The Seduction of Spontaneous Combustion

Some like it hot, but how hot is too hot? A corollary to the composting obsession with steam is a fixation with heat, more and more heat all the the time, which can lead to fiery consequences much more literal than metaphorical. Pile fires are a real risk and relatively common mishap at commercial composting facilities with lots of big, hot heaps, and even smaller home compost operations can spontaneously combust under the right circumstances.

But why try to make your compost hot, on purpose? After all, past a certain temperature, the buildup of heat in compost starts to kill off the desirable bacteria that are otherwise happily eating the refuse and turning it into dirt. But while the bacteria might be absent, the heat still encourages other chemical reactions that can help the compost break down faster than purely biological action.

Of course, opinions vary on the target range of ideal compost temperature. Everybody seems to like temps up to about 140ºF/60ºC. True hot heads go further, even up to and a little over 160ºF/72ºC, which is where commercial compost operations tend to keep their piles.

Hotter than that, and you’re possibly playing with fire whether you want to or not. Too much sustained extreme heat starts a chain reaction inside a compost pile that’s difficult to safely arrest. You can consult this long and detailed explanation for all the chemical and biological details, but the TL;DR is more heat dries out the pile faster, which makes it heat up faster and dry out more, et cetera, with each uptick in heat increasing the chance that something in your compost pile will catch fire, which increases heat and dryness even further to accelerate the reaction, and so on.

Absent sticking a meat thermometer in your compost to keep an eye on temperature—which plenty of people do—the general advice is to keep your compost pile reasonably wet, and turn it occasionally. Note that if the compost is too hot, you should only make it wetter—turning an overheated pile can cause it to suddenly go from smoldering to openly flaming due to the introduction of combustible oxygen.

Compared to big industrial piles, the risk of home compost erupting like Vesuvius is relatively small. But it does happen, and regularly, which is one more among many reasons to not pile up your compost right next to your house or other scorchable structure. On the other hand, ash does make for pretty good compost.

It’s been a year since my father died, which is one of those sentences you’re never prepared to write, even though you know it’s coming and you only ever write it once. Probably 85ish years since the photo above was taken of my dad as a boy.

I wrote last year about my father’s death and my family’s experience of that death, and by now that experience has settled into the permanent place where one keeps such things, inside. It’s strange how it comes back in innocent ways for the rest of your life—the guy painting your house tells you something his dad said, asks if your dad says stuff like that. Or absurd ways, like a Duolingo AI chatbot asking me to explain what foods my father likes to eat, in Italian.

My parents were a largely remote and mysterious presence in my own kids’ young lives, separated by distance, their failing health, then the pandemic, and now death. I regret that separateness now, and one thing I’m trying to get better about is recording and passing on little stories about my parents and their families to my own kids, like the bit about my grandfather Ralph possibly spying on Japan during World War II.

I guess one advantage of being too online for decades is that, barring global collapse (not betting against it!), my children will have plenty of Dad Stories in blog and post form to plow through when the time comes. Maybe they’re reading this right now! Hi kids! If you have my brain in a jar somewhere, please make sure to check my fluid level. If you’re not too busy.