HEPA filters are an essential part of any hospital's air filtration system. HEPA stands for High-Efficiency Particulate Air, and these filters are designed to capture and remove airborne particles, microorganisms, and other contaminants from the indoor air of a facility. In the HVAC configuration, filters are rated according to the MERV rating (Minimum Efficiency Report Value). MERV ratings for standard HVAC systems range from 1 to 16, with higher MERV ratings indicating better filtration.
HEPA filtration systems achieve efficiencies of MERV 17 to 20, making them extremely effective at cleaning indoor air. HEPA filters are commonly used in operating rooms, protective environments, and healthcare facility isolation rooms. They are ideal for very small particles, measured in micrometers or microns (μm). Contrary to popular belief, HEPA filters do not only remove particles larger than 0.3 μm; they use four different filtration mechanisms to effectively trap particles of different sizes. During the first spike in the COVID-19 response in hospitals, mechanical engineers worked with facilities to convert UAH to operate with 100% outdoor air whenever possible. The best practice is to ensure that the HEPA filters are installed in the exhaust of the AHU.
This will allow the installation to protect people in close proximity from exhaust air to the outside. Some AHU installations will not allow facilities to adapt the unit with HEPA filtration due to the long duration of the interruption in hospital operation if the AHUs have to be removed from service. The most innovative way to modify these systems is to install HEPA-filtered ventilator units and close return air diffusers in areas of COVID-19 patients. Some types of biological safety cabinets are designed to supply HEPA-filtered air over the work surface to protect the product on the work surface from contamination. The results showed that the small particles followed the air path and remained suspended in the room due to air recirculation inside the room. Using HEPA filters in conjunction with daily cleaning products can improve air quality within medical facilities.
But an improved HVAC system design will minimize recirculation of COVID-19 contaminated air into the hospital's air distribution system. Installing HEPA filters in return and exhaust air systems is the current best practice approach to intercepting the virus path in the healthcare environment. As formaldehyde vapor-laden air passes through the filter, the vapors are absorbed into the filter media. This is also important to ensure that contaminated exhaust air does not enter the supply air intake grilles. To avoid contamination, people rely on HEPA filters to eliminate microbes and pathogens from the air. Poorly maintained filters with inadequate seals and gaps in the filter media promote the passage of contaminants into occupied spaces.
Therefore, engineering alternatives such as mixing indoor air with outdoor air and recirculating it back to the room and pressurization control are used. HEPA filters containing carbon or activated carbon are also available to filter odors, fumes and gases. Table 1 shows the results of an initial search for key terms with a separate focus on air filtration and air recirculation in health facilities. Using HEPA filters in hospitals is common, but normal HEPA filters may not be enough to sterilize dangerous microbes. The best way to ensure safety is by installing high-efficiency filtration systems that can capture even smaller particles than standard HEPA filters. These publications were then independently reviewed by two experts to determine their relevance to the topic of this literature review, i.e., the effect of air filtration and air recirculation on the spread of pathogens in hospitals.
The results showed that proper installation and maintenance of high-efficiency filtration systems can significantly reduce airborne contaminants and help prevent disease transmission.