Imo, evacuating to another country when a nuclear war looks literally imminent may not even be a good move because you'd have to enter a large city with an international airport with transcontinental flights, and the increased risk while you're reentering the city & waiting for your flight is probably greater than the survival benefits from arriving at your SH destination, not to mention flights would probably be booked out if things really looked that dire. A better strategy would be to evacuate whenever the risk looked heightened, but then you'd run into a "no fire alarm" problem and it'd be very unclear when you should do so, and in any case you'd be doing it repeatedly. The biggest problem with this approach is it wouldn't save you from sudden nuclear war. All it takes is an accident, the risk of which with China now joining Rus + US in adopting Launch on Warning has arguably risen at least 50%. Or something like Kim having a bad day/internal turmoil within the unstable NK regime which had no outwardly visible signs until after the fact, and the Bay Area is gone in a flash. (Looking at you, MIRI and like 3/4 of the entire alignment community based there...)
The best strategy imo is to relocate permanently to somewhere with a much lower risk of attack: e.g., a smaller non-US NATO city like Kitchener, or a very small US city. E.g. the Toronto area may be attacked, but it's pretty unlikely Kitchener would because a marginal warhead would be better spent on another US city, even for Russia with 1500 deployed warheads. And your very small US city/suburban area of 10-20,000 people is quite unlikely to be attacked, because all cities with greater population would be attacked before it, unless it had some unique importance.
Doesn't really make sense to consider yields or anything like that, whether your metropolitan area is annihilated by a single 25 megaton warhead from an R-36M or a bunch of MIRVs in the low hundred kiloton range makes no difference and is just down to which missiles are assigned which targets. No one knows exactly which places would be targeted, just that some places are of course likelier than others, and certain things about strategy (e.g. China has a pure countervalue strategy for now, targeting all warheads at cities only).
Lastly, recall one problem with the strategy of evacuating at the last possible moment when warheads look like they could be falling any minute, is that if many others have the same idea as you, the roads out of the city will be jammed to a standstill. In fact, governments may be attempting to evacuate the cities at that time too. This is another advantage of being in a smaller town/outlying area: you won't be hindered whenever you decide to evacuate.
Yes, if imminent literally means missiles are inbound it is too late, but if you've decided there is a high probability of nuclear attack in the next couple of weeks to months evacuating could still be a good strategy. For Ben Landau Taylors signup list, he certainly means evacuating well before missiles are launched.
Certainly small towns are not at much risk of being hit directly. If you were concerned about an all out war between the US and Russia though, evacuating to somewhere in the southern hemisphere could make a lot of sense.
Yields of nuclear weapons can vary a lot. Like you said, no one knows exactly where would be targeted, but if your near a large city that might be hit, considering how to shelter and evacuate after an attack could still be quite useful. I agree attempting to evacuate a city as missiles were being launched would not result in good outcomes.
I'm curious about your thoughts on this: hypothetically, if I were to relocate now, do you see the duration of my stay in the lower risk area as being indefinitely long? It seems unclear to me what exact signals--other than pretty obvious ones like the war ending, which I'd guess are much less likely to happen soon--would be clear green lights to move back to my original location. I'm wondering because I'm trying to assess feasibility. For my situation, it feels like the longer I'm away, the higher the cost (not specifically monetary) of the relocation.
I personally don't think the risk is currently high enough to justify evacuation if you live in the US (I'm not sure where you're writing from). I think looking at escalations/de-escalations of conflict between nuclear powers as signals of risk makes sense. You could look at estimates like this one (https://forum.effectivealtruism.org/posts/KRFXjCqqfGQAYirm5/samotsvety-nuclear-risk-forecasts-march-2022) or check relevant metaculus questions.
Dosimeters (accidently posted early, still editing)
I spent many, many hours looking at affordable Geiger counters / dosimeters and had difficulty finding a verifiably good one at a reasonable price.
The biggest problem was finding a meter that could get a reading above 99.99µSv/hr, (especially verifiably—someone showing it properly registers high-rad sources). If your city is nuked, it's worthwhile to know if you're getting 300µSv/hr, 3,000 µSv/hr or 30,000 µSv/hr (30 mSv/hr), but if your meter stops at 99 you're out of luck—except that some meters limited to 99uSv/hr do understand doses above that, e.g. this meter registers 0.005 mSv in 59 seconds which is 305µSv/hr, and it can go higher. Here's the thing: at 300µSv/hr, you are getting 7.2mSv/day—which is bad, but not your biggest problem if half of your city is on fire. But at 30 mSv/hr you'll have radiation poisoning in a matter of hours, so leave right now.
