2026-11-09 21:00:00
Eleven years ago I was on the Red Line (not the section that's a trolley), and found myself in a variant of the classic moral dilemma. I wrote about it on Reddit at the time:
Hi! I'm the person who pulled the brake. What I saw:The train starts pulling out of the station. Someone begins shouting that their arm is caught in the door. I look over, see that the door is closed somewhere between their elbow and wrist, but it's not clear exactly where with their jacket on. People, including me, start shouting to pull the brake, but no one does. The train keeps accelerating, and it looks to me like once we get to the end of the station they're going to lose their hand. I get to the back of the car and pull the brake.
After the train stops, the man manages to pull his arm into the train, with his bag still on the outside. If he'd let go of his bag I think he would have been able to do this sooner, but he was panicking as I suspect most people would with their arm half out of the train like that.
I was pretty shaken up, and didn't end up blogging about it, but it came up again at one of our effective altruism dinners. This got me thinking about ways that philosophical problems do and don't translate into real life.
In this situation the stakes were lower than in the traditional trolley problem, and the situation is closer to Scanlon's Transmitter Room (What We Owe to Each Other, quoted jokingly here). The worst case was someone's arm being badly injured, maybe permanently. On the other side was delaying the whole line for an hour, perhaps losing ~4 years of waking life in total (~25k people * 1hr / 16 / 365 = 4.3y). But were these the real stakes?
I now think his arm probably wasn't caught in the door. That's what it looked like to me, and I was very sure at the time, but people who were closer disagree:
I was in the car too -- I could tell that it was just his bag in the door, but in a split second, I was having a hard time telling how big his bag was, and I wasn't about to guess how wide the tunnels were since he wasn't letting go of his bag when the train started moving. I'm glad u/cbr ran to pull the brake -- I was one of the folks yelling to passengers to hit the call button to get the T to stop, and everyone at that end of the train just seemed to freeze. —zapdot
And:
I think what the above poster is saying is that there was a lot of miscommunication inside the car. I watched it happen from the outside and I never saw the dude's hand in the door. I saw him pulling the bag with both hands then I saw the brake come on. —dizzyrags
This illustrates a major way philosophical problems can fail to translate to real life: we're always acting under uncertainty, without knowing the consequences of our options. People understand this, and often "fight the hypothetical", but needing to make decisions when you really don't know whether you've read the situation correctly is a key part of real life morality. We need to make decisions that are robust to us having misinterpreted the situation.
(When Julia found herself in "drowning child" situation it was similar: the hard part was assessing the world, not whether to act.)
The other big way this differs from a textbook thought experiment is that it's not clear that the "inaction" case actually would have avoided a train delay. If I'd been right about his arm, I expect once the accident happened he would have been screaming even more, and I or someone else would have pulled the brake anyway. Which might well mean a worse delay, since now there's an injury involved too.
Which illustrates another way that intuitions built from philosophical problems can lead us the wrong way: this didn't occur to me at the time. It's hard to think very far ahead in an emergency, but morality problems often suggest a frame of mind where we have time to fully reason out the likely effects of each of our options. If I had thought this through it would have been an additional point in favor of pulling the brake. Or maybe I would have thought even further ahead: "if I do not pull the brake, I will become a famous example of a calculating (derogatory) utilitarian. I MUST NOT DO THAT."
Another thing I learned is that the suggestion Cialdini makes in Influence (quoted in Yudkowsky's Bystander Apathy) to point to one single person and ask them for help doesn't reliably work. When this happened I wasn't near the brake and I pointed to the person next to it and shouted something like "you, the brake!" They didn't, so I ran down the train and did it myself.
One philosophical idea that did transfer to real life is the Unilateralist's Curse. Perhaps the reason no one else on the train pulled the lever is that they all correctly perceived that the person was only in danger of losing their bag and not their arm. The one person (hi!) who came to a different conclusion still delayed the train for everyone. I don't think that was fully what happened here, since others were also shouting to pull the brake (though they were not independent observers). But since the "it's ok" position was harder to communicate, I think part of what happened was what we could call "expressivity bias", where an idea that was harder to express lost out, combined with it just being very hard to integrate diverse viewpoints under time pressure in a stressful situation.
As someone who had often speculated about philosophical problems, the experience of being in one was very stressful, and it's not one I hope to repeat.
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2026-11-08 21:00:00
I have very strong views on lying to kids: I think you both should and shouldn't do it. "Lying" covers a range, including saying things that hurt your kids and your relationship with them, and others that help them grow into an appropriately skeptical adult. The distinction is whether I'm leaving them believing something false.
For example, if my kids were asking for ice cream and I thought they'd already had too much sugar, I might be tempted to say "sorry, we're out of ice cream." Or if there's an ice cream truck and I think it's overpriced I might be tempted to say "sorry, I don't have any cash on me." But I'm not willing to say something false with the goal of causing them to believe something false. [1] In addition to that just being wrong:
It's important that the kids know that I'm fundamentally on their side, and lying for my convenience would burn trust when they'd eventually figure it out.
