Basic Documentation

Room Pressurization Applications
Room Pressurization Applications
In most applications, room pressurization is applied to control the direction of room transfer
airflow. Transfer air is air that is not directly supplied to a room or exhausted from the room
by the room’s ventilation system. Rather, transfer air is air that may enter the room or leave
the room as a result of pressure differentials, through passageways other than the ventilation
system ductwork. Typically, these passageways include the clearance area around doors
and poke-throughs around electrical and plumbing services. These air passageways also
include cracks, gaps, and even the porosity that comprises the room construction. In most
situations where room pressurization is required, using close fitting doors can minimize the
amount of these air passageways. It can also be reduced by caulking and sealing of all
cutouts that were made to accommodate electrical conduits, piping, and other room
equipment. However, depending on individual needs and applications, rooms may also be
equipped with air transfer grills to facilitate transfer air movement into or out of the room.
Most room pressurization applications are intended to control the direction of the transfer air
rather than prevent air transfer from occurring. Directional airflow is used to prevent airborne
contaminants from entering or leaving a specific room or cluster of rooms. Room
pressurization for contamination prevention can be grouped into several categories
depending upon the type of room and its purpose. The following subsections describe the
most common room pressurization applications.
Chemical Laboratories
A chemical laboratory room must be maintained at a negative static pressure with reference
to adjoining non-laboratory rooms to ensure that transfer air will not flow out of the laboratory
room and into the adjoining areas. Rather, transfer airflow should be directed into a
laboratory room from the adjacent areas (corridors or other non-laboratory rooms) to prevent
laboratory room chemical fumes from migrating out of a laboratory room. Although it is
desirable to keep laboratory room air from migrating into other areas of a building as a health
safeguard, it is also important from an IAQ perspective. Room air from chemical laboratories
often contains some trace amount of chemical fumes or gasses. Although the concentration
of chemicals or gasses in the air might be extremely slight and not a health hazard, building
occupants may react to the odor and assume that they are being exposed to an unhealthy or
hazardous environment. Therefore, it is advantageous to prevent airflow out of laboratory
rooms by ensuring that the rooms are maintained at a negative static pressure with reference
to adjoining non-laboratory areas.
Biological Laboratories
Biological laboratory rooms must also be maintained at a negative static pressure to prevent
airflow out of the laboratory room. Aside from preventing chemical odors from leaving the
room, the inward directional airflow created by negative room pressurization is intended to
prevent airborne pathogens from migrating out to other building areas. Biological laboratories
are classified as Biosafety Level 1, 2, 3 or 4 with respect to the potential hazard that the
particular laboratory presents due to the substances present and the nature of the work
performed.
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