Tom Brattain
10 HN mentions · mentioned in 6 months, 2014–2023
0:19 · 6.7M views · Sep 29, 2008
A brief demonstration of a railroad tank car imploding after a vacuum is pulled with its safety valves disabled.
HN people link it as a striking illustration of atmospheric pressure crushing vessels, in threads on vacuum airships, hyperloop and the Titan sub.
10 comments from Hacker News
At atmospheric pressure, a given volume of hydrogen weighs approximately 7% (there is some variation with temperature) of an equivalent volume of air. All that is needed to contain hydrogen at atmospheric pressure is a membrane it can't pass through. The inwards force exerted on the membrane by the atmosphere is perfectly balanced by the outwards force exerted by the hydrogen gas. The only structural material required is for the purpose of harnessing the lifting power of the enclosed gas, providing an aerodynamic shape, etc.. Conversely, a vessel containing a vacuum must be built to withstand the 101,325 N/m^2 net inward force exerted upon it by the atmosphere that is not balanced by the outward pressure of the contents of the vessel. Consider, for a moment, what you would need to build a 1 m^2 coffee table out of if 20 elephants were to be able to stand on top of it at once. For the sake of argument, let's say that we had a magical material that would let us build a replica of the Hindenburg that is of equal weight to the original, only with vacuum vessels replacing the hydrogen bags. The Hindenberg contained 200,000 m^3 of hydrogen lift gas, weighing 1,798 kg and displacing enough atmosphere to provide a total lift of 25,850 kg, 10,000 kg of which were considered it's cargo capacity beyond the passengers it carried. This new version of the Hindenberg, despite being built with materials and techniques that are probably well beyond our current level of technology, would carry
Here is your reality: this video You're not entirely wrong however. There is effectively one atmosphere differential at sea level, but framing the difference that way is at worst intellectual dishonest, or at best a rather naive understanding. In actual reality there is a very long tube, and all the surface area is under pressure. In metric is 10,000 kg per square meter, multiplied by all the square meters down the length of tube. Of course this simplified understanding ignores the weight of the transport capsule inside, which causes a momentary higher differential. And, the hyperloop won't work at sea level, as others have pointed out, it would have to be underground to avoid thermal expansion issues... meaning higher pressure.
Airplanes aren't pressurized to sea level... so as they went up, the air inside the tank vented outward into the airplane... and a pressure vessel can easily withstand that... but the problem is that on the way back down to land, the pressure inside the airplane went up far quicker than it could get back inside the tank, so the tank had a much lower pressure inside than that outside the tank. You've obviously never seen what happens to a pressure vessel when the pressure gradient goes the wrong way... Here's an idea of what can happen: this video Imagine being on a plane when a very large object inside of it does that. It could have caused the airplane to implode as well, or have catastrophic damage.
There's obvious differences between the Oceangate sub and this (1 atm difference, this is a thinner steel(?) railroad tanker not a sub), but I think it effectively demonstrates how violent and quick an implosion would be: this video Video contents: An experiment where the vacuum safety valves were removed from an oil tanker railroad car, and a vacuum was placed inside the car, resulting in it crumpling in an implosion. There is no gore or other specific disturbing content
The point is the extreme, rapid force involved. Imploding or exploding, nine atmospheres is gonna suck. 400 atmospheres is... like standing under a nuclear bomb. The good news is it doesn't hurt, at all. Someone else on the thread posted a video of a one atmosphere implosion ( this video ). 400x the pressure here.