2025-10-26 21:00:00
Per the Atlantic's A 'Death Train' is Haunting South Florida:
According to Federal Railroad Administration data, the Brightline has been involved in at least 185 fatalities, 148 of which were believed not to be suicides, since it began operating, in December 2017. Last year, the train hit and killed 41 people—none of whom, as best as authorities could determine, was attempting to harm themselves. By comparison, the Long Island Rail Road, the busiest commuter line in the country, hit and killed six people last year while running 947 trains a day. Brightline was running 32.
Trains running people over is obviously bad, but people also die from being hit by cars. Reading the article I was wondering: are we making a big deal about Brightline because it's big and new, but actually we're better off overall now that there's a train because fewer people are driving and so fewer people are dying? And is this actually counterproductive fearmongering? Nope! Brightline is just really deadly, not just for a train, but even relative to driving.
While Brightline is of course much safer for occupants than driving, what I care about is the overall social impact: are there more or fewer deaths than in a non-Brightline world? This means counting everyone, including occupants, drivers, and pedestrians. Ideally we would compare fatality rates directly: how many deaths are there per passenger-mile for Brightline vs cars? These stats don't exist, but we can get decent estimates:
For Brightline, per the article there have been 185 fatalities. [1] They don't publish a passenger-miles number, but there were about 5M passengers before they opened the Orlando section and then 1.6M long-distance and 1.1M short-distance in 2024. If we guess that the first 9.5 months of 2025 looked like 2024, that's an additional 1.3M long-distance and 0.9M short distance. In total that's 2.9M long-distance trips and 7M short-distance. Based on the distances involved, I'm going to guess 200mi for long distance and 50mi. This gives us a total of 930M passenger-miles, and 20 deaths per 100M passenger miles.
For cars, Florida seems to have 1.42 deaths per 100M vehicle miles. If we guess that there's an average of 1.4 people per car, this is ~1 death per 100M passenger miles.
So Brightline is about 20x more deadly per passenger-mile (counting people inside and outside the vehicle) than driving, and the article isn't fearmongering. The Department of Transportation uses $13.7M for the statistical value of a human life, and 185 fatalities is $2.5B. And it's going up at about $0.5B/year. [2] Without safety improvements, in something like seven years the ongoing societal cost in deaths will have grown larger than it's initial $6B construction cost.
I do expect this to get better over time: some of these fatalities are people not being used to the trains, and as that changes I expect fewer people to do things like cross the tracks where they don't have good visibility or under an assumption that the only trains that might come by are slow freight trains. The government has also been making improvements like adding fencing, and you could probably fence the whole thing for under $100M [3]. Getting Brightline to be less deadly than cars will be a lot of work (a 20x reduction is hard) but since trains elsewhere manage to be much safer this seems plausible.
The key takeaway for me, however, is that people who advocated for Brightline on the idea that it would reduce deaths made a pretty serious mistake. That Brightline would get cars off the road was a standard talking point, and people seemed to assume that this would be be positive from a traffic fatality perspective. Here's the Rail Passengers Association saying this explicitly:
Regular train service along the corridor would remove as many as three million cars from regional highways each year, reducing both commuter stress and road fatalities. With 300 drivers killed in road accidents between 2004 and 2008, Interstate 95 has been ranked as the deadliest highway in the United States. A passenger rail alternative will thus save lives.
Advocates weren't wrong in the general case, since trains are normally much safer than cars even counting non-occupants. The problem was Brightline's specific route, with hundreds of grade crossings in densely populated areas and unfenced tracks that divide many places people want to move between. This is something people who know trains well should have been able to anticipate.
Since Brightline is following the laws, and there are strong legal protections for railroads, even if we decided Florida would be better off with Brightline shut down, it would be very difficult and would likely require federal legislation or a massively expensive buyout. So the best we can realistically do is safety infrastructure improvements, and there's already a lot of political motivation here. A 20x decrease in fatalities sounds very difficult, but combination of additional fencing, improved crossings, and increasing public familiarity with the trains may be able to bring fatalities down to where the train is at least competitive with driving.
[1] Arguably you should not count some fraction of the 37 suicides, as
some of the people may have otherwise have chosen other ways to kill
themselves. But even if we don't count all of them, dropping
fatalities from 185 to 148, the bottom line doesn't change very much:
16x more deadly instead of 20x.