Kids are building a model of what is and is not ok, and "out of ice cream" and "no cash" lead them in the wrong direction.
Instead I would say "sorry, you already had candy" or "the ice cream costs more than I'm willing to pay" (which opens the door for them to offer to spend their allowance). Maybe they fuss, but they generally don't: I try hard to be predictable so this won't be much of a surprise to them, and they know I won't give in to extended fussing.
On the other hand, some false things I might say [2] about ice cream:
In all of these I'm saying a thing I think is false, but, very importantly, I'm not going to let the conversation end with them believing something false. Either they will realize it's false immediately, or I'll need to accept that my playfulness was miscalibrated to their perception and disclose the lie.
This builds the skill of thinking about whether things you hear are true. If I only ever said true things to them we wouldn't be able to practice that. This does need to be matched to their ability: a very little kid will push back on "you're made out of ice cream, and I'm going to eat you up!" but not "we can leave the ice cream out as long as we want, it won't melt."
It also functions as a good jumping off point. If I suggest they pour their ice cream on the floor when they're done with it, that lets me reinforce or explain good behavior. This could go different ways with different kids, with age being a large component. Thinking about how this might have gone with my kids:
Age 7:
Me: When you finish your ice cream, remember to pour it all over the floor!
7yo: That would make a mess. Leftover ice cream goes in the sink.
Age 5 [3]:
Me: When you finish your ice cream, remember to pour it all over the floor!
5yo: That's silly! It goes in the trash.
Me: Actually, leftover ice cream goes in the sink. It's going to melt, and get all liquidy, and liquids go in the sink.
Age 3:
Me: When you finish your ice cream, remember to pour it all over the floor!
3yo: No!
Me: Why not?
3yo: Food doesn't go on the floor!
Me: Where does it go?
3yo: I don't know.
Me: You give it to me, and I put it in the sink.
Age 2:
Me: When you finish your ice cream, remember to pour it all over the floor!
2yo: Ok! [immediately pours ice cream on the floor before I can clarify that this was a joke]
Which does illustrate something important: you really do need to be a good judge of the kid you're interacting with. These depend on the kid knowing the actual rule well enough that you can play with it. I only want to say "let's juggle ice cream" to a kid who knows enough not to try, but if they do know then me being silly about it reinforces the "don't juggle ice cream" norm and signals that I trust them enough to know they wouldn't do it.
The final reason I say false things to kids is just that papa trolling is fun for both of us, as long as I don't do it too much. [4]
It is a bit weird to be both very strongly opposed to lying to kids and also say false things to them many times a day, but "am I leaving them with a false view" cleanly separates the harmful and beneficial cases.
[1] This means we don't tell the kids that Santa
or the Tooth Fairy exist. But we do explain the overall
situation, with how for some families it's a game the parents play
with their kids, so that we don't have our kids going around spoiling
it for other families.
[2] The first draft of this post had "everyone can have ice cream except Nora" but then I checked with her and it wasn't clear she would have understood it to be joking about unfairness. Then I asked her about "when you're done with your ice cream, put it down your sister's back" and she got it right away.
[3] After writing this post I tried it with Nora, age 5.4:
Me: Nora, I wanted to check that you know something. When you're finished with ice cream, it's important to pour it all over the floor.
Nora: No! [laughs]
Me: Why not?
Nora: Because then you and me and Mama would need to clean it all up!
Me: What should we do instead?
Nora: Just leave it alone.
Me: So the cats can knock it over?
Nora: No, put in the... sink... trash... hmm...
Me: Does ice cream go in the sink or trash?
Nora: [whispers] For real, can you tell me?
Me: Leftover ice cream goes in the sink, because it melts, and liquids go in the sink.
Nora: [confidently] You carry the ice cream over to the sink, put it in the sink, leave the bowl in the sink, and then you're done!
[4] I do some of this with adults as well, as a big part of my sense of humor. It's not a considered approach to building skepticism, just what comes naturally. I think some of this is from my upbringing, in a very "questioning is a form of respect "culture (influenced by both the Quaker and Jewish sides of the family).
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2026-11-07 21:00:00
I recently finished the largest set of changes I've made to my rhythm stage setup in 4.5y. The basic interface is similar, but I have a lot more flexibility, more control, more options, and it's easier to travel with. My favorite part is the speech recognition for calling chords.
I started off playing mandolin and piano, and then over the years added progressively more expressive footdrums. I added a breath controller. I built out a complex but expressive system where these different interfaces could interact to let me produce a coherent rhythm section. After a frustrating experience moving from one Mac to another and wanting to simplify, I moved from the Mac to a Raspberry Pi, set it all up as a pedalboard, and then again as a lighter pedalboard.
