The pilot of the helicopter reported that while repositioning closer to the loading equipment, the helicopter experienced collective bounce. He attempted to maneuver the helicopter to avoid equipment and personnel; however, control was lost and the helicopter impacted terrain. The operator reported that there were no preaccident mechanical malfunctions or failures that would have precluded normal operations. The operators manual for the helicopter stated, in part, “Collective bounce is a pilot Induced vertical oscillation of the collective control system when an absolute friction (either pilot applied, or control rigged) is less than seven pounds. It may be encountered in any flight condition by a rapid buildup of vertical bounce at approximately three cycles per second. The seventy of the oscillation is such that effective control of the helicopter may become difficult to maintain. The pilot should apply and maintain adequate collective friction in all flight conditions.”