Opinion

A multi-level postmortem of how our whole house got badly poisoned

​Published on February 14, 2026 4:11 PM GMTTaking reasonable choices is not enough. You need to fight death at every possible point of intervention.Two weeks ago, my flatmates and I published Basics of How Not to Die, to celebrate the one-year anniversary of not dying from carbon monoxide poisoning.This post was written with a rather cheeky tone, mainly by my flatmate Camille. I like the style, but I feel like it lacks hard data, and gives advice that may not actually be worth the cost.In this post, I’ll give you a more detailed look at the entire causal chain that led us to this accident, how each action or non-action felt reasonable at the moment, and what I guess we could have done differently at each point to get a better outcome.I hope that by looking at them, you’ll recognize some of the same patterns in your own life, and maybe realize some ways you would predictably make mistakes that would put you in danger.Remember the signs of carbon monoxide poisoningThe causal chainSo, here’s the causal chain that led to this accident happening, and my take on what we could have done differently at each step to avoid this outcome:We decided to live in a house whose rent is cheap, but the landlord is a cheap-ass who hires the cheapest contractors they can → We knew before signing the lease that the landlord was cheap. We could have seen it as a red flag, and decided to take another placeThe landlord decided to install a useless piece of equipment in our basement (a solar heater), and decided to get it installed in the narrow space where the existing gas heater was located. There’s not enough space to install both correctly, but the landlord insisted the contractors install it there anyway → We could have pushed back on this, but it felt effortful and annoying to convince the landlord that this was a mistake. If it had been installed somewhere else or not installed at all, the gas heater would have continued working fineThe contractors installed the solar heater there anyway, and to do this, they removed a support for the exhaust pipe, and installed equipment that put tension on the pipe → If they had rerouted the pipe and/or added proper support, it would have been fine. We could have monitored the installation and seen that this was a dangerous modification. We could have taken before and after pictures to notice that the support had been removed. We could have asked the landlord to fix this, or fixed it ourselves.We did not notice that there was a risk of the exhaust pipe pulling out, nor did the maintenance technician who came to check the heater a few months before the accident → If we had a better model of risks from heaters and of what the bad contractors had done, we could have seen the issue of improper support and tension.The exhaust pipe pulled out and started producing CO for a while. At this point, multiple things could have made us notice an issue:Two residents went through the basement during this period, and did notice that the pipe was pulled out.They did not say anything → If they had taken a photo and asked an LLM, or just shared it to our group chat, I would have known immediately that this was not good and fixed itThey did not say anything because they knew that the house was shoddy anyway. They flagged it in their mind as “weird, but not weirder than expected given the landlord’s care for things” → Learned helplessness about the state of the house. This could have been avoided by being in a better maintained place, or having a better model of what is actually dangerous versus thing that are non-ideal but fine. It could have been avoided by having a default assumption of things being not fine, of always verifying. It could have been avoided if they had the gut feeling that something going wrong with a gas heater had an unacceptable risk of random sudden death.The heater itself did not have an incomplete combustion detector. I’m not sure if there never was one, or if it had been deactivated/broken → If there was, the heater would have stopped working, and said an error code that would have told us something was wrong, and we would have realized the issue was the pipe. If it was broken, we could have checked and asked for it to be replaced.Usually the heater exhaust is visible whenever we enter or leave the house, as it make a white plume by the wall. Nobody noticed that this was not happening anymore → We could have noticed the change and followed the confusion to realize that the pipe had pulled out.The CO started seeping up from the basement into the houseWe did not have a carbon monoxide detector in our house. French law requires smoke detectors, but not carbon monoxide detectors.We did not realize that the risks were high enough that they were worth protecting against. Having a gas heater, combined with what we knew about the less than ideal state of the house, meant that CO risks were probably 100x higher than base rate. We felt that having a fire alarm was wise and important to protect against tail risk, and did not realize CO was at least as likely → If we had been more calibrated about tail risks on our lives, we would have bought a carbon monoxide detector from the startWe did notice the symptoms, but did not realize for a while they were from CO intoxication. The limiting factor was building common knowledge that something was happening at all. CO poisoning was not on our radar as a hypothesis, so everyone kept rounding off their symptoms to other stuff.We had a bunch of weird residents, and people had weird behavior all the time, so we kept rounding off the symptoms to “normal day in our group house”. We did not notice how their behavior