Yes. You need a NEMA 7, Class I, Div I (or II?) room, capable of ventilation between 100 and 200 surface feet exhaust and makeup rates, with a HC sniffer and alarm at 10% LEL.
The intake must be at floor level, and the make up at ceiling height, located so as to fully sweep the room.
The "or II" comment is because different fire marshals interpret the rules differently. Div I says the atmosphere is always explosive, and Div II says it normally isn't, but has the potential. Clearly a well made closed loop system is Div II, but things can go wrong, go wrong, go wrong.............................., and damage potential is high.
There is also the issue of operator comfort, and HVAC costs. 100 to 200 surface feet is uncomfortable to the operators at low temperatures and the operating costs to temper the air, prohibitive. You can dress them for warmth, but if your makeup air is 107F, which was the 100 year Oregon high when I retired, you also have to find a way to cool them down.
I advocate building a Class I, Div I room, but running the exhaust rates at lower rates, to simply draw any leaking LPG by the HC detector, on the way out, and when it alarms, spooling the exhaust rates to 100 to 200 surface, which happens to be the same exhaust rates recommended for spray booths, by the American Conference of Governmental Industrial Hygienist, in Industrial Ventilation, A Manual of Recommended Practice.
Attached is an example that meets those requirements. While it also shows fire dampers and sprinklers, they haven't been required thus far in NV or WA. An OR installation is pending, with certified equipment, awaiting permitting and certification of the facilities:
