Actually, both propane and butane (or isobutane) are heavier than air and can pool and can be very hazardous. You'll see this in news reports sometimes: propane leaks from a stove overnight and then someone stikes a match in the morning, basically the house is removed from the face of the earth at that juncture. I'm going to go ahead and call that hazardous. Now, the amounts in portable stoves are much smaller, but still I would NOT leave a stove attached to a canister in an enclosed space like a car's trunk. If you left the valve slightly open... Well, that could be, um, bad.

Good tip. A shot of alcohol (methyl, ethyl, or isopropyl) also helps. If you havn't got any form of alcohol along, try this: put your ESBIT tab on the edge of your stove, overhanging a bit. Get your match underneath the ESBIT. When it lights push it into place with your knife. Alternatively, torch type lighters work really well (some time labeled "windproof"). Lastly, you can always shave some bits off the ESBIT with your knife, and the bits will typically light more easily than a whole tab. There are a couple of tricks to working with ESBIT, but it's really a nice fuel after you've got the hang of it. Perfect for office BOB's, car emergency kits, caches, etc. It does have a low velocity flame, so it's VERY susceptible to wind, so inclusion of a windsreen is really important.

HJ