Gas canister safety

[Darren Best]

I have seen a number or posts in the last month or two about different solutions some people have in dealing with different problems concerning gas canisters. Some examples I have seen are using boiling water to test how much fuel is left in the cartridge and using a full 360 degree windshield wrap to increase efficiency.

I accidentally came across an article on this very subject today and thought I would share.

The canisters use singly or a combination of butane, isobutane and propane. The low boiling point of these gases is what creates the pressure to expel the gas from the canister without having to manually pressurize them. Owing to this the canisters are sensitive to temperature.

The DOT sets the pass/fail limit at 50C/122F without any damage or stress to the canister, which happens to be about when you can still touch the canister with your fingers without getting burned. Now obviously manufacturers build in some leeway for a safety margin. But this is the standard safe limit threshold and anything beyond that is a gamble.

The author of the article I read built an elaborate set up to test what would happen when a canister fails and he recorded the temperature at which this happened.

Now it should be noted that if you flip the canister over you will see the bottom is concave, this is a safety feature designed to absorb excess pressure if you should happen to overheat the canister, it will evert and create more space for the expanding gases. This is also a graphic warning to the user that you have exceeded the safety threshold.

When the canister he was using hit 210F it everted and failed completely all at once. Since the canister was not attached to a stove and was not lit, the resulting gas cloud did not ignite. It should be noted that if this happens to you while you are cooking, it will make a large fireball that will burn everything in the vicinity.

So if you use a windshield on a upright canister stove, use a heat shield over the top of the canister to help keep it cool and frequently check the canister that you can still touch it with bare fingers. Also it would be better to not fully enclose the canister with the windshield.

I would highly discourage the practice of using boiling water to see how much fuel is left. Since the canisters are more volatile when nearly empty and you happen to test one on a hot summer day, you could possibly burst one.

If you have a membership with www.backpackinglight.com , you can read the article in it's entirety here. https://www.backpackinglight.com/cg...s_the_hazard_of_overheating.html#.UXhbl0qRfeI

 

[Mike7]

Thanks Elkhunter, that is great safety info and you've given me an idea to add to my yet to be tested creation.

I've seen the Backpackinglight threads about those guys building their own heat exchanging pots, which at least in part effectively creates a windshield coming down from the pot a short ways it seems, rather than coming up from the ground around the canister which could be dangerous as you discuss. I had thought about trying this with my Titanium pot for fun to see if this would change boiling times and efficiency alone. In other words, my aluminum wind screen would cover the lower part of my pot and upper part of the flame only, but my folded titanium or aluminum heat exchanger portion wouldn't be welded to the pot like some of those fancy guys on backpackinglight talked about doing because I don't have that expertise. Instead the heat exchanger would just be supporting the pot up off of the canister stove supports and giving my windshield something to attach to.

I hadn't thought about putting a piece of circular aluminum flashing as a heat shield over the canister as an additional safety feature though. Thanks!

My whole idea above may be a little flawed so I am always open to suggestions. I had to build several little gasifier backpacking cook stoves though before I got one just right, and which could work well without a fan underneath. Luckily aluminum flashing, rivets, and old steel cans are cheap materials though.

 

[Darren Best]

One thing I saw suggested in a few places is putting the canister in a bowl of cool water.

As the liquid fuel evaporates to gas it draws energy from the liquid portion of the fuel and causes it to cool. This is why you see frost on the outside of canisters when you cook in low temps.

The bowl of water gives the liquid fuel something to draw energy from.

Doing this helps maintain a more constant temperature of the canister rather than the normal cooling you get.

Also look into a remote inverted fuel stove with a generator tube like the Optimus Vega, MSR Whisperlite Universal, MSR Windpro II, Kovea Spider and others.

This allows a couple advantages.

You can feed in liquid mode once the generator is hot and this forces the canister to feed the mix at the same rate instead of evaporating the propane off first.

Also it allows you to use a windshield without worrying about overheating the fuel canister.

 

[Mike7]

That all makes sense. The downsides seem to be however, the increased wt of the remote inverted canister stoves, particularly for short trips, and the increased possibility for fuel leaks in the line with added fittings, etc.

