Love it! I expected it to sag progressively. Obviously the cylindrical cap-end structure is strong until the internal pressure gets low enough that some minor asymmetry puts a crease in it.

I had this happen in a company automobile. Another user lost the (vented) filler cap and replaced it with an unvented one. The fuel tank got sucked almost flat by the fuel pump. The final capacity was about a gallon, and I drove it 600 miles stopping at every service point to "fill it up!".

Your basic value is air pressure at 15 psi (pounds per square inch). The tank in the video seems to have gone to about a third of its former size, so I would guess it had two-thirds of the contents removed before it collapsed, so I would work on ten psi at the moment of collapse.

The car might have an upper surface area of 17 x 3 metres - around 50 square metres, which is around 77,000 square inches, so 770.000 lbs, or about 340 tonnes. It would have carried about 90 tonnes of hydrocarbon, (in a cradle with hydrostatic pressure outwards as designed). So the suction force on it is about the same as stacking another 4 full cars on top of it. It should be marked "Do not stack more than 3 high" like you see on electrical goods packaging.

You might better ask "What kind of idiot engineer designs a car like this without automatic safety venting, or interlocks on the pipework and valves?".

DON'T KNOW

This is an experiment obviously. The speed of the implosion

shows that there was no liquid in the tank.

If You drain a liquid from such a tank, and the tank was

absolutely full, then full vacuum will build up with the very first gallon

sucked out, and the implosion wouls start immediately.

(but proceed slowly, with the speed of the liquid drained out)

There is a voice  over a loudspeaker just after the crash:

"Siebenhundertundsechzig! Gewonnen hat Dr. Ing... "

(seven hundred and sixty! The winner is Dr. Ing...."

I think that 760 is the vakuum (millibars) and that

there were bets on the pressure of implosion.

Georg

 BTW,

tank cars on street are typically built to withstand a

pressure of about .3 bars (from inside!).

Even the slightest vacuum (some 20 to 30 mBars)

will produce an implosion.

The tank car in the video obviously is much

stronger, I am not aware of regulations for tank cars

on railroad.

In general: a tank has to be built for a pressure

of 3 bars, then it will withstand  full vacuum.

(rule of thumb)