During the last year and a bit, however, I haven't been tinkering. It did what I wanted, in a reliable and portable fashion. And it was hard to modify: the pedalboard was static, and the Raspberry Pi code wasn't easy to get at either. Which was fine, and probably good for me! I just played a lot of gigs (23 Kingfisher, 3 Free Raisins, 3 Dandelion) and got better at it.
But then it started breaking. My whistle synth box didn't always come up, the drums sometimes needed an external DI, and a USB sound card snapped. Flying back from Atlanta my gear suffered rough enough treatment to bend a USB B connector, and it was clear my system needed some love.
I started with the most urgent portion: the whistle synth. I had Claude port it over to my laptop, where I turned it into a Mac app. This also let me add several more voices, and a mute option that never made loud clicks (I'm not really a hardware person).
This project made me realize that AI getting capable meant that the tradeoffs around laptop-vs-embedded had shifted. I could have everything on my laptop, and without needing to put painfully large amounts of time into programming it could all be fully defined in code instead of manually-configured GUIs. Having it on my laptop would make it easy to apply models to modify and improve it, and open up a lot more lexibility.
I decided to move as much as possible over to the laptop. This meant no more Raspberry Pi, whistle synth box, physical switches for signal routing, and computer code instead of guitar pedals. I moved from:
To:
Four fewer pedals, three fewer DIs, two fewer power bricks, and no little computers. Saves ten pounds: 32lb to 22lb. The Mac weighs ~3.5lb, but I'm traveling with it regardless.
Of these savings, 3lb (2.7lb of talkbox + 0.3lb of power supply) was from giving up the talkbox. I liked how this simplified my setup, including less complex audio routing, but after playing Moondance both Cecilia and I really missed it. So I added it back:
A large benefit of moving to the Mac is I can now see what I'm doing. I control my rig with an external keyboard, covered in little labels that remind me what each key does:
For example, before playing Trip to Moscow I would probably press FB (footbass), S (make footbass play synth bass), FX (breath-controlled keyboard overlay), set the drums to custom kit 63 (electronic kit), and then press L (keyboard velocity-insensitive bass overlay) and change the keyboard to epiano2 when we got all electronic. And press JH (breath-controlled bass-following low bass) at some point partway through for more ability to pulse the offbeat. Without a monitor, I needed to keep this all clear in my head, which was especially important since many settings are modal or interact. I usually didn't mess up, but partly because I tried not to dial in anything with too many presses.
Now I can just represent the state on my monitor:
This is also very helpful for showing which voices apply to which instruments. Previously I needed to remember that on FX (breath-controlled overlay) the B key would give me a supersaw, while on Dc (chord drone) the B key was a different voice (I forget what). Now I can choose a set of voices for each instrument that are the ones that sound best with this kind of control, without worrying about how I'll remember which button gives me which sound.
This is basically all "what I had before, but easier to control". Which is good, but the real payoff comes from making it much easier to extend the system. I've done a lot here, with extensive help from Claude Code, and it's going to take me a bunch of time to learn how to play these new options well.
A big one is that because I now route my mandolin through the system I can replace pedals with code, add more effects than it was worth carrying pedals for, and write effects that consider what other things in the system are doing. This includes using the breath controller as an expression pedal, or tonal effects that care about the active chord. Demo video:
I also added speech recognition, where I can turn things on and off vocally, and even call chords. For chord calling I had Claude make me a custom speech recognizing system for the numbers one through seven (Nashville numbers) trained specifically on my voice and optimized for minimizing latency (decision in 40-170ms). It also runs Apple's in parallel, primarily to allow learning from mistakes but also to handle numbers the custom one misses and any non-number commands. Here's a video from earlier today, showing how I was still working to improve both my call timing and the code that triggers the changes; you can hear that many changes are off by a beat:
Here's a short updated video after a bunch of work this afternoon and evening to make number calling more reliable (af196263f). This involved adding a prior that chords run for a multiple of 2 beats on a grid implied by previous called chords, better word boundary identification, and a bunch of parameter tuning where I made recordings as I worked with it. I'm much happier with it now, and the two mis-timed changes in the video below are me calling early (0:59, 1:15):
I'm also trying to figure out new things I can do with the breath controller, and one thing I've been playing around with is percussion:
Other stuff:
Vocal effects, including ones like a vocoder that care about the currently active chord. Not sure I like any of these enough yet to use live.
Cecilia needs to hear my mandolin playing, but gets plenty of computer overlays in the monitor wash already. This was a problem with talkbox, which can be fed by either the mandolin or computer. Now that it's all running through my box, though, I can make talkbox go to the mandolin output channel if mandolin is included, and to the computer output channel otherwise.
I auditioned and added a lot more voices. Including adjusting which voices are available for which instrument by replacing some that didn't work with that instrument's method of articulation. I don't know if any of them are worth it yet, though: I still mostly do the small number of things I like.
