From The Dim Future Wiki
Endurance is the maximum "hit points" of a permanent or area. This value is not reduced when damage is dealt to the permanent.
Whenever damage is dealt to a permanent or area, add 1 damage counter to it for each point of damage dealt. These counters are not removed at end of turn. Continuously check if the number of damage counters on a permanent or area is greater than the endurance of that permanent or area, if it is destroy the permanent or area.