I was :headscratch: for a few seconds.
Then I realized the near vacuum was there for the entire clip, and was presumably in that state for some time before the clip even began. Some small part of the tank got a dent or a crease, or a minor variance in the metal, a weld, a angled joint for a fitting, whatever... then the pucker spread exponentially fast as it broke the even circular integrity of the tank and the air pressure outside got leverage.
It's funny when you're at a RxR stop, and you're first or second in line of the cars and you can
actually read the sides of the cars and tanks of what's going by sometimes. Anhydrous Ammonia... Liquid molten sulfur... Liquid Carbon Dioxide... Chlorine....
whee!
It's one of those "Failure is not an option." kind of undertakings very few think of, and it's often going right through your neighborhood at 50-60-70mph at 3am. And with a few notable exceptions, they do a pretty good job of it.