Sciencey fun/interesting side bar to this...it isn't dangerous to smoke around those propane canisters. If any were leaking badly enough they would stink...or they would have leaked all the way empty already.
THINK ABOUT IT...when you mount one in your BBQ, it is often less than a foot away from a large OPEN FLAME.
with all the credit card junk mail.....i take the application from one company and put it in the return envelope of another and visa versa.....and mail them off to each other.
or sometimes i'll stuff them with the junk coupons i get and mail it off.