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.
d. Dug-in tents ([Figure H-3]) for hospitals provide more comfort and require less movement than the bulldozer trench; however, they have two drawbacks. First, they offer far less radiation protection than the bulldozer trench, and second, they require considerably more engineer effort. This option should work well with GP tents, but will probably be hard to accomplish with the TEMPER.
e. Sandbagged walls around the hospital tents, as shown in [Figure H-4], or lightly constructed buildings provide protection from fallout. Sandbagged walls 1.2 meters high give significant protection (20 to 40 percent transmission factor); however, the effort required to achieve the protection is such that it is marginally feasible. Sandbagging is an effective means for supplementing other shelters by—
- Bolstering the shielding at weak points.
- Forming baffles at entryways.
- Blocking open ends of trenches.
- Covering windows and gaps.
f. When other shelters are not available, HSS units must prepare foxholes and trenches for patients and unit personnel. As time permits, improve these shelters by deepening, covering, undercutting, and sandbagging.