The helicopter was engaged in an inspection of the oil pipeline between Jackson and St George. The inspection involved landing at various points along the pipeline to allow the technicians to check the pipeline. As the aircraft took off after an inspection stop the front seat passenger warned the pilot about the position of a power line. The pilot attempted to take avoiding action but the aircraft struck the power line. Control of the aircraft was lost and it struck the ground in a nose low attitude and rolled onto its right side. A section of the helicopter's transmission was torn from the aircraft and struck the front seat passenger. During the day the flight had been delayed by problems with the inspection schedule and aircraft fuelling. While waiting in the aircraft for the technicians to complete their task, the pilot was involved in flight planning the next stage length to St George in order to arrive there before last light. The pilot reported that he had seen the power line during the previous landing sequence but had forgotten about its presence on takeoff.