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Creating TB Isolation Rooms
By David R. Linamen, PE, CIPE
Tuberculosis (TB) is the single most deadly disease known to man. Approximately 1.7 billion people are infected with the disease worldwide, representing nearly one third of the world's population. With the exception of some localized problems, the disease has not reached epidemic proportions in the US. In 1994, the Centers for Disease Control and Prevention (CDC) adopted Guidelines for Preventing the Transmission of TB in Healthcare Facilities (Guidelines) in an attempt to minimize the risk that TB might be passed from patients to healthcare workers and visitors. The Guidelines recognize that the greatest risk of TB transmission exists with undiagnosed TB cases. The Guidelines also recognize that a complete program to control TB must include engineering controls to reduce the concentration of infectious droplet nuclei in the air. The Guidelines impose a rather comprehensive list of features, which are to be designed into Airborne Infectious Isolation Rooms. Minimum Standards
Because of the language used in the CDC Guidelines, the requirements are subject to some interpretation, and many healthcare architects and administrators have interpreted the language creatively to mean something far different that what the CDC intended. In general, it was the intent of the agencies developing the Guidelines that they be readily achievable by community healthcare institutions with minimal funds. Anyone who has training in liability issues as they relate to healthcare knows that codes and standards are recognized by the legal community as minimum requirements, so creative interpretation of the Guidelines to minimize cost of implementation is strongly discouraged.
To be entirely successful, a project to develop a new Isolation Room in any institution should include early involvement of the nursing staff who will manage the room, the Infection Control Department, and the maintenance staff as well as the architect and engineer who will design the space. It is absolutely essential that the knowledge and concerns of each of these individuals be considered early in the process while the design is still most flexible. Waiting for periodic design reviews to involve these parties can force compromises that reduce the overall effectiveness of the Isolation Room once it is constructed. It is also imperative that the Isolation Room be commissioned by representatives from the design team and the maintenance department to ensure that each feature and system is functioning in strict accordance with the design intent.
Important Engineering Features
The room airflow should be a minimum of 12 air changes per hour. The Guidelines do not specify if the supply air flow or the exhaust airflow should equal 12 air changes per hour, but making the supply air flow equal to 12 air changes per hour is the most conservative approach. They do specify that the exhaust airflow volume should exceed the supply airflow volume by 10% or 50 CFM, whichever is greater, to maintain a negative pressure within the room with respect to surrounding areas. The negative pressure will cause an inward flow of air into the Isolation Room when doors are opened, preventing the migration of bacteria to the surroundings. The effectiveness of the 12 air change standard has not been proven with regard to minimizing TB bacteria in a room; however, actual experiments have proven that increasing airflow rates in hospitals does reduce total bacteria counts in the air.
Air should be supplied through non-aspirating diffusers to prevent updrafts, and exhaust/return air registers should be located close to the floor at the head of the patient bed. The intent of this requirement is to establish a general airflow pattern, which will help to move TB bacteria from the point of patient expulsion to the exhaust/return air terminal to prevent a healthcare worker or visitor from inhaling the bacteria. The general airflow pattern is achieved by using the proper airflow rate and by proper placement of supply and exhaust air terminals. Remember that air can be pushed much further than it can be pulled, and increasing inlet air velocities at the exhaust air terminal will have little effect on the system's ability to capture bacteria.
Normal ceiling-mounted supply air diffusers actually aspirate and induce warm air to cause mixing. The aspiration results in an updraft of air directly beneath the diffuser face. The induction results in currents of air that swirl horizontally with the ceiling along the path of discharge from the diffuser. This aspiration and induction would actually spread TB bacteria throughout the patient room. The non-aspirating (typically perforated face) diffuser provides a generally laminar flow of air, and proper placement with regard to the exhaust air terminal will result in an airflow pattern that can be used to flush the patient room of unwanted airborne particles. Care should be taken to position patient beds close to intake walls to discourage room visitors from standing between the patient location and the exhaust air intake.
Because supply air diffusers typically supply air at a temperature less than the skin surface temperature of the patient, the placement of a non-aspirating ceiling diffuser is very critical. The diffuser should be placed away from the patient bed, preferably near the point where a healthcare worker or visitor would enter the room. The placement of the diffuser immediately over the patient bed would result in uncomfortable drafts being projected directly at the patient.