[2] The Atlantic says 42 deaths in 2024. At $13.7M/death this is $575M.
[3] The corridor is 235mi, which is 2.5M ft when you count both sides. Installing fencing might be $25/ft, so $63M.
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2025-10-25 21:00:00
I help organize a contra dance in a crowded dance hall, and we've been considering using far UVC to clean the air, reducing infection risk from COVID, flu, and other airborne pathogens. We recently polled the group, and far UVC was very popular, so I think it's likely we'll roll it out. But how should we position the lights?
When I first looked into this, with help from UV researcher Vivian Belenky at the Columbia Center for Radiological Research, they used the OSLUV modeling tool to estimate the efficacy of four lamps on portable 10ft stands, one in each corner. As I started looking into the logistics of setting this up, however, having tall stands on the dance floor seemed difficult to do without some combination of taking up a bunch of floor space and providing a tripping hazard.
Instead of putting them in the corners, a single tall stand in the middle of the stage would be a lot more practical logistically. But would having four lamps so close together be an exposure risk? And how much air cleaning efficacy would we lose?
I prepared two scenarios in the modeling tool, each with four Aerolamps in a 66ft x 40ft x 23ft room. The first case is the one Vivian and I had worked in, with a lamp 10ft up in each corner (config):
The second is what I'd prefer to do, four lamps at the front of the stage, 13ft up (10ft stand + stage height) in the center (config):
On safety, the modeling software evaluates against ANSI/IES RP-27.1-22 using ACGIH (2022) TLVs for 222 nm, and both scenarios are well below limits, even standing in the part of the floor with the highest exposure. [1]
On efficacy, average fluence was 0.289 uW/cm2 (stage) vs 0.306 uW/cm2 (corners), a 5.6% decrease. [2] This is small enough that I think we should go with the logistically easier one, and put them on a single stand on stage.
[1] Specifically, measured over an 8hr period, it estimates maximum
skin and eye doses as:
| Corners | Stage | |
|---|---|---|
| Skin | 16.68 mJ/cm2 | 26.08 mJ/cm2 |
| Eye | 30.41 mJ/cm2 | 39.45 mJ/cm2 |
These are low enough that they'd be safe even for full days: the place where any of these scenarios gets closest to the limit is eye exposure in the stage scenario, and that would require ~30hr of continuous exposure to reach the 8-hour TLV.
Of course if you are moving around the room, as dancers do, your dose is far lower, because you won't be in the single worst place the whole time. The weighted skin and eye doses, again for an 8hr period, are:
| Corners | Stage | |
|---|---|---|
| Skin | 0.12 mJ/cm2 | 0.18 mJ/cm2 |
| Eye | 0.62 mJ/cm2 | 0.81 mJ/cm2 |
[2] The actual effects on pathogens are not linear in average fluence, however, because there are two effects working in opposite directions:
Some pathogens are inactivated with very low levels of UV, and the coverage pattern in the stage case has more areas with no coverage than in the corners case.
Other pathogens are only affected at higher levels, and the maximum fluence in the stage case is higher.
The OSLUV tool gives estimates that translate the full fluence distribution into inactivation to account for these effects. The overall impact, however, was very small (sheet). I saw decreases of the UV equivalent CADR of 5.7% for bacteria, 5.7% for coronaviruses, 5.1% for influenza, and 6.9% for phages.
2025-10-23 21:00:00
I've had a lot of people reach out to me who are interested in working on biosecurity, but have a background in software engineering / computer science. A lot of these conversations have looked something like:
A: I'd be really excited to work on biosecurity, it seems really important and relatively neglected. Are you hiring for software engineers at SecureBio?Me: I wish we were, you seem really great! But I don't know when we will be, depends on funding and some strategy questions.
This has now changed, and SecureBio is now hiring for two different software engineering roles that don't require a biology background:
NAO: Bioinformatics Engineer. An in-person role on the project I lead, developing a metagenomic biosurveillance system to detect stealth pathogens.
AI: Software Engineer, AI Safety and Biosecurity. A remote role on the project Seth leads, evaluating frontier AI systems, with a focus on biosecurity and misuse risk.
Consider applying?
Happy to answer questions!
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2025-10-20 21:00:00
An honest attempt to describe what you're technically supposed to do if you follow the posted policies. I don't think anyone actually expects you to do this!
