)... Air is compressed in the compressor stages (front end) of the engines as we all know.. A portion of that now high pressure air (the rest goes into the combustion chamber, gets mixed with burning fuel, heats up, expands, drives the turbine section of the engine, spits out the nozzle, providing thrust, etc.) is "bled" thru valves and tubes (this is called "bleed air") called "bleeds" into the cabin (thru heaters/air conditioning packs). you can use it for many purposes, pressurization, starting engines, etc. Any excess pressure from the cabin is let out thru an "outflow valve" in the back of the cabin. A big adjustable hole. The outflow valve operates automatically. As the engine RPM changes, altitude changes, holes get punched in the skin of the cabin, windows get blown out, etc. Only when you are not getting as much bleed air as is being blown out will you get decompression.

    Think of it more like blowing up a balloon with an automatically adjusting hole in it that wont let you blow it up past a certain point.. Air in minus air out = cabin pressure.

  17. Bill says:

    Ok take a baloon fill it up with hot air (easier if you are a politician). Put a piece of tape on the baloon. Push a pin through the tape and baloon. you will see that the air comes out but does not tear the baloon. Planes are not made of rubber and will not tear like rubber. A bullet hole in aluminum will not cause it to tear apart and rip people apart.

  18. Anders says:

    A small hole (like a bullet hole) will cause decompression but no explosion (se balloon example above).

    The air passing over such a hole will cause some extra underpressure but the amount limited.

    Every single case where people have been sucked out of an aircraft has happened after some form of drastic structural failure. Like the cargo door latches failing, entire cockpit window being removed or worse.

    // anders

  19. brainfart says:

    I recently saw this episode. OMFG! Apart from being surprised that they really showed in detail exactly where to place a bomb to effectively destroy an such a big plane with only 100g of high explosive (!!!) and how to improvise a shaped charge with commercially widely available detcord and some paper I really liked it a lot. I wonder how that episode made it past the homeland security censors, considering that the Lockerbie jumbo was destroyed by several hundred grams (almost a pound) of high explosive.

    Now imagine someone managed to simultaneously detonate TWO or more such small bombs, e.g. by radio, one in the freight compartment (Lockerbie style) and another one in the passenger compartment, then that jet is guaranteed to crash. Richard Reid, the British shoe bomber, might have succeeded in bringing down a jetliner if he had seen that episode and his lighter had worked.

    If people really think hard this episode of Mythbusters should be a huge wakeup call. How hard is it to get 100g of well sealed and hidden high explosive on board? That's only two liquid ounces. How hard is it to hide a detonator? How difficult is it to get some sheet metal past the security at airports into the plane? Two small linear shaped charges assembled in flight and placed at the right position (as shown on Mythbusters), or a slightly modified maglite with some hidden "goodies" (metal reflector with exposives packed behind it), or a shaped charge without metal and filled with water(!!!), or a flying plate charge, or a can of coke with a liquid explosive with its bottom producing the shaped charge effect... there are endless possibilities. Add some bad weather and a 737 including its passengers is toast. You just need to know where to place that charge. Which already was obvious to some of us (plus every damn engineer), butnow everyone can find out. Well done!!!

    And BTW, it wasn't a Boeing 737 they blew up. It was an old DC7 or DC9.

  20. Okay... If people needed Mythbusters to see how to blow up a plane, they REALLY need to pay more attention in physics class - not to mention most of the Internet should be banned, 'cause you can find easy recipies for explosives, blueprints for airplanes and more out there.

    My point is: If someone wants to kill you, they WILL SUCCEED - it's not hard to kill somebody, and it's not particularly hard to blow up a plane.

    All it takes is some determination. A shaped charge in the cargo department isn't going to work, btw, unless you have controll of the placement of the cargo (and if you do, then there wouldn't really be any problem placing charges at all...) and a shaped charge in the cabin is a little more troublesome to fix - unless you're about to go up in smoke with the rest of them - never been much fan of self-sacrifice, myself. But then again, you could probably manage to hide away a shaped charge in one of the toilets, or pack it into one of the meal-trays (I used to work at a caterer who made airplane meals - NO CHECKING WHATSOEVER of the meal-trays - they were put on the plane by us at the caterer, and we also did the cleaning and preps of the inside of the planes - wouldn't been hard to hide something).

    And for Mythbusters - I think perhaps the program wasn't entirely to-the-point on the decompression issue - I would much more like it if they took a plane up there in the sky and tested it :D

  21. godhalo9 says:

    it was a dc7

  22. james says:

    i KNOW its not a myth....... its happend before, a passenger plane at high atitude was flying along... when the cargo door at the bottom opened by ITSELF.... instantly ripping a large section out of the aircraft due to EXPLOSIVE DECOMPRESSION taking with it, a row of passengers, amazingly the pilots got oxygen down in time, then did a nose dive to get to a low atuidude where it was warmer and air was thicker and managed to land at the closest airport, saving over a hundred lives, there is a picture after the emergency landing here (copy and past link into address bar) :

    http://content.answers.com/main/content/wp/en/thumb/9/96/300px-Unitedairlinesdisasterhonolulu.jpg

    it was a falty door, a problem with the old 747's, an investigation was done, and i belive the problem is now fixed.

  23. brad says:

    i am doing a science experiment on this and i would like to thank you for this info.

  24. Orion says:

    A balloon pops when pricked because the skin has considerable stress energy stored up in it and no way to prevent this from all being reelaed at once. Modern airliners are designed with this in mind.

    The early Brittish airliner, it was discovered well after the fact, had large areas of high stress in the skin and concentrated at joints and rivets, expscially at an inspection port on the upper fuselage. Because the engines were underpowered the engineers designed the skin and truss system as weak as possible to minimize weight. After repeated pressurization cycles the skin near the inpsection port gave way and peeled back like a banana skin, in millisectons, creating a cyclonic force inside the plane that scuked nearby (weakly bolted) passenger seats out of the plane. Didn't matter if you were belted in or not; the force was great enough to rip your seat out iof its restraints.