Pressure measurement for variable volume supply and exhaust systems is critical. Many designers elect to use variable volume supply and exhaust systems to minimize the energy required to condition the supply air as well as to operate the supply and exhaust fans. Variable volume schemes should be scrutinized carefully. Since the minimum airflow requirement of 12 air changes per hour for a newly constructed or renovated room is already well above the air volume that would typically be required to heat or cool the space, there will probably be little opportunity to reduce energy consumption by implementing a variable volume strategy.
If variable volume is used, it is imperative that accurate, reliable controls be used to sense the pressure differential between the patient room and the surroundings and adjust the fan operation to maintain the desired pressure differential. The Guidelines specify a minimum pressure differential of 0.001 inches w.g. (water gage) or an inward velocity of 100 feet per minute for the Isolation Room. A number of sensitive differential pressure measurement devices can be used for this application. Some engineers have developed a preference for devices, which measure airflow velocity between the patient room and the surroundings because there is a direct correlation between velocity and differential pressure. Low air flow velocities can be measured more accurately than low pressures.
The Guidelines require that Isolation Rooms occupied by TB patients have differential pressure monitored daily by a differential pressure measuring device or by using smoke tubes to observe the direction of airflow virtually. If smoke monitoring is used, periodic testing should be done with an air measurement device (a manometer) to verify an inward flow rate of 100 feet per minute into the room. If pressure-sensing devices are used, negative pressure should be verified at least once per month using smoke tubes. The Guidelines further state that pressure-sensing devices must be located at the bottom inside of the Isolation Room door and must provide a visible and/or audible alarm when low air pressure is sensed while incorporating a time delay to allow persons to enter or leave the room without activating the signal. If an Anteroom is provided with the Isolation Room, the Guidelines require that the Isolation Room be maintained at negative pressure with respect to the Anteroom. The pressure relationship between the Anteroom and the corridor is left to the discretion of the designer.
The Isolation Room should be well sealed from the surroundings to help maintain the pressure differential. Penetrations through walls must be sealed, and drywall ceilings should be used. Swinging doors are easier to seal than sliding doors.
HEPA filtration can be used as a method of air cleaning that supplements other recommended ventilation measures. HEPA filters remove 99.97% of particles 0.3 microns and larger. TB bacteria have a rod-like shape with a minimum diameter of 0.5 microns. The ability of HEPA filters to remove TB bacteria from air has not been studied, but TB bacteria are similar in size to aspergillus spores. Therefore, HEPA filters can be expected to remove TB bacteria from air. HEPA filters should be used:
* When the HVAC system configuration dictates recirculation of air from the Isolation Room to other parts of the facility.
* When it is impossible for air from a TB Isolation Room and/or local exhaust devices to be exhausted directly outdoors.
* When air is being recirculated into the same TB Isolation Room.
It is not necessary to filter air exhausted from TB Isolation Rooms prior to discharging it to the atmosphere. Some institutions use HEPA filtration in the exhaust air stream as a secondary means of protection against TB bacteria being entrained into air intakes and then being resupplied to the facility. It is important to recognize that a resistance of HEPA filters to airflow increases as the filters trap other dust and dirt particles, and a means of adjusting the fan system to accommodate this increased pressure drop should be provided. If HEPA filtration is used, the system should have the following features:
* Filter mounting to prevent leakage between the filters and the supporting framework.
* Quantitative leak testing using the Dioctal Othalate penetration test performed at the initial installation and whenever filters are changed or moved. The test should be repeated every six months the filters are in use.
* A manometer or other pressure-sensing device should be installed in the filter system to provide accurate means of determining the need for filter replacement.
* Ductwork leading to the filters should be labeled "contaminated air." Installation of HEPA and pre-filters should allow for maintenance that will not contaminate the delivery system or the area served. Only properly trained persons wearing respirators should perform maintenance.
Design of TB Isolation Rooms into an Existing Facility
The Guidelines provide a specific process for doing a risk assessment to determine the number of Isolation Rooms that should be provided in a healthcare facility. Typically where multiple Isolation Rooms are needed, they are located in a "suite" arrangement or "stacked" in a patient wing. When TB Isolation Rooms are arranged in a suite, they can use a common corridor that serves as an Anteroom for all of the Isolation Rooms. The drawback of this arrangement is that housing non-TB patients in the suite could subject them to the risk of contracting TB.
