I'm at an industrial job site and don't have my 54, 58 or 59 with me...(Safe at home..lol)...I'm installing a propane vaporizer and I know that 5 psig is max pressure for propane to enter a building unless there are "special" conditions (welded pipe, etc...) that will allow me to go up to a max 20 psig. I've got an engineer who insists I can go higher...I would like to quote him the exact code (NFPA ? , section ? and page ?) that references pressure into buildings and put an end to this minor dispute....I think he has a line loss issue and that may have to be addressed as well...This is a good place to start...Any help would be MOST appreciated 
....Lee
....Lee