Mythbusters Explosive Decompression Experiment

The myth that Mythbusters was interested in was whether a single shot from a
handgun can cause an explosive decompression. The answer is no.

Deliberately firing three rounds into the shatter-proof plastic of an
airliner window probably would not cause an explosive decompression, either.
It would just make three holes in the window. Eventually you could probably
put enough holes in the window to cause it to break, but that might take so
long that it still would not cause an explosive decompression.

Nevertheless, Mythbusters tried on the show to simulate the effect of an
entire window blowing out using high explosives. While the air rapidly left
the fuselage, there was no "siphon" effect that would carry people or
objects of any size out of the fuselage.

An explosive decompression is almost instantaneous. There can be no "siphon"
effect. If the air is just running out of the airplane, there is a "siphon"
effect, but no explosive decompression.

Anyone who has been in an altitude chamber knows that when you create an
explosive decompression the occupants just sit there. They don't even feel a
breeze. There is a brief moment of fog as water vapor suddenly condenses out
of the air. During a slow decompression the occupants do not feel a breeze,
either, unless they are sitting right next to the valve.

A good vacuum cleaner should be able to generate 8 lbs psi if you block the
hose opening. When you take your hand off the opening (and, you will note,
you *can* take your hand off the opening unless you are some kind of
weakling) the vacuum cleaner does not cartoon-like suck up everything in the
room. Things more than a few inches away from the nozzle do not feel the
effect of the vacuum cleaner. Really, when you make a hole in the fuselage,
all you are doing is creating a little vacuum cleaner. Make the hole small
enough and it will whistle.

I think the people who worry about getting sucked out of an airplane by
decompression are the same sort of people who had childhood fears about
being sucked down by the bathtub drain or getting sucked up by the vacuum
cleaner. Such fears are irrational, Hollywood plays up to them, but they are
there nonetheless.

While I would agree that three shots would probably result in three holes,
you cannot discount the possibility of three random shots causing enough
damage to the window to result in total failure. Consider the demolition of
buildings, a small amount of explosive is placed at some structurally
significant points and down it comes!

As far as the siphon effect goes, it definitely exists, even though I may be
using incorrect terminology. Try this experiment: Drive down the road in
your car at highway speed, with all of the windows closed except the
driver's. Then take an ordinary tissue and release it about a foot away from
the window. Voila, it will be "sucked" out of the window. Obviously a tissue
is not a human being, but the effect of both decompression and this "siphon"
effect could combine to create enough force to pop a human out.

And on a lighter note...I have seen several vacuum cleaners that would suck
up a human. They're typically in places like plywood factories and such.


"C J Campbell" wrote in message
...
The myth that Mythbusters was interested in was whether a single shot from
a
handgun can cause an explosive decompression. The answer is no.

Deliberately firing three rounds into the shatter-proof plastic of an
airliner window probably would not cause an explosive decompression,
either.
It would just make three holes in the window. Eventually you could
probably
put enough holes in the window to cause it to break, but that might take
so
long that it still would not cause an explosive decompression.

Nevertheless, Mythbusters tried on the show to simulate the effect of an
entire window blowing out using high explosives. While the air rapidly
left
the fuselage, there was no "siphon" effect that would carry people or
objects of any size out of the fuselage.

An explosive decompression is almost instantaneous. There can be no
"siphon"
effect. If the air is just running out of the airplane, there is a
"siphon"
effect, but no explosive decompression.

Anyone who has been in an altitude chamber knows that when you create an
explosive decompression the occupants just sit there. They don't even feel
a
breeze. There is a brief moment of fog as water vapor suddenly condenses
out
of the air. During a slow decompression the occupants do not feel a
breeze,
either, unless they are sitting right next to the valve.

A good vacuum cleaner should be able to generate 8 lbs psi if you block
the
hose opening. When you take your hand off the opening (and, you will note,
you *can* take your hand off the opening unless you are some kind of
weakling) the vacuum cleaner does not cartoon-like suck up everything in
the
room. Things more than a few inches away from the nozzle do not feel the
effect of the vacuum cleaner. Really, when you make a hole in the
fuselage,
all you are doing is creating a little vacuum cleaner. Make the hole small
enough and it will whistle.

