According to the pilot of the public use, multi-engine helicopter, he performed an autorotation and landing after exhausting the helicopter's fuel supply in flight. The pilot reported that while acting as the Helicopter Commander during a brush fire containment mission, the complexities involved with managing the fire increased and as a result, the pilot stated, "I failed to re-adjust my station time appropriately for my aircraft." He reported that both engines lost power and he executed an autorotation and touchdown onto down sloping terrain. Upon impact with the ground, the main rotor blades flexed down and severed the tail boom. The helicopter sustained substantial damage to the tail boom, the main rotor and tail rotor blades, the main rotor drive system and the primary flight controls. The pilot reported no mechanical failures or anomalies prior to flight that would have prevented normal operation.