73 mirrors. The mirrors were aligned with the photo slot structures, each of which consisted of two steel sight tubes 13 foot long with a 6’x 6” opening. These tubes were embedded in concrete with the long axis of the tubes at right angles to Stations 24, 6 and 7. The interiors of these openings were provided with hinged plywood covers and the exteriors with guillotinetype blast covers which could be closed by a timing signal. A hydraulic cylinder arrangement was provided for opening these blast covers, and hydraulic dash pots were used to absorb the shock of closing. Located in front of the viewing slots was Station 1590, which in conjunction with bill- board type baffle Stations 1591 to 1596, was used to collimate the light path from Station 24. A steel blast door was required for the corridor entrance and a lead-filled blast door was provided between Rooms 2 and 3. Other doors were of plywood with light ventilation louvers. CHAPTER II, SECTION 3 Power was supplied from the island distribution system through a 120-ampere fuse cutout, then through a 45 KVA dry-type transformer at 4160 - 120/208-volt, 3-phase. User- furnished special relays and panels were installed by the Contractor. A 1400-cfm ventilating fan was used for the utility room, with a pneumatic-operated butterfly valve installed in the air inlet duct. A direct expansion coil 2 square feet in face area was installed in the air supply to dehumidified areas. Also installed in this duct were 1’-8” x 1’-4” x 2” filters for moisture elimination, a 10 KW reheat coil, and a 650 cfm primary air fan. The freon - 12 refrigerant sys- tem consisted of a DX coil, 67,500 btu compressor unit, and a matching water-cooled condensor. Two vertical centrifugal self-priming 18gpm pumps circulated salt water for cooling to the refrigerant condenser. A total of 605 cubic yards of concrete was poured. The concrete cylinder breaks for 28 days averaged 4,326 psi. tm Figure 2-83. Station 1524 Mirror Shed and Pump House Page 2-95