I think the people who worry about getting sucked out of an airplane by
decompression are the same sort of people who had childhood fears about
being sucked down by the bathtub drain or getting sucked up by the vacuum
cleaner. Such fears are irrational, Hollywood plays up to them, but they
are
there nonetheless.

On Tue, 13 Jan 2004 09:37:56 -0600, "Bill Denton"
wrote:

Given that it is fairly rare for someone to only fire a single shot under
these circumstances, shouldn't the effect of the typical three shots have
been considered? While a single shot to the window only created a single
hole, would it not be possible for three shots into that same window to
compromise the window structure resulting in the entire window failing and
coming out of the aircraft?

Their test sequence was this:

1. One bullet hole in the glass. No big deal.

2. One bullet hole through the side of the plane. No big deal.

3. They blew out the whole window with a small shaped charge.
Buster the dummy got sucked out the hole. I don't
know whether he had his seatbelt fastened. He
might have lost his arm and died if the plane had
been in flight. They glossed over the differences
between their static test and a real-life situation.

4. They blew a hole in the side of the fuselage with a shaped
charge. I forget the power of the load. The resulting
explosion created a hole in the fuselage reminiscent
of the fuselage that failed due to metal fatigue on
a trans-Pacific flight. They showed pictures of
the airliner after the incident. A stewardess lost
her life, but the passengers and the plane survived.

I'm not an engineer so please forgive me if this next is in the "duuuhh"
category. Assuming a breach the size of a window in an aircraft in flight,
would not some type of "siphon" (or whatever) effect occur from the movement
of air across the fuselage, which would further remove air/people/etc from
inside the fuselage?

They speculated only the passenger next to the window would be
affected. Once decompression is over, the flow of air would be
a great deal less, I imagine.

Marty
not an engineer, either

On Tue, 13 Jan 2004 10:22:03 -0600, "Bill Denton"
wrote:

As far as the siphon effect goes, it definitely exists, even though I may be
using incorrect terminology. ...

The first two blowouts of the plywood shield over the
cockpit windows demonstrated this pretty effectively.
In the first case, a plastic bag got sucked through
a relatively small opening. In the second, a whole
seat got blown out the window and was found
about 175 yards away from the plane. This was
at about 6 pounds per square inch of pressure.
They seemed pretty impressed.

I don't know whether the seat was bolted down
at the time.

Marty

"Martin X. Moleski, SJ" wrote in message
...
| On Tue, 13 Jan 2004 10:22:03 -0600, "Bill Denton"
| wrote:
|
| As far as the siphon effect goes, it definitely exists, even though I may
be
| using incorrect terminology. ...
|
| The first two blowouts of the plywood shield over the
| cockpit windows demonstrated this pretty effectively.
| In the first case, a plastic bag got sucked through
| a relatively small opening. In the second, a whole
| seat got blown out the window and was found
| about 175 yards away from the plane. This was
| at about 6 pounds per square inch of pressure.
| They seemed pretty impressed.
|
| I don't know whether the seat was bolted down
| at the time.

It was just the seat cushion, even though they said it was the seat. The
frame of the seat is bolted down, but cushions are often not attached to
anything at all. They also tend to be light weight.

"Martin X. Moleski, SJ" wrote in message
news | On Tue, 13 Jan 2004 09:37:56 -0600, "Bill Denton"
| wrote:
|
| Given that it is fairly rare for someone to only fire a single shot under
| these circumstances, shouldn't the effect of the typical three shots have
| been considered? While a single shot to the window only created a single
| hole, would it not be possible for three shots into that same window to
| compromise the window structure resulting in the entire window failing
and
| coming out of the aircraft?
|
| Their test sequence was this:
|
| 1. One bullet hole in the glass. No big deal.
|
| 2. One bullet hole through the side of the plane. No big deal.
|
| 3. They blew out the whole window with a small shaped charge.
| Buster the dummy got sucked out the hole.

No he was not. Buster the dummy remained in his seat for all the tests,
although he was crushed by the seat in front of him on the fourth test. The
tray table also hit him in the throat. His arm was pulled out the window on
the third test, but it remained attached to the rest of him. But Buster was
never sucked out any of the holes. The shaped charge was used for the fourth
test. The window was blown out using explosive putty around the edges. The
shaped charge was used to destroy the whole wall. Given that Buster
represented a terrorist using a shaped charge on the fourth test, he
probably richly deserved getting blown up, crushed and burned. :-)

Buster wore his seat belt for all tests.

