Steel Shelter Design Features

The overall design of our underground steel shelter provides protection from blast, earth movement, fire, radiation, EMP and chemical and biological war gasses. This is accomplished through careful engineering and design of the shelter body, doors, air filtration systems; and the geometry of the entrances and the installation process.

Shelter Body

Corrugated steel pipe (CSP) shelters were tested and proven at the Nevada test site to blast pressures of 200 psi. In order to achieve protection to that level, the shelter must have an arched ceiling and the dirt cover over the shelter chamber must be equal to or greater than the diameter of the shelter. At this depth, 'earth arching' is achieved. Care must be taken to properly match the gauge of the steel to the shelter diameter. Eight-foot shelters are built of the proper gauge to be placed into a 16-foot hole and to safely withstand the burden of 8 feet of dirt cover plus the additional overpressure of 200 pounds per square inch of air blast. Nine-foot shelters will reach this level of protection in an 18-foot hole. Ten-foot shelters are designed to be placed into a 20-foot hole with 10 feet of cover. Flat roofed steel shelters will not withstand these heavy over burdens because they cannot achieve "earth arching". They will fail catastrophically under these overpressure loads.

The thermal pulse from a nuclear weapon will not penetrate through the dirt cover, into the interior of the shelter. The pulse, however, can oblate steel from the outside door, if the shelter is near the area of detonation. When shelters are located near nuclear targets, a sacrificial cover is provided for placement over the steel hatch door.

Radiation: Protection from gamma radiation can be achieved with as little as 4 feet of dirt cover or 3 feet of concrete cover. Every 4 inches of dirt (and 3 inches of concrete) gives a halving thickness, or protection factor (PF) of 2. Ten halving thickness is required to diminish (attenuate) medium to high levels of radiation to an acceptable level.

Six to 8 feet of dirt cover is required to attenuate initial radiation to acceptable levels. Initial radiation occurs within the first minute of the blast and within a 1-½ mile radius of ground zero. Blast damage is also an issue at that range. All Utah Shelter Systems shelters are designed to withstand gamma and initial radiation, as well as high blasts in the initial radiation zone.


The greatest risk for radiation accumulation is through the entrances. Steel doors are not thick enough to attenuate gamma radiation to acceptable levels. Utah Shelter Systems has designed the entrances to attenuate gamma by providing a 90-degree turn, and long vertical and horizontal runs. Larger diameter entrances require longer horizontal runs. We can customize your entrances to your desired diameter. If the shelter is near a nuclear blast target and there is a threat of initial radiation, six feet of shielding must be placed into the horizontal run to protect the interior of the shelter. We also have a special 'T' shaped entrance, if desired, to provide storage space for the shielding material. Shelters this close to targets should have entrances no greater than 4' in diameter.

For further information on Radiation, see Weapons Effects.

All of our shelters have two entrances to assure egress in the event one entrance is blocked by debris. All entrances are protected with steel hatch type blast doors, or concrete filled vertical doors.

Distance and geometry play an extremely important role in the attenuation of radiation. It is mandatory that nuclear shelter entrances have both a vertical and horizontal component, connected with a 90-degree turn. To properly attenuate gamma radiation, the total entrance length must be at least 4 times the diameter, with the vertical and horizontal legs as close to the same size as possible.

Gamma radiation is a factor during the first two weeks after a nuclear event. Gamma radiation is directional and will not 'corner' well. The 90-degree turn between the vertical and horizontal run will attenuate 90% of the gamma radiation and the horizontal run will reduce the remaining radiation to a small fraction. Large diameter entrances require long runs and are not practical in the attenuation of initial radiation.

Initial radiation is more penetrating than gamma radiation. It is a factor during the first minutes of the explosion, and affects all the area within 1-1/2 miles of the blast. People sheltering within that area will have lethal levels of initial radiation if they do not properly shield against this effect. The vertical and horizontal runs should each be between 10 and 12 feet long, and the diameter of the entrance should not exceed 48". Initial radiation is not significantly attenuated by 90- degree turns. The horizontal run of the entrance, therefore, should be filled with shielding materials after the occupants have entered the shelter. Water, rice or any other material containing large amounts of hydrogen make good shields against initial radiation. These principles must not be compromised! Larger diameter entrances are comfortable and convenient, but the occupants may not survive if they are within the 1-1/2 mile zone of detonation.

Entrances may be put into buildings such as the home, garage or outbuildings. However, to protect against debris or fire, always place one entrance into the yard, exterior to the building. Entrances may be placed on either the ends or the sides of the shelter. Side entrances free the interior flat ends for furniture or bathroom use. However, when figuring transport costs, a side entrance increases the overall width and will possibly increase the transport cost.

EMP Protection

Protection from EMP is accomplished by completely surrounding sensitive electrical equipment with metal. This metal encasement is called a 'Faraday Cage'. Steel shelters form a natural faraday cage. Our hatch doors have special metal paint and gaskets that create metal to metal contact with our bunker entrances. If commercial power, antennas, or other electrical wires are brought into the bunker, we design wave guides, filters and delta Y transformers into the system. In our own personal shelters, we double protect all critical radios and other vulnerable equipment in an interior faraday cage to assure their survival. A simple, inexpensive faraday cage can be constructed from a steel garbage can. Wrap your equipment in soft towels or place them in cardboard boxes before placing them into the cage. Do not ground the can to the bunker hull.

For further information on EMP, see Weapons Effects.

ANDAIR Ventilation Systems

All of our shelters are fitted with the Swiss made ANDAIR ventilation systems. These motorized systems can be run manually or by electricity and come complete with a prefilter, high effeciency filters (both HEPA and Charcoal), hose, metering device (controls the amount and velocity of air coming into the filter), and two blast valves. It is designed to force a positive pressure into the shelter, so that contaminated air cannot intrude to the inside through tiny leaks in the structure. These filters have been tested against all known war gasses.

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