I was wondering how effective nuclear shelters actually are? If you assume that your house is equipped with a bomb shelter (aka fall-out shelter). The construction of the shelter is not over the top, just a concrete lined bunker set into the ground say 3m below the surface of the ground. (which is already quite OTT)


  • how devastating is the explosion of a nuclear bomb? what damage would occur to the sub-structures and for what distance
  • how fast does the radiation spread? could you be effectively notified via cellphone to "bunker up?"
  • how long would you need to stay in said bunker (if you can actually survive the other effects)
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    $\begingroup$ There is a difference between a "bomb shelter" and a "fallout shelter" $\endgroup$
    – chbaker0
    Commented Oct 15, 2014 at 22:12
  • $\begingroup$ My high school (built in 1960) had "fallout shelter" signs, which as a joke. The shelters were basically just the crawl spaces and pipe chases under the floors, surrounded by the foundation. These spaces all had air vents, to the outside, to prevent moisture build up. The only real purpose was for security theater, so the community felt "safe". $\endgroup$ Commented Oct 16, 2014 at 18:25
  • $\begingroup$ I remember reading (although i don't remember where) that the effects of nukes are massively overexaggerated by the US (and the soviets alike, it seems) so the "mutually assured destruction" scenario can be held up. Look at a documentary about Hiroshima and Nagasaki: It is quite impressive how many people survived in regular bomb shelters, even in the middle of the city. And even more, people continued to live there, for many years (and the US studied them. They did not help, just study...) $\endgroup$
    – Burki
    Commented Dec 15, 2015 at 8:30
  • $\begingroup$ @Burki: I don't know about an organized conspiracy-esque effort to exaggerate the power of nukes, though it's certainly true that they have an unwarranted... mystique? However, Little Boy and Fat Man had yields of just 15 KT and 21 KT; later strategic warheads can have 1,000x that yield. $\endgroup$
    – user243
    Commented Jan 6, 2016 at 14:20

3 Answers 3


Historically, the two nuclear devices detonated in war have been set off in the air. So I'll look at those for the effectiveness of bomb shelters.

If you are Ground Zero, you're probably screwed. about 50% of the total power of a nuclear blast is unleashed as a pressure wave. While you are underground and that offers some shelter, the pressure will propagate through the ground as well, and still hit you with enough force to, likely, liquify your organs. A 1MT nuclear device produces an overpressure wave strong enough to inflict heavy lung damage for 3~4 kilometers, not counting the rupture of blood vessels, etc. Again, this will be dampened by being underground, so dial it back a bit, but it's a reference point.

Part 2 of the blast is Thermal Radiation...heat. You can pretty safely ignore this if you are in a bunker, the ground eats up thermal radiation with ease.

Ionizing Radiation makes up about 5% of the blast strength, and this is pure radiation...it moves at the speed of light.

The last 5-10% of the power of the explosion is in residual radiation, which is what we traditionally think of when we think 'Fallout.'

So, as for how your bunker will do against a hypothetical 1MT nuclear device...

Blast wave

If you are within 2.4 km, you are likely dead from overpressure, and your shelter probably collapsed. Out to about 6.2 km, you might survive it, but will probably be bleeding from some orfices and be rather bruised. Beyond that, you might be a bit battered, but should otherwise be okay

Thermal Radiation

You are underground, you can pretty much ignore this.

Direct Radiation

A properly constructed Fall Out Shelter is designed to reduce the effects of radiation by about 1000x. So, while those on the surface are going to take a lethal dose of radiation out to about 2.3km, and will be quite screwed all the way out to 2.9. You can reduce your radiation exposure by 1000x, since you are in your bunker. So, if you are far enough out to survive the blast wave, the immediate radiation isn't really a threat either.

Indirect Radiation

This stuff gets carried a really long way. On the plus side, it decays exponentially. Roughly 70-80% of the fallout from a nuclear explosion (it is scattered wide, not in big chunks) has decayed within 10-20 days, and it has dropped to reasonably low levels within 100 days. But again, your bunker allows you to reduce radiation exposure by 1000x, so you are still safe, and can probably emerge in less than 100 days, provided that repeated nuclear attacks aren't occurring.

