Ladder Derrick (Figures 10:9 and 10:10)

10.8 This technique can be applied, where the structure from which the casualty has to be removed, is so unstable that it cannot be used in any way to assist the operation. The ladder derrick is self-supporting. The first step in erecting the derrick, is to rig the head of the ladder as in Figure 10:9. The snatch block is attached as for the leaning ladder, and the 24mm rope is secured with a Bowline or Figure of Eight Loop as near as practicable to (but not below) the bondwire attachment for the snatch block. This is used as a back guy and carries the main load. Next, a 16mm rope is middled and Clove Hitched to the top of the ladder strings, and the ends are crossed to form the side guys, A front guy can be attached to the head of the ladder to assist with erection and stabilisation. A 16mm rope is reeved through the snatch block and is used for lowering the stretcher.

Three anchors are selected to support the back and side guys. In good holding ground, a one to one picket system is usually sufficient for the back guy and single pickets for the two side guys. If possible, the side guys should be located forward of the point, where the ladder is to be footed. Anchors should always be positioned at least twice the height of the ladder, out from its foot.

The ladder is now erected under the control of the leader. All guys should be controlled and if a front guy is attached, rescuers can haul on this to assist in getting the ladder into the vertical position. Once there, it is extended to the required height and, after being squared up by the leader, the guys are made fast with round turns and two half hitches. Remember the guys stretch when under load and may have to be adjusted from time to time.

If necessary, the foot of the ladder should be dug in or secured to pickets. From here onwards, the operation is the same as for the leaning ladder method. At all times while the rig is under load, the anchors should be carefully watched to ensure they remain secure. Nine is the ideal number of rescuers required for the ladder derrick, although seven can be used if the two side guys are left unmanned. If this is the case, one rescuer should be detailed to check the three sets of anchors.

Fig 10:9 Ladder derrick head detail

Fig 10:10 The ladder derrick