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Operating Room Air Filtration Systems

Because of the various demands made by specialized procedures, healthcare facilities, have many areas where filtration must be of the high­est efficiency. This usually includes operating theaters, outpatient surgery suites, labor and delivery, bone mar­row transplant, isolation rooms, criti­cal care, intensive care, and several other area designations as well.

The High Efficiency Particulate Air (HEPA) filter provides the best pro­tection from infection and contamina­tion from airborne microorganisms, especially when engineered so that the filter is mounted at the terminal of the duct, commonly referred to as ceiling mounted HEPA filters or modules.  These filters have a long history of providing protection against air­borne diseases.  Currently, there is no ordinance or federal regula­tion, or even a mandate to have them installed in hospital operat­ing rooms. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), the American Institute of Architects (AIA), and the Joint Commission for the Accreditation of Healthcare Organizations (JCAHO) all recom­mend HEPA filtration. JCAHO serves as an accreditation organiza­tion to monitor hospitals and medical care facilities and requires hos­pitals to design, install, and maintain ventilation equipment to appropri­ate pressure relationships, air exchange rates, and filtration effi­ciencies for ventilation systems areas specially designed to control airborne contaminants.  Such contaminants may include biological agents, gases, fumes, and dust particles. These specially designed areas include; Special Procedure rooms, Delivery Rooms with patients diag­nosed or suspected of having airborne communicable diseases such as TI5, patients in protective environment rooms, those with immunodeficiency conditions, or bone marrow transplant patients. Also included are labo­ratories, pharmacies, and sterile supply rooms. (1)

Most healthcare facilities that do utilize HEPA filtration in critical care areas apply this technolo­gy because they understand the value in terms of reducing the number of nosocomial (Hospital acquired) infections. The CDC estimates that over 90,000 people die each year from nosocomial illness. They also state that over 50% of these cases are preventable.   This can be accomplished by utilizing high qual­ity HEPA filters in the air distribution system. In fact, ASHRAE: recom­mends MERV 17 or 99.97% HEPA filters at the outlet of Orthopedic, Bone Marrow Transplant, and Organ Transplant Operating Rooms. (2) 

(1) JCAHO Hospital Accreditation Standards; 2004 Environment of Care 7.10 -No. 15
(2) ASHRAE Handbook 2003 Health Care. Facilities 7.3 Table 1

Transmission of diseases by the air­borne route is usually done by droplet nuclei, small droplets of moisture, or dust particles in the size range of 1 to 5 micrometers. These small particles can stay suspended in the air for long periods of time. Small microorgan­isms and viruses usually “ride” on these particles that can affect open wounds or are breathed into the deep lung section where they can cause potential disease and infection.

Although the sources of these contaminants are many, people are the biggest carrier of contaminants requiring extensive covering of operating room personnel with clean garments to prevent contamination. Poorly maintained HVAC units are also responsible for unwanted contaminants entering a room via the HVAC distribution system. Therefore, the terminal HEPA filter is the popular choice to provide maximum filtration from any airborne contaminant that might enter the HVAC unit or ductwork downstream of in-line unit-mounted HEPA filters.

Ceiling mounted HEPA modules deliver clean, filtered air in a flow to the room that provide a sweeping effect that pushes contaminants out via the return grilles that are usually mounted on the lower wall. While there is no true unidirectional air­flow, this top to bottom flow closely duplicates a “piston-effect.” With ceiling mounted HEPA units, the air is as close to unidirectional flow in operating rooms as is feasible, based on the various types of equipment and instruments that typically interrupt unidirectional airflow patterns.

 Ceiling Mounted Ducted HEPA filter Terminal Unit

Ceiling Mounted HEPA Filter Module



HEPA filtration in operating rooms of a healthcare facility provides the highest quality of air cleanliness, helping safeguard the life and health of the patients and the healthcare workers. These systems should be designed and installed by people knowledgeable in HEPA filters and HEPA filtration systems and should provide for scheduled periodic testing to assure HEPA system integrity.

Finally, the system is only as good as the integrity of the filter system. All HEPA filtered systems should be designed to incorporate scheduled periodic in-situ testing of filters, gaskets and housing with appropriate challenge agents and testing equipment. This usually involves an upstream introduction of DOP (or some appropriate acceptable challenge agent) and downstream scanning of the face of the HEPA with a forward light-scattering photometer. This testing procedure allows the system to be integrity-tested and certified to assure that there are no leaks in the critical components of the HEPA ceiling module.