The COVID-19 pandemic is a watershed event which has changed the focus on infection prevention and control (IPC) for commercial buildings and healthcare settings, probably forever! While the initial focus was on surface disinfection, further research revealed that the primary mode of coronavirus transmission was through the air. The need for interventions to protect building occupants became clear and has spurred a huge reaction from opportunists looking to help solve this problem. Unfortunately, many of these opportunists not only lack experience in airborne IPC, they also do not have the benefit of historical lessons learned.
In our attempts to protect staff, visitors, clients, patients, and residents in our commercial and healthcare settings, it is important, to rely on interventions that are tested, tried and true. This is not the time to prey on the fears of the masses and to experiment with their health.
Upper-room germicidal ultraviolet (UR GUV) systems have been used for decades as an intervention in hospitals, schools, and diverse commercial settings as a cost-effective way to reduce the risk of airborne infection from multiple diseases. First used in schools in the 1940s to protect students from influenza, measles and chickenpox, UR GUV creates a disinfection zone above the room occupants.
As convection and ventilation air currents within a space create air mixing between the lower and upper portions of the room, airborne microbes become exposed to the GUV rays in the upper portion. The DNA of the bacteria, as well as the DNA and RNA of viruses, are damaged by the GUV light which prevents them from reproducing or causing infection. This lowers the concentration of infectious microbes in the air and therefore reduces the risk of infection.
UR GUV has often been used for IPC of pulmonary tuberculosis (TB). TB bacteria are spread through the air. To show its effectiveness as an intervention against TB, studies were done in South Africa and Peru, in active TB wards. Air was exhausted from the active TB ward to one of two animal rooms containing Guinea pigs (which are very susceptible to TB).
On alternating days, the UR GUV fixtures would be turned off or on. When on, the air would be exhausted to one guinea pig room, and when off, the air would be exhausted to the other guinea pig room. Both studies showed an 80% reduction in TB infection in the guinea pigs receiving air treated by the UR GUV systems.
Based on these results and other historical information, the WHO published their 2019 guidelines for tuberculosis IPC in which they recommended the use of UR GUV systems for airborne IPC in TB settings. Since then, some studies have shown that SARS-CoV-2 (the virus responsible for COVID-19) is more susceptible to GUV than TB, which would imply that UR GUV systems should provide similar if not better protection for this virus. The US CDC has recommended the use of UR GUV in its tuberculosis guidelines for several decades.
Is UR GUV the only tool that I should use against SARS-CoV-2 in buildings? Absolutely not! There are many solutions that will be helpful in reducing risk. The key is to know which ones to apply and when, as well as knowing the anticipated benefits and costs. Several interventions are listed below with pros and cons of each.
HVAC Filter Upgrades
Upgrading the filter efficiency on your HVAC unit may be one of the easiest and least costly things to do. An upgrade to MERV 13 may dramatically increase the particle removal efficiency within the system. However, an increase in filter efficiency will lead to a rise in filter resistance and a decrease in airflow through the system. Diminished airflow, even with higher filter efficiency, could have a negative impact on IPC in occupied spaces (insufficient pressure control and ACH).
In-duct GUV
Installing in-duct GUV for “on the fly” disinfection of airborne microbes can be quite effective without leading to a decrease in airflow. In-duct GUV may increase HVAC airflow back to design state depending on how it is installed. If installed near coils it could decrease bioburden on the coils and improve air flow and energy efficiency.
Achieving disinfection on the fly requires a high level of GUV irradiation and the system should only be designed by a trained and certified professional. The facility-wide impact of in-duct GUV and increased filter efficiencies in HVAC units will be limited by the air flow of the HVAC system. If the HVAC system is not designed for an adequate amount of airflow, increasing the microbe removal efficiency will have a limited benefit.
Room Air Purifiers (Portable and Fixed)
Room air purifiers usually consist of a fan to move the air and a series of filters, usually including a HEPA filter. These devices are available in portable, ceiling-mount, in-duct, and wall-mount configurations. These devices, if properly designed and applied may be able to help meet IPC goals within a space as they can usually achieve the airflow and removal efficiencies required.
