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Dynamic Air Cleaners and Airborne Pathogens We have had a number of inquiries concerning the ability of Dynamic Air Cleaners and our Germicidal Systems to effectively deal with airborne pathogens generally and Anthrax specifically. The purpose of this paper is to lay out some of the facts about Anthrax and our systems. Anthrax For some background, the following is from a Center for Disease Control paper entitled "Clinical and Epidemiologic Principals of Anthrax". The highlights are ours. Anthrax
is one of the great infectious diseases of antiquity. The fifth and
sixth plagues in the Bible's book of Exodus (1) may have been
outbreaks of Anthrax in cattle and humans, respectively. The
"Black Bane," a disease that swept through Europe in the
1600s causing large numbers of human and animal deaths, was likely
Anthrax. In 1876, Anthrax became the first disease to fulfill Koch's
postulates (i.e., the first disease for which a microbial etiology
was firmly established), and 5 years later, in 1881, the first
bacterial disease for which immunization was available (2). Large
Anthrax outbreaks in humans have occurred throughout the modern
era—more than 6,000 (mostly cutaneous) cases occurred in Zimbabwe
between October 1979 and March 1980 (3), and 25 cutaneous cases
occurred in Paraguay in 1987 after the slaughter of a single
infected cow (4). Anthrax
is caused by infection with Bacillus anthracis, a gram-positive
spore-forming rod. The spore form of this organism can survive in
the environment for many decades. Certain
environmental conditions appear to produce "Anthrax
zones," areas wherein the soil is heavily contaminated with
Anthrax spores. Such conditions include soil rich in organic matter
(pH <6.0) and dramatic changes in climate, such as abundant
rainfall following a prolonged drought. Partly because of its
persistence in soil, Anthrax is a rather important veterinary
disease, especially of domestic herbivores. In addition to
encountering Anthrax while grazing in areas of high soil
contamination, these herbivores may also acquire the disease from
the bite of certain flies (8). Vultures may mechanically spread the
organism in the environment (9). Anthrax zones in the United States
closely parallel the cattle drive trails of the 1800s (10). Use of Dynamic Air Cleaners for the Capture and Destruction of Airborne Pathogens It should be said at the outset, that the goal of any system designed to deal with an uncontrolled release of pathogens is the reduction of risk rather than elimination of possibility. There are many pathways for the pathogens (Anthrax for example can be inhaled, eaten, or absorbed into the skin). Therefore the typical approach to the control of infectious disease is "belt and suspenders". Control strategies can be highly effective in minimizing the risks. This can be especially true in the case of Anthrax, which typically requires a relatively high dose to infect. To re-state of few key points from the CDC paper, Anthrax spores are in the 2-6 micron range; they are fairly hardy and can live for years unless inactivated; and when generated for mass dispersal would tend to have a static charge. In the 2-6 micron range, our Panel Air Cleaners will have a very high capture rate. We would recommend 2" Panels at a face velocity of 300 fpm or less. At this, the single pass capture rate will be greater than 95%. Further, the fact that the spores may have a static charge would give them a greater affinity for the polarized fibers of our media. Because the spores can survive for long periods, beyond capturing them, it is important to be able to inactivate and/or inhibit them as well. This will reduce the risk to both occupants and maintenance workers. There is no question that UVC can inactivate bacterial spores and other pathogens on a surface, the question has been how to meaningfully apply that fact to an air stream. UVC needs proximity and contact time to be affective. Bulbs in a duct may or may not provide the necessary intensity. UVC can be used in conjunction with high-efficiency passive filters, however, the light will not penetrate the high density media. Anthrax spores require a fairly high dose of UVC to be inactivated. We have seen differing numbers on this in the literature, but the necessary dose seems to be in the 22,000 microWatt-seconds/cm2 range (this is over twice the UVC necessary to inactivate TB, for example). This dose could be difficult to ensure with stationary bulbs in an air stream in part because of the level required and in part because air speed going through an air intake. Our G-375 and GDM-1000 combine our basic air cleaning technology with a travelling UVC light that is constantly scanning the surface of the media pad. Our standard G-375 and GDM-1000 units deliver close to 100,000 microWatt-seconds/cm2 per pass of the UVC light. Our Sterile Sweep combines a high-intensity UVC bulb with an oscillating parabolic reflector that focuses a powerful beam of light onto the media of a standard Panel or other surface. The affects of UV are cumulative, and the repeated exposure of the pathogens to this beam will inactivate them. Our germicidal systems are, we feel, the most affective way to apply UVC to an air stream. They are used to capture and inactivate pathogens in a variety of infection control and food processing applications. We have not tested our units specifically on Anthrax itself, but the principals of inactivation are the same as those of other organisms. Our systems have been successfully used and tested on a range of bacteria and molds (which are typically much more resistant to UVC than bacteria). In an application with high face velocities, a high-efficiency final filter may be recommended. While there is no 100% solution, we feel that we have a potent weapon to help significantly reduce the risks of a pathogenic aerosol. Specific Control Strategies While there are various vectors for dissemination and transmission of pathogens, two have been of particular concern: 1.) a room or area inside a building, such as a mail room, where there is a release of pathogens; and 2.) entrainment into the outside air intakes of pathogens released from outside the building. The goal in the first instance is to minimize the risks to the people in the space; the goal in both instances is to prevent to HVAC system from becoming a means to distribute the pathogens. As with any control measures, what is ideal and what is doable may not be the same thing. Most HVAC systems in most buildings were designed to heat and cool air for comfort and not address biological warfare. Therefore retrofits to these systems are constrained, certainly in the near term, by such factors as space, pressure drop, and cost. The following focuses on practical measures that would be fairly straightforward to implement. In the case of a mail room, the first point to make is that persons working in an any area where a potential hazard is known to exist should, of course, wear all necessary personal protection. However, one of the basic principals of industrial hygiene is that personal protective gear should be the last line of defense and that all practical external control measures should be implemented first. There are a myriad of strategies for dealing with mail before it is opened. Those, however, are not our expertise. The two basic strategies for contaminants introduced into the space are source capture and negative pressurization coupled with air cleaning and exhaust. The G-375 was designed to draw in air exhaled by a TB patient, clean it, and return it to the space. This unit could be used over a mail sorting table to draw in any contaminants released in to the air. Again the overall space should be negatively pressurized. Further, any air leaving the space would be cleaned and, ideally, exhausted to the outside. If this is not practical and the air must be returned to the general HVAC, it should be thoroughly cleaned. The GDM-1000's or a combination of 2" Panel and the Sterile Sweep would be applicable here. For central system applications, while the outdoor air intakes are the primary concern, control measures should be implemented into central filter bank. There are three reasons for this: 1.) such a system would clean both the outside air and the return air; 2.) UVC output and therefore effectiveness can be adversely affected by temperature (especially low temperature) and humidity extremes; and 3.) a central air cleaning system can allow for a significant reduction in outdoor air while still complying with ASHRAE and local standards. For these applications, the GDM-1000 and/or 2"Panels or V-Banks coupled with the Sterile Sweep would be used. An additional strategy for central systems would be to install our 1" Panels into VAV or filter supply grills. Contaminant control in critical areas such as operating rooms and chip manufacturing cleans the air before it goes into the space rather than before it goes through a coil. We at EDG have a longstanding commitment to and reputation for providing innovative and effective air quality solutions. Since the United States was attacked, the focus of our company has been to help in any and every way that we can to address the threats that face our nation
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