Compliance News: Plenum Requirements for Egress Corridors in Health Care Facilities

By Robert Trotter, CBO, CFM


In the built environment a plenum is a separate space for air circulation for HVAC systems, typically provided in the space between the structural floor/ceiling and suspended-grid acoustical tile ceiling. Incorporating a plenum can have its design advantages but corridors serving adjoining areas of health care occupancies are prohibited from being used for a portion of an air supply, air return, or exhaust air plenum.

Using building cavities as return air plenums can draw them below atmospheric pressure if not properly designed, causing outdoor air to be drawn into the building fabric. In humid climates, this can result in condensation of moisture from outdoor air within architectural cavities, consequently resulting in mold and mildew growth. Also, under certain circumstances, plenum configurations can have an adverse effect on life/fire safety. Clearly, plenum returns should not be used where codes prohibit them, such as health care occupancies, where individual space pressures must be controlled. These provisions are prescribed in the NFPA 101®, Life Safety Code® and NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems.

Health care organizations that receive Medicare and Medicaid funding from The Centers for Medicare & Medicaid Services (CMS) must comply with the 2000 edition of NFPA 101®, Life Safety Code®. Chapter 18 New Health Care Occupancies, section 18.5.2.1 and Chapter 19 Existing Health Care Occupancies, section 19.5.2.1 under Building Services both state, “Heating, ventilating, and air conditioning shall comply with the provisions of Section 9.2 and shall be installed in accordance with the manufacturer’s specifications.” Life Safety Code section 9.2 states “Air conditioning, heating, ventilating ductwork, and related equipment shall be in accordance with NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, or NFPA 90B, Standard for the Installation of Warm Air Heating and Air-Conditioning Systems, as applicable, unless existing installations, which shall be permitted to be continued in service, subject to approval by the authority having jurisdiction.”

Any hospital accredited by The Joint Commission must comply with the 2011 Hospital Accreditation Standards. Specifically, Life Safety Standard LS.02.01.30 Element of Performance 13, “Corridors serving adjoining areas are not used for a portion of an air supply, air return, or exhaust air plenum.”

Note: The Joint Commission interprets the NFPA code to allow incidental air movement between rooms and corridors (such as isolation rooms) because of the need for pressure differentials in health care facilities. In such cases, the direction of airflow is not the focus for this element of performance. For the purpose of fire protection, air transfer should be limited to the amount necessary to maintain positive or negative pressure differentials. (For full text and any exceptions, refer to NFPA 90A-1999: 2-3.11.1.)

Section 2-3.11.1 states: Egress corridors in health care, detentionand correctional, and residential occupancies shall not be used as a portion of a supply, return, or exhaust air system serving adjoining areas. An air transfer opening(s) shall not be permitted in walls or in doors separating egress corridors from adjoining areas.

• Exception No. 1: Toilet rooms, bathrooms, shower rooms, sink closets, and similar auxiliary spaces opening directly onto the egress corridor.

• Exception No. 3: Use of egress corridors as part of an engineered smoke-control system.

Fire in egress corridor scenario: With a plenum arrangement with a diffuser or return air grille located in the egress corridor, as well as adjoining areas such as patient rooms, the above-mentioned provisions would be prohibited in health care occupancies. Smoke and products of combustion accumulating in the plenum

would be able to enter the patient rooms through the return air grille, resulting in a critical life safety consideration.

Fire in egress corridor scenario: With a plenum arrangement with a diffuser or return air grille located in the egress corridor and ducted HVAC for the adjoining areas such as patient rooms, the above-mentioned provisions would be acceptable in health care occupancies because the plenum would not be serving adjoining areas. Smoke and products of combustion accumulating in the plenum would not be able to enter the patient rooms.

Fire in patient room scenario: With a plenum arrangement with a diffuser or return air grille located in the egress corridor and ducted HVAC for the adjoining areas such as patient rooms, the above-mentioned provisions would be acceptable in health care occupancies because the plenum would not be serving adjoining areas. Smoke and products of combustion accumulating in the room would not be able to enter the plenum, nor could they enter patient spaces through the return air grille in the corridor.

When the plenum is found to serve adjoining areas in existing health care occupancies, corrections must be made to bring the building into compliance. An evaluation of the design and as-built conditions are important in taking corrective measures. Where corridor walls extend to the floor or roof deck above, smoke dampers may be an option to separate the egress corridor from adjoining areas. Under this arrangement, the plenum would be fully functional during normal operating conditions, but upon activation of a fire alarm system the dampers should automatically close. Depending on the number of openings to protect in corridor walls above the ceiling, another option is to install ceiling dampers at the return air locations. The ceiling dampers installed in corridors at the return air locations may be the most cost-effective way to separate the egress corridor from adjoining areas and achieve compliance.

Note: This article is based upon the comprehensive cover story article by Bob Trotter entitled “Plenum Requirements for Egress Corridors in Health Care Environments” in the July 2011 edition of Engineered Systems (Volume 28 No. 7) www.esmagazine.com. For further information, please contact Bob at: rtrotter@ssr-inc.com.

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