However, drawbacks include high energy usage, periodic replacement of expensive high-efficiency filters and potentially expensive installation, which give them a high cost of ownership when used as a facility-wide solution. They are often best used for specific areas where other methods of control are not a viable option.
Increased Ventilation
Ventilation is often misunderstood. True ventilation is the replacement of building air with air from outside. Ventilating a space that has perfect air mixing, at an air change rate of 12 air changes per hour (ACH), is said to remove 99.999% of airborne contaminants in one hour. Most commercial spaces are designed with much lower ventilation rates and do not have perfect mixing.
In most cases, increasing outside air volumes would dramatically increase the cost of energy required to heat or cool a space. Increasing the volume of air moved through a building would likely require the installation of larger duct work to facilitate the higher airflow rates. While ventilation is considered the best control method, the expense of retrofitting is usually prohibitive.
Upper Room Germicidal UV (UR GUV)
UR GUV systems (that are properly designed, installed operated and maintained) have been shown to inactivate airborne microbes at a rate that is equivalent to 10-24 ACH of exhaust ventilation. These highly effective systems are relatively easy to install and require little if any change to existing systems. As such, they have a low to moderate cost of purchase, installation, operation, and maintenance. With a low energy impact on a facility and a low cost of long-term maintenance, these UR GUV systems have a very low cost of ownership.
Proper Implementation of UR GUV Systems
While the installation process of UR GUV systems in relatively simple, there is a great amount of planning that must precede the installation. Like all the systems mentioned above, these systems must be designed by experienced UR GUV experts. The development of a national training and certification program for technicians and consultants working with GUV systems would help to ensure that the experts have the proper knowledge and technical expertise to provide this function.
Proper Dosing
The first step in designing a UR GUV system is to determine the dose of GUV required within a space for the system to be effective. There is currently discussion within the ASHRAE GPC-37 subcommittee on UR GUV on the most accurate formula for determining dosing. One formula currently used considers the volume of a space (up to 3 m [10′] in ceiling height) and then multiplies that volume (in meters) by 0.012 W of UV.
This will determine the total watts of GUV output from a fixture(s) required for an effective system. It is important to note that the GUV output of a fixture is very different from the nominal or GUV rating of a lamp. The GUV output of a fixture should be determined by an independent laboratory such as Intertek or UL, that has experience conducting these tests.
Fixture Selection
Fixtures should be UL1598 listed for electrical safety, UL867 or UL2998 listed for zero ozone generation, and be tested by an independent laboratory for GUV output. Fixtures should also have built-in capability to adjust the angle of GUV output for safety considerations.
Fixture Placement
Once the number of fixtures required for proper dosing is determined, the next step is to identify optimal fixture placement. Fixture locations should avoid obstructions within the space that could block or reflect the GUV energy. Spreading the fixtures throughout the space to reduce the overlap of GUV and minimizing GUV energy losses to walls and ceilings is also important.
Safety Certification
The last step in the installation process is the final acceptance safety test. Unlike UVA and UVB which can cause skin cancer and cataracts, there are no known long-term health consequences from accidental exposure to UVC energy. GUV is within the UVC region which can cause temporary health consequences, such as photokeratitis (eye irritation) and skin erythema (like sunburn), when improperly installed.
These undesirable health outcomes can be avoided by proper installation and testing for GUV levels in the occupied space. Many systems can be adjusted so that safety in the occupied space can be maintained without sacrificing the GUV output required for effectiveness.
When measuring levels of GUV in occupied spaces, it is imperative to use appropriate devices that are capable of accurately measuring very low levels of GUV. These tests should only be performed by individuals who have gone through a training process specific to UR GUV systems.
Conclusion
UR GUV systems are not the only tool that we can use to protect building occupants from airborne infectious diseases such as COVID-19 and tuberculosis However, they are a cost-effective risk reduction tool which, when properly installed and tested, can play a significant role for IPC within commercial and healthcare settings.
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