The Problems

If you are within 19km, you need to be in your bunker when the bomb hits to avoid injury. If you are above ground, the thermal blast will give you first degree burns across any part of you facing the blast (15km = 2nd degree, 12km = 3rd degree, within 10km, you, and everything around you, are now on fire.). You still have time to get below ground before the fallout starts coming down, but you are definitely injured. The thermal radiation is one of the longest range effects of a nuclear blast...being underground when that happens does a LOT to protect you.

Your bunker also needs some more advanced equipment...air recycling and cooling especially. You can't vent to the outdoors, that's full of fallout. And dirt is a great insulator, so you'd overheat within days.

Thankfully, you would probably have notice of an incoming nuclear strike before it hit. We are really good at figuring out missile trajectories, and if an ICBM was headed your way, a warning would go out to seek shelter before the bomb hit...then it's a race.

And aircraft dropped bomb would be harder, as would a suitcase nuke. But, in general, if you are outside of 19km, you could survive this 1Mt explosive without being in your bunker when it hits. Closer and you'd be injured, but might survive, too close, and you are dead meat.

So, all that said, early warning is the best protector against nuclear strikes, if you have a shelter to hide in.

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    $\begingroup$ @Zibbobz Plants won't be viable--plants only produce oxygen when they get enough light. Where are you getting that light in a fallout shelter? On the other hand, good enough filters will keep enough of the fallout out. Fallout shelter survival is quite possible. Long term survival in the world you'll emerge into is another matter... $\endgroup$ Commented Oct 15, 2014 at 23:44
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    $\begingroup$ @Hightower Mushrooms don't produce oxygen. They consume it. $\endgroup$
    – Zibbobz
    Commented Oct 16, 2014 at 12:04
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    $\begingroup$ @Zibbobz you won't need to produce oxygen, you'd just need to scrub the incoming air to remove dust (which will likely be heavily contaminated both chemically and radiologically). $\endgroup$
    – jwenting
    Commented Oct 16, 2014 at 12:22
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    $\begingroup$ If "within 10km, you, and everything around you, are now on fire" on the surface, isn't that liable to do something like suck the air out of your shelter, unless it is somehow able to remain airtight? Also, what are the odds that your air scrubber has sufficiently unblocked access to the air above after the buildings all collapse and are thrown around on the surface? And what power source is going to keep your air scrubbers and other needed devices working for 100 days? And aren't there various forms of radioactive material left that last for years or millennia? $\endgroup$
    – Dronz
    Commented Jan 18, 2015 at 7:48
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    $\begingroup$ In the Hiroshima/Nagasaki bombs, air raid shelters 0.5 mile from ground zero were undamaged. Seems to me a 1 MTon blast your shelter should be undamaged at 3.3 km (assuming overpressure scales on a cubic basis). Do you have a reference for the data you used, perhaps a nuke calculator? At 3 meters underground 3.3 km from zero in a concrete bunker, I would expect to survive the immediate effects with high probability. $\endgroup$ Commented Dec 15, 2015 at 3:02

I once visited a professional cold war era nuclear bomb shelter in Berlin. It had a capacity of around 3000 people, air filtration systems, food and water reservoirs, the works.

Also, according to their info it would do a fairly good job to protect you against the the actual blast and initial radiation and heat wave - a direct hit not included. But that is the easy part!

Air filtration systems will have to change filters regularly, otherwise they clog up and everyone suffocates. Water and food will run out. In the case of the Berlin shelter, we were told that supplies would last about 1 week tops, if the bunker was at full capacity (apparently that was about standard at the time).

But what then? You'll have to evacuate 3000 people from the middle of a highly radioactive field of debris. There will be no cars, hell, there will be no roads! The officials in this bunker told us that you would need to get all the people to a distance of at least 100km within 4 hours to avoid serious radiation poisoning (yes this depends on a lot of factors). Well, without cars or roads you know this isn't going to happen... Meaning while everyone survived the blast, they die a week after getting out from radiation sickness.

