This Hiker Exploded a Can of Fuel Through the Ceiling. Don’t Make the Same Mistake.

If you’ve got a bin of not-quite-empty fuel canisters in your garage, you’re not alone. Partially-used isobutane canisters cause headaches for backpackers: They won’t last the duration of your trip, but no one wants to waste pack space on extra canisters. And so the collection grows.

Some thrifty ultralighters have found a solution: Gizmos like the FlipFuel Fuel Transfer Device  allow you to transfer isobutane between canisters, consolidating your stash, and allowing you to pack a full canister without a trip to the gear shop. But while these tiny devices make the process simple, it’s not without risk.

Numerous backpackers have posted online about inadvertently exploding fuel canisters during the transfer process. One Redditor admitted that they “managed to fracture a countertop, break a window, cover my kitchen in thousands of shards of glass, and embed a canister of IsoPro in my ceiling,” after heating it in a water bath on the stove. Another poster “singed hair off my head, blew up my stove, blew out a door and a window, and made my wife quite upset,” after placing a full canister in a pot of boiling water.

Both of these backpackers admit that user error led to these detonations. Still, there are few failsafes in place when it comes to handling canisters in ways not intended by the manufacturer. (Brands like MSR maintain that their canisters are not refillable.) While plenty of backpackers manage to consolidate fuel without incident, it’s important to understand the process before trying it yourself.

so I blew up a fuel canister

According to the FlipFuel site, the device works best when you create a temperature differential between the two containers: “Fuel moves from the warmer canister (higher pressure) to the cooler canister (lower pressure), consistent with Boyle’s Law. That’s why it’s important to warm the donor canister slightly—such as by leaving it in the sun—and chill the receiving canister to encourage flow.”

No problems yet—sun-warmed temperatures or the chill of the freezer are consistent with conditions you might encounter on a backpacking trip, and fuel canisters are designed to withstand those. However, when overzealous backpackers try to speed up this step by heating the donor canister even more, things can go very wrong.

“The truth is, only a small temperature differential between the canisters is necessary to transfer fuel. We do not recommend warming a fuel canister using any other method,” says Eric Flottmann, founder of FlipFuel.

Adam Trenkamp, Lab Test Editor at Outside and mechanical engineer, explains further: “When you heat a gas, it expands. This is true for all materials: gasses, solids, and liquids. When the fuel is heated in a sealed container, that expansion leads to increased pressure (like adding more air to your car or bike tire), which will keep building even as it is heated. Since fuel canisters aren’t made with a pressure release valve, the canister eventually explodes due to the building pressure.”

This is the same mechanism that can cause danger when using a wind screen around a canister stove—overheating causes the pressure to skyrocket inside the canister until—BOOM.

Lesson number one? Careful how you heat that canister.

“Warming the canister in your hands, briefly in sunlight, or in a warm room will not raise the pressure enough to cause an explosion,” Trenkamp says. “72°F to 85°F should be all you need. It’s better to freeze or cool the receiving canister that will be on the bottom to create the temperature differential needed to transfer the fuel from one to the other.”

Flottmann says that it’s equally important to avoid overfilling a canister during the transfer process. Overfilling carries the same risks as overheating—once the overfull canister heats up, there’s less space for the gas to expand. If this pressure becomes excessive, the vessel could explode.

“We recommend transferring fuel in short bursts and using a scale between transfers to ensure that the receiving canister does not get overfilled,” he says.

Trenkamp suggests noting the weight listed on the fuel canister, or weighing a full can, and ensuring you don’t surpass that value as you refill. He notes that overfilling a canister can also cause liquid fuel to escape when you attach the canister to a stove.

“The problems this immediately causes should be evident—everything the fuel touches is now extremely flammable, including your hands,” he says.

Additionally, FlipFuel advises to “only transfer the same type of isobutane fuel between compatible canisters. Do not attempt to mix fuel types, such as transferring propane into an isobutane canister or vice versa.”

While the process of transferring fuel between canisters is simple, the consequences of doing it wrong can be dire. Never heat a fuel canister beyond warm ambient temperatures, and take special care not to exceed the capacity of the topped-up canister. It’s never a bad idea to conduct the whole process outside and away from flammable surfaces.

When in doubt, spend the $6 for a new can of fuel. Sometimes, a little more bang for your buck isn’t worth it.