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Ammo box


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Posted by supertigrefan on 17/11/2018 17:55:53:
Posted by PeterF on 17/11/2018 17:01:47:

No, if a lipo battery catches fire, it does not need external oxygen, it is a reaction of the chemicals in the battery and as they react they give off a lot of high temperature gas, and if this happens in a sealed container it will pressurise it and potentially burst it, so you need to remove some of the seal to stop it being pressurised. Think of the lipo charging bags, these are not sealed.

Edited By PeterF on 17/11/2018 17:02:38

Andy, you have a valid point.

Lithium is an Alkali metal and reacts with water or water vapours present in air and will ignite and burn in the presence of oxygen, exclude H2O and the reaction will not occur. An oxidizing agent produces it's own source for burning, Lithium is a reducer, not an oxidizer.

Edited By supertigrefan on 17/11/2018 17:58:25

Sorry Supertigrefan, the lithium batteries that we use for RC flight are lithium ion batteries not lithium batteries and lithium ion batteries DO NOT contain metallic lithium, the lithium is present in lithium salts / compounds such as lithium cobalt oxide, or lithium iron phosphate amongst others. This is a common misconception. Lithium metal batteries are things like the button cells CR2032 or some of the lithium non rechargable batteries for digital cameras. When a lithium ion battery suffers a thermal runaway, the lithium compound in the anode can decompose and release oxygen gas, thus the battery can provide its own source of oxygen to burn with the graphite cathode or the polymeric membranes. Some types such as the lithium iron phosphate are less likely to have thermal events because the lithium compound is more stable than others such as the lithium cobalt oxide. My company that I have just retired from as a chemical engineer makes compounds for lithium batteries.

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Posted by supertigrefan on 17/11/2018 22:10:08:

So the OP would be best off looking for a container with the ability to 'contain' a fire?

Yes, but you can not contain it unless the container can tolerate a high pressure. Hence you need some venting and hope that less secondary damage occurs from the hot gases because most of the heat is contained and the burning battery does not ignite anything else. The expensive batt safe is vented, but that has some form of mesh or gauze to try and arrest any flames if they try and exit the container. An ammo box is a good compromise being steel, but it is not designed to contain pressure with the seal.

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Posted by PeterF on 17/11/2018 22:33:49:
Posted by supertigrefan on 17/11/2018 22:10:08:

So the OP would be best off looking for a container with the ability to 'contain' a fire?

Yes, but you can not contain it unless the container can tolerate a high pressure. Hence you need some venting and hope that less secondary damage occurs from the hot gases because most of the heat is contained and the burning battery does not ignite anything else. The expensive batt safe is vented, but that has some form of mesh or gauze to try and arrest any flames if they try and exit the container. An ammo box is a good compromise being steel, but it is not designed to contain pressure with the seal.

I don't think I've ever seen an ammo box "in the flesh" so I don't know how the seal is retained or what it's made of.
Would the seal stay intact or in place under the gas pressure resulting from a fire. Or is the seal likely to blow out at some point thus relieving the pressure before anything worse occurs ?

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I know they are more expensive but I use and love Batt-Safe. Check out their web site for videos and details.

I work away from home for 2 weeks at a time and I could never forgive myself if I had a battery mishap while I was away. How would my wife and family deal with a house fire and where would I stand with insurance dramas after the event. Buys me a lot of peace of mind and for me that’s worth the extra coin. Plus they are really convenient for a charging station.

I get that they’re not everyone’s ideal, just my 2p worth.

TP

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There have been dozens of tests run on ammo boxes, fire safes, lipo sacks (real ones and knock offs), breeze blocks, battery bunkers and the more recent commercial solutions like the Batt-Safe etc for safe storage of lipos and videos posted online. If you are using lipos you really should familiarise yourself with what a lipo fire looks like and how they behave. Needless to say a burning lipo can, and often does, vent with large volumes of gas/vapour and putting one in a completely closed container is not a good idea.

The burning battery needs to be able to vent, whilst keeping any flames inside the container. A real Lipo Sack will do this nicely - a knock off LipoBag may not do so - many of them have been shown to be flammable and less useful than a chocolate fireguard.

The Sentry firesafe has been shown to be a good solution, working well in tests - the vapour can escape but the flames don't and they don't explode. Likewise ammo boxes with the seal removed and some holes drilled seem to work well - but a closed, sealed ammo box is a no-no -lots of videos showing what happens then.

Tipsy Pilot makes a good point. My current system consists of a couple of firesafes and a couple of real LIpo Sacks, but the number of lipos climbs and coming up to the winter lay off is a good time to review those storage choices. One of the key things is to store at a storage voltage rather than fully charged, it's also better for the packs themselves.

