How effective is the radiation protection?

NORAD S-Series bomb shelters provide a Total Rems in Shelter (TRS) of less than 5 rems at the shelter design pressure of 10 psi. The TRS rating includes radiation entering the shelter from air pipes, entranceways and overhead. Radiation doses used for this rating are described in Principles of Protection. As we say on our Blast Shelters page (Point Z is where the entrance meets the hull):

“To be a ‘blast shelter’ the structure must have a TRS or Total Rems in Shelter rating. The TRS indicates how many rems the shelter occupants will receive at specific distances from ground zero from overhead, entranceways and air ducts. NORAD S-Series Underground Shelters have a TRS of 4-10. Shelterists will receive a maximum of 2 rems radiation at Point Z during a bomb blast creating 10 psi over pressure (see Point Z image below). The TRS measures all forms of radiation from all shelter exposure points.”

Where to Hide If a Nuclear Bomb Goes Off In Your Area

nuclear bomb exploding over city via, by Patrick Allan , Gawker MediaMar 22, 2017, 02.30 AM IST This is advice I hope you never need but should know anyway. A nuclear attack is everybody’s worst nightmare, and the immediate aftermath is just as bad, if not worse, than the explosion itself. Here’s what you should do if you survive the initial blast. You’ll know a nuclear bomb went off near you if there’s a sudden flash of bright, white light, which may or may not give you flash blindness if you’re within 50 miles or so of ground zero . If that bright, white blindness eventually clears up, and you don’t suddenly feel at peace, you’re alive. Other signs of a nuclear blast include near instant first-degree to third-degree burns if you’re within 10 miles or so, and of course, the trademark mushroom cloud looming over the skyline. As soon as you realize what’s happening, researcher Michael Dillon, from the Lawrence Livermore National Laboratory , suggests you find shelter immediately in order to escape nuclear fallout . In his report for the journal Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences , Dillon recommends hiding within the most dense building material possible. The thicker the better. For example, sturdy brick or concrete structures that lack windows, or heading underground to a cellar, basement, or sub-basement. Hiding in such a place will expose you to just 1/200 of the fallout radiation you’d be exposed to outside . Obviously, an actual bomb shelter is ideal, but most people aren’t near those. This FEMA graphic , recently shared by Business Insider , gives you an idea of good places to go:

FEMA housing nuclear protection lifehacker Wooden structures, like most houses and smaller one story buildings, won’t do much good against fallout radiation, unfortunately. Is it better than nothing? Kind of, but Dillon recommends you move to a better location if possible. If you can dash to a more dense, protective shelter in about five minutes of exposure, go for it. If getting there would take longer, say up to 15 minutes of exposure , stay where you are for at least an hour, then make your move. A good portion of the intense fallout radiation will have subsided by then, reducing your exposure some. While you wait in your dense, thick-walled shelter, the EPA suggests you stay away from any doors or windows, take a shower or wipe down exposed parts of your body with a wet cloth, and ditch your now-contaminated clothing . Stick your contaminated clothing in a plastic bag, seal it off, and get it far away from you and others. While you shower, use shampoo and soap, but do not scrub or scratch your skin. And do not use hair conditioner, as it will bind radioactive material to your hair. Once clean, blow your nose, then wipe your eyelids, eyelashes, and ears to remove any leftover material. Lastly, make sure you only drink bottled water and eat food from sealed containers until a rescue team can get to you. As you wait, listen to the radio to stay up to date on where you can find help and get screened for contamination .

How Deep Does A Shelter Have To Be?

Let’s looks at what earth above the shelter actually does. First, it provides radiation shielding for both gamma and neutron radiation. Secondly, it provides counter buoyancy to keep the shelter in the ground during high water tables. Third, it provides mass to keep the shelter temperature stable and keep it from overheating when people live inside. In tactical situations we could talk about effects of artillery shells falling on or near the shelter but that is another whole area that will not be addressed here.

Radiation Shielding Overhead

Every shelter has a radiation design dose which is the type of radiation and the level of radiation the shelter is designed to resist. There is an Overhead Radiation Design Dose and an Entranceway Radiation Design Dose. We will focus here on the Overhead Radiation Design Dose.

Let’s arbitrarily set the radiation design dose based on a 100 KT surface burst nuclear weapon of 50% fission and 50% fusion. Let’s also set the design pressure of the shelter to resist 10 psi of overpressure which is 0.9 miles away from ground zero for this size weaponi.

There are many materials that can be used to shield radiation but there is no material cheaper than earth. A neutron radiation dose is reduced in half when passing through 4.7 inches of earth. Gamma radiation is reduced in half when passing through 5.5 inches of earth. A very handy table used to determine the Overhead Radiation Design Dose is shown below.