Another major problem is battery life—good luck recharging without electricity.
Amazon has many false listings of "Geiger counters" or "dosimeters" that are actually EM meters. If it measures V/m or teslas, the listing is a lie. Lying is crazy popular on Amazon.
There are other features to look for such as data logging, but I had my hands full just looking for the essentials. See also: Geiger counters 101 video.
Many meters
can't detect all types of radiation (look for gamma + beta detection at least), so your actual dose may be higher than the meter shows (radioactive fallout will have all kinds of radiation, except maybe muon; gammas are notable because they can pass through walls; alpha radiation is easy to block, and often, detectors are too shielded for alphas to reach it),
are not accurate because they are just "counters" that don't measure the energy of each detected particle*. This video is notable because one Ecotest product shows 13 uSv/hr and another Ecotest product shows 61 uSv/hr for the same radioactive plate (Ecotest has a good reputation, and both products are expensive). Not sure why the readings are so different, but in general, Geiger counters are calibrated against a specific radiation source which will have a different average energy level per particle than radioactive fallout (whose composition varies over time, in fact).
I recently got a cardiac function test that gives 10-30mSv of radiation depending on equipment sensitivity (which determines the dose the doctor gives you)
Fukushima residents are not allowed to return home unless the dose is below 20 mSv/year
Natural background radiation is 1-2 mSv/year (0.11-0.23 µSv/hr)
Affordable recommendations:
Smartphone Geiger counters are the cheapest and smallest options. This video shows that the "FTLAB" meter ($45 CAD) can register at least 300µSv/hr, but if it overloads, the reading will be near zero. Don't forget to download the app!
NR-750 is $79 CAD on Amazon. The Amazon listing for NR-750 seems to contradict itself, saying "Dose equivalent rate: 0.01~1000μSv/h (maximum 10mSv/h)" Make up your mind, is the maximum 1mSv/h or 10? Other listings say the same thing. But 1mSv/h should suffice. Only problem is, I've seen no one verify it can handle large radiation measurements.
Bosean FS-600: prices vary and I've found no comprehensive reviews. Some people like it, but it seemed not very sensitive in this review.
There are supposed to be various low-precision, low-cost geiger counters and passive dosimeters (such as cumulative exposure 'credit cards') for emergencies, but I just haven't been able to find much information about them. For example, this page tells me that a "pocket ionization chamber" can operate without batteries, but another page tells me they are battery-operated, and neither page discusses actual models, prices, where to buy, or how hard it would be to read a no-battery device in the dark.
Their purpose is to load up your thyroid with iodine, so that it does not absorb radioactive iodine-131 during nuclear disaster. Note: iodine-131's half-life is 8 days, so most of it is gone after a few weeks.
Adult dose: 130 mg, 1x per day when exposed. Whereas the FDA document says to soak the tablet and then crush it, this video says to swallow whole without chewing or breaking. I think I'll just follow the directions on the bottle. Safe to eat with food. Pregnant/breastfeeding women are advised to avoid (but I'd say just use smaller doses).
Side effects: "allergic reactions including angioedema, hemorrhage, fever, rash and lymph node swelling"
Do not overuse. Prolonged use causes "iodism","characterized by a burning sensation in the mouth or throad, stomach irritation, colds, sneezing, metallic taste, evere headache, raw teeth and gums, decreased/increased thyroid function", or "potassium toxicity, characterized by muscle weakness and irregular heartbeat".
It seems potassium iodate is cheaper than iodide, and iodate (dose: 170 mg) is more stable in hot/humid climates, but iodate is a "stronger intestinal irritant".
I bought a couple of other products not on OP's list:
Portable medkit
Multipurpose unit with hand crank, solar panel, USB output for phone charging, battery, flashlight and radio (here's another and another and another.) Does this product category have a name? I bought two of them and a simple solarphonecharger, assuming that at least one of these cheap Chinese models will break right away, and if not, it's still nice to have three things.
