By Walton McCarthy M.E.

Underground shelter buyers need to understand the life saving components they are buying. There are no federal agencies or consumer organizations protecting shelter buyers from deceptive product claims. Knowing how the life saving components work gives you the power to know if your purchase will save your life — or not.

You can’t know the radiation danger inside the shelter without knowing the radiation level outside of the shelter — see Deception #8



FEMA does not certify or approve underground shelters. FEMA publishes tornado shelter guidelines. They do not publish or suggest any Nuclear-Biological-Chemical (NBC) warfare shelter guidelines or standards. A shelter manufacturer may claim that its shelter meets or even exceeds FEMA tornado shelter guidelines. But there are no FEMA NBC shelter guidelines, and there are no FEMA shelter certifications or approvals since FEMA is not a certifying agency. Underground shelter manufacturers can claim anything with no data to support their deceptive protection claims and that is exactly what is happening. Shelter manufacturers are unchecked.


Virtually all of the underground shelter manufacturers use unrated air filtration united to keep their shelter prices down. The problem is, these air filtration units don’t work! NBC filtration relies on TEDA carbon, which is extremely expensive. Cheap air filters contain only a small percentage of TEDA carbon in amounts that will not make NBC environment air safe to breathe.

Residence time” is how long the dangerous airborne agent stays in contact with the filter media. To filter NBC air, filtration units must use 100% ASZM TEDA carbon with a minimum 0.25 seconds residence time. Always check the air filter manufacturer specifications for ASZM TEDA carbon percentage and residence time.

Activated carbon with anything less than 100% of ASZM TEDA has a residence time of 0.0 seconds and will not make the air safe for people to breathe in a chemical warfare environment. A properly rated NBC air filtration unit for an underground shelter supplying 100 cubic feet per minute sells for approximately $10,000 to $14,000 because it uses 100% TEDA carbon and in the right volume to allow complete filtering of all chemical warfare agents. TEDA carbon for a 100 cfm NBC unit sells retail for just over $4,000. Most of the so called NBC air filtration units on the market are selling the entire NBC filtration unit for $2,500 because they do not have enough TEDA carbon or residence time to filter chemical agents but make the buyer feel good. A dummy NBC filter makes the shelter a coffin in NBC environments. The right equipment is just more expensive.


Many of the NBC air filtration units sold with underground shelters have a HEPA filter efficiency of 99.97% which is not good enough to remove or capture biological agents. The efficiency must be 99.99% @ 0.3 microns to completely filter or capture biological agents carried on dust or aerosol particles. This filter is more expensive and requires a more powerful more — and therefore more expensive — air blower.


Few of the NBC air filtration units have a pressure gauge to tell the shelterists when to change the filter and ALL shelters in the fallout area will have to at least change the pre-filter after the first 24 hours and discard it outside of the shelter. If the filter is not changed, the filter element itself will emit strong radiation doses inside the shelter.


A proper NBC air filtration unit has a bag-in/bag-out system to allow replacing the pre-filter, carbon filter, and HEPA filter without coming into contact with it. It will have to be changed to prevent radiation doses inside the shelter.


A fallout shelter typically is not designed for any overpressure.  so it has an overpressure rating of 0 psi.  For a 100 KT surface burst weapon, the overpressure drops to 0 psi at just over 2 miles from ground zero. At this distance there would be approximately 8,500 rems of gamma radiation from fallout on the ground surface.  At 100 miles away, the overpressure is still 0 psi but there is virtually no radiation from fallout.  The problem is that a fallout shelter can claim to allow no radiation to enter the shelter because the shelter was designed for 0 psi at 100 miles away where there is no radiation outside of the shelter on the ground. Every person who is considering purchasing or building an underground shelter must determine how much radiation enters the shelter at what distance from ground zero from a given size weapon. This is the very first step in designing any shelter to shield people from radiation.  (See Weapon Effects Table)


Almost all the companies selling underground shelters do not state how much radiation enters their underground shelter from overhead or from the entranceway and air ducts. The uninformed buyer purchases a shelter assuming that very little or no radiation enters the shelter because the manufacturer does not state any performance data for their shelter. Most underground shelters on the market allow a sickening or sometimes a lethal radiation dose to enter the shelter even when 4 miles away from ground zero from a small kiloton terrorist size weapon. Because the manufacturer does not state what the pressure rating the shelter is designed for, which dictates the distance from ground zero and the radiation level outside at that distance, the customer cannot claim deception by the manufacturer because the shelter manufacturer did not state any performance data. Therefore the buyer has little recourse against the shelter manufacturer. However, the manufacturer was in a position to know and should know the radiation doses inside the shelter, otherwise its underground shelter is not fit for NBC protection.


