"Ignoramus14003"

| Even easier (and safer) would be to put down a hose from a compressor,
| and let it pump air for a day, while at the same time trying to smell
| the air coming out. I would think that if there is no perceptible
| smell, including from an air sample from the bottom, there should not
| be much risk of an explosion. But, better safe than sorry.

I would not want to bet my life on that option. Especially since the simple
act of cutting can release more fumes.