Because the airflow requirements for TB Isolation Rooms are much greater than the requirements for other patient spaces, most facilities find it necessary to provide new supply and exhaust air systems to serve the Isolation Rooms. Many institutions dedicate the exhaust air system to serving only Isolation Rooms. Fitting a dedicated supply and exhaust duct network into an existing facility typically causes many problems for a designer. Obstructions of other building services in ceiling cavities often require the supply and exhaust ductwork to transition and turn many times between the air handling equipment and the room air terminals. It is imperative that the effect of these transitions and turns is considered in sizing fans for supply and exhaust air systems. Frequently, the installing contractor will elect to take a different route for the ductwork than intended by the designer, and the modified route could add offsets in the ductwork that increase resistance to airflow. It is important that the duct system designer include spare capacity in the fan systems to overcome unexpected resistance to airflow in the final installation. Some designs include a redundant exhaust fan so that negative pressure can be maintained even if a fan fails or is shut down for service. If an exhaust riser duct is used to exhaust several stacked rooms, the exhaust grilles should not be tapped directly into the riser because this arrangement will be difficult to balance. A separate branch exhaust duct should extend from the exhaust grille near the floor up to the ceiling of the patient room and should then connect to the exhaust riser duct. The intent of the CDC Guidelines is actually quite simple, and careful implementation of the Guidelines coupled with sound design practice will result in a successful project. P
David R. Linamen, PE, CIPE, is a Principal with Burt Hill Kosar Rittelmann Associates, an architectural and engineering firm with locations in Pittsburgh, Pa; Butler, Pa; Philadelphia, Pa; Boston, Mass; and Washington, DC.
TB Concerns for Regulated Medical Waste Treated Off-Site
By Patty Kimball, PhD
Off-site transportation of untreated medical waste is becoming more and more difficult. Federal regulations, now focused on packaging and transporting medical waste as well as worker safety issues for waste handlers, have raised the awareness generator liability. The Department of Transportation (DOT) requires that hospitals comply with hazardous materials regulations for off-site transportation and comply with stringent packaging, labeling, and manifesting requirements. In addition, air emission and water discharge requirements may well increase the cost of treatment at traditional commercial medical waste treatment facilities. The combination of the new requirements essentially "raises the bar," demanding service, operating efficiencies, and regulatory compliance.
The National Institute for Occupational Safety and Health (NIOSH) conducted an evaluation of a medical waste processing facility in Morton, Wash, in response to an outbreak of tuberculosis (TB) among the employees at the facility. The follow-up report, "Health Hazard Evaluation Report" (HHE), was published in October 1998 and identified several factors present in the facility that could contribute to employee exposures to pathogens potentially present in the medical waste. The report concluded that the facility should require laboratory facilities to decontaminate infectious cultures prior to disposal."
In 1997, OSHA published its proposed standard to regulate the occupational exposure to TB. After NIOSH investigated the facility and the follow-up (HHE), OSHA reopened the rulemaking record to address specifically the potential for significant occupational exposure to TB at medical waste treatment facilities (Docket H-371, June 17, 1999). In response to the reopening of the rulemaking record on occupational exposure to TB, several written comments were received.
NIOSH commented, "A more appropriate and efficient prevention method would be to require facilities, such as laboratories and clinics to decontaminate materials potentially contaminated with viable TB bacteria (e.g., cultures, stocks, or tissues) at the site where they are processed prior to sending them offsite for disposal." The Medical Waste Institute who represents private and public companies that treat, handle, dispose of medical waste commented, "Cultures and stocks of Mycobacterium tuberculosis and other active cultures should be decontaminated at the point of generation." The fourth edition of "Biosafety in Microbiological and Biomedical Laboratories" published by the CDC in 1999 states, "Infectious Waste from BSL-3 laboratories should be decontaminated before removal for off-site disposal."
Regulated medical waste is considered Hazardous by the DOT, and generators are required to comply with hazardous materials regulations for off-site transportation and abide by stringent packaging and transportation standards for waste cultures and stocks of infectious substances. Specifically, waste cultures and stocks must be transported by contract carriers in containers that meet DOT's UN Packaging Group II requirements. Alternatively, treatment of these materials on-site prior to transportation and disposal would eliminate the need to comply with these complex DOT standards.
As a matter of compliance as well as concern for workers and public health, laboratory wastes that may contain infectious substances should be treated in the laboratory or hospital prior to shipment off-site for disposal.
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