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#41
01-10-2013
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I read with interest all of the comments and recommendations about charging lipos. Makes you a bit wary about these things, although I recall the odd nmhi going pop. Not as catatophic unless you were close by!!
What I want to know is when should you dispose of a lipo. How much swelling is acceptable, any at all? What other defects commonly occur which render them suspect. Do the BRCA ,Electric Board, have guidlines? Keith 
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#42
01-10-2013
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I'm putting the wheels in motion to organise a controlled destruction test of the various options we have for lipo containment whilst charging.
May take a bit to get responses from the distributors etc but i'm aiming at a completely unbiased independant experiment. I feel that we just don't know enough about the different types/options to be recommending and relying on them in case of incident, a £2.50 import special may contain a fire for 20 seconds longer than a £15 branded shiny sack for all we know or vice versa. 20 seconds longer is a better chance to get everyone the hell away from it! If any fellow oOplers, manufacturers/distributors/shops/BRCA Officials are reading this and wish to be involved then feel free to contact me. This topic crops up on here every few months and there have been incidents that sparked the topic each time, no point sitting round talking or expecting BRCA organisers to do something extra on top of their busy workload as volunteers... i'm a BRCA member as we all are so will be doing this to help any future decision making on safety and hopefully will bring more light on subject to help us all understand more.
__________________
Mr F.Chimp
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#43
02-10-2013
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Quote:
If the LiPo is in a pouch and the flap remains open or closed, dumping sand on it will stop more oxygen getting to the LiPo and stop the hot ashes spewing out. Because the sand is porous, pressure can't build up. Starved of oxygen, the fire goes out and the sand stops the hot ashes spewing out on to the surroundings. If the LiPo is in a metal box with vents the sand cannot get to the source so the fire keeps burning. The fire starts due to the exothermic reaction of the separators and and conductors with the lithium, and then becomes a runaway above 150C to 200C as the electrolyte burning self-sustains the fire. In a metal box there is no way that the sand can get to the fire and smother it, so the gases keep on coming out. The electrolyte in a Lithium cell is hydrocarbons. That promotes burning. Gases ethylene (used as an anaesthetic!) and ethane are given off. Burning the plastic cases releases dioxins that are carcinogenic. That's why allowing the gases to vent in a confined space is not desirable, and using the pouch where you can get the fire out ASAP is the lower-risk option. At home if something happens when no one is around then the lowest risk is to contain the heat so that there is no 'collateral damage'. The vented steel box provides the best answer there. As the fire burns at up to 800C, make sure you metal box is insulated or placed on a large ceramic tile or concrete floor. A hot metal bottom to your tin that is sat on a carpet... There isn't one single answer to situations where risks are different. I look forward to the results of your tests and to seeing what data we can use to reduce risks further. Clearly the lowest possible risk is to not use LiPo, so let's all be careful what we wish for here...
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#44
02-10-2013
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Quote:
My research so far suggests that the most common cause of cell failure during early life is manufacturing faults. These manifest themselves in the early life of a cell. Bearing in mind cells are designed for lives of 300 to 500 cycles, our use at race meetings, where we might get 20 uses in a month at best, counts as early life. Swelling has multiple causes. Cathode materials can vaporise and decompose, gases can be released at temperatures above 60C in both charge and discharge cycles and local shorting can occur where the polymer separator material melts and prevents a short, but releases gas. No one, not even the Government departments in UK, US and Japan know for sure what amount of swelling is 'acceptable'. For as many opinions there are as many counter-opinions. We simply do not know. This thread is getting to the point where people might think we are all going to hell in a handcart. We are not. This technology is good for our sport and in the wider commercial market (something like 6 billion Li-ion-technology cells were shipped around the world last year either individually or in products with less than 20 reported incidents) the risks are considered acceptable for use to use, and aircraft to ship. Let's keep it in proportion and talk about reducing risk, not eliminating all possible incidents.
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#45
02-10-2013
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Where i admire and respect the action took to quickly contain the incidents at meetings using buckets of sand...
the best course of action and only recommendation is to get everyone away from the fire and fumes and monitor the situation... if the Lipo container does not 'hold' the blaze suitably and does cause a fire to spread then call the professionals in to deal with it, they have the training, equipment and breathing apparatus to take the risks. Currently there is an issue with sand bucket availability at meetings/clubs/venues and if it is a sensible option to deal with any incident then it needs to be looked at and taken on across our hobby. A powder extinguisher would be the next best thing for sure. The most important thing is awareness and understanding... it's ok watching youtube videos of idiots blowing up lipos for a laugh etc but educating us all on the safest way to deal with a lipo fire is the best way to stop injuries. Lipos are safe if they are used as intended and the guidelines we already have are followed. Using swollen packs needs addressing if it is proven that they are volatile, far too many racers will take the punt at charging them and continuing to use them because of being tight with replacing them or trying to finish a meeting. On a positive note i have already had a response from one distributor this morning who is keen to be involved in some testing of the lipo charge container products they sell and have stated they have nothing available info wise from manufacturer to judge how safe it is or what temperatures or pressures it will contain. The main aim of the test is to learn more about these containers in 'use' and be able to have info to be able to recommend the best product types for use in our hobby. And it is to be done controlled, fairly, in no way to damage sales or r/c companies reputations and no, i won't just be blowing lipos up in my back garden for a laugh! We all have to own and use these containers in our sport but unless a lipo blows whilst in the sacks etc we have no idea if they will do the job. On another note... if any oOplers wish to learn more about fire safety or become qualified to deal with incidents then i recommend attending MSA Circuit and Rally marshall training days, i'm sure they are still free of charge and you can get signed off as fire safety trained... BRCA is MSA affilliated so i'm sure it would be a good thing to have some more trained racers at meetings. 
__________________
Mr F.Chimp
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#46
02-10-2013
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Surely if the lipo is in a bag and the bag hasn't split/opened then the sand has no direct access to the lipo to stop the fire, it will only cover the bag and stop oxygen being available to the fire. Their will still be some oxygen trapped inside and should self extinguish?
The same applies to a metal tin, the sand won't cover the lipo only the container therefore stopping oxygen getting to the fire. The big advantage with the metal tin is it won't split open and start spitting hot fragments of a barbecued lipo at everything in close proximity.
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