I added French Canadian feet back into the system, after discarding them when I switched to the Raspberry Pi. They're no longer samples, but synthesized, which lets me use how hard I stomp or the breath controller to adjust how hard the hit is. I like these a lot, and used them live to good effect at the one gig I've done since this change.
I also added a "stompy feet" option which is feet with a bassier kick, a "bare feet" option with sounds synthesized to imitate my own bare feet, and a "hand drums" option which was a Claude "happy accident" that sounded interesting enough to keep. I'm not sure I'd actually use either of the second two, though.
When used stand-alone, the Focusrite 2i2 takes in a mic (whistle bass, calling chords) and mandolin and gives two channels (computer and mandolin + feet, though really it's "doesn't go to Cecilia's monitor" and "does go to Cecilia's monitor"). I've also added integration for my custom 1818VSL mixer, in which case you skip the 2i2, run the mic and mandolin into channels 1 and 2, and all my processing happens automatically before the mixer sees channels 1 and 2. Kind of an automatic effects loop.
I added recording to the custom VSL mixer, including logging MIDI signals and keyboard presses so it's easier to evaluate later (or tweak if we wanted to turn recordings into another live CD).
I'm toying with starting to run our own monitors by default with the VSL, since it has enough output channels to pass my normal outputs to the sound board and then also give a mix to each of us. I'd use XLR Y-cables on the other inputs so the board would also get a full copy of everything.
Outputs can now be stereo, in case we wanted to switch to in-ear monitors. But I really like stage wedges for feeling connected to the dancers: being responsive to them in the moment is, to me, a big part of the appeal of playing live for dancing. And it would be a fourth thing connected to my head (after the mic, talkbox tube, and breath controller) making me even more borg.
My keyboard (Yamaha P-121) includes USB audio support, and I already have it connected to my computer over USB for MIDI purposes. Using this stream avoids several lossy steps, and I've made the VSL mixer bring it on as an "input 9" when available. Sadly if I'm ever working with someone's P-125a keyboard, the "a" means that they dropped the USB audio feature.
I added a bunch of features with technocontra in mind (kick ducks, pads, weird effects) but I don't think I like any of them even for technocontra. Not sure yet.
I tried a version where whistling picks a chord, but didn't end up liking it at all.
One cool thing about a whistle-controlled synthesizer and speech recognition is that I can do both of them at once on the same mic: they're very easy to tell apart.
Overall, I'm still mostly playing live with only a small portion of the possibility space I've built for myself with this instrument. Some of this is that a lot of things that are possible turn out not to be very effective in a noisy dance hall, or just don't sound good anywhere. Some of this is that there are some very neat things that it's possible to do that I haven't practiced well enough to take advantage of. And some is that I just forget to try some things live.
When I switch to pedals choosing bass instead of being drums it now switches to a preset that's a better fit for that, so I press one button ("DCN": drum chooses note) instead of several ("DCN", "FB", "D", "v", "+", "+", "+", oct up).
This post took me way too long to get out, both because I keep adding to the system and because I'd rather make demo videos once I'm good at controlling the system. Since that kept resulting in not publishing, I've lowered my threshold to get something out. I can always follow up as I do more, and several of the ideas above would have been better as their own posts.
The code is all on github if you or your agent would like to look:
2026-11-06 21:00:00
Reading the comments on my post on junk I was surprised to see the extent to which people's relation to rarely used possessions varies.
Some people forget rarely used possessions, and get minimal benefit from having them stored. When they need something, they don't know whether they already have it, and the effort to maintain an index [1] wouldn't be worth it. Ben writes:
I end up with curtains I don't need. I decide to store them for the future in case they are helpful. Years pass. I need new curtains. I have forgotten the ones I kept, so I buy new ones and put them up. Months later I find the ones I kept while looking for something else.
Other people know exactly where everything is, and can walk down to the basement and make a beeline for a tiny thing they put down there years ago. Sarah writes:
I can remember where I put a specific doohickey that my brain labeled as "this could be useful" years later with very little recall effort; something will come up that actually matches the need for the thing, a little triumph, and I go to the spot where I buried my acorn and get it.
I'm somewhere in between, though closer to Sarah. I usually remember what I have stored when it could be relevant, though I'm less good at the where. One strategy I use a lot is to imagine I'm putting the object away, and I'll even walk the path. Wherever seems good now has a good chance of being the place that seemed good when I actually did have the thing to put away. Other times, though, I have no idea whether any of my stuff might be useful for a problem or project, and I'll just wander around the basement looking for ideas.
Then there's another way people vary, which is how much having stuff, even out of sight, weighs on them mentally. For some people, including me, it's mentally costless. Just like it's not a problem that I "have" 2,615 blog posts, or that I've read hundreds of books, I don't think about the objects in the basement when they're not relevant. To others, however, "excess material is like a pressure on my mind until it's properly stored, sold, donated, or otherwise disposed of." And some find this so burdensome that they don't believe it when we say it's not.
