Stations 20a through 20f - Engebi and Runit - NOBL. For making various blast measurements, NOBL had a blast line established on Engebi and Runit, The Station 20 series were small concrete walls 5 feet high, lfoot wide, and 29 feet long, the middle 8 feet of which were fabricated steel sections to hold the various pressure gauges, These walls were mounted on concrete footings 4 feet by 2 feet, 9 inches, by 33 feet, the long axis being on a radial line from zero, To give a smooth wall sur- face, the specifications stipulated a trowel finish, On October 17, 1949, the chief of NOBL Blast Program proposed that H&N and his engineers have a meeting to firm up the designs, This meeting took place on January 30, 1950, in Washington, D.C., with representatives from NOL, BRL, and H&N present, The H&N representatives proposed that a revision in tolerances would make an appreciable difference in the costs of the units, This change was made on final drawings, Tolerances for location of walls were given on June 21, 1950. H&N was instructed to locate the walls within 36 inches of proposed locations; measure final location to within 1 inch; and align wall to +12 minutes of arc on a radial line from zero, A final conference was held on July 7, 1950, at which time minor problems were discussed, Approval of steel plate material was given by NOBL on July 10, 1950; fabrication began shortly afterwards. Stations 21a, b, and c - Engebi_ - NOBL. Same as Station 20, stations placed along a second blast line on Engebi. These Stations 22a and b - Engebi, Runit, and The Aomon Group - NOBL. These stations consisted only of standard tents without special floor slabs and were erected at the Users' request in the field. Station 23a - Engebi, The Aomon Group, and Runit - NOBL, These structures, called "blast huts," were 15 feet by 10 feet by 7 feet with 18 inch concrete sides and roof, They served as recording shelters for NOBL, A print of the proposed layout was given to H&N on January 30, 1950, at a meeting in Washington,D,C, existing buildings built for the Sandstone test, The stations were These were altered by the addition of four 6~inch conduits through the 18 inch walls, a 14 inch by 10 inch ventilation duct, and 135 feet of "Unistrut" channeling to fasten equipment in place. Station 23b - Engebi - NOBL. In order to increase the working area in Station 23a on Engebi, an additional building 15 feet by & feet by 7 feet was built immediately adjacent to Station 23a, one side of the new building tying into the existing footing, The layout for this station was provided by NOBL on January 30, 1950, The entrance to Station 23b was through Station 23a, via a 2 foot, two inch by 6 foot, 6 inch opening that had to be cut out of the existing 18 inch wall. This new addition was amply provided with slots to insert fastenings that anchored equipment in place, Stations 24a and b - Engebi - NOBL. Same as Station 22,