You can’t know the radiation danger inside the shelter without knowing the radiation level outside of the shelter. The first step in designing an NBC underground shelter is to establish a pressure rating and distance of the shelter from ground zero for a given size nuclear weapon. At this location, gamma and neutron radiation doses are well established from actual nuclear weapon testing for both air and surface burst nuclear weapons.[i]

This Radiation Design Dose is the dose of gamma and neutron radiation that the shelter is designed to resist. There is an Overhead Radiation Design Dose and an Entranceway Radiation Design Dose. Educated buyers should ask for both values. Based on these design doses, the shelter manufacturer should be able to state what radiation doses shelterists can expect inside the shelter at the design pressure or distance from ground zero for a given size weapon.

The old Protection Factor system used for fallout shelters does not account for radiation entering the shelter from the air ducts or entranceways, only from overhead. Most of the radiation entering an underground shelter is through the entranceway.


The second step is to determine what depth of overhead shielding, usually earth, will reduce the outside radiation levels to safe levels inside the shelter. A shelter located 1 mile from ground zero from a 100 KT nuclear weapon will be exposed to approximately 10 psi. This same shelter with 4 ft of earth and 1 ft. of concrete overhead will expose shelterists to 6 rems from overhead in the first 30 days which is more than 99% of the total dose possible.[ii] This is an acceptable dose if this were the only source of radiation. Most shelters on the market will allow more than 50 rems to enter the shelter from the entranceway. Add this to the radiation entering the shelter from air ducts and from overhead and shelterists will experience radiation sickness requiring medical attention which will probably not be available. Therefore a dose that causes sickness may result in death if no medical help is available.


Assuming it is not damaged or corroded, the common shipping container can only support one foot of overhead earth. But even with 6 ft. of earth overhead, a shipping container door end used to enter the shelter allows in lethal radiation doses. Unless steel is 1.1 inches thick, it provides no radiation shielding. But it is a really cheap structure! The layperson consumer never asks “how much protection” does the shelter offer and from what? Virtually all shelter manufacturers cannot answer this question which is in fact their business.


Defects in material and workmanship warranties don’t cover shelter collapse due to poor engineering or corrosion. Corrosion is a natural process, and therefore not a defect. A “defects” warranty shelter could collapse and kill its occupants, and the manufacturer could claim that corrosion is natural process, and is not covered under the warranty. An underground shelter warranty for life against Defects In Material and Workmanship is not a warranty.


Underground Shelter Manufacturers all claim to have the best shelter but no data to support what makes it the best. The best shelter has a published Radiation Design Dose Overhead, a published Radiation Design Dose for the Entranceway and Air Ducts, a published Protection Factor Rating that is high, a published Total Rems in Shelter that is below 25 rems, an air filtration system with published data showing 100% TEDA at the right residence time, a Bag in Bag Out filter change, a published Shelter Pressure Rating, and a published real structural warranty for a given period of time. A shelter with real protection costs more because it contains the quality components required to save your life.


There has only been one book in the past 40 years to address a set of standards for underground shelters. It was written by Walton McCarthy with help of a committee of government, university and industry experts and has been on the market for 20 years. Principles of Protection: The U.S. Handbook of NBC Weapon Fundamentals and Shelter Engineering Design Standards, 6th edition, 2013, Brown Books, defines scores of engineering standards for proper shelter design protection from nuclear blast, radiation, biochemical threats and EMP.


The nuclear shelter engineering book’s committee included experts from the US Department of Energy, US Department of Defense, Strategic Applications International, Nuclear Engineering Laboratory from the University of Illinois, Oak Ridge National Laboratories, Chemical Division of Edgewood Arsenal, Brookhaven National Laboratory, US Defense Nuclear Agency and the US National Bureau of Standards.

Principles of Protection is available on Mr. McCarthy has designed, engineered, manufactured and installed more than 1,400 shelters since 1977. More details on Walton McCarthy can be found on Mr. McCarthy is presently the principle engineer for NORAD Shelter Systems LLC.

Phone: (972) 913-6882





Darik McCarthy, Sales Engineer

NORAD Shelter Systems LLC®

675 Town Square Blvd

Garland, Texas 75040 U.S.

[i] PRINCIPLES OF PROTECTION, The US Handbook of NBC Weapon Fundamentals and Shelter Engineering Design Standards, 6th edition, 2013, Walton W. McCarthy M.E. Brown books. Appendix A

[ii] PRINCIPLES OF PROTECTION, The US Handbook of NBC Weapon Fundamentals and Shelter Engineering Design Standards, 6th edition, 2013, Walton W. McCarthy M.E. Brown books. Figure 13-1 p. 420 and Figure 13-4 p. 424

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

Underground Shelters Gallery

S16x8 Underground Shelter End Wall Construction

S16x10 Bomb Shelter Pictures

S16x16 Bomb Shelter Pictures

S16x24 Bomb Shelter Pictures

S16x40 Bomb Shelter Pictures

S16x80 Bomb Shelter Pictures