Bike lights explode, almost burn down cyclist's house

[MikeF]

Water + Lithium.....? Bang?

Yes if it's metallic, but AFAIK a compound is used in rechargeable electrical cells. eg Sodium + water = bang, but sodium chloride + water ≠ bang.
As per above FAA advises using water.

[[XAP]Bob]

BTW one friend of mine (an electrical engineer who spent his life working in the industry) used to have no truck with so-called 'double insulated' electrical appliances; he would invariably replace the two-core mains cable with three-core and give the fuse a better chance to blow to earth (or indeed an earth leakage trip a better chance to work). If he were still alive I have little doubt that he would advocate using a typical cheapo Lithium battery charger inside a well grounded metal box of some kind, so that any fire would be contained and any (consequent or causal) electrical fault would not cause a hazard either.

cheers

What did he connect the earth wire to in the appliance?

[Brucey]

What did he connect the earth wire to in the appliance?

I'm not sure exactly what he did in every case but even if the earth wire was not connected to anything much inside the appliance, there was still a benefit for things such as garden tools where there is a very real chance of damaging/severing the cable.

In the case of something like an electric drill I would suppose that there could be a safety benefit in connecting the motor/gearbox metalwork to ground, but in some tools that might also increase the voltage stresses in some parts of the insulation.

cheers

[edocaster]

To get an 'explosion'

a) the box would have to be entirely closed and/or
b) there would have to be some means of liberating a large amount of gas very suddenly.

I did not stipulate the former and the latter seems unlikely.

The FAA video certainly showed a few explosions. The 'vent with flame' behaviour, if constrained tightly, can create huge overpressure. This is particularly a problem inside torches (although charging typically doesn't take place with cells in torches). There's at least one forum where I've seen the results of a messy explosion - namely most of the large glass panes in a guy's apartment shattered to smithereens. Granted, he bought one of those ridiculous hobbyist torches the size of a thermos flask, but the basic principle is the same.

[Brucey]

my understanding (which may be incomplete) is that the individual cells are designed to vent at a certain overpressure. If you are saying that, when constrained in a bad housing of some kind, you may get higher pressures than intended and multiple cells venting simultaneously then I'd agree this is a distinct possibility. But if it is just a four-pack of shrink-wrapped cells for a bike light, it is a bit less likely?

cheers

[andrew_s]

I saw a video (probably linked from CPF) where a 2 x CR123 torch exploded.
The owner noticed it fizzing in his belt holster, took it out, dropped it as too hot to hold, and got his phone out to record it. Shortly afterwards, it went bang, with one half of the torch ending up about 30m off, having taken the leg off a chair and gone through the UPVC frame of a sliding patio door on the way

[Erudin]

Tesla car catches fire… again:

https://www.rt.com/news/327752-tesla-electric-car-fire/

[Brucey]

I saw a video (probably linked from CPF) where a 2 x CR123 torch exploded.
The owner noticed it fizzing in his belt holster, took it out, dropped it as too hot to hold, and got his phone out to record it. Shortly afterwards, it went bang, with one half of the torch ending up about 30m off, having taken the leg off a chair and gone through the UPVC frame of a sliding patio door on the way

CR cells are lithium (one use) cells and they do contain potentially explosive material; if they catch light adding water doesn't improve matters. They are rather different to lithium rechargeables!

When CR cells were first produced they contained no internal series resistor; it turned out that if they saw a dead short they would explode in a few seconds. They had to withdraw them from sale and since then the spec has included a series resistance which means that (in theory) they are less likely to go bang so violently.

cheers