 

[Darren Best]

The Kovea Spider weighs 6.0 oz, Optimus Vega 6.3 oz, Trangia gas burner 6.3 oz, Windpro II 6.6 oz, Primus Express Spider 7 oz. (I listed the Express Spider because it can do 119 minutes of burn time on 8 oz of fuel, making it twice as efficient as a Pocket Rocket)

The little top mounted burners vary from 2.5 oz to 3 oz, not that much of a weight difference.

I have not seen any data on how often the remote hose and connections fail, if at all.

 

[Mike7]

Thanks Elkhunter for the stove references. That Kovea Spider seems to have just about nailed it, with very little if any downside with respect to wt, packability, performance, etc. I have never personally used the remote canister stoves but had heard a couple of not so great stories previously. It sounds like they are getting better and now have more upsides and more all around performance and safety.

I also see that the ultralight packer crowd already uses some upright canister 'modified windscreen' types of products like I was contemplating in order to increase efficiency while not carrying a heavier heat exchanging pot...
http://www.backpackinglight.com/cgi...tml?forum_thread_id=72108&skip_to_post=615364

 

[Darren Best]

Total power output isn't the whole story, efficiency matters a lot. I get a kick out of guys that post about stuff that didn't work and you find out they didn't work it through all the way. The one that really gets me is how alcohol doesn't burn in the winter, someone forgot to tell the Swedes that 80 years ago.

The Trangia is a shining example of this, even though it's standard configuration is alcohol, it does very very well in even the worst weather. Put one of the gas burners in it and it does great with those too. It's just how well the windshields are designed. With the gas burner in it, even at half power, it still boils water in five minutes and by going to half power I can get five hours of burn time from one 8 oz canister. I dare you to try and get a Pocket Rocket to do that.

A guy has to look at his cooking gear as a complete system and think from there. Also you have to test it in bad weather every chance you get to make sure it's going to do what you want it to. Sometimes just one little minor thing can mean the difference between "it's a piece of crap" and "it's awesome".

There is something I call fiddle factor, it's how much you have to fiddle around and babysit something to make it work. It is a combination of simplicity and reliability. I can start the Trangia and wander off and do camp chores or finish setting up camp for a few minutes and come back and the stove is still working, every time, that's how reliable and simple it is. You can bump it or nudge it and it won't fall apart in four different directions, it all locks together.

But the posters that said it in that forum are right, by the time you add in all the extra stuff that an upright canister needs to work reliably in all weather, you are at the same weight or more as one of the remote stoves, with all the drawbacks of the uprights and none of the benefits of the remotes.

I have seen conflicting information on how much the heat exchange pots weigh, I would like to get my hands on one and see just how good they are. I don't completely trust things I read on the net, I like to try stuff out for myself, you would be surprised at how often someone swore something as fact and I didn't get the same conclusions.

Total weight carried isn't just about how much the stove or the pots weigh, it's also about how much fuel you have to take with you. I read a blog post about a guy that was just raving about how awesome the MSR Reactor was and it was because it was so efficient that it cut his fuel load in half. Bear in mind that he was hauling in 95 lbs of white gas on his expedition, so you can see it's a specialized situation. But it certainly gets the point across that you can't look at the pieces of a whole system and get a clear picture of that system.

 

[Diveslot6]

Informative post, thanks...

...and no doubt the basis for some fuel canisters (MSR) that are not approved for shipment by air cargo. Awhile back, I looked into the air cargo issue. Snow Peak and Primus cylinders were approved for shipping by air cargo and no doubt other brands too.

Only canisters with special permits listed (special permit DOT SP10677 for Primus) can be shipped by air cargo. If you don’t have the DOT SP number, you can search onliine or bring canister to your air cargo company to check.

I would do a new search, but at the time, to confirm a special permit for your specific brand, the websites were:
http://www.phmsa.dot.gov/hazmat or
http://www.phmsa.dot.gov/hazmat/regs/sp-a/special-permits/list or
http://www.phmsa.dot.gov/staticfiles/PHMSA/SPA_App/OfferDocuments/SP10677_2006030078.pdf for info or to look up SP number.

Any fuel shipment by air cargo requires hazmat fee, $30 and some paperwork. The $30 fee is per bill, so you want to ship all your hazmat materials at once. Thanks again for the post, Elkhunter_241.

 

[Darren Best]

Interesting, I thought that all gas canisters had been banned from air shipping. I knew about the hazmat fees for ground shipping which makes buying canisters prohibitive and many places won't even sell them online anymore because of this.

MSR's higher propane content is probably what causes it from being shipped by air.