Standards for safe propane filling depend on the container being filled, of which there are two types common for RVs in the USA: DOT cylinders and ASME tanks for motorhomes. (Canada has its own standards.)
- ASME tanks on motorhomes are horizontal and fixed-mount.
- DOT cylinders are portable and typically (but not always) upright.
Standards for propane filling (and storage, handling, transportation, installation and use) are covered by NFPA 58:
NFPA 58: Liquefied Petroleum Gas CodeAccording to NFPA 58, DOT cylinders may be safely filled either by weight or by volume. By their very nature not lending themselves to filling by weight, ASME tanks are filled by volume. (Note that while NPFA 58 mandates OPD valves, it does not permit relying on them for fillers. Ask me why if you are interested in rationale.)
- Filling by weight involves weighing on a scale.
- Filling by volume involves use of the "spew" valve. (It never involves simply filling by gallon.)
The various states stick with some version of the NFPA standards, though very often with local modifications. For instance, because the NFPA addresses considerations of safety, but ignores environmental concerns, some states mandate various means of making sure that no propane is released into the air. Similarly, some states mandate filling only by weight, not by volume. All in all, you're looking at 50 different sets of rules for propane filling in the US, though, again, all relate in one way or another to the standards from the NFPA.
I should add that at least one state that I know of -- there may be more -- does not involve itself at all with propane safety standards, relying instead on private industry to specify standards of safety.
๐Lynn