Portable butane stove and 12x227g fuel canisters (how long will that last 4 people? a month?). The propane equivalent cost a lot more; didn't seem worth it.
Electric generator (hmm, where can I put this gasoline so the blast won't ignite it? Storing it in my house doesn't seem ideal in non-emergency scenarios... on second thought, maybe a solar array+battery+inverter setup would have been better... I wonder if a nuclear blast would fry an outdoor solar system, though, so that one would have to keep the system offline and wrapped in foil so that it would still be usable after a blast. Better yet, I have my eye on the EB3A power station, which provides enough power to be useful, is light enough to be hand-portable, and cheap enough that it's no tragedy for it to gather dust in peacetime. The only problem is that I can't find an electric stove or microwave that uses more than 200 and less than 600 watts. I realize it would take several hours of solar power to cook a small meal with this, but what if there's no way to buy fuel?)
I'd also like to find a rainbarrel that isn't too expensive, and an extra supply of convenience items, e.g. lip balm, toilet paper. You're making a prepper out of me, Fin!
NB It's iodide, not iodine (potassium iodide, KI) and it MUST be pharmaceutical grade, NOT photo grade. If you see someone dosing out Lugol's iodine to kids, politely take it off them and use it for wounds or sterilising fruit/veg.
If you don't have tablets, but do have pharmaceutical grade KI powder, you need a very accurate balance to weight the correct dose for children, something like this: https://www.amazon.co.uk/dp/B07RZR5HYF
Buy it now. In an emergency, deliveries may be problematic.
Some other resources, which might be useful in other continents:
Hey! This is a really nice, well-written guide. I found it helpful, since I've been thinking about nuclear risks too (probably a bit too much) in light of recent events. I'd definitely advise you to cross-post this great sequence to LessWrong, where additional people would see it and it might get even more traction. LessWrong is a more generalist forum, they're more interested in personal tips and self-improvement (including early covid-preparation advice back in 2020), so I think they would really appreciate it.
I think this guide is unnecessarily pessimistic about surviving the blast. A dedicated fallout shelter building will survive 20 psi overpressure, and being away from windows will save you from the third degree burns and flying glass that do a lot of the damage in explosions. Also fires will start: if you live in the Berkeley Hills, this can complicate your situation tremendously.
To avoid as much of the fallout as possible. I suppose evacuating opposite of downwind would also be good, but less important to spell out since to evacuate opposite of downwind you would have to already be opposite of downwind. Basically don't go closer to the blast or closer to downwind of the blast if at all possible.
For comparison, this analysis finds a 0.4% yearly risk, which is in line with the EA survey and other estimates I've seen, so I'm strongly inclined to think that the 0.1%-1% order of magnitude is the correct place to be.
Thanks for sharing! As a heads up, several of the amazon links go to items that are sold out or no longer exist (which makes sense given that there's more demand for those items right now, and it's hard to keep links like this up to date).
Thanks for pointing that out. Perhaps I should remove them. I didn't do much research into what the best options are, just thought that would reduce the cost of searching for people.
This is a crosspost from the new Animal Welfare Alignment Newsletter by Anima International. You can subscribe on Substack if you are interested in following these efforts. Audio reading also available on Substack.
The goals of this post are to:
1. Raise a question I see as crucially important to the goal of aligning AI to animal welfare...
Hello! I'm Justin Portela. I got hired by GWWC to make YouTube videos after AI in Context did such a kickass job.
My channel is using that same cinematic, high-production value beauty to talk about everything in the EA universe that isn't AI.
...
This is a linkpost for Request for Proposals: Research and Applied Work on Digital Minds.
I'm glad to announce a request for proposals for research and applied work on digital minds at Longview Ph...
This doc is to help you prepare for the tail risk of nuclear war. Estimates vary, but an EA Forum survey put the annual probability of US-Russia nuclear war at 0.24%. This doc will go into some detail on threat models of nuclear war and then go over preparations you could make to survive being near a nuclear event.
Threat Models
Nuclear Bombs
To get a sense of how a nuclear bomb damages an area, the distance of radioactive fallout, etc. you can check out NukeMap. The damage caused by a nuclear bomb or missile being detonated is going to depend on many factors including bomb size, detonated on ground or in air, weather, etc. This chart includes some distances and effects for different yields and detonation heights. Yield can vary a lot and is difficult to estimate because yields are often secret and can be changed in similar sizes of missiles because the nuclear material is not a heavy part of the missile. Historically, ICBMs in the Russian Arsenal include a range from ~40 kilotons to ~6 megatons. The largest bomb ever tested was Tsar Bomba, which had a yield of about 50 megatons.