Great to hear that you've decided to attend your first contra dance! It's really easy to get started, they're a lot of fun, and it's a friendly and welcoming community. You just show up, the caller tells you what to do, and in a few minutes you're dancing. It's got the best learning curve out there!
There's one minor exception, however, which is that some dances are "fragrance free". For these you'll need a little prep: plan to start getting ready about three weeks before your first fragrance free event. I know this can be a bit more time than you were expecting to invest before learning whether this is an activity you'd enjoy, but trust me: it's worth it!
It can be a little hard to figure out whether a dance you're considering attending is fragrance free. While some dances list it on the homepage, you can't count on that. For example, it could be at the bottom of the code of conduct or listed on a dance etiquette page. The safest thing to do is to read the whole website, but of course that's a ton of work so you might want to write to the organizers.
Once you find the policy, it probably looks something like:
These Dances are Fragrance Free - please do not wear perfume, cologne, or other scented products, as some of our dancers are chemically sensitive, and experience discomfort when exposed to these materials.
Read it carefully! While many people initially interpret these policies to prohibit perfume, "scented products" includes soap, shampoo, conditioner, deodorant, laundry detergent, etc. I recommend you start three weeks before the event, and spend a week noting the ingredients on each product you use. Read them over, looking for the words "fragrance" or "parfum". If you don't see those, there's still some chance that it's a scented product, unfortunately: sometimes individual fragrance ingredients are mentioned by name instead. I recommend taking a picture of the ingredients and uploading it to an LLM with a prompt like "are any of these ingredients fragrances"?
Note that some products will say "unscented", but still have fragrances. This is very confusing, but the basic idea is that an "unscented" product is intended not to smell like anything, and might include "masking fragrances" to cover the scents of the ingredients. Products that say "fragrance free" are a better bet, but the term is not heavily regulated and there are products out there like this eucalyptus lavender soap bar that say "free from any fragrances" but also have strongly scented essential oils:
Two weeks week before the event you should have your list of the products you need to find substitutes for. It's the same deal as before: analyze ingredient lists on potential replacements, and again LLMs may be useful. Here are some product lists that might be helpful in getting started: EastBayMeditation, FGC. If the cost is a burden, and a full set of personal care products can be a substantial investment, consider writing to the organizers to ask if they have a fragrance-free fund.
With medical products, like a medicated shampoo that happens to be scented, sometimes a fragrance free replacement is not an option. I'd recommend talking to the organizers: they may be willing to consider an exception. This is another reason to start early, since most of these events are organized by committees and can take a while to come to a decision.
About a week before the event you should have acquired all your replacement products: now it's time to start using them! The goal is that by the time you attend the event you no longer have any lingering fragrances on yourself or your clothes. For clothes in particular scents can last a long time, so the safest thing to do is clean your washing machine (wash the machine with baking soda, then again with vinegar) and then wash your clothes twice. If you use a laundromat there aren't any good options, since fragrance free laundromats are essentially not a thing, but if you ask around you may be able to find a friend who has their own machine and either already takes a fragrance free approach or is willing to help you out.
At this point, you're ready to attend the dance! Make sure you're wearing clothes that have been washed since you transitioned away from scented products. It's also a good idea to bring your own hand soap: it's sadly common for fragrance free dances to have scented products in their bathrooms. I hope you have a great time!
While this post is using satire to make a point, my core view is that it's fine for dances to have whatever approach to fragrances they choose as long as they're thoughtful about what they actually expect attendees to do and communicate it clearly. When I've written about this before I've read a lot of comments from people who don't see a problem with the status quo. My target with the satire here is dances that put a few words about a policy on their page that they don't actually expect people to follow, don't put effort into ensuring potential attendees see, and sometimes even blatantly subvert by having scented products available at their dances.
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2025-10-15 21:00:00
The situation in the contra dance world with "fragrance free" is a mess. Many dances have very strict policies, but they don't emphasize them. Which means they're not dances that work for people who need the strict policies, but at the same time are putting attentive and careful people through a lot of work in avoiding common scented products.
For example, if you look at the Concord Thursday homepage or FB event there's no mention of a fragrance policy. At the end of their Code of Conduct, however, there's:
Consider: We are a fragrance free event. Please do not wear scented products.
