Originally Posted by
Waterhorse
The risk of a lithium battery fire is a real and significant one onboard. The power supplies onboard are not as reliable in terms of voltage and frequency as the plug in your house, this increases the risk of an onboard battery fire. Consequently if a device is just being charged it must be monitored. That is why we insist that a charging device is visible and monitored by the person whose device it is. You cannot be asleep or out of sight of your device. In order to prevent endless circular arguments with passengers about this issue we say that unless you are using a device it must not be being charged and not in use.
As you say this is a real risk.
paul4040 see the LAX Fire
for a real world example. Lithium battery fires are dangerous because they can
generate their own oxygen, and pouring water on
is a very bad idea as the reaction produces hydrogen which is bad m'kay, especially when you already have a flame present.