States generally keep modern yields secret, but common yields of ICBMs in the US and Russian arsenal would almost certainly include warheads with yields in the 100-500 kiloton range and might include weapons of 1 to 6 megatons. I’m basing this guess off of Wikipedia’s list of nuclear weapons.
Nuclear War
Estimates vary, but an EA Forum survey put the annual probability of US-Russia nuclear war at 0.24%. Living in the US, Russia, Canada, and Northern Europe this is the most concerning nuclear threat. 9 countries possess nuclear weapons.
Nuclear Winter
Nuclear winter is a controversial risk. During the cold war the security community and the scientific community disagreed about how bad a nuclear winter would be or even if it was possible. The cooling effect depends on a lot of things. How much smoke is created, how much of it is black carbon, how high is that lofted in the atmosphere, what is the weather, were there firestorms, what materials were burned, etc. Looking through the scientific literature, there’s a lot of uncertainty, but in an all out nuclear war between Russia and the US, a nuclear winter lasting months to years seems plausible. If there were a nuclear war between, say, India/Pakistan (about 100 nukes each) there would likely be global climate effects, but probably not nuclear winter. If you were prepping for nuclear winter you’d want months of stored food and water in a place away from potential targets. In the case of nuclear winter, you’d likely want to evacuate to somewhere in the southern hemisphere.
EMP
The probability of large scale damage from EMP could be higher than other kinds of damage from nuclear weapons because it takes fewer weapons to affect a large area. A single nuclear weapon detonated high enough in the atmosphere could affect an area about the size of the US. What we know about EMP comes from tests done by the US and Russia during the cold war. The US test took out all known satellites at the time and the russian test irreparably damaged several miles of power lines. The major concern from EMP is damaging the electrical grid. The US electric grid depends on Large Power Transformers. If the large power transformers were damaged it could take a long time to replace them. They depend on a lot of custom parts and rare materials. Large Power transformer production takes 1 to 2 years. Perhaps that would be sped up in an emergency or it could take longer if critical resources or supply chains are damaged. I could also imagine transitioning to more localized grids in that situation, but that would still result in unreliable electricity for long amounts of time.
Nuclear Power Plant Meltdown
Nuclear power plants could melt down or be the target of terrorist or state action. The radiation from a power plant meltdown is much worse than from a nuclear bomb because a nuclear bomb contains far less radioactive material. If there is a meltdown in your area you should evacuate or shelter in place depending on what emergency authorities say, what level of radiation is currently in your area, and how adequate your shelter is. The WHO estimates 4,000 direct deaths from the Chernobyl Disaster, but that number is fairly controversial. Contaminated food sources could also be concerning. Contamination occurred from the Fukushima Daiichi disaster, but this article suggests the risk from that contamination was fairly low.
Radiation
Here’s a handy visual on radiation dosage. Risk of harm from radiation depends on both the dose and the dose rate. 1,000 microsieverts over an hour is much more damaging than 1,000 microsieverts over a year.
Some of the relevant numbers from the infographic . . .
Microsieverts
Over what time period?
Effects
100,000
1 Year
Lowest annual dose where we have solid studies on increased cancer risk
500,000
1 Day
Decrease in blood cell counts, returning to normal after a few days if exposure stops.
1,000,000
Hours
Temporary radiation sickness, low blood cell count, not fatal.
4,000,000
Hours
Bleeding, hair loss, possible death within 6 weeks, death more likely if untreated.
6,000,000
Hours
Usually fatal within 2-4 weeks if untreated
10,000,000
Hours
Fatal Dose, Death within 2 weeks
Prepare Before
Sign up for Emergency Alerts
The government may send out emergency alerts via text. In order to receive these, the alerts will need to be turned on in your phone. In theory these alerts should only be about disasters in your geographic region or imminent threats to your safety. Amber alerts are different and you can choose to turn those on or off separately.
Instructions to turn on alerts for iPhone and android
The alerts are tied geographically to your phone. So you should get an alert even if you are not at your home zip code.
