Positive Pressure rooms maintain a flow of air out of the room, thus protecting the patient from possible contaminants and pathogens which might otherwise enter. The most common application today is HIV Rooms and rooms for patients with other types of immunodeficiency. For such patients it is critically important to prevent the ingress of any pathogens, including even common fungi and bacteria which may be harmless to healthy people.
Design criteria for HIV Rooms are similar to those for TB Rooms. Air supplied to or recirculated in HIV Rooms is normally filtered through HEPA filters, and UVGI systems are sometimes used in conjunction with these. Anterooms are recommended and the air pressure differential criteria as described for TB Rooms applies similarly.
Approximately 15% of AIDS patients also suffer from TB, and this presents a unique design problem. One solution is to house the positive pressure (HIV) room within a negative pressure (TB) room, or vice-versa, which would be similar to a pair of nested biohazard levels. A much less expensive alternative is to design an entire house or building as a positive pressure (HIV) room, and this makes the outdoor air play the part of the second pressure barrier as it will effectively sterilize any exiting pathogens. Exhaust HEPA filters are still recommended, however, to protect any passersby.
A smoke test can help determine whether a room is under positive pressure. A tube containing smoke is held near the bottom of the positive pressure room door, about 2 inches in front of the door. The smoke tube is held parallel to the door, and a small amount of smoke is then generated by gently squeezing the bulb. Care is taken to release the smoke from the tube slowly to ensure the velocity of the smoke from the tube does not overpower the air velocity. If the room is at positive pressure, the smoke will travel under the door and out of the room. If the room is not a positive pressure, the smoke will be blown inward.
A tissue under the door would blow toward the corridor if the room is positively pressured. Instead of trying to remember the pressure requirement for different room types you only have to know that air should flow from CLEAN to DIRTY. The min. requirement for AHU filters in a patient care area is.....90%