When you watch this video of a tank car implosion…

… the immediate thought might be, “that would never happen in real life.” Yet is does, as you can see in this article:

Over/Under Pressure Relief Required for System Safety

Incident #1 is described in this way:

The general-purpose tank car in the photo below was being steam cleaned in preparation for maintenance. The job was still in progress at the end of the shift so the employee cleaning the car decided to block in the steam. The car had no vacuum relief so as it cooled, the steam condensed and the car imploded.

You can try it at home with an aluminum can and some steam with this simple demonstration:

Why does the can implode? When water turns to steam, it expands by a factor of about 1,600. When the steam cools, it turns back into water, reducing by a factor of 1,600. You can see that reduction and an explanation in this video: