The propane in your passenger cabin is on the downside of a 1 psi regulator (iirc), no? And the gas is outside in a tank made to hold it. There are other considerations as well; I read some time back that a Nat'l professional organization representing automotive A/C service techs was suing the manufacturers of hydrocarbon "refrigerants" because of all of their members (apparently a considerable number) that had been injured trying to service systems that had been filled with explosive gases unbeknownst to them. 

I think it's like the point made in the seat belt discussion; the decisions we make don't just affect us but can have wide-ranging unintended consequences for lots of other ppl. 

In regards to A/C in a Vanagon, probably the best solution would be to get an R134a compatible compressor and barrier hoses and proceed normally. The trade-off there is limited to money, basically.

Cya,
Robert

-----Original Message-----
From: Tom Hargrave [mailto:thargrav@hiwaay.net] 
Sent: Sunday, June 20, 2010 1:40 PM
To: 'Robert Fisher'; vanagon@GERRY.VANAGON.COM
Subject: RE: Freeze-12 and other A/C supplies

I look at it this way.

All of these products are far less explosive than the propane plumbed in to power your stove & heater. They are also far less explosive than the gasoline sloshing around in your gas tank!

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of Robert Fisher
Sent: Sunday, June 20, 2010 3:10 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Freeze-12 and other A/C supplies

--snip--
turns out that Freeze 12 seems not to have propane or other flammable component, but there are good reasons that regulatory agents rule against a product and that manufacturers recommend that things be done in a certain way.
--snip--

Freeze-12 doesn't have propane but according to the MSDS the R142b component is "extremely flammable" and breaks down into some pretty nasty gases due to "thermal decomposition". 
Freeze-12 is on the EPA's "acceptable subject to use" list, as well as some others that have less than 5% isobutane. Perhaps they feel that at level the explosive potential is low enough to be acceptable? I haven't seen where it was illegal in some individual states; does anybody have a link to that?

I guess you picks yer poisons...

Cya,
Robert