Ventilation: Engineering Controls for TB



Michigan Department of Labor and Economic Opportunity

Michigan Occupational Safety and Health Administration

Consultation Education and Training Division

VENTILATION: ENGINEERING CONTROLS FOR TB

Ventilation Prevents Spread

Ventilation is a control method intended to prevent or reduce the spread by reducing or removing the microbial contamination of air.

Controlling the spread at the generation point is very important and is called source control. Providing good source controls can prevent facility outbreaks of TB.

When ventilation is used along with respirators, ventilation duct filtration systems, UV lights, and other infection control methods, the risk from TB can be substantially reduced. Alone, none of the above-mentioned controls are ideal nor can they theoretically completely eliminate the risk of TB transmission to employees or to other patients.

TB transmission is dependent on the generation of infectious droplets from known or suspected TB patients created during activities such as coughing, spitting, and singing. These droplets typically measure 1-5 microns and can be captured using HEPA filtration.

Local Exhaust

Local exhaust such as hoods, booths, or tents remove airborne contaminants at or near their source of generation. For example, booths may be required for sputum induction or other high-risk procedures that generate droplets. Booths used for source control should be instantaneously exhausted so that 100% of airborne particles are removed. Booth exhaust fans should maintain sufficient negative pressure inside the booth with respect to

adjacent areas, so that air current flows into the booth and prevents infectious droplets from moving to adjacent rooms and hallways.

Ideally, air should be exhausted directly to the outdoors away from air-intake vents, people and animals, in accordance with federal, state, and local regulations concerning environmental discharges.

If direct exhaust is impossible, the air from the booths should be filtered through properly designed, installed and maintained HEPA filters. HEPA filters will capture 99.97% of the particles 0.3 microns or larger.

Isolation Rooms

Individuals with suspected or confirmed infectious TB must be placed in respiratory acid-fast bacilli (AFB) isolation rooms. Removal and ultimate dilution of infectious droplets is the primary ventilation goal for isolation rooms where suspected or known active TB patients are housed. Contaminated air must be exhausted directly to the outside or filtered through properly designed, installed and maintain HEPA filters.

Negative pressure must be maintained in isolation rooms. Negative pressurization can be created in any room when exhausted air is approximately 20% greater than the rooms supplied air. At least six air exchanges per hour (ACH) should be achieved for existing building. New buildings or renovated facilities should achieve 12 or greater ACH. Homeless shelters, drug treatment centers, or other facilities that intend to transfer suspected or known TB individuals to another facility for treatment and therapy, do not need to establish AFB isolation rooms.

Air current should be established in order to create a downward air flow. Locate air-supply ducts at ceiling level and exhaust ducts near the floor. This air flow direction is very important and is determined by the differences in air pressure between adjacent areas, with air flowing from high to low pressure areas. Air should flow from the hallway into the isolation room. An appropriately pressurized anteroom will help maintain proper air flow in critical areas while allowing necessary patient and staff movement.

Air pressure differences are best maintained when doors are dept closed. Movement of people, temperatures, and the effect of vertical openings like stairwells and elevator shafts as well as malfunctioning of ducts, fans and other ventilation equipment can alter the air pressure differences, which is why air flow must be diligently monitored and documented.

All areas to which an infectious tuberculosis patient might be admitted should be evaluated for its potential for the spread of TB bacilli droplets. TB isolation rooms should be monitored for negative pressure daily while in use relative to hallways and all surrounding areas. At a minimum, a non-irritating smoke trail or some other indicator should be used to ascertain the direction of air flow from outside the room to the inside, when the door is closed. When the room is not in use, conduct this monitoring monthly and document.

Air handling systems connected to local or isolation rooms must be labeled with a TB warning sign. Warming signs should be located where maintenance personnel would have access to duct work, fans, or filters during maintenance or repair work.

Supplemental Controls--HEPA Filters

HEPA filters may be used in general-use areas, i.e., waiting room, emergency room, when recirculating indoor air. The HEPA filter can be a portable unit or part of the centralized air-handling unit or even a whole-wall HEPA filtration unit with laminar air flow. In isolation rooms these filters can only be used as a supplemental control and are not a replacement for negative pressure ventilation.

A regular maintenance program is required to monitor HEPA filters for possible leakage and for filter loading. Keep documentation. A manometer should be installed in the filter system to provide an accurate means of objectively determining the need for filter replacement. Installation should allow for maintenance without contaminating the delivery system of the area served.

UV Irradiation

These systems are optional as an additional control where exposure to TB bacilli risk is particularly high. UV radiation cannot be considered a substitute for ventilation requirements due to low efficacy of these systems. UV may be used on recirculating air in general-use areas. Consultation from a qualified expert should be obtained before and after UV lamps are installed.

For further information, please contact the Consultation Education and Training Division at (517) 284-7720.

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