The illustrations in fig. 8 show how to lay a concrete block wall. More detailed instructions may be obtained from your local building supply houses and craftsmen. Other sources of information include the National Concrete Masonry Association, 38 South Dearborn Street, Chicago, Ill., the Portland Cement Association, 33 West Grand Avenue, Chicago, Ill., and the Structural Clay Products Association, Washington, D. C..

An outdoor, aboveground fallout shelter also may be built with concrete blocks. (See fig. 9, double wall shelter.) Most people would have to hire a contractor to build this shelter. Plans are on pages 22 and 23.

This shelter could be built in regions where water or rock is close to the surface, making it impractical to build an underground shelter.

Two walls of concrete blocks are constructed at least 20 inches apart. The space between them is filled with pit-run gravel or earth. The walls are held together with metal ties placed in the wet mortar as the walls are built.

The roof shown here (fig. 9) is a 6 -- inch slab of reinforced concrete, covered with at least 20 inches of pit-run gravel. An alternate roof, perhaps more within do-it-yourself reach, could be constructed of heavy wooden roof beams, overlaid with boards and waterproofing. It would have to be covered with at least 28 inches of pit-run gravel.

The materials for a double wall shelter would cost about $700. Contractors' charges would be additional. The shelter would provide almost absolute fallout protection.