There was a bulk fuel storage tank just behind the ground school. Beside this mound there was a warning sign along the lines of "AVGAS-No Smoking Within 100 Yards".
One day, Flt Lt Pete Sharpe (a Yorkshire navigator of great renown) and who was the funniest guy I ever worked with, got a ground school course on top of the grass mound just after lunch erecting a parateepee whilst their survival fire was already blazing.
Now Pete had already established that AVGAS had not been stored there in living memory and that the tank was actually full of water.
Not many people knew that.
Flt Lt Frosty Winterbottom, who was Deputy I/C Groundschool, came back from lunch and saw this happy band with raging fire atop an apparent bulk storage tank full of AVGAS.
It really did not do his heart any good at all.