The crew was pressure testing the BOP’s and various members were attending to different tasks in preparation to drilling out the surface casing shoe. The upper Kelly cock did not hold its pressure for the required time so the decision was made to adjust the valve and retest. The floorhand put on his fall arrest harness and the driller hoisted him up 12 metres (40 ft.) above the rig floor using the winch line. From that position he could turn the valve slightly and then they could retest. When this was accomplished, the driller started to lower him back down on the winch line. For reasons that cannot be explained, the floorhand swung himself over to the derrick leg supported his own weight and the line went slack. It appears that he disconnected from the winch line, lost his grip on the derrick and fell about 10 metres (33 ft) to the floor.