This isn't just asking people not to wear perfume or cologne: products not explicitly marketed as "fragrance free" generally have at least some scent. Trying to pick some very ordinary products that don't mention that they're scented on the front, when I read the ingredients they all list both "fragrance" and several scented ingredients (camphor, limonene, benzyl salicylate, etc):
Amazon
Basics Liquid Hand Soap
I'm not trying to pick on this one dance; it's common to have a policy like this without being explicit that the dance is asking everyone who attends to go out and buy new shampoo. Take the JP dance, which has, on their homepage:
These Dances are Fragrance Free - please do not wear perfume, cologne, or other scented products, as some of our dancers are chemically sensitive, and experience discomfort when exposed to these materials.
This suggests that by "scented products" they mean "things you wear specifically to give you a scent, but clicking through it's clear that they don't allow mainstream soaps, shampoos, deodorants, etc.
Some others I just checked:
One thing to keep in mind with these restrictions is that the impact is partially along racial lines. It's much easier to find fragrance-free products for white-typical hair; people with tightly curled or coiled hair are going to have a much harder time. Fragrance free products for these hair types do exist, but it's a significant investment to find them and figure out what works for your particular hair. There's also an interaction between race and culture, where in some communities, disproportionately black and hispanic ones, wearing scents is just a normal part of being clean. A lot of communities with these policies also worry about why their dance community is so much whiter than the area, and while I don't think this is a major contributor I also doubt it helps.
I've raised this issue before, but it didn't seem to have an effect, so I'm going to try a different approach of suggesting a range of alternative approaches that I think would be much better:
Say "fragrance free" and mean it. Include it in all your publicity the same way you would "mask required". Spell out what this means in terms of how to find products. I don't know any dances taking this approach.
Say something like "no perfume or cologne: don't wear products intended to give you a scent". This is the approach Beantown Stomp has taken.
Don't have a policy, accept that most people will show up having used scented products and a few will show up strongly scented. This is the approach BIDA uses.
I normally try pretty hard to follow rules, but this is one I dont' fully follow. My impression is that few attendees are taking the policy literally, and I don't think they actually mean that I shouldn't attend if I washed my hands after using the bathroom at a gas station on the drive over. I don't like this situation, however, and I think, as with speed limits people are used to ignoring, this approach is corrosive to the important norms around respecting policies. If you currently have a simple "fragrance free" somewhere on your website, consider one of the alternatives I suggested above?
EDIT: there's some discussion around what fraction of the population needs this kind of policy, with someone linking a CDSS document which says "chemical sensitivity is an invisible disability that affects around 30% of the population". I realized I have some relevant data on this: when I used to organize Beantown Stomp we had a "low fragrance" policy:
Some dancers are sensitive to fragrances, so we'd like to keep this a low-fragrance environment. Please don't wear perfume, cologne, body spray, or other products intended to give you a scent. If your shampoo, conditioner, deodorant, or laundry detergent are mildly scented, however, that's ok.
On the registration form we asked dancers to choose one of:
In 2020, 3% of dancers chose (a), 97% chose (b), and no one chose (c). This isn't the same as polling on a true fragrance free policy, but I would expect to see an even larger discrepancy there, where most people who would benefit from a "fragrance free" policy are covered by policies prohibiting "products intended to give you a scent".
2025-10-13 21:00:00
A dance organization I help run, BIDA, recently ran a survey. Several of the questions asked how folks felt about using far UVC and glycol vapors to reduce risk from COVID, flu, and other airborne pathogens. There were 208 respondents, which is pretty good!
When asked how their attendance would change if BIDA used these interventions, the response was:
| Unchanged | Increased | Decreased | |
|---|---|---|---|
| Far UVC | 75% (153) | 25% (50) | 1% (1) |
| Glycol Vapor | 77% (156) | 14% (29) | 8% (17) |
There were also free response answers, which you can read in the full writeup, on the BIDA blog. Summarizing them:
On far UVC, the person who said their attendance would decrease didn't give a comment giving more detail. The other comments were broadly supportive (~54) people, followed by neutral (~18 people), uncertain and wanting more information (~11 people), and skeptical that the lamps would actually reduce infections (~9 people).
On glycol vapors, the most common response was generally positive about more ways to reduce infection (~37), followed by wanting more information (~19), not caring (~17), strongly disliking the idea (~14), and more complex views (~10).