    Modern airliners are designed with this in mind. Trusses are closer together, there are more rivets, and the rivet holes are annealed to reduce stress as much as possible. A small hole will not cascade into structural failre and windows are designed not to give way so fast that an internal cyclone forms. Thanks to reseach into these eacly tragedies airplanes are much safer.

  25. Daniel says:

    Did everybody forget that the world's first airliner, The Dehaviland Comment had a serious problem with explosive decompression? It had square windows, they would shatter, and the whole aircraft would explode.

    I think that this proves the mythbusters wrong. Who's to say that the DC9 they did the experiment on wasn't just built pretty good? They never perform any experiment nearly enough to prove anything except that they can vaguley produce a recreation of whatever myth they're trying to bust.

  26. paul says:

    There are a few things the mythbusters failed to take into consideration when busting the explosive decrompression myth. The first being they only pressurized the cabin the difference in psi between the outside airpressure at roughly 35,000ft and what an airplane would be normally pressurized at (again around roughly 8,000 ft).That ratio would make the inside airpressure four or five times greater than the outside air pressue. on the ground i think the ratio would only be about two to one. Secondly I sincerely doubt that that aircraft was exactly %100 sealed of any other airleaks since they did a slap dash job of sealing it with plywood and caulk. who knows what other little leaks were in the rest of the aircraft. I used to deliver bulk goods in pneumatically discharged trucks and believe me, even little leaks made a BIG difference in unloading. Even though the pressure gauge may have read a optimum pressure for discharging, it took way longer if there were any leaks in the seals of hatchcovers, hoses, etc. I know this is a bad analogy but the difference is like pushing a boat off from a stationary structure such as a dock, or trying to push a boat through the water by kicking water with your feet. Secondly the volume of air inside the plane makes a big difference. The dc-9 they used was a relatively small jetliner. A 747 would have much more volume and therefore more air wanting to escape making it more explosive (again the same as in pneumatically discharged trailers). And as others have stated previously, just the movement of the aircraft through the air would contribute to the vacuum like effect (just as smoke will tend to be sucked out of a moving vehicle). Furthermore, just for the record, a National Airlines flight flying over New Mexico in 1972 or 73 had its right engine blow up, cracking a window and one passenger was sucked out the small window (google it, you'll find it) So it is no myth.

  27. Aron says:

    Mystery solved!

  28. Anders is a MORON says:

    Yes, all the terrorists are going to be effectively blowing up airplanes just cause of a Myth Busters episode. You could say the same about Wiki, they give airplane specs on fusilage depth and cabin width ect... Stupid Wiki encouraging terrorists to bomb planes. I bet since this episode aired there has been increased bombings on Airplanes...hahaha, anders seriously??? You put way to much thought into bombing airplanes, to say your definitely off center would be an understatement.

  29. ATP 451 says:

    Having spent 2 decades as a pilot and extensive research on air crash analysis... Explosive decompression is no joke. There has been no myth busted. Metal fatigue is relative. They never did a cold soak. -50 F reacts different to stress than surface/average temp metal in terms of playability and tensile strength. It would have had to been simulated to correct parameters. As for the straw. Yes, airliners leak and the pressure taken off of the engine for pressurization does keep it constantly filled like that of a bounce house at a carnival. But, here is where things change. a standard cruise could be looked at as 300 KIAS. But it is not. It is looked at as Mach .82(give or take) This is because of different pressure and airflow concepts that develop that close to mach 1. depending on where the bullet hole opens into the airflow, you will have different results. Do some homework and research NTSB crash results in reference to decompression. A cracked window has explosive decompressed. Indicated airspeed is not used in kts. at FL350. If you want to bust a myth. take a junker 727 up to FL350 and cold soak it, and fire around until it decompresses. Discovery has the reputation for sensationalistic nonsense. Some of us or spouses have been their Editors. Skunk Works has different conclusions on pressure capsules. Just because it is on TV does not make it correct...

  30. Disillusioned says:

    Mike Teague had a lot of the info correct, however an aircraft couldn't maintain cabin pressure if even a single window was missing. The uncontrolled leakage of an aircraft is about the size of your palm (a few square inches). Any more than this and the aircraft may not be able to maintain proper cabin pressure.

    Also, not pointed out by mythbusters is the laminar flow of air going past at 600mph would be severely disrupted by a bullet hole, causing turbulent flow behind the protruding skin tear, and possibly ripping the hole even bigger than normal. In any case, a 1" square hole could lead to cabin decompression at some non-trivial rate (on many older airplanes the cabin pressure outflow valve is nearly closed during flight meaning the cabin is barely able to maintain pressure).

  31. consrignt says:

    It was a DC-9 not a 737.

    I think you mean comet not convair

  32. noob says:

    I haven't seen this ep yet, but if I understand the part where you say they recreated the pressure difference, than the test was wrong. For example. the original difference between 1 bar and 0.5 bar is 0.5. The recreation would have 1.5 bar and 1 bar for the same 0.5 bar difference. But the original ratio is 1:0.5 =2 while the recreation is 1.5:1=1.5! This would mean the test off and on the weak side!

  33. Ben Cambone says:

    Wouldn't the air pressure at 35,000 be considerable less than at ground level where they performed their tests?

  34. says:

    […] angeht, haben sich die Mythbusters mal damit befasst und konnten den Effekt nicht reproduzieren: The Truth About Explosive Decompression Uncontrolled decompression - Wikipedia, the free encyclopedia Wahrscheinlicher ist, dass die hohe […]

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