Originally it was planned to build one dome shelter 150 feet in diameter -- a size proposed by the designer, American Machine and - Foundry Company, as most practical for this type, However, it was decided that the required engineering data for design, loading, response, and mode of failure, could be obtained from a 50~foot dome so instead of one 150-foot dome, three 50-foot domes are being tested at pressure ranges from 20 to 70 pounds per square inch, \ t The construction method for these shelters consisted of heaping up a dirt mound of the required size, covering it with the reinforcing steel, and then forming the concrete shell by the "shotcrete" method. After the concrete hardened, the mound of earth was removed and space under the dome became available for shelter and for instrumentation. Although dome shelters could be constructed either above or below ground, all of the test structures were exposed to blast without the aid of earth cover. The dual purpose shelter ‘is of conventional underground design and was built at a cost of approximately $200,000. It is under three feet of earth and is approximately 90 feet by 90 feet. Access is gained by means of an auto ramp, with the longitudinal axis radial to Ground Zero, Closure is effected by means of a reinforced concrete door weighing approximately 100 tons, mounted on a monorail. The roof slab, two feet six inches thick over drop panels, is supported by nine columns on 29-foot centers and bearing walls. FCDA tested three reinforced concrete family type underground shelters, at pressure ranges from 30 to 65 psi. The family shelter has been designed to provide nuclear blast protection and minimum living facilities for a group of approximately six persons, It is designed to withstand overpressures of 30 psi or more and reduce both the initial and fallout radiation to a safe level. This reinforced concrete shelter has an underground chamber seven foot square and six and one-half feet high, connected with the surface by a corridor containing two right angle bends and an inclined entrance-way where a steel plate blast door is located. It is also connected with the surface by a corrugated steel, round, emergency escape hatch which could be used if the entrance-way was blocked. It is believed that the cost of finished and supplied shelters of this typewould be from $1,800 to $2,500 in the average locality. Foreign Shelters Through the cooperation of AEC, the Department of Defense, and Department of State, FCDA was able to accede to requests from the French and West German Governments to test their shelter designs. The actual tests are being conducted by American contractor personnel acting as agents of the governments concerned. gg : \