The "burden" axis probably leads to minimalism fads: people with a "burden" disposition like to write and share self-help books on how to avoid it. But maybe an even bigger contributor is cultural holdover. When objects were more durable and people were less wealthy, keeping things in case you needed them someday was very helpful! So some of us inherited strong "keep things" culture. But someone living in an apartment has a small amount of valuable space, and using it to store things you probably won't need is not worth it. Plus, if you're moving every September 1st, it's even less worth it! [2] Pushing the culture to update is probably valuable, even if the advice doesn't suit everyone: it helps people get out of patterns that are a bad fit for the way their particular brain works.
I am curious what leads to this range of dispositions, though, and how people distribute along the "remember where stuff is" and "having stuff is a mental burden" axes.
[1] My grandfather took this a different way: he had a very thorough
index. It was pages and pages of small items he happened to have in
his basement, along with exactly where to find them. Each shelving
unit, dresser, or bookcase had a letter; each shelf or drawer had a
number. You could look through it in alphabetical order:
...
Vacuum tubes, Q3
Varnish, B10
Velcro, J2
Viola Case, G8
Violin Carving Tools, D3
Violin Rosin, J12
Voltmeter, Q1
...
Most summers we'd visit for a ~month, because my aunt was a teacher with summers off and could watch the group of cousins. We'd have the run of the house, and would often make projects from things in the basement. We never asked what we could use, and I suspect we made a mess of his system, but he didn't seem to mind.
[2] Even though accumulating low-value stuff works well for me dispositionally, I didn't do very much of it until we bought a house which had an unfinished basement.
2026-11-05 21:00:00
In many disasters sheltering in place can make a lot of sense, but what about fire? As someone who lives in one of the densest municipalities in the country, with 3-story wooden buildings packed close together, is fire likely enough to rule out any kind of "stay put" approach? After having Claude do some rough calculations I think probably not.
Very few houses are lost to fire anymore, but this is mostly downstream from putting a lot of effort into suppression. From when a fire is reported until firefighters are on the scene is typically an impressive three minutes, and they can very quickly be delvering massive amounts of water onto a fire anywhere in the city. If an emergency were bad enough to break or overwhelm this system, a fire anywhere could lead to city-wide distruction.
Still, I really didn't have a good sense of scale here. If we had a month-long fire suppression outage, are we talking 10%, 1%, 0.1% chance of fire? Historically, I would have tried to do a BOTEC, but these days I set Claude on the problem. I started with Opus 5.5, but after it didn't seem to be doing a great job I spent $29.93 to put Fable 5.1 on the problem (prompts). I don't know if Claude would beat an expert here, but after skimming what it did I think it's well above my historical level of modeling.
It estimated from historical fires, and thought our monthly risk was ~1% (but could easily be 5x higher or lower), and if our block worked together in a disaster we might reduce risk by 4x. It also thought that my dad's house in Medford (less dense) was ~4x safer, as was my sister's house in Brattleboro VT (even less dense). If you want to play with it for your house, feel free to point an LLM at the code.
For three New England houses, the modeled chance of burning during 30 days without fire suppression is about 1.2% in dense Somerville, 0.30% in Medford and 0.24% in Brattleboro if nobody defends the house. Preparing one house cuts that by between a fifth and two fifths, and a whole block preparing cuts it four to eight times. The estimates are rough: for Somerville, changing one assumption at a time moves the figure between about 0.2% and 6.5%. Chance that the house burns in a 30-day period with no hydrants or fire department, using annual-average weather and the central ignition rate. Somerville and Medford share the same weather, and both are seasonal: about half of each house's risk comes from red-flag days, and dry gales at Boston Logan fall almost entirely between November and April. Brattleboro is not seasonal, because its nearest airport record has no such days. Red-flag days matter for both Massachusetts houses, but more in Somerville. On a red-flag day a fire can reach the Somerville house from a median of about 7,400 buildings and the Medford house from about 1,900, because the streets around the Medford house are less tightly packed. Red-flag days are 48% of the do-nothing risk for each; windy-and-dry days add another 36% in Somerville and 12% in Medford. In Brattleboro nearly all the risk is fire in the house's own cluster of buildings on ordinary days. The Keene record has no red-flag day in 20 years, and if one came, a fire could reach the house from about 150 buildings. The model treats every building as a node and asks, for one house, which other buildings' fires would reach it. "Wind" is the fourth-highest hourly sustained wind of the day, so at least four hours at that speed. Somerville and Medford use Boston Logan; Brattleboro uses Keene, the nearest long airport record. One