I'm always looking forward to being proved wrong!
Ok, so what's the difference between flammable and explosive?
I tend to agree with you: if there is a leak, it should be detectable, either from the smell or the performance loss however, I think that the Germen township fire department (Indiana) would disagree with you:
Link
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Here a set of facts about propane.
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BTW, the additive is called
Mercaptan.
Here's
yet another link to a thread about some poor fellow who's having problems with a propane heater. (note: there is a difference between a gas line in a house, and a propane tank, but not much)
Right now, I'm living up to my avatar name: I don't use any refrigerant, except for the one in my refrigerator! I'll be doing that next year.