was different from usual → If we had a better model of what was driving everyone’s behavior, we could have noticed that the weird behavior on those days was caused by people feeling off, not from them acting within their usual boundsWe did not notice correlated issues. Many people had been having headaches for the past days, but we did not realize this was happening to so many of us → If we had common knowledge of the number of people having headaches, we would have realized it was very improbable that they were uncorrelated, and would have realized something was off.One resident had a great meditation experience, where they felt connected to the universe and felt universal love. We though “Wow! Good for them! They made progress on their meditation path” → This was a sign of intoxication. We could have realized it was some sort of psychedelic effectOne resident felt weak and off. He had trouble staying up. He told us it was probably food poisoning or a cold or something. Sometimes we feel off in a way that’s hard to pin down to a precise cause, and in those case, our default algorithm is to wait until we feel better. → We could have realized that it was not usual symptoms of either food poisoning or cold. In this case, it was getting worse and worse, not better.One resident started getting migraines. They have those regularly, but usually they know the trigger. They assumed it was one of those unexplained ones, where no obvious cause could be found.Also, CO poisoning in an environmental affliction that decays very slowly. So, the source of the symptoms was being in the house, but CO stays for so long in the blood that going out of the house for a while did not improve symptoms, which made it hard to form the hypothesis that it was related to being in the house.Nobody noticed that their symptoms were common symptoms of generalized hypoxia → If we were better at diagnosing medical conditions from our symptoms, someone would have noticed it was hypoxia, which would have triggered far more alarm than our other hypothesis. From this point, the CO hypothesis would have come quickly.As the CO saturation got up over multiple days and was mostly concentrated in our living room, the residents who had been in the house the most had 5x higher CO saturation than those who had been there only to sleep. This made some residents feel very ill while me and others were feeling fine, which made it harder to realize it was because of something happening in the house.Eventually, we figured it out because five of us were in our living room and shared that they were feeling off in various ways, and that created common knowledge of the correlated issues. We immediately concluded there must be a common cause, started brainstorming, calling emergency services, and quickly figured out it was carbon monoxide.Here are the cost we incurred because of this accident:One day of lost work and wages for 8 peopleFour weeks of not having hot water, while we waited for an inspection that would allow the gas provider to provider us gas again.For me, a ~100€ hospital bill, because I did not have my social security card on me and failed to get through the process of getting reimbursementSo, some cost, but it could have been much worse. If we had not been in the same room this morning, there was some risk we might have taken until the evening to notice, and there was some low risk someone would have fallen unconcious in their room and died in the meantime.I could not feel safe anymoreThe words update was feeling like I was much less safe than before. It was weak, just a bit more of anxiety, of worry, especially when inside our house, but it did decrease my quality of life. I had been suprised by the accident, and higher anxiety was a way to be readier for a world where the rate of surprise encounters with death was higher than I expected before.The way out was to process the issue, to figure out what I had done wrong, so I could reliably avoid this class of issue in the future. I did an early version of this postmortem, through conversations and notes, until I trusted that my future would not involve more near death encounters than I expected before the accident.I think my other flatmates also went through this process in their own way. Camille through writing the bulk of Basics of How Not to Die, Elisa through writing her testament.My updatesLooking back over all the causal chain, here’s the generalized actions I think me and my flatmates could have taken to avoid this outcome.Calibrating on which tail risks we were actually exposed to, both through knowing population base rates and specifics of our situation, and taking cheap opportunities to protect against thoseAvoiding living spaces where landlords care more about saving money than the safety of the residentsDoing our own evaluation of critical systems like heaters. Trust, but verifyTraining in disagreeableness, to feel comfortable pushing back against the landlord when they were prioritizing their profit above our safetyLearning more about our biology and which symptoms are indicative of which dangerous conditionLearning more about the other residents, to notice which behavior are within bounds and which are indicative of an issueProactively raising potential issues, be they about the house or about one’s health state, to build common knowledge and notice patterns. Better to have some noise than miss a critical info.I’m not sure which ones I would have actually taken. All of them come with tradeoffs, costs in time and money that might not be worth the risk reduction.At least, I’ll keep them on my mind. Maybe they’ll help me notice, next time I’m taking reasonable choices that bring me ever closer to an accident.Discuss ​Read More

