Unintended condensation caused the car full of vapors to collapse upon itself
(implode):

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."
Keep in mind that steam has around 1600 times the volume of condensed water -
also see the video!