UKC

I've never had a cannister stove do anything other than what it should, so I wondered if the collective wisdom of UKC could advise me on this one.

I have just returned from a camping trip with some students. During preparation of the evening meal, a gas cannister exploded. According to the student concerned, he screwed the stove to the cylinder (cylinder top type stove), heard gas coming from the join between stove and cylinder, and still decided to go ahead and light it. He says the cannister burned from the joint for 10-20 seconds before exploding. The stove itself, he says, separated from the cannister and flew high into the air.

Now, I have a suspicion that this was a deliberate explosion, possibly done by heating the cannister directly. The stoves are fairly new and were checked over before going on the trip. The cannister was partially used on an earlier trip, and was trouble free. While there is a burn to the top of the cannister, the valve and screw threads look intact. I am also suspicious that the bottom of the cannister is discoloured brown on the outside (the side printed with batch number etc.) while the inside is clean. The stove could not be found.

Photos here:

https://drive.google.com/open?id=0B3cU5PSRakgec0p5SEZ5UVFtRVU
https://drive.google.com/open?id=0B3cU5PSRakgeQVE2WlhzcllsVm8
https://drive.google.com/open?id=0B3cU5PSRakgebGdXLWlydW81eFU
https://drive.google.com/open?id=0B3cU5PSRakgeR01kZ3dhRkxxV2s
https://drive.google.com/open?id=0B3cU5PSRakgeUXhrWVlkNXI0RDA

Any thoughts?

In reply to nikkormat:
Looks like the base was directly heated, I'd put a few quid on it being deliberate having done it myself a few times

In reply to nikkormat:

How come the canister is so battered (big scratches in the paint? Also, if the bottom blew out what's going on with the dent in the top? I'm also suspicious about the loss of the stove. Surely you'd go looking for it as if the stove exploded when in use, someone would be nearby and would probably be injured, which is another question, was anyone injured?

In reply to nikkormat:
The student could have cross threaded the stove while putting it on maybe? I'd have been quite surprised if the Lindal valve would have opened if this were the case though, the nipple inside the valve is quite small.
If there was someone injured as a result of this I'm not sure UKC is the place to discuss it.

In reply to gethin_allen:

Good points; I am no physicist, but I can't see why the top would be dented in that way.

Thankfully, nobody was injured. I searched for the stove myself, and couldn't find it.

In reply to nikkormat:

I know that many fire services have a special team to deal with children and teenagers who behave dangerously around fire. Personally I'd make a referral and ask their opinion of the photos.

http://www.london-fire.gov.uk/JuvenileFireSettersInterventionSchemeJFIS.asp For example.

In reply to spenser:

I think the benefit of the number of experienced people on UKC probably outweighs the issues you mention, but perhaps this thread could be moved to the pub so it disappears?

In reply to nikkormat:
Maybe consider sending the damaged canister to Primus for analysis? I'm sure if it was due to a failure of their product they would certainly want to know, on the other hand they may well respond pointing the finger at misuse.

How old are these students?

In reply to nikkormat:

It appears that the base was blown off? If there was a small gas leak through the thread at the top - sufficient for the can to not void itself in 20 seconds - I can't imagine sufficient air getting in through that gap against the exiting gas to create an explosive mix inside the can. The gas inside the can should not be explosive as there is no oxygen(air) air there for it to react with.

If the flame spread from the stove to the point where gas was exiting the thread, that might heat the can and the gas inside it enough to rupture the base, which could then be followed by a loud fireball as the remaining gas was released into air. A heat source applied to the base might do similar...

Honestly though doing it on purpose would be less reprehensibly dim that knowingly lighting it in the presence of a gas leak... so hang 'em either way! Also ask to see any recent videos on their mobile phone...

In reply to marsbar:

Cheers for the link, marsbar. We're not in the UK (Czech Republic), but it's definitely a point worth raising.

In reply to Trangia:

I considered that, but I was pretty certain at the time that this was deliberate; more convinced now. The student is 17 and intelligent enough to know better.

Thanks for the replies folks.

As for moving/removing the thread, I am okay with that. I just wanted some thoughts from others.