​Published on February 14, 2026 4:11 PM GMTTaking reasonable choices is not enough. You need to fight death at every possible point of intervention.Two weeks ago, my flatmates and I published Basics of How Not to Die, to celebrate the one-year anniversary of not dying from carbon monoxide poisoning.This post was written with a rather cheeky tone, mainly by my flatmate Camille. I like the style, but I feel like it lacks hard data, and gives advice that may not actually be worth the cost.In this post, I’ll give you a more detailed look at the entire causal chain that led us to this accident, how each action or non-action felt reasonable at the moment, and what I guess we could have done differently at each point to get a better outcome.I hope that by looking at them, you’ll recognize some of the same patterns in your own life, and maybe realize some ways you would predictably make mistakes that would put you in danger.Remember the signs of carbon monoxide poisoningThe causal chainSo, here’s the causal chain that led to this accident happening, and my take on what we could have done differently at each step to avoid this outcome:We decided to live in a house whose rent is cheap, but the landlord is a cheap-ass who hires the cheapest contractors they can → We knew before signing the lease that the landlord was cheap. We could have seen it as a red flag, and decided to take another placeThe landlord decided to install a useless piece of equipment in our basement (a solar heater), and decided to get it installed in the narrow space where the existing gas heater was located. There’s not enough space to install both correctly, but the landlord insisted the contractors install it there anyway → We could have pushed back on this, but it felt effortful and annoying to convince the landlord that this was a mistake. If it had been installed somewhere else or not installed at all, the gas heater would have continued working fineThe contractors installed the solar heater there anyway, and to do this, they removed a support for the exhaust pipe, and installed equipment that put tension on the pipe → If they had rerouted the pipe and/or added proper support, it would have been fine. We could have monitored the installation and seen that this was a dangerous modification. We could have taken before and after pictures to notice that the support had been removed. We could have asked the landlord to fix this, or fixed it ourselves.We did not notice that there was a risk of the exhaust pipe pulling out, nor did the maintenance technician who came to check the heater a few months before the accident → If we had a better model of risks from heaters and of what the bad contractors had done, we could have seen the issue of improper support and tension.The exhaust pipe pulled out and started producing CO for a while. At this point, multiple things could have made us notice an issue:Two residents went through the basement during this period, and did notice that the pipe was pulled out.They did not say anything → If they had taken a photo and asked an LLM, or just shared it to our group chat, I would have known immediately that this was not good and fixed itThey did not say anything because they knew that the house was shoddy anyway. They flagged it in their mind as “weird, but not weirder than expected given the landlord’s care for things” → Learned helplessness about the state of the house. This could have been avoided by being in a better maintained place, or having a better model of what is actually dangerous versus thing that are non-ideal but fine. It could have been avoided by having a default assumption of things being not fine, of always verifying. It could have been avoided if they had the gut feeling that something going wrong with a gas heater had an unacceptable risk of random sudden death.The heater itself did not have an incomplete combustion detector. I’m not sure if there never was one, or if it had been deactivated/broken → If there was, the heater would have stopped working, and said an error code that would have told us something was wrong, and we would have realized the issue was the pipe. If it was broken, we could have checked and asked for it to be replaced.Usually the heater exhaust is visible whenever we enter or leave the house, as it make a white plume by the wall. Nobody noticed that this was not happening anymore → We could have noticed the change and followed the confusion to realize that the pipe had pulled out.The CO started seeping up from the basement into the houseWe did not have a carbon monoxide detector in our house. French law requires smoke detectors, but not carbon monoxide detectors.We did not realize that the risks were high enough that they were worth protecting against. Having a gas heater, combined with what we knew about the less than ideal state of the house, meant that CO risks were probably 100x higher than base rate. We felt that having a fire alarm was wise and important to protect against tail risk, and did not realize CO was at least as likely → If we had been more calibrated about tail risks on our lives, we would have bought a carbon monoxide detector from the startWe did notice the symptoms, but did not realize for a while they were from CO intoxication. The limiting factor was building common knowledge that something was happening at all. CO poisoning was not on our radar as a hypothesis, so everyone kept rounding off their symptoms to other stuff.We had a bunch of weird residents, and people had weird behavior all the time, so we kept rounding off the symptoms to “normal day in our group house”. We did not notice how their behavior was different from usual → If we had a better model of what was