Schematic of a network of<unk> s where air (shown in blue) flows in one direction from the corridor into the negative<unk> <unk>  (green). Exhaust air is safely removed from the area through a ventilation system. Negative<unk>  is generated and maintained in a<unk>  by a ventilation system that continually attempts to move air out of the<unk> . Replacement air is allowed into the<unk>  through a gap under the door (typically about one half-inch high). Except for this gap, the<unk>  is as airtight as possible, allowing little air in through cracks and gaps, such as those around windows, light fixtures and electrical outlets. Leakage from these sources can make it more difficult and less energy efficient to maintain<unk>  negative<unk> . Because generally there are components of the exhausted air such as chemical contaminants, microorganisms, or radioactive isotopes that would be unacceptable to release into the surrounding outdoor environment, the air outlet must, at a minimum, be located such that it will not expose people or other occupied spaces. Commonly it is exhausted out of the roof of the building. However, in some cases, such as with highly infections microorganisms in biosafety level 4<unk> s, the air must first be mechanically filtered or disinfected by ultraviolet irradiation or chemical means before being released to the surrounding outdoor environment. In the case of nuclear facilities, the air is monitored for the presence of radioactive isotopes and usually filtered before being exhausted through a tall exhaust duct to be released higher in the air away from occupied spaces.
Negative room pressure
Negative pressure ventilator
High-frequency ventilation
Prone ventilation
Mechanical ventilation
Artificial ventilation
Positive airway pressure
Non-invasive ventilation