Tanks and cylinders. Episode fifty of the Gas Service Animated series.

On natural gas the utility owns the supply. On propane, the supply sits in the yard — and the container, its valves, and its first regulator live under their own book: NFPA fifty-eight. Know the hardware and the rules that come with it.

Two container families. ASME stationary tanks — the one-twenty through thousand-gallon horizontal bottles permanently set at homes — built and stamped to the pressure-vessel code, in service for decades. And DOT cylinders — the portable twenty- through hundred-pounders — which carry a stamped date and must be requalified, typically after about twelve years, before refilling.

The number that rules every fill: eighty percent. Liquid propane expands hard as it warms, so a container is never filled full — the top twenty percent is vapor space, the safety margin that absorbs a hot afternoon. And filling is judged by the fixed liquid level gauge — the little bleeder that spits white when liquid reaches eighty — not by the float gauge, which is a fuel gauge, not a filling instrument.

Every container carries a pressure relief valve, aimed up and away, with its protective cap in place. It's the last line against fire and overfill — never plugged, never aimed at a building, never missing its cap. If a relief has ever discharged liquid or ices up, the container gets qualified service before it gets refilled.

Placement is a table, not a guess. NFPA fifty-eight sets separation distances by container size — a typical five-hundred-gallon tank sits at least ten feet from the building, from ignition sources, and from the property line, with bigger tanks pushed farther. When you find a tank against the siding under a dryer vent, that's not a style problem — that's a code call.

Cylinders have their own etiquette. Small DOT bottles carry overfill-prevention valves. They ride and store upright, valve up, plugged — and never, ever indoors or in a basement: a heavy vapor and a stairwell are a bad chemistry set. Exchange-cabinet rules exist for a reason; a cylinder in a kitchen is a stop-work moment.

At the container, the first regulator hangs under the dome with its vent pointed down — rain, ice, and insects fall away instead of in. A vent aimed up is a bowl collecting the exact blockage the no-gas season warned about. Under the dome, vent down, screen intact: that's the health check.

And the working boundary: the container, its valves, the first-stage regulation — that's the supplier's licensed world under fifty-eight. From the point of delivery on — the line to the house, the second stage, the appliances — you're in NFPA fifty-four, the world this whole channel lives in. Same yard, two books; know where you're standing.

Containers in one breath. ASME tanks stay; DOT cylinders date out at about twelve years. Fill to eighty by the bleeder, never past. Reliefs capped and clear; distances by the table; cylinders upright and never indoors. Vent down under the dome — and the point of delivery splits the books. Next: two-stage regulation.