Dist. GZ MSD 0.5 MI 0.6 MI 0.7 MI 0.8 MI 0.9 MI 1 MI 10 MI 25 MI 50 MI 100 MI
Overpressure psi 200 30 21 15 12 10 8 0 0 0 0
Initial Gamma rems 25,000 25,000 10,000 4,500 2,000 1,200 500 0 0 0 0
Fallout Gamma rems 9,554 9,554 9,554 9,554 9,554 9,554 9,554 5,800 3,800 375 100
Neutron rems 1,000,000 80,000 25,000 15,000 7,000 4,000 1,600 0 0 0 0
5.5 517,277 57,277 22,277 14,527 9,277 7,377 5,827 2,900 1,900 188 50
11.0 258,639 28,639 11,139 7,264 4,639 3,689 2,914 1,450 950 94 25
16.5 129,319 14,319 5,569 3,632 2,319 1,844 1,457 725 475 47 13
22.0 64,660 7,160 2,785 1,816 1,160 922 728 363 238 23 6
27.5 32,330 3,580 1,392 908 580 461 364 181 119 12 3
33.0 8,353 1,165 501 337 236 199 170 91 59 6 2
38.5 4,176 583 251 169 117 100 85 45 30 3 1
44.0 2,088 291 125 84 59 50 42 23 15 1 0
49.5 1,044 145 62 42 30 25 22 11 7 1 0
55.0 522 73 31 21 14 13 11 6 4 0 0
60.5 261 37 16 11 8 6 5 3 2 0 0
66.0 69 18 7 5 3 3 2 1 1 0 0
71.5 35 6 3 2 1 1 1 1 0 0 0
77.0 17 3 1 1 1 1 1 0 0 0 0
82.5 9 2 1 0 0 0 0 0 0 0 0
88.0 5 1 0 0 0 0 0 0 0 0 0
93.5 2 0 0 0 0 0 0 0 0 0 0
99.0 0 0 0 0 0 0 0 0 0 0 0
104.5 0 0 0 0 0 0 0 0 0 0 0
110.0 0 0 0 0 0 0 0 0 0 0 0
115.5 0 0 0 0 0 0 0 0 0 0 0
121.0 0 0 0 0 0 0 0 0 0 0 0
PRINCIPLES OF PROTECTION, The US Handbook of NBC Weapons Fundamentals and Shelter Engineering Design Standards, 6th edition, 2013, Walton McCarthy M.E. Brown Books.
Effects Rems
50% Lethal 200-450
radiation sickness 50-200
blood effect 25-50
safe 0-25

Shelter Types And Ratings


The Reality Of Underground Shelter Types And Ratings

by Walton McCarthy

What is a “BUNKER”?

“Underground bunkers” were shelters designed to protect occupants from the bomb blasts of World War I and WW II. A bunker is an empty structure incapable of protecting occupants from modern warfare threats. A bunker typically does not have a life support system or any air filtration. It has a 0 psi overpressure rating, meaning that it is only effective for protection from small air dropped bombs like what was used in WW II in England . A bunker is a very short term structure considered obsolete by modern standards since it does not meet any established engineering standards for radiation shielding, chemical weapons air filtration, biological weapon air filtration, and it is not suitable even for the duration of a typical hurricane.


A survival shelter is a cheap short-term shelter that has little or no published performance data, has no published Radiation Design Dose from overhead or from the entranceway that the shelter is designed for,  has no published ratings for pressure,  no published internal radiation doses that shelterists can be expected to receive,  does not list the distance from ground zero that the shelter is designed for and  usually has a weak or no warranty.  This type of shelter has a short-term air filtration system and meets virtually no commercial or military standards, and meets no manufacturing standards.


A fallout shelter is designed primarily to protect shelterists from gamma radiation during the fallout period. This type of shelter has a rating of 0 psi of overpressure. Like all underground shelters, it should be water controlled and must provide for a twenty-eight-day period of fresh air, light, heat, flushable toilet, water, food, sleeping, radio communications, and usable space. In general, it must meet all the requirements of the blast shelter except for those relating to overpressure and temperatures from sustained fires. The shelter is a dual-purpose shelter if it can also serve as a basement or extra housing facility. Personal or family shelters are designed for use by up to ten people. A group shelter is made up of a number of family shelters, where there are two or more families together. These shelters may be connected through a common tunnel or just grouped together to make a community shelter.


This is a shelter meeting all the requirements of the fallout shelter plus a resistance to overpressures from 1 to 9 psi. It is not capable of shielding from initial nuclear radiation (neutron radiation).

S16x40 Bomb ShelterWhat is a “BLAST SHELTER”?

A shelter meeting the requirements of a fallout shelter and designed to protect its shelterists from the effects of blast, sustained fires, and overpressure from 10 to 40 psi is a blast shelter. Above a 40-psi overpressure, the shelterists will need to be restrained in seat belts. The blast shelter must also be specifically designed to protect the shelterists from large doses of neutron radiation. Above 50 psi the shelterists would be severely injured, even if the shelter is designed to withstand the blast and radiation. Just as a chain is only as strong as it weakest link, the shelter’s weakest link can be blast pressure resistance or radiation shielding. A properly-rated 40-psi shelter must be able survive the blast undamaged and must be able to provide radiation shielding at the 40-psi level. It makes little sense to survive the blast and then die of radiation sickness a few days later. A shelter psi rating is based on three factors, 1) the shelter pressure rating, 2) the shelter radiation shielding dose, and 3) the hatch and air manifold design. It is erroneous to claim a 30 psi rating for a shelter, if at that distance from ground zero, a lethal or sickening dose of radiation enters the shelter from overhead or the entranceway. Below at 0.5 miles from ground zero an overpressure can be expected in the 30 psi range. A shelter at this distance with 48 inches of earth over the crown of the shelter ceiling (44 inches in the table) would allow approximately 291 rems inside the shelter which would be lethal to the shelterists. Any shelter with 48 inches of earth over the shelter ceiling should be rated a 0 psi making it a fallout shelter. The doses in this table are from overhead only. There are other tables showing the entranceway doses. The radiation doses from all sources, overhead, entranceway, emergency escape, air ducts, all allow radiation to enter the shelter. Radiation from all sources must not exceed 25 rems in the first 30 days. The goal would be to design the shelter for a maximum of 5 rems from all sources of radiation. This rating system is known as the TRS rating or Total Rems in Shelter. A shelter with 48 inches of earth (nearest lower number is 44) would have a TRS Rating of 23-10 meaning that the shelter would allow 23 rems of radiation to enter the shelter at the 10 psi distance.