These results show a community that's strongly in favor of far UVC, which makes a lot of sense to me. The efficacy of UVC is proportional to sight lines, since it's beams of light, so it's a great fit for a big room with a tall ceiling. We'd need four lamps, which would cost $2,000. This is a meaningful amount of money, but with a total of 5,400 admissions at our dances in the 2024-2025 season and the lamps lasting at least 5y it's ~3¢/person-hour. For comparison, we spend about ten times that much per person-hour to provide people with disposable N95s.
The situation with glycol vapors, however, is much less clear. The evidence on safety is if anything stronger than on far UVC, and it's incredibly cheap (a $50 gallon of Triethylene Glycol is good for about 2y of dances). But we also have a significant number of people who don't like the idea (8% saying they'd attend less; ~14 negative comments out of 97). Reading through the comments I think some objections would turn out not to be an issue once people had experience with glycol vapor:
"I don't know much about them, but the CDC says they can irritate eyes and lungs": the level in the air is very low, and no one reported irritation at the trial dance.
"I have a sensitive nose and an aversion, sometimes reaction, to strong scents, especially chemical ones. I am deeply grateful for the fragrance free policy and am worried that this may adversely affect my experience and ability to attend and that of those similarly situated": Similarly, no one reported being able to smell the vapor at the trial dance. But BIDA also doesn't prohibit fragrances, and it's common for dancers (especially newer dancers) to wear scents, so I'm a bit confused about their reference to a 'fragrance free policy'.
Other objections, however, are from a perspective where experience wouldn't be relevant:
"I absolutely would not attend any event that had this in the air."
"I'm not comfortable with chemicals being deliberately pumped into the air by a DIY project. If there is a commercial system on the market using this technology, that would change my opinion."
All this has me feeling like I shouldn't push for us to deploy glycol vapors now, and the key thing is getting a commercial system on the market to address concerns. But then I go back and read the comments of people who are really positive on them:
"It would GREATLY improve my safety, comfort, and enjoyment!!! I hope other dances can also take these same precautions! Thank you for doing this work. (I LOVE SCIENCE when it's used for good. Thank you for this work!)"
"I would be more comfortable and feel safer, to the point where I might be okay with dancing unmasked."
"Also strongly in favor, for the same reasons. Let's do both!"
"Increase safety comfort and enjoyment so so so much!!!"
Overall I'm really torn on glycol vapors: the community is, on balance, in favor of them, and I think the evidence is really positive. On the other hand I also respect people having a high bar for evidence for things you breathe in. The board hasn't met to talk about this yet, and I'm not sure which way I want to push. Thoughts?
EDIT: in the comments people brought up the idea of having glycol vapors at only some dances. This could allow people with strong opposition the option to keep dancing while others could still get the benefits about half the time. If we did this, it could be either just the masked dances (to offer an extra safe option) or just the unmasked dances (to bring up the level of safety): which might be more popular? I categorized the responses (script) to look at the relationship between whether someone preferred more vs less masking and whether their attendance would go up or down with glycol vapors.
I started with the full 208 responses, discarded two people who said they didn't dance at BIDA because they didn't live in town, and then discarded another six who didn't answer all four of "I currently attend BIDA: ___", "If we started requiring masks at all our dances, I would attend: ___", "If we stopped requiring masks at any of our dances, I would attend: ___", and "If BIDA added Glycol Vapors, my attendance would: ___". This left me with 200 responses. I considered a response as inconsistent on masking if they said they'd attend more if we always required masks and also more if we stopped ever requiring masks, and also as inconsistent if it was the other way around. Here's what I found:
| attendance with masks | |||||
|---|---|---|---|---|---|
| higher masked | no change | higher optional | inconsistent | ||
| attendance with glycol | increase | 14 | 5 | 8 | 2 |
| same | 29 | 53 | 69 | 3 | |
| decrease | 4 | 5 | 8 | 0 | |
Looking at the table, if we were going to have glycol at only either mask-required or mask-optional dances it should be the mask-required ones: 30% of dancers who prefer masked prefer glycol vapors, vs 9% of dancers who prefer mask-optional and 8% of who said masking changes wouldn't affect their attendance. I also looked over the free text responses, and a large majority of the people with the strongest objections to glycol vapors preferred less masking.
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