the pit shown. A scale model of this door is also on display. The door consisted of heavy sheet steel plate with reinforced steel beams welded on the front and was located at a pressure range of approximately 35 pounds per square inch. The extent of the damage was limited to the stripping of the upper outside flanges. Using the knowledge gained from this test, doors will be designed for use on group blast shelters.

To determine the effectiveness of our most recent family-blast shelter designs and to collect data which might lead to a more economical design, we tested 3 identical shelters at a range of approximately 30, 50, and 70 pounds per square inch. (See slide No. 22.)

SLIDE NO. 22.-Family blast shelter (4 to 6 persons).

Slide No. 23 is a view of the completed structure which shows the steel rectangular door, the main entrance and two ventilation pipes, a concrete block encasing an antenna, and an embankment of earth to provide protection from radiation.

The only damage suffered by these structures was that of dishing in the door of the shelter closest to the ground area and bending the ventilation pipes on all structures. (See illustration No. 24.) The information gathered in this test has already been incorporated in a new family-blast shelter bulletin.

SLIDE No. 23.-Completed structure which shows the steel rectangular door, the main entrance, and two ventilation pipes.

Past tests have shown that average commercially available doors become dislodged and fail to provide a pressure seal and create a missile hazard when exposed to low-blast pressures.

The

Five types of doors were designed for industrial and general use to provide protection on the periphery of potential target areas. doors were tested at approximately 312 and 7 pounds per square inch. The types shown in slide No. 25 from left to right are solid plywood, wood plank, cellular steel, hollow plywood, and steel plate.

At the 32 pounds per square inch range, all of the doors satisfactorily withstood the blast and the damage was limited to scorching the paint. At the 7 pounds per square inch range, all doors stood up satisfactorily withstood the blast except for the hollow-plywood door which had been redesigned and strengthened. (See slide No. 26.)