In “What Is Upper Room UVGI?” we address the what and the how of UV equipment located in the upper portions of an indoor space but what about the why? Why do organizations like the Centers for Disease Control and Prevention (CDC) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommend upper room UVGI to help prevent the spread of infectious diseases?

As we recently discussed in “CDC Ventilation Guidance: Upper Room UVGI and In-duct UVGI Systems for Air Cleaning,” in its updated guidance as part of a recommended “layered strategy to reduce exposures to SARS-CoV-2, the virus that causes COVID-19,” the CDC suggests: “Consider using ultraviolet germicidal irradiation (UVGI) as a supplement to help inactivate SARS-CoV-2, especially if options for increasing room ventilation are limited. Upper-room UVGI systems can be used to provide air cleaning within occupied spaces, and in-duct UVGI systems can help enhance air cleaning inside central ventilation systems.” The following offers just some  additional readily available resources on the use of UV to disinfect the air and, more specifically, the use of upper room UV.

“There is a long history of investigations concluding that, if used properly, UVGI can be safe and highly effective in disinfecting the air, thereby preventing transmission of a variety of airborne infections.”

The History of Ultraviolet Germicidal Irradiation for Air Disinfection

In this public health report author Nicholas G. Reed, with the U.S. Army Center for Health Promotion and Preventive Medicine, Laser/Optical Radiation Program, Aberdeen Proving Ground, MD, USA, tracks the “long history” of using UV as “an established means of disinfection and can be used to prevent the spread of certain infectious diseases.” The informative and interesting report includes its historical use including how, between 1937-1941, upper room UVGI was “successfully used” to “prevent the epidemic spread of measles among children in suburban Philadelphia day schools, where infection outside of school was unlikely.”

Reed also cites a series of articles published in the 1970s that detailed the results of using upper room UVGI in a model room aerosolized with bacteria (Serratia marcescens). From Reed’s report which also speaks to the value of fans in greatly increasing the efficacy of upper air UV (Aerapy’s  Zone360, Zone180, and PSF Series, for example, feature integrated fans):

“The effects on disinfection rates in the lower room from air mixing via convection and a ceiling fan were studied and mathematically modeled. It was shown that temperature gradients and ceiling fans could greatly affect air mixing in a room and, thus, the rate of disinfection in the lower room. By supplying air cooler than the lower-room air to the upper room and/or using a ceiling fan, the efficiency of UVGI in disinfecting the lower room was greatly increased. The ability to prevent the spread of infectious organisms throughout a building by placing UVGI in corridors was also demonstrated.”

Note: This principle of using fans to “suck up the air” (as one expert puts it) into the upper room to increase UVGI efficacy is further addressed in “What Is Upper Room UVGI?”

The first clinical trial using upper air UV to prevent tuberculosis (TB) transmission, published in 2009, is also featured by Reed. The trial, using guinea pigs, showed the following:

“On alternating UV-on and -off days, one group of guinea pigs breathed air from the TB ward with upper room UVGI and a mixing fan turned on, and a separate control group of guinea pigs breathed air from the TB ward with upper-room UVGI turned off…Results showed a 34.9% infection rate in the control group and a reduced rate of 9.5% in the group with UVGI. TB disease was subsequently confirmed in 8.6% of the control group compared with 3.6% of the group with UVGI.”

Reed’s thorough report, including an abundance of cited reference material, offers a wealth of information.

READ THE REPORT HERE

“Research indicates that an appropriately designed and maintained upper-room UVGI system may kill or inactivate airborne TB bacteria and increase the protection afforded to healthcare workers while maintaining a safe level of UVGI in the occupied lower portion of the room.”

Environmental Control for Tuberculosis: Basic Upper-Room Ultraviolet Germicidal Irradiation Guidelines for Healthcare Settings

Published by the Department of Health and Human Services (HHS), with the CDC and the National Institute for Occupational Safety and Health (NIOSH), these guidelines are “designed to provide information to healthcare managers, facility designers, engineers, and industrial hygienists on the parameters necessary to install and maintain an effective upper-room UVGI system.” As described in the document: “The use of ultraviolet germicidal irradiation (UVGI) in the upper portion of rooms or areas is an environmental control measure that may be effective in killing or inactivating air-borne M. tuberculosis generated by persons with unknown or unsuspected infectious TB.”

ACCESS THE GUIDELINES HERE

“Control of seasonal influenza has for decades relied on large-droplet precautions even though there is evidence suggesting a far greater importance for airborne transmission by small particles. For instance, a 1959 study of influenza prevention in a Veterans Administration nursing home identified an 80% reduction in influenza in staff and patients through the use of upper room ultraviolet germicidal irradiation (UVGI)…This suggests that air currents to the higher-room areas where the UVGI was present carried the airborne infectious particles, and they were inactivated. The inactivated (noninfectious) particles were therefore unable to infect staff and patients in control areas with UVGI, as compared to areas without UVGI.”

ASHRAE Position Document on Airborne Infectious Diseases

ASHRAE finds UVGI (upper room, in-room, and in the airstream) as one of its “strategies of interest.” The organization also includes in its position paper suggested “emergency planning” measures for engineers. As described in the paper:

“Four worldwide (pandemic) outbreaks of influenza occurred in the twentieth century: 1918, 1957, 1968, and 2009 (BOMA 2012). Not classified as true pandemics are three notable epidemics: a pseudopandemic in 1947 with low death rates, an epidemic in 1977 that was a pandemic in children, and an abortive epidemic of swine influenza in 1976 that was feared to have pandemic potential. The most recent H1N1 pandemic in 2009 resulted in thousands of deaths worldwide but was nowhere near the death toll of the 1918 Spanish flu, which was the most serious pandemic in recent history and was responsible for the deaths of an estimated more than 50 million people. There have been about three influenza pandemics in each century for the last 300 years. If a new outbreak occurs and is caused by a microorganism that spreads by the airborne route, fast action affecting building operations will be needed. Some biological agents that may be used in terrorist attacks are addressed elsewhere (USDHHS 2002, 2003). Engineers can support emergency planning by understanding the design, operations, and maintenance adequacy of buildings for which they are responsible and helping emergency planners mitigate vulnerabilities or develop interventions. For instance, there may be means to increase dilution ventilation, increase relative humidity, or quickly apply upper room UVGI in an emergency room, transportation waiting area, shelter, jail, and crowded entries to buildings in an emergency…”

Further, in its recommendations, ASHRAE advises:

“Some infectious diseases are transmitted through inhalation of airborne infectious particles, which can be disseminated through buildings by pathways that include ventilation systems. Airborne infectious disease transmission can be reduced using dilution ventilation; directional ventilation; in-room airflow regimes; room pressure differentials; personalized ventilation; and source capture ventilation, filtration, and UVGI.”

Among its specific recommendations:

“Building designers, owners, and operators should give high priority to enhancing well-designed, installed, commissioned, and maintained HVAC systems with supplemental filtration, UVGI, and, in some cases, to additional or more effective ventilation to the breathing zone. Filtration and UVGI can be applied in new buildings at moderate additional cost and can be applied quickly in existing building systems to decrease the severity of acute disease outbreaks.”

READ THE POSITION DOCUMENT HERE