As I understand it, propane itself is odorless. Gas companies add a marker gas to it, which serves two purposes. It acts as a warning in case of a leak, but it also gets stronger in smell when the gas gets low, and the ratio of marker gas to propane increases.
I have read that propane has approximately the same pound for pound explosive potential as C4, but don't know how accurate that comparison is.
With regard to safety of "empty" storage containers, I have had two friends over the years who had lost their fathers before they had reached their teens due to welding accidents. In each case, the father was going to make a clamshell barbecue by cutting a 55 gallon gas drum in half with a torch. Both men thought they had properly emptied the drums. Each was killed by the resulting explosion, one due to shrapnel through the skull.