driving everyone’s behavior, we could have noticed that the weird behavior on those days was caused by people feeling off, not from them acting within their usual boundsWe did not notice correlated issues. Many people had been having headaches for the past days, but we did not realize this was happening to so many of us → If we had common knowledge of the number of people having headaches, we would have realized it was very improbable that they were uncorrelated, and would have realized something was off.One resident had a great meditation experience, where they felt connected to the universe and felt universal love. We though “Wow! Good for them! They made progress on their meditation path” → This was a sign of intoxication. We could have realized it was some sort of psychedelic effectOne resident felt weak and off. He had trouble staying up. He told us it was probably food poisoning or a cold or something. Sometimes we feel off in a way that’s hard to pin down to a precise cause, and in those case, our default algorithm is to wait until we feel better. → We could have realized that it was not usual symptoms of either food poisoning or cold. In this case, it was getting worse and worse, not better.One resident started getting migraines. They have those regularly, but usually they know the trigger. They assumed it was one of those unexplained ones, where no obvious cause could be found.Also, CO poisoning in an environmental affliction that decays very slowly. So, the source of the symptoms was being in the house, but CO stays for so long in the blood that going out of the house for a while did not improve symptoms, which made it hard to form the hypothesis that it was related to being in the house.Nobody noticed that their symptoms were common symptoms of generalized hypoxia → If we were better at diagnosing medical conditions from our symptoms, someone would have noticed it was hypoxia, which would have triggered far more alarm than our other hypothesis. From this point, the CO hypothesis would have come quickly.As the CO saturation got up over multiple days and was mostly concentrated in our living room, the residents who had been in the house the most had 5x higher CO saturation than those who had been there only to sleep. This made some residents feel very ill while me and others were feeling fine, which made it harder to realize it was because of something happening in the house.Eventually, we figured it out because five of us were in our living room and shared that they were feeling off in various ways, and that created common knowledge of the correlated issues. We immediately concluded there must be a common cause, started brainstorming, calling emergency services, and quickly figured out it was carbon monoxide.Here are the cost we incurred because of this accident:One day of lost work and wages for 8 peopleFour weeks of not having hot water, while we waited for an inspection that would allow the gas provider to provider us gas again.For me, a ~100€ hospital bill, because I did not have my social security card on me and failed to get through the process of getting reimbursementSo, some cost, but it could have been much worse. If we had not been in the same room this morning, there was some risk we might have taken until the evening to notice, and there was some low risk someone would have fallen unconcious in their room and died in the meantime.I could not feel safe anymoreThe words update was feeling like I was much less safe than before. It was weak, just a bit more of anxiety, of worry, especially when inside our house, but it did decrease my quality of life. I had been suprised by the accident, and higher anxiety was a way to be readier for a world where the rate of surprise encounters with death was higher than I expected before.The way out was to process the issue, to figure out what I had done wrong, so I could reliably avoid this class of issue in the future. I did an early version of this postmortem, through conversations and notes, until I trusted that my future would not involve more near death encounters than I expected before the accident.I think my other flatmates also went through this process in their own way. Camille through writing the bulk of Basics of How Not to Die, Elisa through writing her testament.My updatesLooking back over all the causal chain, here’s the generalized actions I think me and my flatmates could have taken to avoid this outcome.Calibrating on which tail risks we were actually exposed to, both through knowing population base rates and specifics of our situation, and taking cheap opportunities to protect against thoseAvoiding living spaces where landlords care more about saving money than the safety of the residentsDoing our own evaluation of critical systems like heaters. Trust, but verifyTraining in disagreeableness, to feel comfortable pushing back against the landlord when they were prioritizing their profit above our safetyLearning more about our biology and which symptoms are indicative of which dangerous conditionLearning more about the other residents, to notice which behavior are within bounds and which are indicative of an issueProactively raising potential issues, be they about the house or about one’s health state, to build common knowledge and notice patterns. Better to have some noise than miss a critical info.I’m not sure which ones I would have actually taken. All of them come with tradeoffs, costs in time and money that might not be worth the risk reduction.At least, I’ll keep them on my mind. Maybe they’ll help me notice, next time I’m taking reasonable choices that bring me ever closer to an accident.Discuss ​Read More

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