Refilling small gas canisters (perfect for light hiking) with larger ones is a great camping sustainability and cost saving “hack” that has become really popular. With a 100g gas canister often costing around £4 in the UK and a 300g can available as low as £6, it is easy to see why (200% more gas for 50-100% more cost!). Added to the cheapness of adaptor valves to connect cylinders, from just £3-4, it’s almost a suprise everyone isn’t doing it.
Not only does refilling offer a very noticeable cost saving it reduces landfill/ transport and material costs so it also has a clear sustainability angle. The gas exchange valves to do this are easily available starting at just a few pounds.
Youtube videos abound on the topic and although I do it myself there are a few dangers to be aware of. Flammable gas under pressure has the potential to kill, or cause life changing injury, so here are a few things everyone doing this should know about to minimise risk. It is worth noting that this article is about risk minimisation, there will always be some risk inherent in refilling gas canisters.
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1. Wrong gas types – Refilling canisters with different gases/ gas mixes
Most gas canisters used for camping or lightweight hiking are butane/ propane mix. This combines the low temperature performance of propane with lower cost and lower vapour pressure of butane allowing a lighter canister design. At around zero degrees celsius (30deg F) the vapour pressure of a 50/50 butane propane mix is around half that of 100% propane.
So perhaps the biggest single risk people seem to take anecdotally is to refill with 100 percent propane, e.g. through an adaptor to fill with gas from a Red Calor gas bottle. At a normal range of operating temperatures a canister refilled with propane will be operating at a minimum of two times the pressue it would be expected to encounter. Now most things are engineered to exceed expected forces, but the dangers here are pretty apparent. Butane at 40deg C will create less vapour pressure than a propane at 0 degrees C.
Looking at a typical mix, such as the Coleman Extreme mix, this is a 70/30 butane propane mix. It only takes a temperature of 15 deg C for a refill in pure propane to exceed the vapour pressure that the 70/30 mix would generate at 40 deg C. Especially in warmer climates in a sunny tent on a hot day 40 deg C is easily achievable!
There is one caveat here. If you refill with a mix containing a lower proportion of propane, or refill with pure butane, as some adaptors are designed to do from the “hairspray” type cans, you are somewhat negating this risk. The sacrifice being low temp performance. i.e. pure butane will struggle to make you a tea on a frosty morning.
2. Overfilling the canister
So having established we are using the right type of gas the next most commonly cited danger is overfilling. Gas containers are typically filled to about 80% leaving space for the liquid gas to expand at changing temperatures and also for the gas to “boil”/ vapourise allowing it to be used.
So when using a valve to swap gas from a larger to a smaller bottle there is clearly a risk of this. Cylinder rupture and the realease of a large volume of gas in an enclosed space = potentially catastrophic kaboom.
Fortunately this can be easily avoided by using scales to weigh the bottle before and periodically whilst filling. i.e. if the quoted new weight of the gas canister is not exceeded the danger is negated. i.e. a C100 coleman type cylinder contains approximately ~100g of gas with a gross weight of 175g. My suggested method would be to refill in 15 second bursts weighing in between.
3. Overwarming the donor canister
I order for the gas to flow from one canister to the next we want higher pressure in the donor canister than the receiver canister. The easiest way to achieve this is by creating a temperature differential. This can be done by cooling the receiver canister or heating the donor or both. Obviously safest of all is just cooling the reciever. 20 minutes in the freezer will suffice here.
On no account should you heat the donor canister excessively, a bit of lukewarm water should suffice. There are some nice accounts of people blowing up their kitchen by popping the donor can into boiling water. Given what is needed is just enough of a pressure differential to get the gas moving if you are freezing the receiver it is just not necessary. With a 70/30 propane/butane mix a temperature differential of just 10 degrees should be plenty sufficient, even allowing for the cooling of the donor cartridge
4. Using damaged gas cartridges
The other recommendations are pretty easy to follow, with simple rules to follow. This one is a bit more tricky as what constitutes problematic damage. Essentially it is impossible to tell 100% but any material damage to the structure of the can, either through corrosion or dents, scrapes, nicks has potential to weaken the cartridge.
So this comes down to judgement, but generally whilst a bit of light surface rust, or a minor dent is likely to cause an issue, I would tend to retire any canister that did not look pretty close to new.
5. Refilling too many times
Like point 4 its a little tricky to judge what consitutes “too many” times to refill. You have to consider though that these cartridges are designed as single use items. The thread and Lindal Valve themselves are therefore not built for years of use and will wear out. Again whilst a level of contingency is engineered into these things, and it is likely the same valve exists on the 500g bottle as the 100g one, a reasonable rule of thumb would probably be refilling 5 times for a 100g bottle inspecting the canister carefully between fills.
Even if we err on the side of caution and stick to that 5 refills limit, the typical cost of five 100g canisters (£15-£20) versus refills from a £7-8 500g canister makes the saving of refills quickly mount up!
So there we have it 5 things to consider to make refilling camping gas canisters safer. Of course it goes without saying that refilling in an area with no naked flames, and good ventilation is a must. #