Well duh! Of course if you compress gas into a cylinder and then put it in a hot place, (garage, under tank, in the sun in the back of the truck), the temp will raise even more and burst the expansion cap. That plug is there to save you life! He should be thankful it popped and didn't burst the tank. That would have been a mess to clean up if the tank blew next to him....... Anyway these bottles are safest placed outside of the stand in good air circulation in a cool room. I am surprise the burst cap was so low.. Scuba tanks are filled to 3000psi and the caps blow at or around 4000. Imagine a cap holding on one of those tanks and it blowing on your back...LOL..... The sharks would really love that! Not to mention your buddy gets a front row seat at the feeding frenzy.... Of course after you jump into the cooler water that is about a billion to one chance of that ever happening considering they are hydro tested every five years....
Good info to know though.. Thanks for the article, I think I'd have a little more than dirt to clean up. Laundry would probably be first.