I am trying to think of a phrase that means something like "margin of error" or "buffer," but specifically applying to spare capacity of a working team within a company. "Bench" sort of works for sports people, but it's not ideal because a bench is for players who can substitute in for other players, and I want to evoke the idea of additional workers waiting in the wings who can step in to accommodate a surge in demand.
I'm wanting to say something like
We are operating with razor-thin _______"
... fill in the blank? And "margins" doesn't work because that sounds like it's about profitability. Any ideas?