My point is: a bomb shelter which protects you against the initial blast is the easy part. But to actually help you survive it must be stocked for a very long habitation, and/or it must also provide you with effective means for you to escape the radiation zone after your supplies eventually run out.

If I could pick, I'd probably go for haz-mat suits and off-road motorcycles for everyone in the bunker. That might give you a chance to get away with most of your DNA still intact. ;)

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    $\begingroup$ Don't forget to stock some potassium iodide! $\endgroup$
    – Wingman4l7
    Commented Dec 15, 2015 at 19:23
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    $\begingroup$ How could I forget, I actually have some at home: in Switzerland, where I live, the government actually distributes potassium iodide pills for emergency use to all citizens living within 20 km of a nuclear power plant. $\endgroup$
    – fgysin
    Commented Dec 16, 2015 at 7:06
  • $\begingroup$ Iodide or iodate? I'm told a sufficient dose of iodide is very hard to swallow ( makes you gag). $\endgroup$
    – nigel222
    Commented Dec 16, 2015 at 20:03
  • $\begingroup$ It's Potassium iodide. There is even a homepage about it from the Swiss Government (only in German/French though): jodtabletten.ch Wiki also confirms it's use in other countries: en.wikipedia.org/wiki/Potassium_iodide#Nuclear_accidents $\endgroup$
    – fgysin
    Commented Dec 17, 2015 at 9:35

Fat boy was the larger bomb that was dropped in Japan during ww2. This bomb is estimated to have been 18-21 kilo tons. The largest bomb built was 50 mega tons (2,500 times stronger). Built by Russia, at the time they claimed the ability to make a 100 mega ton bomb by replacing the lead component with uranium. (The bomb used lead to reduce fall out for the nuclear test.) Most modern nuclear warheads are 12-24 megatons with the ability to device into 12 charges and hit 12 targets with a single warhead making each 1-2 megatons. Roughly 50-100 times more powerful than the larger bomb in ww2.

For the air inside a shelter blast valves are needed for the air vents to prevent over pressure and super heated air from forcing its way through those. Cheyenne mountain (NORAD mountain) is rated for a 30 megaton blast at a distance of 1.2 miles. At weakest point is 2,000 feet of granite. The entrance is on a side tunnel which is down a mile off a curving tunnel. It has a 23 ton door and then another 23 ton door.

  • $\begingroup$ Yes. A small amount of radiation lasts for years following a nuclear blast. Although this radiation is not an immediate threat it has shown to result in increased incidences of cancer in Nagasaki and Hiroshima. Assume 1 hour as 100%. 7 hours is then 10%. 49 hours (about 2 days) 1%, 2 weeks 0.1%. 14weeks 0.01%. 96 weeks (almost 2 years) 0.001% 13 years 0.0001% 92 years 0.00001% (as can see radiation in small amounts stays around a while). $\endgroup$
    – Eric
    Commented Jun 2, 2016 at 0:05
  • $\begingroup$ On another note brick has slight radiation. Not much but close consistent exposure can increase incidence of some cancers (like with a brick house and you sleep against the wall) If have wooden interior walls those are better to have bed up against. Or if not better to have foot of bed against the brick. $\endgroup$
    – Eric
    Commented Jun 2, 2016 at 0:08
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    $\begingroup$ Cheyenne or NORAD mountain has blast valves upon blast valves to protect their air. They have an underground lake for their water. Another lake for in case of fire. They have a small lake of diecel fuel to power their generators for emergency electricity. The buildings within the mountain are on massive springs so can shift with the seismic activity from a blast and the lines interconnecting the buildings are designed to shift as well $\endgroup$
    – Eric
    Commented Jun 2, 2016 at 0:14
  • $\begingroup$ Battery energy storage or some form of generator would be needed to power the neccesitys (like air filtration) $\endgroup$
    – Eric
    Commented Jun 2, 2016 at 0:19
  • $\begingroup$ You should edit your post to clarify the difference between a missile with MIRV (i.e. multiple independent warheads) and the yield of a single big warhead. $\endgroup$
    – o.m.
    Commented Jun 2, 2016 at 5:56

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