Medical Air Solutions, Inc.

The mechanical design elements of a new hospital isolation room should, at a minimum, meet all local code requirements, as well as OSHA requirements and CDC recommendations.

B Architectural Considerations

Architecturally, an isolation room should meet all the detailed requirements for a single-patient room, including a dedicated adjacent bathroom. Architectural design elements should also meet local code requirements. For example, California requirements include:

To increase the effectiveness of negative pressure, the architectural elements should ensure that the isolation room suite is sealed, except for a half-inch high air gap under the door. Towards this end, the ceiling should be plaster rather than removable ceiling tiles, and lights should be surface-mounted. Gasketing should be provided at the sides and top of the door, and at ceiling and wall penetrations such as those around medical and electrical outlets.

The location of the proposed isolation room should also be considered: areas prone to strong drafts, such as those near elevator banks or doorways, should be avoided if possible. Isolation room doors should be equipped with self-closing devices.

When designing a new negative pressure isolation room, exhaust should exceed supply by at least 100 CFM. The actual pressure differential created at the door by the offset depends on how well the room is sealed and the size of the air gap under the door. In reality, no room can be perfectly sealed. It cannot be assumed that the total offset is being made up by air coming in under the door.

To contain odors, the isolation room bathroom, where applicable, should be at negative pressure with respect to the isolation room. The bathroom ventilation should comply with local requirements. For example the California Mechanical Code (CMC) mandates an air change rate of 10 ACH, negative pressure, and direct exhaust to the outdoors for bathrooms. In general, an offset of 50 CFM is sufficient between the bathroom and the isolation room.

Both the isolation room and the combined isolation room and bathroom should be at negative pressure. In other words, not only must the total exhaust for the isolation room plus bathroom exceed the total supply for isolation room plus bathroom, but the isolation room exhaust should also exceed the isolation room supply. This can be illustrated with the following simple example.

Assume an isolation room with a dedicated bathroom. Supply air to the isolation room is easured and found to be 200 CFM.

The isolation room volume is approximately 1,000 cubic feet, so the supply air change rate is 12 ACH.

You are installing a new exhaust fan with a capacity of 300 CFM that will serve only the isolation room suite. Local codes mandate a minimum air change rate of 10 ACH in toilet rooms. The toilet room volume is approximately 240 cubic feet, so a minimum of 40 CFM exhaust is required.

How should the 300 CFM of exhaust air be split up between the bathroom and the isolation room?

The preferred arrangement is to exhaust 250 CFM at the isolation room and 50 CFM at the bathroom (as shown in the diagram on the next page), rather than 200 CFM at the isolation room and 100 CFM at the bathroom.

The Reason

Each arrangement will result in both a 100 CFM offset across the isolation room door and an equal volume of air moving through the isolation room. But only the preferred option provides more exhaust than supply in the isolation room itself and increases airflow towards the head of the bed.

Also, code officials may require that direct exhaust from the isolation room exceed direct supply air. The latter option would result in a room with supply equal to exhaust.

Exhaust air removed from isolation rooms is likely to contain infectious particles. Consequently, this air should be discharged directly outside the building, where the particles can be diluted by outdoor air and killed by sunlight. While not included as a minimum recommendation by the CDC Guidelines, the optimum type of exhaust system should serve only negative pressure isolation room suites, i.e., a dedicated exhaust system. Where applicable, this exhaust system should also serve the dedicated isolation room bathroom and anteroom.

Over time, dust and lint can collect at exhaust grilles and in exhaust ducts. Seals at duct joints also break down and leak. These two effects result in diminished exhaust airflow from the isolation room. To compensate, exhaust ducts should be oversized.

Maintenance personnel and contractors often re-route ducts to accommodate new services. To help protect these workers from potentially contaminated isolation room exhaust, the exhaust ductwork should be permanently labeled. The label should read, "Caution Ð Negative Pressure Isolation Room Exhaust," or similar words to that effect. The labels should be attached at most 20 feet apart, and at all floor and wall penetrations.