And sometimes they even float.


"C J Campbell" wrote in
:


"Martin X. Moleski, SJ" wrote in message
...
| On Tue, 13 Jan 2004 10:22:03 -0600, "Bill Denton"
| wrote:
|
| As far as the siphon effect goes, it definitely exists, even though I
| may be using incorrect terminology. ...
|
| The first two blowouts of the plywood shield over the
| cockpit windows demonstrated this pretty effectively.
| In the first case, a plastic bag got sucked through
| a relatively small opening. In the second, a whole
| seat got blown out the window and was found
| about 175 yards away from the plane. This was
| at about 6 pounds per square inch of pressure.
| They seemed pretty impressed.
|
| I don't know whether the seat was bolted down at the time.

It was just the seat cushion, even though they said it was the seat.
The frame of the seat is bolted down, but cushions are often not
attached to anything at all. They also tend to be light weight.

OK...that point was not clear in your original post. My answer was based on
the fact that fuselage-mounted static ports (as opposed to under-the-wing
a'la Piper) are located on the sides of the fuselage precisely because there
is neither positive nor negative pressure acting on the skin of the airplane
in flight.

The shaped charge demonstration hardly belongs in this discussion, because
the odds are that it would kill the airplane...Mythbuster's original
argument was whether or not a bullet would cause that kind of destruction,
as visualized by a lot of folks who do not understand pressurization.

Bob Gardner

"Mark" wrote in message
om...
"Bob Gardner" wrote in message
news:qmHMb.35613$nt4.69560@attbi_s51...
The speed of the airplane at altitude has nothing to do with it. The
pressure differential between the cabin and the great outdoors is the
only
factor...airspeed does not exert any pressure on the sides of the
fuselage.

Bob Gardner

My point was that the explosion *could* cause other damage which
*could* bring the airliner down (the Souix City Iowa crash of a United
DC-10 for example). In the case of the MB episode, they wanted to see
IF a decompression could bring down an airliner. Well, the last
explosion was large enough to cause a very rapid decompression,
however with the plane sitting on the ground that's ALL that occured.
If the aircraft was in flight you might have ruptured hydraulic lines,
fuel lines, airframe damage and the large hole in the fuselage that is
causing a lot of drag. All these factors would increase the origional
damage in a more serious emergancy.

So, if the MB'ers were ONLY trying to prove they could cause a rapid
decompression then the speed of the airliner in flight is not a
factor. However if the goal was to see if a rapid decompression could
cause an airliner to crash, then you have a lot more factors to
consider than the initial incident.

I really like MB as a show however it's chewing gum for the mind. I
feel their attempts at trying to prove or disaprive a myth is far from
the final word. I'm sure everyone in the scientific community likes to
tune in each week and laugh at their methods.

Exactly my point...if there is neither positive nor negative pressure
measured at the location of the static port on the fuselage skin, then
motion through the air, in and of itself, plays no part in the bullet hole
scenario.

Bob Gardner

"C J Campbell" wrote in message
...

"Kyler Laird" wrote in message
...
| "Bob Gardner" writes:
|
| The speed of the airplane at altitude has nothing to do with it. The
| pressure differential between the cabin and the great outdoors is the
only
| factor...airspeed does not exert any pressure on the sides of the
fuselage.
|
| So...it doesn't matter where one places the static port?

I have seen static ports located just about everywhere on fuselages. It
probably does not matter much as long as it is on the side of the
fuselage.
If there really was a big pressure difference due to the slipstream on the
fuselage then most static ports would be located toward the aft end,
because
the biggest low pressure area would be towards the front, just like a
wing.
It appears that the biggest factor in locating the static port is
convenience of plumbing the static lines.

In article LP_Mb.45273$nt4.79391@attbi_s51,
Bob Gardner wrote:
the fact that fuselage-mounted static ports (as opposed to under-the-wing
a'la Piper) are located on the sides of the fuselage precisely because there
is neither positive nor negative pressure acting on the skin of the airplane
in flight.

Are you sure the instruments aren't just calibrated for the error?


--
Ben Jackson

http://www.ben.com/