These Emergency alerts don’t work on all older phones.
There is a setting in your phone that needs to be turned on in order to receive the alerts. It is the emergency and public safety alerts. It was unclear the difference between “Emergency Alerts” and “Public Safety Alerts”. Probably best to leave both on.
Consider subscribing to local emergency alert systems.
In the Bay Area, the AC Alert system exists. Subscribe to receive text messages and/or emails with local emergency alert information.
Sign up for Ben Landau Taylor’s Evacuation Email
Ben Landau Taylor wrote up a blog post on evacuating if a nuclear war seems imminent. You can sign up to receive an email if he decides to evacuate here.
Consider Evacuation Triggers
Your evacuation trigger could just be receiving the email from Ben. You might also consider . . .
Threats from leaders of nuclear countries
Non-nuclear war between nuclear powers
Coup or collapse of the government of a nuclear power
Plan an Evacuation Route
For leaving before a nuclear event
If you’re leaving before a nuclear war, places in the southern hemisphere are better. Most nuclear powers and their potential targets are in the northern hemisphere and nuclear winter models show most effects in the northern hemisphere.
You probably already know that New Zealand and Australia are good bets. Here’s a list of countries that are mostly food exporters and have typically been easy to get visas to if you live in the US or EU.
If you have to stay in the US, get away from major population centers and military bases.
For Missiles Inbound
You would shelter in place or go to the nearest available shelter. See the “Survive During” section for detailed information on sheltering.
Plan ahead on where you could run to whether it’s your home or a group shelter. Generally you want to be behind thick/dense material. Being able to seal off your room from the outside world is valuable as is good air filtration.
Since I live in Berkeley I would run to the Bart tunnel if I knew a nuclear missile was incoming. It’s just a couple minutes from where I live, and it’s underground with cement walls for shielding.
Emergency Radio - Stay up to date on emergency recommendations during the disaster
Shield the electronics - The effects of EMP on personal electronics are not well studied. To ensure your electronics are protected, wrap them in one layer of plastic (could be a ziploc) and then 5 layers of aluminium foil.
Plastic Sheeting and Tape - Seal off your shelter for the first few hours of fallout.
N95 or P100 - An N95 or P100 can reduce the amount of radioactive particulate you breathe in if it’s in the air.
You should already be storing some food and water for a variety of disasters.
Prepare for a world without electricity
In addition to the things in Preparing for Power Outages in Disasters, you’d need to shield your personal electronics to be sure they’d survive an EMP. You can do this cheaply by wrapping electronics in plastic wrap(or a ziploc), then 5 layers of tin foil.
For a HEMP(High-altitude Electro-Magnetic Pulse) the electrical grid could be out for months, so having alternate electricity would be more important than other disasters. Solar panels or gas storage might be options if you’re willing to put in a lot of effort for the tail risk here.
Store Water
As with other disasters you’ll want to store water for sheltering and evacuating. In a nuclear emergency, avoid tap water as it could have picked up radioactive particulate.
You’ll want to be able to evacuate elsewhere. In a nuclear emergency be sure to bring your geiger counter and masks as well (masks can help filter out radioactive particulate).
You’ll need a place as close by as possible with as many layers of material between you and the outside world as possible. If you’re in the blast radius you're probably just dead, so this is for if you’re outside the blast radius and preparing to avoid radiation.
If you’re in a home, a basement would probably be your best bet. Unless there were more adequate shelter within a couple minutes run of your home. If you were in a basement you’d also want to cover up any exits or floor level windows with as much material as you could (boards, books, etc.).
Once the radiation has died down(FEMA recommends waiting 24 hours) you should evacuate. Evacuate in a direction not downwind if possible. On the California Coast wind often travels from west to east, so it would make sense to evacuate north or south.
You may want to use a public shelter if it’s close enough. To find the nearest open shelter in your area, text SHELTER + your ZIP code to 43362 (4FEMA).
Decontaminate
If you think you’ve been through an area with radioactive particles on your way to shelter, you should decontaminate.
Perform decontamination in a room that you will not shelter in
Remove all clothing
Wash yourself with tepid/lukewarm water (cold water might trap radioactive material in your pores, hot water increases absorption rate through increased skin blood flow).