part of the model is fitted to data, the short-range spread curve. The rest is checked against historical fires where that was possible. Short-range spread, fitted to Los Angeles 2025. The data are LA County building footprints joined to CAL FIRE damage inspections for the Eaton and Palisades fires: about 45,000 buildings, of which about 22,000 inspected residences are the targets. Each residence's chance of burning is modeled as a background term, set by how much burned 50–250 m away, combined with a per-neighbor spread probability for each destroyed building within 40 m. The data show no downwind stretch and no effect of building height. Lost, or merely damaged. Where little else nearby burned, houses within 1 m of a destroyed building were lost 95% of the time. At 2–3 m, 51% were lost but 76% were damaged; at 6–8 m, 40% and 58%. Many exposed houses caught fire or were scorched and then survived, most plausibly because someone put the fire out. With nobody to do that, damage is the better guide to what would be lost, so the model uses the fit to any damage. Its 50% distance is 5.2 m (90% interval 4.9–5.6 m from a spatial block bootstrap) for a 120 m² source, and it falls off roughly exponentially. An earlier version of this model used buildings lost (50% at 4.3 m) and a curve shape that could not rise above 75% even for touching buildings. A physics cross-check, and taller houses. Treat a fully burning house as a flat radiator at 84 kW/m², the figure behind building-code separation tables, and ask where the heat reaching the neighbor exceeds what ignites it. For a one-storey Los Angeles house facing stucco, the 50% distance is 3.7 m, close to the 3.5 m fitted for houses lost. For heat enough to ignite wood or vinyl siding, or to break windows, it is 6.0 m, close to the 5.2–6.2 m fitted for any damage. For a 2.5-storey New England house with wood or vinyl siding next door it is 7.5–9.5 m, that is 1.25 to 1.6 times the Los Angeles figure. The model stretches the fitted curve by 1.3. That is a judgment: the physics supports it and the Los Angeles data, with little variation in height, do not show it. The same calculation puts ignition at 4 m near 95%, well above the 64% used. Real fires are less regular than a flat radiator: walls face different ways, fences and trees intervene, and some houses burn down before they radiate much. The fitted curve keeps that irregularity. The calculation also shows that radiant heat from one house cannot ignite another beyond about 15 m, so spread at that range in Los Angeles was wind-driven, and the model removes it on days without strong wind. Does the fit measure spread, or only correlation? Fires were simulated on the real LA footprints with known spread parameters, then fitted the same way. Across five parameter sets and three background levels, the recovered curve was within about 0.05 of the true probability at 2, 5 and 10 m. This test was run on the earlier curve shape. Chelsea, Massachusetts, 1908. A gale reported at 40–45 mph burned about 2,800 buildings over 492 acres. Nearly everything between the railroad and the waterfront burned, and one building was lost north of the tracks. Run on today's Chelsea footprints with red-flag settings, a fire front arriving at the upwind edge burns 90% of the downwind district on average, and a single ignition inside it burns 100 or more buildings in 82% of runs. The model also burns 13% of the buildings just north of the railroad, where in 1908 firefighters held the line. Without the adjustment for taller houses the front burns 85%. Today's Chelsea is a stand-in: it was rebuilt after the fire, and 1908 roofs were largely wood shingle. Chelsea 1973 sets the red-flag threshold. On October 14, 1973, a fire burned 18 blocks despite a very large mutual-aid response. Boston Logan recorded sustained wind of 35–50 km/h from the west and humidity of 23–28% that afternoon. The red-flag class starts just below that day's wind. Spread rates. The 1908 fire reached its far end, 2.4 km away, in five hours: 480 m/h. In Kobe in 1995 fires spread at 20–30 m/h in light wind, and about 20 m/h faster for each extra metre per second of wind, which gives roughly 180 m/h on a windy-and-dry day. These set the travel-time limit. Kobe 1995 as a calm-day check. Kobe had light wind (2.6 m/s), humidity near 70% and no hydrant water. Of 150 surveyed fires, 49% stayed in one building, 29% burned 1,000 m² of site area or more, and 4.7% burned 33,000 m² or more. In dense Chelsea streets the model's calm days give 16%, 69% and 3%, and its ordinary days 13%, 76% and 26%. So the model now spreads fire further than Kobe saw, most of all on ordinary days. Kobe's brigades put out many fires early and others stopped at wide streets and concrete buildings, so some gap is expected, but this is the least settled part of the model. Around the three houses themselves, ordinary-day fires stay small, with a median of 3 to 8 buildings able to reach each house. Defense levels against bushfire evidence. At Mount Macedon in 1983, residents who stayed had about a 90% chance of saving the house, against about 44% losses among those who left. On Black Saturday in 2009, 77% of defended houses survived against 44% of unattended ones. Those imply defended houses were lost 20–40% as often. The model's "prepared" level gives 60–80%, weaker because most exposure here is heat from a burning neighbor a few metres away. No data were found