When I built my new shop, I left a 15'x3' blockout in the concrete floor for a mechanics pit. The building inspector would have wanted fall protection railings, probably some expensive wiz bang co sensor system interlocked with a $$$ wiz bang alarm, and an $$$$$ explosion proof exhaust fan, etc, etc.
when I dig it and complete the concrete it I will have a couple of co sensors, and a 12 volt marine bilge blower to exterior. can add a fold down cover for foot traffic.