In reply to nikkormat:

To me it sounds like an unlikely story I'm afraid.

I can't really imagine a cannister exploding even with the valve fully opened and ignited, they're specifically designed not to do this. The only situations I can think of that could cause an explosion are a hole in the cannister or the cannister being heated.

In reply to wintertree:

Mobile phone footage is a very good call.

In reply to marsbar:

youtube.com/watch?v=UM0jtD_OWLU&

In reply to nikkormat:

I wouldn't try to punish, odds are they gave themselves a fright anyway, just write it up as reported so that the paper chase stops at the missing stove. A repeat lesson on how to use the stove, including a check to make sure no cross threading and listen for gas leaks would be my choice, along with student not having a stove for the next while and extra washing up may make the point too.

I'd assume that the canister was set on top of another stove and in blowing up, damaged the stove it was on, hence the missing stove.

In reply to nikkormat:

Contender for a Darwin award: gas is escaping from between the canister and the stove and he still lights it? It's not going to end well.

If he was heating it on a flame, well he's still a candidate for a Darwin award. A bit of copper to shift some heat downwards is sufficient if it's really cold.

The fact that the canister blew apart? - Well, I think we can say with confidence that the conditions to which it was exposed exceeded the design specifications.

In reply to nikkormat: If the canister had a bad connection and was leaking gas that gas could build up round the base of the cannister if not windy and may have ignited when the flame spread from the top to the join between stove and canister, which could explain the burnt base.

In reply to nniff:

IMHO there is no way that there was a stove attached to that when it exploded. For starters the canister failed at the lower rim, so the main part would still be attached to the lost stove. Secondly the thread looks perfect, not even evidence of cross threading. No burn marks or physical damage.

Burnt paint on the lower half of the can tells you the whole story.. missing stove? Buried somewhere or in the river as suggested above.

99.9%

In reply to minimike:


But why would someone do that? They will soon be able to vote FFS!

In reply to Garbhanach:

Wouldn't the leaking gas flame-off, not form a symmetrical pattern of heat damage around the base of the can? A pattern that happens to mimic the effect of it being left on a fire / on another stove? The incidents I can recall of camping gas cannisters exploding were when heat deflectors / shields were badly designed or installed backwards and directed heat back onto the cannister.

In reply to spenser:


I have witnessed such behaviour a wee while ago. Two mates (over 18s) cross threaded the stove and still lit it. Soon, the canister went on fire and they just backed off, panicking. Since it happened in front of a church in a small village around people, I just poured some water over it and it was all good.

I wouldn't blame the student, albeit using malfunctioning stove is a bit silly.

In reply to minimike:

100% agree.
Kid's knackered the burner somehow, got rid of it, then set fire to the gas cylinder.

In reply to minimike:

I was thinking that if the person involved is intelligent, he's either been daft for continuing to light the stove after hearing hissing, or dafter for heating up a gas canister. Some kind of talk on the seriousness of burn injuries, and having it put quite directly how daft he's been could possibly be a plan. When I was a youth, I think any significant adults I knew at the time would have put it as 'You've either been daft, or very daft'.

I guess it's easy to jump to conclusions when online and without having been there when it happened, but it almost looks like the bottom is blackened from being heated before the canister exploded, with the top being dented when it fell back to earth again. The angle the dent is at, it's easy to picture a stove still being on top of the canister when it fell back to earth again, with the deformation happening when the stove hit the ground as the canister twisted around it. Having made mistakes when faffing about with metal and things, to me it looks like the kind of dent that would need some force on the end of a lever to create - with the length of the stove being the lever.

It 'could' just be an innocent accident though...

In reply to nikkormat:
I don't see how a stove leaking and burning at the top can scorch the bottom of the stove before it scorches the top.
That is not how conduction, convection or radiative heat transfer work.

Pressure unlikely to build up in a leaking cannister and probably not in just 20 seconds.

youtube.com/watch?v=aDIWMp3cIPM&

An extrenal fireball isn't going to neatly scorch the bottom of the canister and nothing else.

I'm guessing it was in open air as you don't mention injuries.