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Just bear in mind that some of the Lipo bags that are on sale have been shown to be useless - they are flammable and burn if exposed to flames. The original, genuine Lipo Sack developed by Mark Wood is the genuine article and has been demonstrated to be effective in containing a lipo fire. The videos are out there on You Tube - loads of them - showing the horrible quality of some of the cheap. knock-off, lipo safety bags that are on sale. All that shines isn;t necessarily fireproof.

https://youtu.be/w97BDrNJvXg

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For most of my years service with HM Coastguard we transported signal and distress flares in ammo box's that were not sealed.

Just before I retired we were issued with bespoke box's that looked nothing more than a biscuit tin that was more holes than metal and it's liner was just a cardboard box! To say we were sceptical would be an understatement.

However a demonstration with a parachute flair set off inside changed our minds, As you may know such flares burn at a very high temp but all those small holes disipate it very well with little flame exiting the box. Amazing

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That makes sense - the idea is to constrain the flame front and let the gases dissipate - that's how the Lipo Sack works. The problem comes when the bag itself if flammable and just catches fire. I do have a few of those cheapy bags, but don't use them for anything other than tiny 1S cells and certainly wouldn't put anything larger in there. I couldn't recommend buying a lipo safety bag unless it had been demonstrated as being made of non-flammable fibreglass cloth, designed to be fireproof.

I guess you could make your own, out of a BS standard fire blanket - but as has also been demonstrated online, those fabrics are intended for pone time use and they can shed fibres, making them less than ideal for extensive use.

My pal Mark Woods was a US Navy electrician and came up with the original Lipo Sack design somw years ago, using the fireproof material similar to that employed on board US warships, extensively tested and they do work.

 

 

Edited By leccyflyer on 18/11/2018 09:20:57

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Posted by supertigrefan on 18/11/2018 10:29:55:

The considerations are:

1. An unsealed container will allow the gases to escape into the compartment supporting breathable air, so in layman's terms the poisonous gases from a vented container will contaminate the air you are breathing in.

2. The heat produced by a decomposing Lithium Ion battery needs to be contained to prevent the spread of that fire.

3. Any damage caused by an explosive force inside the container needs to be minimised.

"Lithium-ion battery fires generate intense heat and considerable amounts of gas and smoke. Although the emission of toxic gases can be a larger threat than the heat, the knowledge of such emissions is limited."

**LINK**

My experience with 'abused' Ammo boxes is that they will contain a detonated Thunderflash…..that's an impressive feat.

The choice is your own.

Edited By supertigrefan on 18/11/2018 10:30:26

A thunder flash is a grown up banger. Argue until you are happy, but trying to contain a fire in a sealed box not certified or designed to contain pressure is a very bad idea. The idea is to contain the fire while you take steps, in the opposite direction, at speed.

An ammo box and it's seal is designed to keep the rain out, and be tough enough to protect the contents from damage.

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I have mulled over a response, or even thought why bother, but I have a major concern. There are beginners reading this, and misinformation on a public forum can cause serious grief.

I have a degree in Chemistry. In ancient times I was employed as a research chemist, employed by ICI, for a time, in the development of novel plastic explosives, for military use. I was briefed and trained in the storage and use of this stuff.

An ammunition box is, in this case, a NATO pattern box with a rubber seal. The basic design comes from America, and is a waterproof box what keeps bullets clean. American weapons are light, accurate, (expensive, delicate) and need good clean ammunition. Hence the rubber seal. Russian boxes are sealed sardine tins. Other nations use waxed/tarred cardboard, and nowadays, plastic. There is no intention to contain the content when burning starts. Why bother, a bit of galvanised tinplate ain't going to stop much. If you doubt me, look in Wikipedia. I checked today.

You have stated, in a gassing fire, the seal will release pressure. I would invite you to provide your measured source for this assertion. It was designed to be a moisture seal, and any other functionality is, I maintain, coincidental.

To keep lipo batteries in a sealed box without a proper vent is dangerous.

Furthermore, you have asserted that a thunderflash is contained when it goes off in a sealed ammo box. Now I admire your reflexes, light it, seal the box, scamper off, all in the five second fuse. ( and I have checked, it's the same 5 seconds today as it was in 1971). But, if it made a mark on your memory, and that seal did not vent pressure. The box bulged. Ring a bell?

And a thunderflash, is still a big banger, cardboard, 3 gram load, (and again, I have checked today, same as they ever were) and the same safety sheet I read today, says don't hold it when it goes off, you will get burnt. No mention of missing bits. That's a banger, and it bulged the box.

I repeat, to keep lipo batteries in a non vented box is dangerous. If your box explodes, as you say is your choice, but at least, just before your head restraint goes through your head, so will the thought, I told you.

Sorry about, the larger type, typed offline, and don't know how to re-size.

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