Apartments A–E were ventilated by an unbalanced
mechanical ventilation system. The mechanical supply
fan distributed outdoor air to rooms through the supply
diffusers mounted at the ceiling, and the supply diffusers
were connected to the mechanical supply fan
through a single duct located in the ceiling. Indoor air
was exhausted through uncontrolled leaks and through
exhaust vents located in the kitchen and bathrooms.
The fan speed was controlled with a switch with three
settings: off, low, and high. The fan was operated at
high speed during the sampling period