Negative Pressure AII Room Design

Architectural and Engineering companies invariably will attempt to design infectious isolation rooms by utilizing a house air handler unit (AHU). Invariably this approach is doomed to failure over the long haul. There are reasons why this is so and they can be easily rectified, with an alternative approach that is well documented and is budget conscious.

First of all, house air handlers are required to supply temperature and humidity adjusted air to a multitude of locations throughout the hospital and at different times of the day or night. AHU systems, by their nature, are neither constant nor consistent. These are two basic requirements for an airborne infectious isolation (AII) room air supply and exhaust. The AHU must be flexible to provide this comfort air to various departments throughout the hospital served by the AHU. To achieve this the AHU must incorporate what are known as VAV (variable air volume) systems. The VAV units allow the AHU to move air from one area to another dependent on individual area requirements. In the process of doing so they increase or decrease air volume in various areas to maintain the comfort elements.

There are four basic factors required to design and establish an AII room that will be consistent. They also must be certifiable (annual certification required by OSHA with additional JCAHO “Environment of Care” requirements):

1. 12 Air changes per hour (ACH) minimum

2. Constant negative pressure at 0.010” W. C. minimum

3. Correct t Airflow dynamics in the room (air moving from room entrance to exhaust)

4. Exhausted HEPA filtered air to the outside via dedicated ducting

Initially the AHU should be capable (if designed and specified properly) to provide the correct ACH in the isolation room as well as negative pressure. Over time, air handlers become over-taxed by adding more and more areas using up its excess capacity by the expansion of adding departments or even wings of the hospital. Therefore the ability of the AHU to meet specific demands of ACH and negative pressure in the AII diminishes. It doesn’t t take long for the AHU’s capacity to be reduced to the point where it cannot sustain the isolation room’s negative pressure requirements.

A far more effective method to maintain proper ACH and negative pressure is to install in each isolation room a dedicated HEPA filtered auxiliary motor/blower air purification system. These systems can be adjusted to provide a consistent ACH as well as constant negative pressure providing the room is properly sealed. These units will exhaust air independent of the AHU, thereby assuring the protection of staff and others that enter the AII room.

Specifying and design of AII rooms, while not “rocket science”, should be performed by those who are conversant with all the regulations, standards and guidelines. This is a sub-specialty area of HVAC that frequently falls outside of the expertise of most commercial HVAC companies. To ensure accurate and cost effective equipment and design its advisable to have an organization who specializes in this field or air purification and pressurization.

Medical Air Solutions specializes in negative and positive pressure environments in the healthcare market. If you would like additional information please call us at 1-800-645-1059.