the top of the tower and under the skip floor, From these sheaves, the cable ran down outside of the tower (parallel to the main hoist cable) to the skip hoisting machine mounted on the ground near the main hoist- ing machine. The hand winch and accessories, located in the tower cab, consisted of a lightweight spur-gear, hand-cranked portable winch, equipped with a brake, and with a capacity of 650 feet of 3/16 inch wire rope. The accessories consisted of mounting brackets for the winch and guides and sheaves for the wire rope. Considerable study and investigation was given to safety devices for the skip hoist, Various passenger and freight elevator manufacturers were consulted, with the final conclusion that standard type instantaneous safety rail grips and standard type overspeed governors as manufactured and used by the Kimball Elevator Company would be most adaptable and satisfactory for application to the skip hoist. The overspeed governor required some minor modifications toqerate the instantaneous safety grips, as applied to the skip hoist platform. Be- cause no standard device was available, a broken rope device for opera- ting the safety grips was designed by H& N. This device consisted of a spring loaded idler sheave held in normal position by tension on the hoisting cable. In the event of a break in the cable, the spring lifts the idler sheave and actuates the instantaneous safety rail grips. All of these safety devices proved very satisfactory in drop tests which were made before shipment overseas. Standard elevator-type bronze guide shoes were used to guide the skip platform on the guide rails. Figure 5.11-1 shows detail of a safety rail grip, and Figure 5.11-2 shows the overspeed governor used in 200 foot and 300 foot towers. The skip hoist platform (elevator cab) had to be designed to accommodate the safety devices, guide shoes, and limit switch strikes. The floor and railing of the skip were substantially the same as that used for Sandstone, but the overhead frame was designed to open the trap door in the tower house floor when the skip came up through the floor and to provide support for a controller in the skip. The hoist rigging for the skip hoist was mounted entirely below the house floor so that the entire floor area would be clear when the trap door was closed. tower. Figure 5.11-3 shows the skip hoist cab assembly for a 300 foot Because many safety features were of a new design, a requirement was set up in the specifications that a section of guide rails 30 feet high be erected and the skip platform mounted thereon to test the safety devices, Drop tests were made and the safety grips, overspeed governor, and broken rope device were individually tested to the complete satisfaction of the Sandia representative, the AEC Contract Administrator, and H & N designing engineers, The hoist rigging for the main hoist was mounted on the structural A-frame above the tower house so that the load block could be raised entirely above the roof, Figure 5.11-4 shows the main hoist sheave assembly and cable arrangement for a 300 foot tower, 5-132