Explosive Decompression

[missourigunner]

a quick question, will a firearm, fired inside an aircraft in flight when the Bullet strikes the fusselage or window cause explosive decompression? it is hard for me to believe, that something as small as a .22 caliber could cause this type of damage.

[ATW525]

Only in Hollywood.

[blackmind]

Nope.

As I've heard it discussed, the apertures that are part of the plane's system for pressurizing the cabin are far larger than the hole a bullet would make. Larger, that means, than the window pane that a bullet might pass through.

Let's think about it. Would they have designed a plane with windows so large that the plane would explosively decompress if one of the windows simply failed on its own, or got punched out by some object inside the plane?

Plus, the plane is not pressurized like a CO2 cartridge. It's not packed up like crazy with pressure. When an airliner is up there flying at like 32,000 feet, it's pressurized, I am told, to about 8,000 feet of "atmosphere" inside. They don't keep it filled with "sea level" density air. Even if the plane were to have sea level density air in it, and it flew somehow to the top of earth's atmosphere to where space begins, it would be pressurized at a ratio of ONE atmosphere inside to ZERO atmosphere outside -- a difference of the pressure of only one atmosphere, or 14.7 pounds per square inch.

I realize that things are complicated by the speed at which the outside air is passing over any hole that might get made, lowering pressure along the skin of the plane. Not sure, though, how much that actually increases the pressure differential.

I just know that I have been informed that the "explosive decompression" you see in the movies is just that -- "in the movies."

Not the first, or the last, time that Hollywood will do violence to actual understanding of the real world. (Remember the "armor piercing handgun bullets" of Lethal Weapon III, which could penetrate the scoop of a front-end-loader? :barf: )

-blackmind

[sendec]

Nope, as proven by those paragons of the quasi-scientific method, the Mythbusters.

[progunner1957]

"Explosive decompression" is a load of crap that Hollywood has sold to the public. Before becoming disabled, I was an FAA licensed Airframe and Powerplant Mechanic - an "aircraft mechanic" for U.S. Air. I worked on Embraer 135, 140 and 145 pressurized cabin passenger jets.

These jets have two outflow valves that open and close to maintain cabin pressure at +7 PSI (+7 if memory serves - it's been awhile) over ambient (outside) pressure. The "holes" in the aft pressure bulkhead where these valves are located are 10 inches in diameter; there are no people, luggage or "tuna carts" (food service carts), flight attendants or passengers being sucked out into the sweet by-and-by when they open.

One of my instructors in A&P school flew on Navy P3 Orion sub chaser aircraft for 22 years, and personally experienced six depressurizations as a result of "pressure hull failure" (AKA bullet holes courtesy of Soviet MIG fighter aircraft) and other causes.

No one was ever sucked out of the P3's when these events occurred. He said the only evidence of a hull failure was the appearance of fog in the cabin due to the oxygen molecules in the air exiting the small hole at a higher rate than the water molecules in the air could, thus leaving a cloud of condensation behind - similar to the fog military jets produce when they break the sound barrier.

The only place that "explosive decompression" happens is in the movies - thank goodness! The vast majority of "the Sheeple" do not know the facts about "ED," which I'm sure helps feed their fears of guns on board passenger planes.

[Redworm]

I was under the same misconception, not only due to hollywood but due to a few teachers that pretended to know what they were talking about.

Although one thing that's always stuck out in my head is this. Part of the reason for my misconception is that I have this innane fear of being sucked out of an airplane. I know it's a huge rarity but the fear comes from being a bit too young when I first watched the movie "Alive". Now in that case the people getting sucked out wasn't due to explosive decompression; instead it was because the tail section had broken off which weakened the structure nearest the hole (and thus the seats themselves simply didn't hold) and what I'm assuming is the vacuum effect caused by the plane continuing to fall through the air at a few hundred miles per hour.


Now from the book I know that people did in fact die from falling out of or being sucked out of the airplane as it was crashing. What I'm wondering is if this was only due to the weakness of the structure due to the tail being lost or if the vacuum effect actually had anything to do with it.

Any thoughts?

[gddyup]

Red, I'd venture that it's a little bit of both structural integrity being compromised and the fact that once you have a hole that big, you're gonna have 200-300 mph winds blowing on those passengers. Just a guess at the speed, but imagine even hitting those people in those seats with a sustained blast of 150 mph wind!

I'd think that those two factors would be enough to "suck" them out of the plane. I'm sure vacuum is involved to some degree since the pressure of the air forcing by the opening would be greater than the pressure inside the cabin, but I'd guess that there's more to do with the velocity of the wind and integrity more than anything in the case of that air crash.

[mete]

It was made famous by a James Bond movie. There was a sudden decompression of an airliner in Hawaii when a large section of the upper fuselage came off .IIRC they only lost 1 or two and that was to the wind not the decompression.

