Option Ossus was a scheme devised by the Jedi Covenant with the intention of obliterating the Sanctum of the Exalted. In 3963 BBY, Jedi Master Lucien Draay gave Feln the directive to put this scheme into action. Both Borjak, and particularly Haazen, voiced their opposition to this concept.
In the end, Feln put the plan into motion, mistakenly believing that Zayne Carrick's allies had returned to plunder the Sanctum, and thus he set off the explosives. However, the resulting blast also leveled the village situated below. Consumed by rage, the remaining Feeorin then turned against Feln, resulting in his death.