don't want fireworks before the 4th

Scored 2, 55 gallon drums at the local farmers co-op for 10 bucks. gonna start on a UDS.
Both these are closed top with no cap on the bung. they are stamped
" methylene... danger.. explosive " evidently they used alcohol in the auto department as a degreaser.
these drums are empty, and I need to cut the tops off. Is there a chance of vapor still being in these drums? I'll be using a sawzall to cut the top off so it should be spark free.
I thought about going down to the carwash and filling them full of soapy water untill all the air is out.

any thoughts?.......... anyone who grills cant be afraid of fire....but a 55 gallon bomb,,,that scares me.

thanks. I have some firefighter friends and they say that anykind of vapor that is ingited can create a fireball 100 time bigger than the container. 100 X 55 is freakin scary....even a small propane bottle is a disaster if things go wrong.:mad2: