[*] 1/2 VALUE LAYER THICKNESS--THICKNESS OF A GIVEN MATERIAL WHICH REDUCES THE DOSE OR DOSE RATE TO APPROXIMATELY ONE-HALF OF THAT FALLING UPON IT. =============================================================
_Table H-2. Transmission factors for Nuclear Radiation[*]_
================================================================== INITIAL ENVIRONMENTAL SHIELDING NEUTRONS GAMMA RESIDUAL ------------------------------------------------------------------
BUILT-UP CITY AREA (IN OPEN) 1.0 0.5 0.7 FOXHOLES 0.3 0.2 0.1 FRAME HOUSE: FIRST FLOOR 1.0 0.9 0.5 BASEMENT 0.5 0.3 0.1 MULTISTORY BUILDINGS: TOP FLOOR 1.0 0.9 0.1 INTERMEDIATE FLOORS 0.9 0.9 0.02 LOWER FLOOR 0.9 0.5 0.1 BASEMENT 0.5 0.3 0.01 SHELTER, CLOSED 91 CM (3 FT) (EARTH COVER) 0.05 0.02 0.005 ARMORED VEHICLES: ARMORED PERSONNEL CARRIER 0.3 0.2 0.1 TANKS 0.3 0.2 0.1 WOODED FOREST 1.0 1.0 0.8 ------------------------------------------------------------------
[*] INSIDE DOSE = TRANSMISSION FACTOR TIMES OUTSIDE DOSE. ==================================================================
H-3. Expedient Shelters for Protection Against Radiation
_a._ In many cases it will be unnecessary to construct field expedient or other types of fallout shelters. There are many structures and terrain features available that afford a degree of fallout protection. Existing fallout shelters are tunnels, caves, culverts, overpasses, ditches, ravines, and man-made structures. The best existing shelters are basements. Figure H-1 shows typical protection provided in buildings. Windows can be sandbagged or covered with dirt from the outside to provide additional protection.
[Illustration: _Figure H-1. Typical shelter protection provided in buildings._]
_b._ Planners should attempt to locate HSS units near existing shelters, whenever possible. However, if an HSS unit is already established, or must be established where fallout shelters are not available, then a shelter must be constructed. Elaborate shelters are not required, since they usually only need to be occupied for a few days. There are a number of field expedients that will serve to save personnel and patients even though they may not be comfortable for those few days.
_c._ When engineer support is available, a bulldozer trench about 2.7 meters (9 feet) wide and 1.2 meters (4 feet) deep can be dug (Figure H-2). The length of the trench will be determined by the number of patients/personnel to be sheltered. About 0.6 meter (2 feet) length of trench is required for each person to be sheltered. These trenches reduce exposure of personnel lying on the floor to about 20 to 30 percent of the radiation that they would receive in the open. Protection and comfort can be improved, as time permits, by digging the trenches deeper; undercutting the walls (care must be taken in this option; the earth may cave in); erecting tents over the trenches; and providing improved flooring. When used with other individual and collective protection measures, bulldozer trenches provide adequate fallout shelters for most situations; they can be provided in a minimum of time and effort. Trenches should not be dug in areas subject to flooding during rainstorms; a berm should be formed on the uphill side of the trench to direct water around the trench in the event rainfall occurs in the area. Undercutting will not be possible in sandy soil; also some form of support to keep the walls from caving in is required.