Just because most people have probably not seen a glass of liquid propane before at our atmospheric pressure. Just thought it was cool. Not my picture, but someone took this near here during the cold snap we are just finishing up. Goes liquid at -44
Likely not much if anything. LP like gasoline and so on needs to vaporize to catch fire. That is a still photo so impossible to tell if it's "boiling" in the glass. If it actually is, then it would definitely catch fire.