The neurasthenia and lower serum albumin in workers were due to the bad ventilation in the laundries and the chronic exposure of workers to tetrachloroethylene.
A fortress is easier to protect because it's simpler: it has no windows, few doors, no skylights, or vent systems through which an intruder might sneak.
But even if it is a ventilation pipe is also divided into several, there is a simple dust, smoke, exhaust pipe, but also have a special rule out harmful gas pipeline.
Another example is the heat recovery ventilator which is closed off in a small closet, to prevent air from the basement from coming up through the walls.