[Capt. Charlie]

When an airliner is up there flying at like 32,000 feet, it's pressurized, I am told, to about 8,000 feet of "atmosphere"

Blackmind hit it right on the money! I flew to Orlando last year and being bored, I keyed the altimeter on my watch just before takeoff. The pilot announced an altitude of 31,500 feet and my altimeter said 8,200 feet. Sure accounted for my ear pop .

[RWK]

The answer, as already reported, is NO; this is based on 35+ years (Navy and Lockheed Martin) in the airplane design (etc.) business. Key factors (simplified) include:
a) The aircraft’s Environmental Control, Systems (ECS), a combination of air conditioner and pressurizer, has a far greater capacity to add air/pressure than a small hole can permit to escape;
b) The fuselage/empennage is not COMPLETELY airtight and, therefore, the ECS is constantly adding air to the air vehicle;
c) While most commercial aircraft have substantial cursing altitudes (>33K, for example), they do not have to deal with the extreme low ambient pressures of “near space” (>60K);
d) The standard cabin pressure maintained is not 0/sea level, but normally >4K.

With this said, a BIG break in the airframe’s – especially the fuselage/empennage – pressure skin, especially at high altitude, could cause rapid depressurization, but nothing “explosive”.

[swmike]

The big concern seems to be in regard to air marshalls shooting at any hijacker, missing and puncturing the skin. I have been on DC-10s when door seals have failed. Biggest problem is the noise. Nobody gets sucked out and the pressurization equipment was able to keep sufficient pressure to prevent deployment of the masks. Doubt that a round from a 40 cal would do more.

[KLR]

Post 9/11 when federal agents were ordered/strongly encouraged to carry onboard (and the airlines dropped their objections) we had a pilot come talk to us. He basically said that ED is all Hollywood. He said holes in aircraft were okay (but to be avoided). He said that holes in pilots were to be avoided at all cost.

[USP45usp]

but but but, it has to be true, the brady center and the vpc say it's true so it just has to be

Wayne

[jetdriver]

As it has been said - no. "Rapid decompression" is probably a more accurate term, as explosive deals more with catastrophic structure/material failure that happens in less than 0.1 secs. Getting sucked out of the airplane, etc. is pure Hollywood, unless of course the hole is enormous, and occurs almost instantly, so that the aircrafts emergency pressurization cannot keep up.

The real threat here is not getting sucked out of a gaping hole in the fuselage, but becoming hypoxic, losing consiousness and eventually dying. Hypoxia can be rather insidious, provided the onboard failsafes and pilots do not catch the rise in cabin altitude (a la Payne Stewart type accident). In a rapid decompression scenario, at approx. 35k feet and above, a cloud will form instantly in the cockpit/cabin, from the rapid cooling/pressure change of the air. Something they never show in a movie. Also, chances are the air will be filled with debris, dirt in the carpets, pocket change, documents/papers, instrument approach plates/maps etc., fly about. At this altitude, the average pilot has less than 10 seconds to don their O2 mask before becoming unconscious. And if you are a passenger, forget it. Those little yellow cup style passenger masks are only rated to 25k feet, so even if your pilot is on the ball, gets his/her mask on and executes an emergency decent, odds are you're still going to take a nap.

Thats why depending on what regs your pilot/airline operate under, above 35k if one of the pilots leaves the flight deck, the other will don the mask, and one pilot will have the mask on at all times above Flight Level 410 (41,000ft). Just in case.

[CarlosDJackal]

The biggest problem with having to shoot inside an Airliner is not rapid decompression (as hollyweird would lead you to believe) but what the projectile might hit. While most sytems are redundant, a hit on any of the more important systems (engine, fuel line, Pilot, Co-pilot, etc) could result in a catastrophic faialure or outright crash. JM2CW.

[Redworm]

He said that holes in pilots were to be avoided at all cost.

lololol that's gold


As to a bullet hitting other systems, that seems to make sense. I can't imagine there's too many critical systems placed anywhere within or directly around the passenger compartment itself. It seems the only way a bullet is going to damage flight critical systems is if it goes into either the flight deck or the engine itself. Correct me if I'm wrong but the avionics computers would all be housed underneath the flight deck, all of the hydraulics have multiple redundancies, and jet fuel simply won't ignite because of a bullet or spark.

I think the majority of my worries of allowing passengers to carry (aside from my previous misconception about explosive decompression) comes from the fear of having a slew of untrained trigger happy folks in an enclosed space from which I have no hope of escape. Then again I worry about untrained people with guns no matter where I am; unless the research I've done over the past few weeks concerning my newfound interest in guns, a CCW doesn't mean the holder is actually safe with a gun anymore than a driver's license means the holder is safe behind the wheel of a car.

I'm sure we've all seen the spaced out soccer mom yapping into a cell phone with screaming demon spawn kids in the back of a big 3/4-ton Suburban...

[JohnKSa]

a hit on any of the more important systems (engine, fuel line, Pilot, Co-pilot, etc) could result in a catastrophic faialure or outright crash.