Maintenance workers may also shut down the exhaust fan without realizing this will cause a loss of negative pressure. To avoid this possibility, a permanent warning sign should be posted on the fan at the electrical disconnect and at appropriate electrical panel breakers. The sign should read, "Negative Pressure Isolation Room Exhaust Fan Contact Infection Control Coordinator Before Turning Off Fan", or have similar wording. The sign should also include the telephone number of the infection control coordinator and the room number(s) of the isolation room(s) exhausted by the fan.

The exhaust fan discharge should be located and designed to minimize the possibility that this air is inhaled by people who are outdoors or inside the building. Exhaust air should be directed away from occupied areas (i.e., walkways) or openings into the building (i.e., windows or outside air intakes).

To promote dilution, the fan discharge should be directed vertically upward at a speed of at least 2000 feet per minute (FPM). The discharge location should be at least 25 feet away from public areas or openings into a building.

If a suitable discharge location is unavailable, then the exhaust can be disinfected using a HEPA filter. In this case, a HEPA filter must be installed in the discharge duct upstream of the exhaust fan. This is not a desirable option, however, because it will be considerably more expensive to install, maintain, and operate than a simple exhaust fan assembly.

G Permanent Room Pressure Monitor

After a new isolation room is constructed and before it is occupied, the mechanical contractor will adjust the airflow quantities as directed by the engineer to ensure that it operates as designed. However, mechanical systems do drift out of balance over time. It is important to regularly check that an isolation room is still operating under negative pressure; planning for this should be included in the initial design of the mechanical room.

The most reliable way to monitor negative pressure is to install a permanent electronic room pressure monitor as part of the construction project. When properly selected and installed, a room pressure monitor can provide continuous qualitative and quantitative confirmation of negative pressure across a room boundary. This is in contrast to routine periodic smoke testing, which merely provides an indication of directional airflow at the moment of testing.

Continuous monitoring can provide instant notification if the pressurization fails or fluctuates during the day. Most monitors consist of two main components: a wall-mounted panel and a sensor. The panel is usually mounted on the corridor wall just outside the isolation room suite and displays the pressure difference in units of " W.C.

There are two common types of permanent pressure monitors: those that measure and display the actual air pressure difference between the isolation room and the reference space (direct type); and those that measure the velocity of air moving between the two spaces through a fixed opening and convert this to a pressure value (indirect). Both types require an electrical power connection at the wall panel. Either type is suitable for a negative pressure isolation room, but indirect monitors generally provide a more accurate pressure reading.

Pressure differentials across room boundaries can be very small, often in the range of thousandths of an inch. For example, the CDC Guidelines recommend that negative pressure be at least minus 0.001" W.C. Some devices that measure differential pressure are not accurate to this level. Before specifying or purchasing a room pressure monitor, make sure that the device is capable of accurately and reliably measuring a pressure difference this small.

To record a pressure differential directly, two readings are required: the air pressure in the room and the reference pressure in the corridor. A remote sensor to measure the room pressure is installed in the negative pressure room wall or ceiling. Another sensor measures the air pressure in the corridor. The difference in these two pressure values is the relative room pressurization, which is displayed on the panel.

If there is an anteroom between the isolation room and the corridor, the pressure differential to be measured is the one between the isolation room and the ante room. In this case, both measurement points are remote from the corridor panel.

If there is no anteroom, the reference pressure can be measured right at the panel, and only one remote reading is required.

The location of the remote sensors will affect the accuracy of the measurement. They should be installed as close as possible to the isolation room door, but away from drafts.

Tubing will need to be run from the panel to the sensor(s). For new construction, this tubing will typically be run out of sight inside wall cavities and above the ceiling. Air tubing is usually rigid plastic, but can be made of copper.

The sensing component of a velocity-reading room pressure monitor consists of an air tube with an interior velocity sensing element. The tube is installed in the wall between the isolation room and the anteroom or corridor. An electrical device measures the air velocity and direction. This signal is run back to the wall panel, where it is converted to a pressure readout.

Again, care should be taken when installing the sensor. It should be located above or next to the door, but away from the influence of drafts. To help shield the sensors, louvered cover plates are usually provided on both sides of the wall. The signal between the sensor and the wall panel is a low voltage electrical signal instead of the air tubing used in direct pressure monitors.

