THE PLT WAS CONDUCTING SIGHT-SEEING FLTS FROM A RODEO/FAIRGROUND AREA. DURING A CRITICAL PART OF A TAKEOFF, A TAIL ROTOR BLADE SEPARATED & THE PLT LOST DIRECTIONAL CONTROL. HE ATTEMPTED AN AUTOROTATIVE LANDING. AFTER SPINNING AROUND ABOUT 3 TIMES, THE PLT PULLED FULL COLLECTIVE, JUST BEFORE THE HELICOPTER CRASHED, BUT IT WAS STILL BADLY DAMAGED. AN INVESTIGATION REVEALED THAT A TAIL ROTOR TENSION-TORSION (T-T) BAR ASSEMBLY, PN 24-55106, HAD FAILED WHERE THE ATTACHMENT BOLT GOES THRU THE T-T STRAPS. A METALLURGICAL EXAM REVEALED CHLORINE RICH DEPOSITS IN THE FRACTURE AREA. THE GREASE FROM THE T-T BAR CAVITY HAD DARKENED & THE CAVITY FOR THE OTHER SET OF T-T STRAPS CONTAINED A SMALL AMOUNT OF FLUID WITH AN UNPLEASANT ODOR. AN ANALYSIS OF THE GREASE REVEALED EXCESSIVE AMOUNTS OF CHLORINE. THERE WAS EVIDENCE THAT WATER & CHLORINE CONTAMINATION HAD RESULTED IN STRESS CORROSION & EVENTUAL FAILURE OF THE T-T BAR ASSEMBLY.