Beware!

So I'm sitting outside while Dustin's working on a machine of some sort that's about a foot in front of me, enjoying actually getting to talk with him.  (Yay!)  In the middle of a sentence, he's cranking (don't know if that's the proper term or not...) something and then a hissing sound starts and he flinches while repeating very quickly, "Please don't explode.  Please don't explode.  Please don't explode.  Please don't explode."