In addition to providing a continuous readout of the pressure difference, the wall panel should include an audible and visual alarm to warn staff when pressurization is lost.

The alarm will sound when the measured room pressurization drifts to less than the monitor’s reference pressure value. The reference pressure value is programmed by the user. It will be a value between the steady state pressure differential maintained by the room and zero (neutral pressure).

For example, in a room with a steady state pressure differential of minus 0.03" W.C., the alarm could be programmed to activate when the pressure differential falls to minus 0.001" W.C. Minus 0.001" W.C. is the reference pressure value.

The wall panel should also allow staff to program a built-in time delay between loss of pressurization and alarm activation. The time delay will allow staff a sufficient interval to routinely enter and leave the room without setting off the alarm. A typical time delay is 45 seconds.

The audible alarm is usually a beeping sound, which will stop when negative pressure is restored or when a "mute" button on the panel is pressed. The visual alarm usually consists of a red warning light. Most wall panels also have a green "normal" or "safe" light, which indicates that the monitor is operating and negative pressure is within programmed parameters. Unlike the audible alarm, the visual alarm will not reset when the "mute" button is pressed. After negative pressure is restored, the lights will either automatically reset or the "reset" button must be pressed, depending on the brand of the monitor. In case no one was present, the latter option will indicate that negative pressure was temporarily lost.

In addition to the alarm included on the wall panel, most room pressure monitors include an extra identical signal that allows a "safe" or ‘alarm’ signal to be connected from the wall panel to a remote location. Common locations for this remote alarm are the nurses’ station, the engineering department, and the central switchboard.

It is usually possible to connect the alarm signals from a number of isolation room monitors to a remote alarm panel. In California, for example, the hospital building codes require that negative pressure isolation rooms be equipped with an alarm that annunciates at the room and at a nurses’ station or other suitable location.

Other Optional Features

There are a number of room pressure monitors available with additional options. Examples of such options include: an amber "warning" light that illuminates during the time delay when negative pressure is lost; adjustment for use in positive pressure rooms; and control of a fan or damper to maintain negative pressure.

The monitor installer’s responsibilities should include verifying the operation of the sensor. A detailed checklist is included as Appendix D. The following should be completed before the room is used to isolate suspected or confirmed infectious TB patients:

1. Verify that the alarm works. Hold the room door open. After the time delay, the audible and visual alarm should annunciate. The alarm should reset after the "mute" or "reset" button is pressed and/or the door is closed again.

2. Verify that the monitor is correctly reading the pressure. While the door is held open, the pressure reading should be at or near 0" W.C.

    

3. Instruct staff in monitor usage. The floor staff who depend on the monitor for their safety should feel comfortable using it. They should receive detailed instructions on how the monitor works and how it is used. The checklist should be completed for each isolation room monitor in the facility. A copy of the completed checklist should be kept in the Policies and Procedures binder for that department.

To validate the continuous pressure monitor, negative pressure should be verified monthly with smoke trail or similar testing. The results should be recorded. Space for this is included in the checklist.

Most manufacturers recommend that each monitor be recalibrated annually. The recalibration procedure will depend on the monitor type and should be available from the manufacturer. ICS recommends that a new monitor checklist be completed at the same time.

If space and budget permit, an anteroom should be provided between the negative pressure isolation room and the corridor. This will help prevent infectious particles in the isolation room from escaping to the corridor.

When an isolation room door is open, negative pressure is immediately lost. If there is an anteroom that is negative to the corridor, then the overall integrity of the suite is maintained. The anteroom provides an "air lock" between the isolation room and the rest of the facility.

An anteroom should be at positive pressure with respect to the isolation room, and at either neutral or negative pressure with respect to the corridor. Because smoke may migrate from the corridor if there is a fire, some codes and regulations mandate that the anteroom be neutral to the corridor, rather than negative. However, in practice this is very difficult to accomplish. It is not easy to balance airflow to a space so that it will be positive at one door and neutral at the other.

Furthermore, air pressure in the corridor will vary due to external factors such as elevators and corridor doors to the outside.

Local codes should be consulted regarding other design elements of anterooms for isolation rooms. For example, California requirements include:

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