Vent Mod is an addition to Black Mesa's "We've Got Hostiles!" chapter, adding new areas to the last bits of the chapter. This mod re-adds and revamps the vent sections of the chapter, which were cut from Black Mesa due to their inadequacies. The issues that they had in the original have been (hopefully) done away with.
Version 2.2 of the Black Mesa Vent Mod. The zip file contains all of the relevant materials.