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Research Highlights
Biological Inactivation Efficiency of HVAC In-Duct Ultraviolet Light DevicesOne potential method of terrorism is the intentional introduction of biological warfare agents (BWAs) into the heating, ventilation, and air-conditioning (HVAC) systems of target structures in order to distribute pathogens. Introducing BWAs into an HVAC system could harm many people, so there is an urgent need to identify and test devices that can destroy BWAs as they move through an air handling system. One technology that may meet this need uses ultraviolet (UV) lights deployed inside the building’s air ducts. Short-wave ultraviolet radiation in the “C” band (UVC or UVGI — germicidal irradiation) has been used for many years to inactivate microorganisms. Early research in this area focused on the controlling infectious pathogens in medical facilities. UVC effectively killed Mycobacterium tuberculosis, the causative agent of tuberculosis, and other bacteria including mycoplasma, as well as viruses and fungi. In testing and evaluating homeland security related technologies, EPA provides unbiased, third-party performance information that can supplement vendor-generated information. This information helps decision makers purchase and apply the tested technologies. EPA conducts its evaluations under rigorous quality assurance protocols to generate high-quality data. Test DesignThe UVC devices are designed to be mounted inside an HVAC system to inactivate bioaerosols as they migrate through the air handling system. The devices were tested separately in a laboratory-based test duct with advanced aerosol and microbiological generation and measurement equipment. Testing was conducted using three microorganisms, two bacteria (one spore-forming and one vegetative) and one virus, whose structural characteristics and susceptibility to UVC inactivation make them reasonable surrogates for BWAs. Each device was tested three times, once for each test microorganism. Test microorganisms were generated and introduced into the test duct upstream from the installed device. As air flowed through the duct, the bioaerosols passed through the device and were exposed to UVC.Each device's ability to destroy the bioaerosols is reported as airborne inactivation efficiency. The greater this percentage, the more effective the device. To determine efficiency, bioaerosol samples were taken from the duct upstream and downstream from the device. These samples were cultured, and the bacterial colony forming units (CFUs) or viral plaque forming units (PFUs) were counted. Device efficiency was then calculated as a percentage from the ratio of the upstream to the downstream counts. Performance and ResultsAll UVC devices were ≥99 percent efficient at inactivating the vegetative bacteria. Three UVC devices were ≥93 percent effective for all three microorganisms. Five devices had ≤46 percent efficiency for inactivation of the spore form of the bacteria and two had ≤46 percent efficiency in destroying the virus.
a: The systems were run at 0.93 m3/sec (1970 CFM), except the Novatron device was run at 0.14 m3/sec (300 CFM). Other attributes besides airborne inactivation efficiency were assessed. These included dosage measurements, power consumption, single measurement intensity, pressure drop across the device, and air temperature rise through the device.
Contact: Kathy Nickel |
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