Is it legal to refill disposable 1 lb propane cylinders?

Refilling a disposable 1 lb propane cylinder is not, by itself, what federal law forbids. The printed rule is "Federal law forbids transportation if refilled", and the regulations behind it bind people moving hazardous materials in commerce, not an individual driving their own cylinder for non-commercial use. PHMSA still says never refill one, because it was not designed to be filled twice. The legal route is a refillable 1 lb cylinder.

Is refilling a disposable propane cylinder illegal?#

Two answers circulate: "illegal, up to five years in prison" and "legal but unsafe". Both start from the same printed line, and each is right about a different person.

What the cylinder is. The green 16.4 oz cylinder is built to 49 CFR 178.65, titled "Specification 39 non-reusable (non-refillable) cylinders". Every one must be marked DOT-39 and NRC, with its pressures, maker and lot, and, if made since 1 October 1996, "Federal law forbids transportation if refilled-penalty up to $500,000 fine and 5 years imprisonment (49 U.S.C. 5124)".

Who the regulations bind. 49 CFR 171.1 applies the Hazardous Materials Regulations to each person who offers a hazardous material for transportation in commerce, causes it to be transported in commerce, or transports it in commerce. "Filling a hazardous materials packaging" is a regulated pre-transportation function, so a business is regulated from the moment it refills.

Who they do not bind. The same section lists activities the regulations do not cover, and number (6) is "transportation of a hazardous material by an individual for non-commercial purposes in a private motor vehicle, including a leased or rented motor vehicle". PHMSA's interpretation 19-0017 applied that logic to a dive shop filling a private diver's SCUBA cylinder: transport "by a private individual for non-commercial personal use is not considered transportation in commerce."

What PHMSA says anyway. Its December 2017 guidance is blunt: "DOT 39 cylinders, of any size, are strictly non-refillable." The reason is physical, not legal: "These types of containers were not designed to withstand the stresses of emptying and refilling." It records incidents with refilled DOT-39s, "including one fatality."

So "illegal" is correct for anyone in commerce: a store, a reseller, a campground selling refills, a guide service or contractor. "Legal" is correct only in the narrow sense that a private camper refilling their own cylinder and driving it in their own car is outside the federal transport rules. Neither makes the cylinder fit to refill.

Who the federal rule covers, case by case#

The table applies those texts to the situations people ask about. It covers federal transport law only, not state fire codes or park rules.

The table rests on the regulations' own definitions, not on a court ruling. A camper who sells refilled cylinders to the next site is no longer acting for non-commercial purposes.

What the penalty on the label really is#

The label quotes the law as it stood when the cylinder was made: "$500,000 fine and 5 years imprisonment" since October 1996, and possibly "$25,000" before. Neither is current.

The civil figures are adjusted for inflation and were last revised in December 2024, so read the eCFR, not the cylinder.

Why a refilled DOT-39 is a bad pressure vessel#

Built for one fill. A DOT-39 is proof tested at the greater of 180 psig or the pressure of its contents at 130 degrees F (54.4 degrees C). For pure propane NIST gives 273.4 psia at that temperature, about 259 psig (17.8 bar). Sample cylinders from each lot are burst and must not fail below 2.0 times test pressure, about 517 psig for propane. Nothing in the specification tests a cylinder that has been emptied and filled again, or requires an inspection before a second fill.

Filled by weight, to 42 percent. Under 49 CFR 173.304a, liquefied gas is filled by weight, to a limit set by its specific gravity. Propane at 60 degrees F has a density of 506.7 kg per cubic metre (NIST), a specific gravity of 0.507, which falls in the 0.504 to 0.510 band: 42 percent of the cylinder's water capacity. A 465 g (16.4 oz) charge at 42 percent needs at least 1.108 litres of water capacity, about 67.6 cubic inches, inside the 75 cubic inch ceiling the same section sets for a DOT-39 holding LPG.

Why 42 percent. Liquid propane expands as it warms: NIST's liquid density falls from 506.7 kg per cubic metre at 60 degrees F to 439.9 at 130 degrees F. In a 1.108 litre cylinder, a correct 465 g fill is 83 percent liquid by volume at 60 degrees F and 95 percent at 130 degrees F. The vapour space left is the cushion. Once liquid fills the cylinder, further warming has nothing to compress, and pressure climbs far faster than the vapour pressure curve until the pressure relief device opens. 49 CFR 173.301 requires one on every DOT-39.

What an overfill costs. We model the same 1.108 litre cylinder and ask at what temperature the liquid alone fills it:

A real cylinder may hold slightly more than this minimum, which moves every row up somewhat. A parked vehicle runs roughly 22 degrees C above the air outside within an hour, as storing gear between trips sets out, so a 25 degrees C day gives about 45 degrees C inside, past the liquid-full point of a 10 percent overfill.

Refillable 1 lb cylinders: the legal route#

A refillable 1 lb cylinder is not a stronger disposable. It is built to one of the reusable specifications 49 CFR 173.304a authorises for LPG, such as DOT 4BA or 4BW, and is expected to be filled, emptied and requalified.

