THREE PAX RPRTD THAT JUST PRIOR TO REACHING THE HELIPAD, THE HELICOPTER'S FORWARD MOVEMENT STOPPED AND THE HELICOPTER WOBBLED OR YAWED FROM SIDE TO SIDE. THE PAX'S RPRTED THAT THE PILOT APPEARED TO BE TRYING TO GAIN ALTITUDE AND GO FORWARD WHEN THEY HEARD A LOUD NOISE. THE HELICOPTER THEN DROPPED IN A TAIL LOW ATTITUDE AND CRASHED INTO PRESSURIZED NATURAL GAS COMPONENTS. ESCAPING GAS IGNITED WHICH RESULTED IN AN INTENSE FIRE. AN EXAM REVEALED THAT TWO BLADES ON THE L ENG'S GAS PRODUCER TURBINE WHEEL HAD FAILED FROM FATIGUE AND LODGED AGAINST THE PWR TURBINE NOZZLE VANES. AN INVESTIGATION SHOWED THAT THERE SHOULD HAVE BEEN SUFFICIENT PWR TO SUSTAIN FLT WITH THIS FAILURE. THERE WAS EVIDENCE THEENGINE HAD LOST POWER AT A CRITICAL POINT DURING THE APCH AND THE PILOT ATTEMPTED TO MANUEVER THE HELICOPTER ONTO THE HELIPAD. HOWEVER, THE TOE OF THE RIGHT SKID CONTACTED THE TUBULAR FRAME OF A HOTHE RGT SKID CONTACTED THE TUBULAR FRAME OF A HORIZONTAL SAFETY FENCE (AROUND THE HELIPAD). SUBSEQUENTLY, THE FENCE WAS BENT INWARD AND DOWNWARD BY THE AIRCRAFT.