L P G is a one -off burning process, the worst that can happen ( if you aren't completely stupid, is your steaks finish up raw or turned into charcoal ). With a REFRIGERANT, it a continual reuse system, The amount used in car A/C is only 400 -600 gms, so the chance of contaminants is quite low, However if you use large industrial quantities of any of the HC refrigerants, chance of contamination increases significantly. The freezing point of water (a common contaminent ) is 0c Therefore what happens at zero, -5, -20, etc, The TEV ices up and you get no flow therefore no cooling effect, and a ruined product. Thouands of dollars/pounds lost, What's your insurance cover like ? Alternatively look at Tamehere NZ 5th April 2008 500Kgs of Hychill -50 Exploded and killed a Senior Fire Officer and serious injury to seven others. So the moral of the story is :- Short time monetary gain can have SERIOUS consequences for more than just the engineer working on the plant, How do you think the engineer at Tamehere slept for the weeks following the fire and death of a fireman ?