Sunday, August 06, 2023

Why burning batteries is not a big problem for EVs

My nephew is an electric vehicle (EV) engineer in the UK (mainly buses, as it happens), but he doesn't actually drive an EV himself. I asked him about this once, and he says it's too expensive to charge with electricity in England (electricity is relatively expensive there, but I don't think he's done his homework there, as Britain's RAC reports), and also he's worried about them bursting into flames overnight while charging. 

I did't take him to task there and then, but I wondered if he had a point about that. According to SlashGear, lithium-ion batteries in fact can (and do) catch fire if they become damaged and short circuit internally, or if they enter into a "thermal runaway" due to a manufacturing defect or degradation, or if they are overcharged or charged at an excessive amperage. Once on fire, they are hard to extinguish - water can actually make things worse, and special chemicals (like copper powder, carbon dioxide, graphite powder, sodium carbonate, or "extinguishing foam") are needed to properly extinguish them.

That said, this is not a very common occurrence. Statistics are hard to find, but Tesla (which makes by far the most popular EV) reports that, between 2012 and 2021, there has been one fire for every 210 million miles driven by Teslas. For context, in that time, there has been one fire for every 19 million miles driven by traditional internal combustion engines vehicles - yes, gas cars burst into flames too - making EVs about ten times safer than gas vehicles (these figurescare from the same SlashGear article).

Another analysis based on data from from National Transportation Safety Board (NTSB) and International Energy Agency (IEA) estimates that 0.025% of battery-electric vehicles are likely to ignite, compared to 1.5% for gas-powered vehicles and a whopping 3.4% for hybrids (including plug-in hybrids). This makes the chances of EVs igniting some 60 times less than gas cars, and 139 times less than hybrids), so, once again, EVs come out as the safest option. (It's not clear from this article why hybrids are at such an elevated risk of fire, and the figures for gas cars and hybrids seems way too high to me, but that's what the study says.)

And just for good measure, data from Sweden suggests that EVs are fully 20 times less likely to ignite than gas/diesel cars (0.004% compared to 0.08%). Note that all of these figures are based on relative percentages, and so are not due to the fact that there are much fewer EVs than ICE vehicles. 

What IS a potential problem for electric vehicle batteries is salt and salt water. After Hurricane Idalia, some firefighting departments in Florida have warned that EVs that were flooded with salt water in the storm surge could be prone to spontaneous fires, because the dried salt can act as a bridge between battery cells and potentially cause fires, even if the EV appears to work perfectly well. This is a very specific problem, and owners of sea-flooded vehicles should probably look to replace their batteries (and maybe relocate to somewhere less disaster-prone).

So, should I go back to my nephew with this data? In the interests of family harmony, probably not.

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