One refillable model page lists 16.4 oz capacity, the CGA600 connection disposables use, and "DOT & TC certified for 12 years (10 years in Canada)", matching the federal 12-year period. The runtime is identical because the propane is: about 22,200 Btu a fill, as how long a 1 lb propane cylinder lasts works out. It feeds a lantern, stove or radiant heater alike.

CleanLA puts a refill at "typically $2-$4 per cylinder". LA County still does "not endorse refilling 1 lb. propane cylinders at home", and calls refilling "safe when done by a professional".

Camping stove types compared puts group car camping on a two-burner stove and a refillable cylinder; a 20 lb tank holds 19.5 cylinders' worth.

Why disposables are under pressure in California#

CleanLA says about 40 million single-use 1 lb cylinders are used a year in North America, over four million in California, and that handling each properly costs local governments and parks $10 to $25. California's Attorney General told PHMSA that an estimated three to four million end up in municipal landfills not certified for hazardous waste.

California's SB 1280 (2024), at Public Resources Code sections 42395 to 42395.2, provides that from 1 January 2028 all propane cylinders sold in the state must be reusable or refillable. Exceptions cover small construction-industry cylinders, tall narrow cylinders and disaster purchasing by public agencies.

On 10 September 2026, PHMSA determined, on an application from cylinder maker Worthington, that federal hazardous materials law preempts that mandate, because it imposes requirements on a federally specified packaging that are "not substantively the same" as the federal ones and is "an obstacle" to their uniformity. Anyone aggrieved has until 9 November 2026 to seek review in a federal court of appeals.

None of it changes the refilling answer: the preemption protects the sale of DOT-39s, not a right to refill one.

Check this before you fill any 1 lb cylinder#

The only measurement that matters is weight. A kitchen scale reading to 1 g is enough, with the tare method stove fuel planning uses for canisters.

1. Read the stamp. NRC or "Federal law forbids transportation if refilled" means stop: single use.
2. Read the date. A refillable more than 12 years past manufacture needs requalifying before another fill.
3. Inspect it. Dents, rust pitting, a damaged valve thread or a bulge retire a cylinder.
4. Weigh it empty and write the tare on it in marker.
5. Fill, then weigh again. Net propane should not exceed the labelled 16.4 oz (465 g). Over about 490 g is a 5 percent overfill: burn it down on an appliance outdoors before it goes near a car.
6. Leak check with soapy water at the valve. Bubbles mean it does not travel.
7. Carry it cool and upright, never in a closed car in the sun, and list the spares on the car camping checklist so nobody is tempted to top one up at camp.

Common mistakes#

Reading "forbids transportation" as "forbids refilling". The text is about transport in commerce. It is why a business may not sell refills, and why the prison warning does not describe a private camper's drive. It is not an engineering approval.

Reading "legal for me" as "safe". The private-transport exclusion says nothing about the cylinder. PHMSA says DOT-39s were "not designed to withstand the stresses of emptying and refilling".

Filling by feel. A cylinder gives no outward sign of a 10 percent overfill, and the commercial duty to fill by weight does not follow it home. Weigh every fill.

Buying "refilled" green cylinders. The seller is breaking the federal rule, and you cannot know how full they are.

Frequently asked questions#

Is it illegal to refill a 1 lb propane tank?#

For a business, yes: selling, shipping or carrying refilled DOT-39 cylinders in commerce is prohibited. For a private individual refilling their own cylinder and driving it in their own vehicle for non-commercial use, 49 CFR 171.1(d)(6) puts it outside the federal transport rules. PHMSA still says never refill one, because the cylinder was not designed for it, and refilled cylinders have caused incidents including one fatality.

What does "Federal law forbids transportation if refilled" mean?#

It is a marking 49 CFR 178.65 requires on every DOT-39 cylinder. A refilled DOT-39 may not be transported under the Hazardous Materials Regulations, which apply to transport in commerce. The penalty printed beside it, $500,000 and 5 years, was the statute when the cylinder was made. Current civil penalties reach $102,348 per violation.

Why can't disposable propane cylinders be refilled safely?#

They are built and tested for one fill, with no requalification and no inspection before reuse, and home refilling drops the commercial duty to fill by weight. On NIST densities, a cylinder 10 percent overfilled is completely liquid-full at about 43 degrees C, a temperature a parked car reaches on a warm day.

Are refillable 1 lb propane cylinders legal?#

Yes. They are built to a reusable specification such as DOT 4BA or 4BW, carry no "NRC" marking, and every one is tested to twice its service pressure, 480 psig for a 240 psig cylinder. One maker states 12 years of certification, matching the federal requalification period. LA County puts a refill at $2 to $4 and a cylinder's life at up to 10 years.

How do I tell a refillable cylinder from a disposable one?#

Read the stamp. A disposable says DOT-39 and NRC and carries "Federal law forbids transportation if refilled". A refillable carries a reusable specification, for example DOT-4BA240 or DOT-4BW240, a manufacture or retest date, and no refilling warning. Both use the CGA600 connection, so they fit the same stoves, heaters and lanterns.

Is California banning disposable propane cylinders?#

California's SB 1280 says that from 1 January 2028, propane cylinders sold in the state must be reusable or refillable, with a few exceptions. On 10 September 2026, PHMSA determined that federal law preempts that mandate. The determination can be challenged in a federal appeals court until 9 November 2026, so check the current position before relying on either outcome.