in comparison to other risks that we accept
I don’t think there are many other risks which we routinely accept which are as disastrous as a high intensity in-flight fire in the cockpit.
the main risk is during charging
I think statistically that is true. But a short circuit can also happen at any time inside the appliance and that could set it off too. There should be a fuse in the battery, but you can have a high load which is not high enough to blow the fuse.
Peter wrote:
don’t think there are many other risks which we routinely accept which are as disastrous as a high intensity in-flight fire in the cockpit.
Risk is a combination of probability and consequence.
The consequence of the wings falling off is even worse than an in-flight fire. Such things have happened, but we accept it because the probability is extremely low thus the risk is also extremely low.
Airborne_Again wrote:
Risk is a combination of probability and consequence.
Yes. Lithium battery powered devices certainly pose a hazard to aviation. But with the correct strategy and equipment, we can altogether prevent them from becoming a risk.
And we need to that, because the consequences of an uncontained fire in an aeroplane, especially if pressurised and flying at high altitude, will be fatal in almost every case. There have even been cabin fires of airliners on the ground with zero survivors. So your risk equals probability times 100 percent fatal outcome. Or every single event will result in casualties unless the fire can be contained.
As already written, the main causes of LiPo fires are overcharging or overdraining and mechanical abuse. There is a video that they keep showing us during the annual fire fighting recurrent course (can’t find it on YouTube now), where a shipment of LiPo batteries falls off a forklift while being loaded into a cargo plane. The box almost instantly starts smoking and erupts into a fireball a few seconds later. There is clearly no such danger on board of a small airplane because you can’t drop anything by more than half a metre which should cause no harm. But overcharging is certainly possible, especially if using some cheapo cigarette-lighter USB plug.
So the strategy of not making a risk from such batteries at all must be:
- Don’t store them in places which are not easily accessible in flight.
- Handle the devices with care. If dropped to the floor or exposed to severe turbulence, treat them as if they could start burning every second.
- Only charge the devices in flight if absolutely necessary (on our fleet this is forbidden altogether). Always keep them in view while being charged.
- Have a safe container (LiPo safe bag or metal box) in easy reach all the time, ideally also an oven glove.
- Get the aircraft on the ground as soon as possible, even if the fire could be stopped.
A quick web search produced this.
The brochure has some information:
AVD is an aqueous dispersion of chemically exfoliated Vermiculite. Vermiculite is the name given to a group of
hydrated laminar Aluminium-iron-magnesium silicates. Raw vermiculite consists of thin, flat flakes containing microscopic layers of water.
AVD is applied in the form of a ‘mist’ or a ‘foam’. The Vermiculite particles within the mist or foam are deposited on the surface of the burning fuel to create a film over the top of the fire. This film instantly dries and because the high aspect ratio platelet particles overlap and bind together, they produce a non flammable oxygen barrier between the fire and the atmosphere. (…) The Vermiculite platelets build a
ceramic type oxygen barrier on the fuel source stopping the fire and smoke/gas generation.
Wikipedia has an article that talks about use for fireproofing: https://en.wikipedia.org/wiki/Vermiculite#Fireproofing
How is this better than an air-tight fire resistant pouch? That also removes all external oxygen. Once that happens the battery chemicals wil continue to react with each other, there is no easy way to stop the uncontrolled discharge, and this extinguisher won’ do that, either.
Vermiculite is used for building insulation and poured into new cavity walls or pumped with by air blowers into old walls, so to me this seems an expensive way to buy it. If it works I would have thought plunging the battery into an old biscuit tin fullof it would be a lot cheaper and just as effective.
Lithium battery fire in an FES glider
Never had the impression I will need one until last month, AAIB did a record publishing this after one month of investigation 
That investigation is really impressive. Very detailed, although inconclusive regarding whether they found the mechanism for the fires (in multiple aircraft).
Rather scary to see a battery going up in flames 4 hours after landing. That’s one thing avgas planes don’t do – spontaneously ignite.
I reckon the AAIB put in the effort because they can see electric planes are going to become widespread in some sectors of GA.
