Most likely (IMO) is mates mucking around, iv'e seen it before and it makes me angry. We all moan about H&S but when you see the stupidity of some people, it makes my blood boil.
I'm (or was until i find another job) a maintenance engineer and have a healthy respect for dangerous equipment. But give a 'helper' such a piece of equipment and common sense goes out the window for them. Air lines being blown at people, a quick blast from a pressure washer to wet a passer by...they'll both do extreme damage if you're too close. Bollock them....and as soon as you're back's turned
.FFS they're at it again. Brainless, that's all it is.