I’ve seen it so many times in movies and TV series: someone opens a door or blows a hole in the hull of an airplane or movie, and everyone needs to hold on to furniture or wall braces to avoid getting sucked out by the strong air flow. Now in another thread there is a nice discussion about what happens in real life (decompression but no fatalities).
What I wonder is how long there will be a significant airflow. In movies you see people struggling for minutes, even if there is a big hole and a relatively small compartment (for instance an open freight door). I can understand that a small hole in a 747 can suck air for a long while, but what about an open door in a small jet?
RIKER: You were right. Somebody blew the hatch. They were all sucked out into space.
DATA: Correction, sir, that’s blown out.
Whatever the truth is, I do know the scene in Aliens went on too long. For all the time the bay door was open, the ship would have sucked itself inside out long before Ripley got the door closed.
I dunno - the Sulacco was pretty big. Around 1/4 mile long.
Of course, it probably wasn’t all open space, but that’s still a lot of air to evacuate. And, as a military ship, they probably had lots of pressurized air tanks to replace air lost to battle damage.
It should have had a fail safe, to prevent both doors being open at the same time. And it should have had a flight crew remain on board, even one person, while the grunts were on their bug hunt.
Ok, I’ll do a back-of-the-envelope calculation to try to get a rough estimate. Let’s say that the velocity of air leaving the plane is constant. (This is certainly wrong; it will slow down over time but this is a rough estimate.) I don’t know how to get a good estimate of what that velocity is, but let’s say it’s like a stiff breeze, say 30 mph. The OP specifies a “small jet”. The Lear Jet 45 has a cabin volume of 375 cubic feet (10.6 m3), so let’s use that. Say the door is 5 feet high and 3 feet wide. So the air traveling at 30 mph (13.4 m/s) through a 15 ft2 (1.4 m2) opening will evacuate about 18.7 m3 per second. So the entire cabin would be evacuated in a little over half a second.
The numbers are probably off a little, especially the air velocity, but there’s no way that the air would be rushing out for more than a few seconds.
The problem with any airplane situation is the air rushing past any opening in the fuselage. Blow out a door and the pressure is released in a matter of seconds, but there’s still 600 mph of wind turbulating™ around that opening, causing more fuss and bother than the initial decompression.
The correct way to calculate flow velocity and pressure drop inside the cabin is to use Bernoulli’s Principle for compressible flow. This equation has to be performed iteratively because it is a non-linear differential equation when you assume a limited volume of air. (Technically there is also the non-ideal gas behavior of air and the nozzle effects the fluid going through the opening but as long as the pressure drop is limited and the aperture is relatively large relative to the mass flow, these are negligible for a first order estimate.)
A rough calcluation of the flow rate of air at STP flowing out into a vacuum is about 128 ft/sec, or 87 mph. The velocity varies as a square to pressure over density, so roughly proportionately. The mass flow rate depends upon the area of the aperture, so the time it will take to evacuate a volume of air down to some pressure is essentially proportional to the ratio of area to volume, but for a small bizjet evacuating through a 150 square inch window it is probably on the order of a few seconds to go from 14.7 psi to 4.36 psi @ 30 kft is probably on the order of 2-3 seconds.
IIRC from the news, the fellow sitting near where the door plug popped off that Boeing, his shirt was ripped off and sucked out (tee shirt?) but because he had his seatbelt on, he was not. (How would that happen? I presume bent double around his lap belt so the wind would catch his untucked shirt and pull it over his head?) It was not reported that anyone further from hole had significant issues although I assume it was not pleasant. And, IIRC, they were only at about 18,000ft, 1/2 atmosphere pressure. Normally a jet would cruise at 33,000 to 41,000? That would be about 1/4 pressure…
Great replies, thanks both of you. So a rough estimate is really in the order of seconds or less. I guess the calculation for a large jet could be done by looking at the proportional larger volume.
Anyway, it looks like the movies are really very much off.
That was my point, I don’t think that scene was realistic. Also, they had to swing him around, in that small jet, so he went out more picturesquely, feet first. Here is a clip of that scene.
Sure, an airliner will have a larger volume. Of course, if you lose a door size section, it will vent faster. There will also be buffeting affecting the people sitting adjacent to the opening even after the aircraft has vented (obviously doesn’t apply in vacuum).
