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Note: This information is intended for use during normal operations. If you are looking for information specific to COVID-19, please visit the Negative Pressure Patient Room page.

Certain rooms within a health care building should be positively or negatively pressurized with respect to surrounding areas. Positively pressurized rooms are usually designed to protect a patient, clean supplies, or equipment within the room. Negative pressure is used to contain airborne contaminants within a room. The 2014 FGI Guidelines/Standard 170-2013 provides lists of rooms that should be positively or negatively pressurized with respect to surrounding areas. The following are examples of positively pressurized rooms:

• Operating rooms
• Delivery rooms
• Trauma rooms
• Newborn intensive care
• Laser eye rooms
• Protective environment rooms
• Pharmacy
• Laboratory, media transfer
• Central Medical and Surgical Supply Clean workrooms
• Central Medical and Surgical Supply Sterile Storage

A room may be pressurized so that it is positive with respect to adjacent areas for several reasons. It may be done to protect patients in operating rooms and protective environment rooms from air­borne pathogens that may be present in adjacent areas. It may be done to protect sterile medical and surgical supplies in supply rooms from airborne contaminants that may be present in adjacent rooms. If these rooms are not properly pressurized, airborne con­taminants from adjacent areas may be pulled into them. Increased concentrations of airborne bacteria, fungi, and viruses within these rooms may contaminate clean equipment or promote increases in nosocomial infections. Positively pressurized rooms are usually the cleanest environments in a hospital. Loss of positive pressure com­promises the aseptic environment within the room.

According to the FGI Guidelines, the following are examples of rooms in hospitals and outpatient facilities that should be nega­tively pressurized with respect to adjacent areas:

• ER waiting rooms
• Radiology waiting rooms
• Triage
• Toilet rooms
• Airborne infection isolation (AII) rooms
• Darkrooms
• Cytology, glass washing, histology, microbiology, nuclear medicine, pathology, and sterilizing laboratories
• Autopsy rooms
• Soiled workrooms or holding rooms
• Soiled or decontamination room for central medical and surgical supply
• Soiled linen and trash chute rooms
• Janitors’ closets

Rooms such as airborne infection isolation rooms are negatively pressurized with respect to adjacent areas to prevent airborne con­taminants (e.g., microbial pathogens, chemicals) from drifting to other areas. Loss of negative pressure within these rooms allows unpleasant odors to migrate through the building and may promote the spread of airborne contaminants. One common use of airborne infection isolation rooms is for patients with active tuberculosis, a disease caused by the bacteria Mycobacterium tuberculosis. The bac­teria are spread in the air from one person to another. A patient with active tuberculosis releases M. tuberculosis into the air when he or she sneezes or coughs. Other people may become infected if they inhale the airborne bacteria. Pathology and histology laboratories use substantial amounts of chemicals, including formaldehyde. If formaldehyde or other airborne chemicals are allowed to drift from these laboratories, building occupants may complain of unpleasant odors. Exposure to these airborne chemicals may also cause adverse health effects.

If rooms are not properly pressurized (positive or negative), several causes are possible. An imbalance may exist between the supply and exhaust rates for the room. Supply and exhaust fans may not be operating properly. Supply diffusers and return grilles within the room should be checked for blockages; occupants may block them in an effort to improve their thermal comfort. Operation of fume hoods and biological safety cabinets within the room and in adja­cent rooms should be checked, as poor performance of these units affects air balance within nearby rooms. Lastly, recent renovations may have altered the HVAC system in a manner that impacts the air balance among nearby rooms.

Excerpt from: Mechanical Systems Handbook for Health Care Facilities
J. Robbin Barrick, PE, and Ronald G. Holdaway, PE
ASHE copyright 2014. .