In reply to nikkormat:

Being a rogue in my youth I can tell you that direct heating from the bottom would have caused the canister to fracture at the weakest point (The base) and sent the cylinder flying. The distortion at the top of the gas cylinder would have been because after serious pressure builds up inside which would have distorted it. I did this many many years ago and would say that you have a naughty student not a defective gas cylinder.

Also his story about leaking around the stove would be false as it would just keep burning until the gas ran out but their would be burn marks at the top of the can not on the base.

In reply to Matt Cooper:

Had an unfortunate event when one of those steamed puddings in a can that you leave simmering in water for about half an hour was allowed to boil dry on a canister stove. The pressure in the steamed pudding can caused that to explode pushing the burner down into the canister. Even with the resulting hole in the canister the amount of air going back into the canister wasn't enough to make it explode and it just kept burning until a few minutes later when we got an extinguisher to it. Also the burner stayed attached to the canister despite quite considerable distortion to the thread and top of the canister.

In reply to nikkormat:
2 things here . The gas cannister was heated on a fire until it exploded as others have said .
The explosion may have been a diversion to steal the burner .

In reply to Rich Ellis:

What he said.

In reply to nikkormat:

As minimike says, if a stove was attached when it exploded, it would be still attached now, or there would be some serious damage to that thread. In my opinion, there was either no stove attached when it happened, or it was unscrewed afterwards. Given that the canister is burned on the bottom, (as it would be if you put it on a stove), it looks like the obvious thing that has happened here is that the canister has been directly heated on a stove.

There is one way to find out - put a gas canister on a stove yourself, and see what happens - it's all in the name of research, of course

In reply to wintertree:


That was my first thought too - it wouldn't explode (due to internal explosion) unless air was entering to create the explosive mixture. It could 'explode' for other reasons, e.g. applying heat externally, increasing the pressure sufficient to rupture, and the gas/air mixture resulting causing an explosion.

As someone else mentioned, the stove has most likely been removed after the event, otherwise it would still be attached, or significant damage to the thread/valve area.

In reply to nikkormat:
You can't have an explosive mix in the canister because air can't get in against the pressure of the fuel and the flow of escaping fuel.

When the canister pressure has decayed you could have an explosive mix at 1 atmosphere if it just happens to contain the correct percentage of fuel.

At normal atmospheric pressure, a 0.5 litre container can hold 0.5g of air which means just 0.1g of oxygen. You can't burn much fuel and create much of an explosion with 0.1g of oxygen.

Your suspicion is far more plausible.

I remember a science demo at school. Take one empty 5L paint tin and punch a small hole in the top, and connect a gas line to the bottom. Turn the gas supply on and let in run for a minute or so to purge the air, then light it at the top. You get a nice yellow flame. Turn the gas off and step back. As the gas inside the can decreases and is replaced by air, an explosive mixture forms after a minute or two, just before the flame dies out. This goes bang very loudly and send the tin and lid flying. Sound familiar here?

In reply to nikkormat:

There is no way the stove was blasted off the top in to the air without damaging the thread.

Burn marks on the bottom too.

The story you have been told does not add up. But I think you know that anyway...

In reply to Dave the Rave:


Exactly why we shouldn't be lowering the voting age!

In reply to pec:

As someone who grew up with Jackass, dirty Sanchez and the like, I grew up doing dumb stuff with my mates. We definitely did stupider stuff than this - and learnt a lot as a result! Doing dumb stuff is an important part of growing up IMHO.

However, in order for the learning to work there must be some consequences. In this case I suspect that justice will be provided appropriately.

In reply to pec:


But then again some older people vote Tory .

In reply to nikkormat:

I've had a small gas stove explode on me - it can happen,

I had a home made metal windshield and it was too close somehow. The tube caught light with the heat and the flame went back up towards the cylinder.... which burst open with a sound to bring the Wasdale campsite to a standstill and the butane cylinder fanned out like a daisy. It all happened in an instant.

I had a 6-month old baby at the time laying about 2m from the stove and it was only the quick actions of my mate, batting the flaming stove away with a frying pan that meant no one was injured.