Unlikely. Planes are big, bullets are small. Systems are redundant.

And pilots are innovative. Someone landed a jet awhile back using only the engine throttles to control the jet after all of the hydraulic systems were simultaneously destroyed.

Pilots/co-pilots are certainly vulnerable, but they're reasonably well protected in a modern, reinforced cockpit. Anyway, presumably by the time shooting starts, the alternative to not shooting is having the plane hijacked and then having the military shoot down the entire plane--passengers and all--to prevent it from being used as a flying bomb.

[Wyo Cowboy]

I've posted on this subject before but I'll add my two and a half cents worth anyway (inflation you know).

Punching a .45 hole, or several will not cause the plane to depressurize. The pressurization system will more than keep up. As an example, a Boeing 747 can loose a passenger window and still maintain the normal cabin pressure (about 7.6 psi difference from the outside. eg 37,000 ft altitude = 8,200 ft cabin). Even the loss of one of the pressurization systems, called a PAC, will not cause a substantual loss of cabin pressure but may result in the need for the plane to descend to a lower cruise altitude (ie 25,000 ft) to maintain proper cabin pressure. Depends on the aircraft.

Total loss of cabin pressure at 37,000 ft will result in a "time of useful consiousness" of about 30 seconds. Pilots are trained repeatedly to don their O2 masks (positive pressure or demand type) one handed, within 5 seconds, and are checked on this at least once a year. The "dixie cup" masks are not positive pressure and are not designed to provide any long term O2 support at 35,000. They are there to provide supplemental O2 during the descent through 25,000 where the non-demand system will provide enough O2 for full cognative fuction. The pilots are, in the meantime, getting that airplane descending at 6,000 feet per minute or more. Because of this "time of useful consiousness" one pilot is required to don thier O2 mask anytime that the other pilot leaves the flightdeck when the plane is above 25,000.


As Jetdriver said, a rapid decompression is a rather dramatic event with the condensation cloud and all of the dust and dirt flying towards the opening. Again, training will offset alot of the confusion which this would cause. The slow loss is a worry if the warning systems all fail. Some smaller aircraft only have one system. Most airliners have several independant warnings, so a slow loss of pressure is usually noticed before the cabin exceeds much more than 10,000 ft. Some of the recent private/corperate aircraft accidents are due to a lack of proper training and/or not following proper procedure. Most pilots, airline/corperate/private, appproach their flying in a very professional manner. But it only take a few (helped along by Hollywood or the ignorant news media) to get the wrong ideas out there.

This is based on the Boeing 737-300 in which I have 12,000+ hours of command time.

[USP45usp]

^

This is based on the Boeing 737-300 in which I have 12,000+ hours of command time.

Well, I think this one was just put to bed .

Thanks Wyo Cowboy, good post.

Wayne

[Capt. Charlie]

This is based on the Boeing 737-300 in which I have 12,000+ hours of command time.

Umm... yup! I think experience has spoken!

How much time do you have on a horse though?

+1 on the good post, Wyo Cowboy.

[progunner1957]

but but but, it has to be true, the brady center and the vpc say it's true so it just has to be

ROFLAMO!!! Good one USP45!!

Yes, airliners are vulnerable to gunfire - 20mm gunfire from F-16's, not 9mm gunfire from Glocks; there is a wee bit of difference...

[Ozzieman]

You better hope your not setting next to it, other wise you will be the plug that stoped up the hole.
I flew in trubo porp aircraft in the 70's and there was a "HOLE" in the back that would open up to drag air from the inside of the aircraft wich had a searies of pipes that connected it to all the electronic equiptment (and we had a lot on board P3-C) The pressurization system was enough to provide enough air at 28,000 feet to have the 12 inch hole (controled by a valve) open over 50% to pull air out of the plane pulling the air though the equiptment to cool it.
So if you hear a one inch hole killed everyone in an airplane, I would suggest a different airline or a different pilot.

[Wyo Cowboy]

Progunner1957 "Yes, airliners are vulnerable to gunfire - 20mm gunfire from F-16's, not 9mm gunfire from Glocks; there is a wee bit of difference...'

Yeah... just a tad.

[Lawyer Daggit]

A friends son was recently in an executive jet and one of the windows 'blew in'. The plane underwent rapid near instantaneous decompression- the pilot took it into a dive to a level where everyone could breathe comfortably- flew back to the airport and they changed planes.

Explosive decompression was I think a figment of James Bond's writers imagination.

[Charlie Golf]

These jets have two outflow valves that open and close to maintain cabin pressure at +7 PSI (+7 if memory serves - it's been awhile)

Normal Max Pressure +7.8 psi (also why there's no need to freak when the wacko in 10A starts pulling on the Exit Row Door at 37,000.....)

Overpressure Relief at +8.1 psi
Negative Pressure Limit -0.3 psi

Don't ask me how I know that