on defending against that. Forest fire in Brattleboro. Vermont averages about 80 wildland fires and 157 acres burned a year, out of about 4.5 million forested acres. The model assumes 30 times as much would burn with nobody putting fires out, in line with 1903, when over 5,000 acres burned before the state had fire wardens. When a patch of forest burns, buildings within 30 m of it ignite with a probability of up to 20%. National land-cover data show forest over 54% of the area within 2.5 km of the Brattleboro house, but the house is a few hundred metres from the nearest patch, and none of the buildings that can carry fire to it stand at the forest edge. The forest term adds less than 0.001 percentage points. A house right at the forest edge would gain about 0.002 points, and assuming a hundred times today's burning in place of thirty would still leave that below 0.01. In this model, the buildings next door matter far more than the woods. What could not be fitted. An attempt to fit ember spotting on the LA data failed: the burn pattern there looks like a regional ember storm, not building-to-building spotting. How much of the wind-driven part of the curve applies on windy-and-dry days is also a judgment, and those days are 36% of the Somerville figure. Two Massachusetts fires that beat a full fire-department response (Lawrence 2008 and Lynn 1981) happened on days the model classes as ordinary. Each row below changes one assumption and leaves the rest alone. Which windy days count as dangerous. Gale-force wind occurs on 3.5% of days at Logan, but 64% of those days have rain. The model counts a gale day as red-flag only if there was no rain that day or the day before and humidity was 50% or lower. That rule is a judgment call, and it matters: Rain mostly stops embers from lighting roofs, debris and fences; it does little to stop a burning house from igniting one three metres away. Half of the red-flag days are below freezing, and snow cover, which the model ignores, would reduce spotting further. How the estimate got here. The Somerville figure has moved a long way as assumptions were replaced with data. The ignition rate. US fire departments attend about 358,000 home structure fires a year, roughly 7 per million housing units per day. With a fire department responding, 24% spread beyond the room of origin and 38% are small confined fires, so between 24% and 62% might grow to involve the building with no response. At about two housing units per 100 m² of footprint, as in Somerville, that gives 4 to 9 per million per day, which brackets the central value of 6. On single-family streets the same reasoning gives 1 to 3, so the Medford and Brattleboro figures may be two to three times high on this count. No measured figure was found for how much a long outage raises ignitions through candles, generators and improvised heating, which pushes the other way. Known gaps. The code is at github.com/jeffkaufman/fire-risk-without-suppression. It runs for any address given coordinates and a nearby airport weather station, and includes the scripts for the fit and for each check above. The three houses' locations are not in it. Data: Historical fires, read in full: Figures taken from abstracts or summaries, not the full papers:Claude Output
Results
House
Do nothing
Attentive, no prep
Attentive and prepared
Whole block attentive
Whole block prepared
Somerville MA (dense two- and three-family streets)
1.2%
1.1%
0.80%
0.87%
0.32%
Medford MA (less dense)
0.30%
0.25%
0.17%
0.16%
0.04%
Brattleboro VT (small town)
0.24%
0.23%
0.19%
0.11%
0.03%
30 days
Somerville, do nothing
Somerville, attentive
Somerville, prepared
Medford, do nothing
March weather
3.0%
2.7%
2.1%
0.65%
December–April weather
2.1%
1.9%
1.5%
0.48%
June–September weather
0.31%
0.25%
0.17%
0.13%
How the model works
Day type
Definition
Share of days, Boston Logan
Share of days, Keene NH
Distance multiplier
Share of the curve beyond 15 m kept
Ember strength, length scale
Calm/damp
Rain that day or the day before
43.0%
37.6%
0.8
none
none
Ordinary
Everything else
54.4%
62.2%
0.9
10%
0.002, 40 m
Windy and dry
No rain, humidity ≤ 50%, wind 32–40 km/h
2.3%
0.2%
1.0
50%
0.010, 60 m
Red-flag
No rain, humidity ≤ 50%, wind ≥ 40 km/h
0.32%
none in 20 years
1.0
all
0.030, 90 m
Calibration and checks
What moves the answer
30 days, do nothing
Somerville
Medford
Brattleboro
Central estimate
1.2%
0.30%
0.24%
Ignition rate 2 to 20 per million per day per 100 m²
0.39% – 3.7%
0.10% – 0.98%
0.08% – 0.79%
Adjustment for taller houses, none to 1.6×
0.47% – 1.9%
0.12% – 0.58%
0.16% – 0.41%
Windy-and-dry days keep 25% to 75% of the curve beyond 15 m
0.96% – 1.4%
0.28% – 0.35%
0.25%
No travel-time limit on wind-driven days
4.6%
0.52%
0.25%
Firefighters save exposed houses as often as in Los Angeles
0.17%
0.05%
0.10%
Gale days counted as red-flag
Share of days
Somerville, do nothing
All of them
3.5%
6.5%
No rain that day
1.3%
2.8%
No rain that day or the day before
0.63%
1.7%
Also humidity ≤ 50% (the rule used)
0.32%
1.2%
Also humidity ≤ 35%
0.16%
0.89%
Version
Somerville, do nothing
All parameters guessed
5.7%
Spread fitted to buildings lost in the LA fires (50% at 4.3 m, not 5–16 m)
1.6%
Day-type frequencies measured at Logan (red-flag 0.32% of days, not 5%)
0.18%
Footprint window widened from 2.5 km to 5 km
0.21%
Spread refitted to any damage, with a curve that reaches 95% for touching buildings, and stretched 1.3× for taller houses
4.6%