Repeat step 3
Ensure contaminated clothing and water does not go into rooms you’ll be staying in. If you have extra cloths/blankets, cover the contaminated material.
Seal off your shelter
Close all windows and doors. Turn off all fans, air conditioners, and anything else bringing air into the house. Seal off the room with plastic sheeting(anything you can do to seal off airflow; garbage bags, plywood, etc.) and duct tape. Remove the seal after a few hours. You don’t want to suffocate, you just want to keep the radioactive particulate from getting in, which will settle out of the air over time.
Directions for Making the Potassium Iodide (“KI”) Solution:
Step 1. Soften the KI tablet:
Put one 130 mg KI tablet into a small bowl. Add four teaspoons of water. Soak the tablet for one minute.
Step 2. Crush the softened KI tablet:
Use the back of the teaspoon to crush the tablet in the water. At the end of this step, there should not be any large pieces of KI. This makes the KI and water mixture.
Step 3. Add a drink to the KI and water mixture:
Mix four teaspoons of juice(you can use water, but juice will make it taste better) mixture made in Step 2. Now you have the final KI solution.
Step 4. Give the right amount of the final KI solution, using the chart below:
How Much of the Final Potassium Iodide (“KI”) Solution to Give Each Day
Age
Once Daily Dose of KI Solution
19 years and older
8 teaspoons
13 to 18 years (150 pounds or more)
8 teaspoons
13 to 18 years (149 pounds or less)
4 teaspoons
4 to 12 years
4 teaspoons
Older than 1 month to 3 years
2 teaspoons
Birth to 1 month
1 teaspoon
What do I do after the explosion?
Some of this will be redundant with what to do if a missile is inbound. Feel free to ignore the advice you’ve already taken.
Take Shelter
Something you can get to as quickly as possible that will be as safe as possible. To find the nearest open shelter in your area, text SHELTER + your ZIP code to 43362 (4FEMA), example: shelter 12345.
Use the visual from the earlier take shelter section to choose a shelter location.
In reality this depends on where you are relative to the bomb went off, how big the bomb was, whether it was air or ground burst, and which way the wind is blowing. You probably won’t know all of those things so here are some heuristics.
FEMA and ready.gov suggest 24 hours. This is when the radiation will be at it’s worst. If you suspect you are in a zone of radiation or downwind you should stay inside for at least 24 hours if you have reasonable shelter.
Several prepper blogs suggest 48 or 72 hours.
From Britannica.com “A nuclear explosion produces a complex mix of more than 300 different isotopes of dozens of elements, with half-lifes from fractions of a second to millions of years. The total radioactivity of the fission products is extremely large at first, but it falls off at a fairly rapid rate as a result of radioactive decay. Seven hours after a nuclear explosion, residual radioactivity will have decreased to about 10 percent of its amount at 1 hour, and after another 48 hours it will have decreased to 1 percent. (The rule of thumb is that for every sevenfold increase in time after the explosion, the radiation dose rate decreases by a factor of 10.)”
Using radiation measuring devices:
If you have a geiger counter or dosimeter, you might use that to determine when to leave your shelter to evacuate the area. The threshold is up to you, there’s not official recommendations about what geiger reading you should evacuate at. Finan would consider the current radioactivity inside the shelter, the radioactivity outside the shelter, and how long to get to a safer place if evacuating.
Example:
If the radiation inside was 400,000 microsieverts and outside it was 1,000,000 microsieverts. Finan would evacuate immediately if he thought it was 2 hours to safety, but not if he thought it was 10 hours.
How will I evacuate if cars aren’t working?
You may think cars would be shut down making it difficult to evacuate, but mostly cars are fine after EMP, especially if they’re turned off.
If your car is not working, consider the time it would take to walk in your decision making.
Seek Medical Attention
If you’ve been near a nuclear explosion or accident you could have radiation sickness. Seek medical attention if available.
What if a nuclear power plant melts down?
In the case of a nuclear power plant meltdown almost all of the advice above applies.
The differences . . .
Because a power plant meltdown doesn’t have the same kind of explosive power as a nuclear bomb, you might be able to evacuate immediately rather than sheltering in place. Evacuate immediately if . . .
Emergency authorities tell you to.
The radiation has not yet reached you (as checked by emergency authorities or geiger counter).
The radiation is not yet very bad outside and you expect it to get worse.
