In this study, OIT is the time it takes the insulation to undergo auto-catalytic oxidation when exposed continuously to a pure oxygen, high temperature environment. Auto-catalytic oxidation appears as a sudden release of heat that quickly chars the insulation. High oxygen concentration (100% oxygen) and high temperatures (130 degrees C to 200 degrees C) accelerate normal oxidation. Actual oxygen concentration in air is 21% and the temperature in Yuma is less than 50 degrees C.
See OIT (in minutes) of Yuma 1978 Cable-Wire Insolation at Various Temperatures graph
* "Under Sheath" means sheathed, insulated wire from
buried, compound-filled telephone cable not exposed to atmospheric