Quote:
Originally Posted by mark christopher
sorry pete but im going to pick up on something here
if there in a sealed bag, how did you get to the source?
your own admission says the bag was NOT sealed and flames shot out!
there is as much chance of smothering the "bunker" than a sealed correctly bag!
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Sorry, not explaining myself too well.
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...