Learn English – “room for error” replacement word

Burst

Definition #2 from Collins English Dictionary:

(intr) to come, go, etc., suddenly and forcibly. He burst into the room.

If you want a word that matches up with capacity, you can use occupancy for this. Per the OED:

1. a. The condition of being an occupant; the fact of occupying; the act of taking, or fact of holding, actual possession, esp. of land (spec. in Law, the taking possession of something not belonging to any one, as constituting a title to it); actual holding of or residence in a place; = ^{_OCCUPATION1, 2}.

[...]

3. a. The state of being occupied or busy; = ^{_OCCUPATION 4}.

   b. Teleph. The proportion of the time during which a circuit or device is handling calls.

   c. The proportion of accommodation occupied or used.