In reply to nikkormat:
Right, update. Sleepless nights and interrogations, pulled fingernails and waterboarding have given me a clearer picture, though questions remain. I am confident that the equipment was in no way faulty.

The student screwed the stove together enough to activate the valve but not enough to seal the stove to the cannister. He then lit it; when it ignited he panicked and kicked it over, then stamped on it to try to put it out. The leverage of canister and stove being stamped on caused the damage to the top. Another student told him that stamping on a burning gas cylinder was not a good idea, so everyone withdrew to a safe distance until it exploded. One student recovered the stove, still attached to the cylinder, and for some reason even he cannot explain, unscrewed it and threw it into the forest.

The black mark visible in the last photo is melted plastic from the stove knob. The scratch after the "S" in Primus was caused by the stove knob scratching against the cannister when it was removed, after the explosion. I tried fitting another stove to the cannister, and the black mark corresponds to where the knob would be if it was not fully tight - only mild resistance at this point. This type of Primus cylinder has a darker coloured base; it is not, as I thought, discolouration through heat. There are still aspects I am not satisfied with; the burn pattern on the cylinder seems odd, and the student who threw away the stove cannot give a good reason for his actions.

Lessons have been learnt from this. Thanks all who have replied.

In reply to nikkormat:

When I was a lad a group of us were camping and did something similar. When fitting a new gas canister, it got caught part way on with gas leaking out and this was accidentally lit. Somehow we got the canister off the stove and lobbed it a long distance away. As I recall, the jet of gas continued to be lit as a flame from the cannister but it never exploded.

In reply to nikkormat:

This is one reason I've never had a gas stove. pressurised paraffin on the other hand......

In reply to graeme jackson:


It's one of the reasons why I am always reluctant not to monitor what bronze DofE participants are doing when cooking. My risk assessment pointed cooking to be one of the most dangerous things they did on an expedition, in terms of the high likelihood and severity (high energy content of fuels, and of pans of boiling water); I've seen what a pan of boiling water spilled down a child's back does (neighbour kid had terrible scarring on his back from such an incident).


Safe as houses. If you live in a house with a flame thrower... Go pressurised petrol for the full experience... I ruled out pressurised liquid fuel stoves for the DofE group I help with; too much skill needed to use, and too many ways for them to go horribly wrong.

In reply to Skyfall:


The pictures show that part of the valve is plastic. The melting of this, in the incident you describe, is most likely why the gas continued to leak after removal of the cylinder from the stove. It's noteworthy that your can did not explode.
The lack of any melting of the plastic valve and the discolouration of the base of the canister point to the most likely cause of the incident described by the OP as the can being heated on another burner.

In reply to captain paranoia:

Spoke to a D of E leader a couple of weeks back....that morning a student had failed to get sufficient heat by fully opening gas valve so thought they could get more gas by loosening stove connection to cylinder! Teacher was using depilation strips to remove glass fibres from hand after successfully putting out the resulting conflagration with a fire blanket.

In reply to nikkormat:
I think your instinct is good and your student has either a bright future in creative storytelling or a short one in arson ahead of them.

Looks like the bottom of the can has blown out through over pressure, probably caused by directly heating the base of the can (lower paint darkened and base inside surface oxidised brown while still hot after the separation). The dent in the top is odd, possibly distortion caused during the base-body separation more likely by rapidly accelerating with a stove attatched (either during take-off or landing). Possibly unrelated. I've blown a few up in my youth by heating in a fire and that's exactly what the bits look like.

It's possible that a small leaking valve fire left burning against the top of the can long enough provided sufficient heat to burst it but looking at the can it doesn't look like the most likely option.

One of the other stoves, the one used to heat that can was likely bent badly when the can burst on top of it, I suspect that's your 'missing' stove 'lost' in the explosion, probably chucked in a hedge somewhere.

I suppose you should be glad your students knew to stand far enough back that they've still got eyebrows, a can that size makes quite a fireball! Interview them separately for your 'complaint to the manufacturer' and I bet the inconsistencies will emerge.
jk

In reply to nikkormat:

Never work with children or animals.

In reply to Dell:

Or children who are animals.