Sorry Ellis, but you are kind of getting carried away with the subject.
Nothing says that the system uses laminar flow diffusers with HEPA filters. The HEPA may be at the central AHU. the HEPA is not the question in the post anyway.
In addition, the project can be in some Banana republic (AND some western republics) that has never heard of HEPA filters. I know of a few places that use window shakers for operating rooms, with no ventilation in the entire hospital. Yet, people survive just fine.
Do they have HEPA filters in those M.A.S.H units?
So "operation theatre" means "Operating Room"?
PS: "window shaker" means "Window mounted AC unit" in my neck of the wood.