Of course, this a film where a painted woman dies because a small patch of her skin at the base of the spine isn’t allowed to breathe, the villain smuggled thousands of pounds of gold by working it into fittings onto the Rolls Royce that he somehow air freights without anyone noticing, and Bond walks around a hotel wearing a terrycloth onsie with no one giving him odd looks. So…maybe not exactly the epitome of realism.
From the preliminary report on the accident where the door ripped off (link to random news page that has the pdf, I don’t like the NTSB page on mobile and I’m lazy)
17:12:33 PST: The recorded cabin pressure dropped from 14.09 to 11.64 pounds
per square inch (psi) when the airplane was at an altitude of about 14,830 ft and
speed of 271 knots (kts). The “Cabin Altitude Greater than (>) 10k ft Warning”
activated. Differential pressure was at 5.7 psi and rapidly decreased to 0 psi over
the next few seconds.
17:12:34 PST: The Master Caution activated. The cabin pressure dropped to 9.08
psi at approximately 14,850 ft and 271 kts.
17:17:00 PST: The airplane descended below 10,000 ft.
17:18:05 PST: The airplane altitude was approximately 9,050 ft and the airspeed was 271 kts. The “Cabin Altitude Greater than (>) 10k ft Warning” deactivated. The cabin pressure was 10.48 psi.
doesn’t - once the pressure delta between out and in gets close to zero - also the carburettor effect come into play?
the fast airstream around the fuselage creating a low pressure zone, sucking “whatever” (mostly air, but also the odd paying customer) through the hole in the fuselage for a prolonged time, just like the airflow into an ICE sucks gas through the the carb’s jet out of the tank.
I reckon this effect might be self-limiting, as there is no constant flow through the fuselage , but IMHO, there should be lower pressure in the cabine, compared to the ambient outside - any thoughts on that?
But without an equivalent feed in (i.e. into the carburetor from the fuel tank) the pressure quickly just equalizes at slightly less than ambient pressure.
Fleming freely admitted he made the 'skin breathes" thing up to add some air (sorry) of mystery to the book. No basis in fact at all - just “truthy”.
The thing I noted about the scene was that when Goldfinger was plugging the hole for about 2 seconds, Bond was still being held horizontal by the wind.
Fleming didn’t make it up – he stole it from Val Lewton’s 1946 movie Bedlam, in which Boris Karloff plays the master of an insane asylum that he runs as his personal fiefdom. He forces an inmate to recite a poem while coated in gold paint, and the poor guy dies of “skin suffocation”.
Val Lewton and Mark Robson appear to be responsible for the myth of skin suffocation. They based the screenplay on William Hogarth’s paintings “The Rake’s Progress”, and Hogarth certainly didn’t say anything about this.
Well, for some reason the entire plane goes out of control due to cabin depressurization (even though nobody passes out). Of course, this is also a film where a self-professed lover of gold (“All my life, I have been in love with its color, its brilliance, its divine heaviness. I welcome any enterprise that will increase my stock!”) agrees to help the Chinese government nuke the United States Bullion Depository and doesn’t even take an ingot as a keepsake, Bond is given a tricked-out supercar which is subsequently crashes into a wall for no reason after pointlessly exhausting its gadgets, the villain puts on a big show about his plan to a bunch of gangsters only to immediately gas them to death, and Pussy Galore is raped out of her lesbianism by Bond and saves him from his own ineptitude. So…from an objective standpoint, not a very rational film. Even the iconic Shirley Bassey theme song makes little sense if you stop and listen to the lyrics, although I suppose we should be happy that they aren’t as banal as “The Man With The Golden Gun”, which was the clear nadir of Bond themes prior to Die Another Day.
I had a point when I began this but it has since escaped like a British secret agent after a villainous monologue explaining his entire plan including details on how to stop it.
While we’re discussing sudden catastrophic cabin pressurization, I have a related question. When a passenger window or passenger door suddenly blows out and the passenger cabin rapidly depressurizes, what happens to the air in the cargo compartment? The floor of the passenger compartment is a very large, flat area, and I would imagine that it would not tolerate much pressure differential before buckling / bowing upward. Are there significant passages through which air can escape from the baggage compartment and into the passenger cabin, helping to keep the cabin / baggage compartment pressure differential from getting too high?