In all cases you want to evacuate perpendicular to downwind of the nuclear plant.
If you do end up sheltering in place because you were close to the power plant or did not get word of the meltdown before radioactive particulate in the air reached you, you may have to shelter in place for longer(because there is more radioactive material in a power plant than in a nuclear bomb). Listen to emergency authorities and use a geiger counter if you have one to determine if it’s safe to evacuate. If your shelter is not very good (eg. a wood framed house), consider evacuating immediately if you can get to safety relatively quickly. Refer to the sections on radiation and taking shelter to determine what seems the safest course of action.
Imo, evacuating to another country when a nuclear war looks literally imminent may not even be a good move because you'd have to enter a large city with an international airport with transcontinental flights, and the increased risk while you're reentering the city & waiting for your flight is probably greater than the survival benefits from arriving at your SH destination, not to mention flights would probably be booked out if things really looked that dire. A better strategy would be to evacuate whenever the risk looked heightened, but then you'd run into a "no fire alarm" problem and it'd be very unclear when you should do so, and in any case you'd be doing it repeatedly. The biggest problem with this approach is it wouldn't save you from sudden nuclear war. All it takes is an accident, the risk of which with China now joining Rus + US in adopting Launch on Warning has arguably risen at least 50%. Or something like Kim having a bad day/internal turmoil within the unstable NK regime which had no outwardly visible signs until after the fact, and the Bay Area is gone in a flash. (Looking at you, MIRI and like 3/4 of the entire alignment community based there...)
The best strategy imo is to relocate permanently to somewhere with a much lower risk of attack: e.g., a smaller non-US NATO city like Kitchener, or a very small US city. E.g. the Toronto area may be attacked, but it's pretty unlikely Kitchener would because a marginal warhead would be better spent on another US city, even for Russia with 1500 deployed warheads. And your very small US city/suburban area of 10-20,000 people is quite unlikely to be attacked, because all cities with greater population would be attacked before it, unless it had some unique importance.
Doesn't really make sense to consider yields or anything like that, whether your metropolitan area is annihilated by a single 25 megaton warhead from an R-36M or a bunch of MIRVs in the low hundred kiloton range makes no difference and is just down to which missiles are assigned which targets. No one knows exactly which places would be targeted, just that some places are of course likelier than others, and certain things about strategy (e.g. China has a pure countervalue strategy for now, targeting all warheads at cities only).
Lastly, recall one problem with the strategy of evacuating at the last possible moment when warheads look like they could be falling any minute, is that if many others have the same idea as you, the roads out of the city will be jammed to a standstill. In fact, governments may be attempting to evacuate the cities at that time too. This is another advantage of being in a smaller town/outlying area: you won't be hindered whenever you decide to evacuate.
Yes, if imminent literally means missiles are inbound it is too late, but if you've decided there is a high probability of nuclear attack in the next couple of weeks to months evacuating could still be a good strategy. For Ben Landau Taylors signup list, he certainly means evacuating well before missiles are launched.
Certainly small towns are not at much risk of being hit directly. If you were concerned about an all out war between the US and Russia though, evacuating to somewhere in the southern hemisphere could make a lot of sense.
Yields of nuclear weapons can vary a lot. Like you said, no one knows exactly where would be targeted, but if your near a large city that might be hit, considering how to shelter and evacuate after an attack could still be quite useful. I agree attempting to evacuate a city as missiles were being launched would not result in good outcomes.
I'm curious about your thoughts on this: hypothetically, if I were to relocate now, do you see the duration of my stay in the lower risk area as being indefinitely long? It seems unclear to me what exact signals--other than pretty obvious ones like the war ending, which I'd guess are much less likely to happen soon--would be clear green lights to move back to my original location. I'm wondering because I'm trying to assess feasibility. For my situation, it feels like the longer I'm away, the higher the cost (not specifically monetary) of the relocation.
I personally don't think the risk is currently high enough to justify evacuation if you live in the US (I'm not sure where you're writing from). I think looking at escalations/de-escalations of conflict between nuclear powers as signals of risk makes sense. You could look at estimates like this one (https://forum.effectivealtruism.org/posts/KRFXjCqqfGQAYirm5/samotsvety-nuclear-risk-forecasts-march-2022) or check relevant metaculus questions.