Exhaust shaft staircase for Bethesda Metro station labeled at The Wilson

There's a door here at The Wilson by Tatte Bakery that is now identified as the access to and from the under-platform exhaust shaft at the Bethesda Metro station. This area is near the south end of the platform, and there will eventually be a new entrance at this corner to the station. What is in this shaft? Controls for exhaust fans, dampers that can be adjusted to change the air flow direction, and a "fan gallery." In some cases, the exhaust shaft is also a designated emergency exit from the station to the surface.