Travel-time limit on wind-driven days
1.2%
What is fitted, what is judgment, and known gaps
Status
Parameters
Fitted or measured
Short-range spread curve for one-storey stucco houses in extreme wind (LA 2025); day-type frequencies and wind roses (airport observations); forest cover (national land-cover data)
Checked against history, not fitted
Spread on red-flag days (Chelsea 1908); the red-flag wind threshold (Chelsea 1973); downwind spread rates (Chelsea 1908, Kobe 1995)
Judgment
The 1.3× adjustment for taller wood-sided houses; how much of the curve beyond 15 m applies on days with less wind; ember strength; the rain and humidity rule; lower ignitability of large and commercial buildings; the defense multipliers; how much a disaster raises ignitions; the forest-fire settings other than Vermont's burn rate
Code and sources
How high is 1% per month? It means in ~6 years it becomes more likely than not. But even a few months of a disaster bad enough to prevent fire suppression would mean widespread starvation, since most people keep very little food on hand (and the density is far higher than the land can support). There are also a lot of very serious disasters where we still have fire hydrants: they're a pretty high priority for emergency response, and living in a low part of the city our water is gravity-fed from Quabbin.
Overall, I don't think I should be factoring fires heavily into thinking about what kinds of precautions and plans it makes sense for us to take. This is surprising to me, given how flammable and close the houses are, but mostly comes down to disasters that are bad enough to lose fire suppression are not very survivable.
2026-11-04 21:00:00
Occasionally people will get excited about a minimalism fad, where you figure out which of your possessions you need and keep only those. As someone who generally doesn't like getting rid of things, I've been thinking some about why, and the main thing I keep coming back to is that random objects can be helpful in unpredictable ways. Here are some things that I kept without a specific use in mind, but that ended up being useful. You could say they saved time or money, but often the biggest gain was from being able to do a project in one go with what I already had on hand:
Ethernet cable. Back in 2019 if you'd asked me whether I would ever use ethernet again, I would have said probably not. WiFi was good enough for everything I was doing. But then I (like a lot of us) suddenly started working from home and got frustrated about how poorly my internet was working for video calls and ran ethernet to my desk. Having cable on hand already meant I could just set it up.
Plexiglass. When I built my accidental electronic instrument I wanted to protect it, and had plexiglass left over from when I added an insulating layer to a single-pane window.
Scrap wood. So many things. To give one example, when one of the stairs in our basement fell apart, I was able to replace it with extras from past projects that I'd kept around.
Similarly, when Lily came back from visiting a friend enamored of their prop axe, she had everything she needed to make one already in the basement:
Computer mouse. One of my housemates was having wrist issues, and wanted to try out using a mouse on the floor. They ended up hating it after a day or so, but being able to pull one out of the junk electronics pile and try it made for quick experimentation.
Plastic sheeting. When we wanted to divide our apartment in two so we could isolate a new housemate I had sheeting left over from an earlier project.
Screen. When I wanted to make a screen door for our kid door I already had window screen lying around.
Hinge. Lily wanted to make a "laptop" for Anna as a present, and I had an old hinge lying around from who-knows-what that was just right for having it stay open at the right angle. Here's the laptop after Anna decorated it:
And with the hinge it closes just right:
Volleyball net. When we went back to the vacation house where Nora had a close call with a fountain, we wanted to put up a barrier. The kids would probably have been fine without, but we wanted something that would clearly mark it as out of bounds. We got some chicken wire, but realized when we were packing that it was only about half as long as we needed. An old volleyball net made up the difference:
Hand saw. I would have said there's no situation in which a traditional manual crosscut saw is the best tool for the job, but when the city cut down the tree in front of our house for being diseased, Lily wanted a piece of the stump to remember it by. She really wanted to cut it off herself, without assistance from electricity or other humans. Luckily, I still had the tool for that:
She did change her mind on help after realizing how hard it was, though I don't think Nora was very helpful:
Having a wide range of objects in the basement is something I find useful on a regular basis. One thing I like about projects is that they often leave me with interesting scraps I can use for other things. I especially like that they're not very valuable, because that means I feel much more free to play with them.
If we were moving often, or didn't have a large unfinished space, of course, the tradeoff would be different. And many things go into the basement never to be used again (so far!) Since we do have the space, though, keeping things without knowing what we might need them for seems well worth it.