On February 15, 2000, at 1628 hours Pacific standard time, a Bell 47G5, N4754R, crashed and burned during takeoff from an agricultural landing site at Riverbank, California. The helicopter sustained substantial damage; however, the certificated commercial pilot, the sole occupant, was not injured. The aircraft was being operated by Greenbelt Aviation as an aerial application flight under 14 CFR Part 137 when the accident occurred. The flight was originating at the time of the accident. Visual meteorological conditions prevailed at the time and no flight plan was filed. The pilot had landed to refill the aircraft's hopper from a truck-mounted re-supply tank. After refilling the hopper, the pilot instructed the ground support person to reposition the truck to the next work site. The ground support person did not remove the loading hose from the hopper and the pilot did not verify that the hose had been removed before takeoff. After takeoff, the helicopter flew about 20 to 30 feet before it was pulled to the left as the hose became taught and finally snapped. The pilot applied right pedal to regain forward attitude but, as he did so, the helicopter lost main rotor speed and abruptly settled to the ground. The main rotor blades flapped down, striking the ground, and shattering the cockpit bubble. The lower Sprague system separated as the aircraft contacted the ground, shifting the main rotor mast. This shift moved the fuel tank and ruptured the main fuel line. The fuel spilled onto the exhaust system and a fire began. After the blades stopped, the pilot exited the helicopter through the broken bubble.