Cargo fire risk

Question

If there is a fire due to a lithium battery in the cargo hold, can modern day technology in passenger planes; fire proof panels, Warning system, oxygen starvation, compartmentalisation, fire suppressants (although I've read halon gas is not effective at extinguishing a lithium battery fire) contain (or even better extinguish the fire) long enough for the pilot to do an emergency landing from 40,000 ft?

Answer 1

The answer is a complicated "Not always, but yes, but probably".

Let's uncomplicate it. First, bad news: Lithium battery fires are difficult to extinguish: they don't require oxygen to burn, and small amounts of water can react with the chemicals to release hydrogen. Fire suppression on passenger airliners uses a fire reaction inhibiting agent (Halon or Novec), which won't extinguish the lithium fire itself, but can stop or slow down the spread of that fire across less-flammable cargoes.

Good news: Lithium fire extinguishers do exist. Some are based on vermiculite-water dispersion. But these extinguishers aren't very capable.

Note how this 400 ml/ 1 kg unit has to be directed at the device, and yet is only approved up to 60 Wh, about two cell phones, while modern laptops range from 75 to 99 Wh. There's no possibility to protect the entire cargo hold this way - the extinguishers would weigh as much as the cargo.

Large commercial lithium battery transport and storage operations use water mist based fire suppression. It works, and it works even in a warehouse, without being directed at the source. But it requires some amount of water and some high-pressure pumps.

Bad news: These water mist systems aren't fitted to aircraft. It would be possible to some extent, since there is already a water tank onboard, and pumps are similar to those used for hydraulics, but it would add weight, and likely be difficult for a retrofit. Maybe someday, when you simply can't legally buy shoes without 8G connectivity, RGB lighting, NSA step-tracking and a lithium battery built in anymore, new planes will be designed with lithium-capable fire suppression as standard. So far they're not.

Good news: Almost all lithium battery fires happen inside the passenger cabin, where they can be taken care of. There have been no cases of lithium fires starting inside a passenger airliner's cargo hold so far. Should it happen, the airliner's fire suppression should be able to reduce the rate of spread of fire long enough to land, or stop it altogether. But there's only enough fire suppression agent for one of the (two) cargo compartments, it's sized for the average expected conflagration.

One reason there haven't been such fires is the rules about only taking batteries and battery-containing devices in carry-on. Batteries alone, outside a device, are barred from transport in passenger aircraft holds. There are lithium-safe containers, and, if your airliner is transporting goods containing lithium batteries commercially, they should at least be in a fire-resistant container.

So-so news: Fires are unpredictable. The fire can self-extinguish, or it can start in a suitcase or a container filled with highly flammable items, and damage something vital before the fire is suppressed; the systems can be misoperated or malfunction. The standard operating procedure in case of a cargo hold fire is to LAND IMMEDIATELY, but planes often fly over the ocean, where it just isn't possible.

Conclusion: There's no guarantee the airplane will have enough time to land. Generally, they are designed to be able to do so, but once a fire does start, the remaining safety margins are fairly thin.