Risk Is Hard: EV + Garage Edition

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A friend recently mentioned some hesitancy around parking an EV in their attached garage. I get that, kind of, we all probably remember the problems that Chevy had with their Bolt EV. They actually said out loud “don’t park it in the garage”. But it’s important to keep some context around the actual risk. While EV do occasionally light on fire, it’s not a thing that happens very often. We actually find out about it because it’s new, and unusual, i.e. news. Where a gas powered car with an internal combustion engine (ICE) is actually designed to light itself on fire, in a controlled way obviously. But “controlled” becomes “uncontrolled” way more often, and when it does, because there’s a large amount of an excellent accelerant on hand (i.e. the gas tank) the outcomes are often exactly what you’d expect. The difference is, that isn’t new or unusual. It’s just a thing that happens, not frequently, but totally within the norm. You don’t have to take my word for it, let’s look at some numbers.

The first set of numbers, which isn’t super important but does provide some useful context. There’s 33.7 kWh of energy in one gallon of gasoline. Which means that most EV batteries can store the same amount of energy as 2-4 gallons of gasoline. It’s also worth mentioning that there are different kinds of batteries (i.e. chemistries) used in EV. The more popular is lithium-ion, which is a better battery for EV use, but does have an elevated risk for thermal runaway compared to the less popular lithium iron phosphate (LFP) – which has very low risk. That’s one of the reasons LFP are great for home energy storage, and what we’re using in our passive house. There are pluses and minuses here, personally I wouldn’t want an EV with a LFP battery. But if fire is a concern that numbers can’t help with, it is an option.

So what about the number that does matter? Well, that’s even worse. ICE cars lead the way both in recalls for fire related risk, and actual fires. By a huge margin. AutoinsuranceEZ crunched the National Transportation Safety Board’s (NTSB), so US only, and found that there were 25.1 per 100,000 vehicle fires for EV compared to 1,529.9 for gas and 3,474.5 for hybrids in their dataset. Raw numbers, almost 200,000 fires for the gas cars and umm… 52 for the EV.

To be fair, we should mention that if an EV does light on fire it’s harder to put out. It’s a more complicated fire and firefighters don’t have as much experience putting out battery fires. So there is some nuance here. Personally, I really struggle to see how the trade-off isn’t still massively in favor of EV though. I’d rather have the massively reduced risk of fire than more fires that are easier to put put out. Your garage can only burn down one time 😛.

All that said, the key takeaways are:

  1. The probability that your car, regardless of energy source, will start a fire in your garage is low. But it’s a lot higher with ICE than with EV, so if you’re fine with parking the gas car in the garage, parking the EV in the garage is more fine.
  2. We’re really bad at measuring risk. It’s easy to discount the problems we’re familiar with and overbalance the risks that are new. Risk assessment is a math problem. Run the numbers, see what pops out. You might be surprised that they contradict a news cycle that promotes flame fanning.

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