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 Centers 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, in the minds of most military and counterterrorism planners, represents the single greatest biological warfare threat. A World Health Organization report estimated that 3 days after the release of 50 kg of Anthrax spores along a 2-km line upwind of a city of 500,000 population, 125,000 infections would occur, producing 95,000 deaths (5). This number represents far more deaths than predicted in any other scenario of agent release. Moreover, it has been estimated (6) that an aerial spray of Anthrax along a 100-km line under ideal meteorologic conditions could produce 50% lethality rates as far as 160 km downwind. Finally, the United States chose to include Anthrax in the now-defunct offensive biological weapons program of the 1950s, and the Soviet Union and Iraq also admitted to possessing Anthrax weapons. An accident at a Soviet military compound in Sverdlovsk in 1979 resulted in at least 66 deaths due to inhalational Anthrax, an inadvertent demonstration of the viability of this weapon. The epidemiology of this inadvertent release was unusual and unexpected. None of the persons affected were children (7). Whether this is due to differences in susceptibility between children and adults or purely to epidemiologic factors (children may not have been outdoors at the time of release) is unclear.
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).
Anthrax spores lend themselves well to aerosolization and resist environmental degradation. Moreover, these spores, at 2-6 microns in diameter, are the ideal size for impinging on human lower respiratory mucosa, optimizing the chance for infection. It is the manufacture and delivery of Anthrax spores in this particular size range (avoiding clumping in larger particles) that presents a substantial challenge to the terrorist attempting to use the agent as a weapon. The milling process imparts a static charge to small Anthrax particles, making them more difficult to work with and, perhaps, enabling them to bind to soil particles (11). This, in part, may account for the relatively low secondary aerosolization potential of Anthrax, as released spores bind to soil, now clumping in particles substantially in excess of 6 microns. This clumping tendency, together with a high estimated ID50 of 8,000-10,000 spores (this is the dose necessary for humans to contract Anthrax) may help explain the rarity of human Anthrax in most of the Western world, even in areas of high soil contamination. Other potential bioweapons, such as Q fever and tularemia, have ID50 values as low as 1 and 10 organisms, respectively.
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.
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.
Dynamic G-375 Wall Mounted Germicidal
Air Cleaner
Traveling UV Bulb
Each particle exposed to UV radiation 15 seconds per pass
Wall mounted unit delivers 375 cfm ----- super quiet
Generates 100,000 microwatts
per square centimeter of coverage
Great Air Cleaner for specific
areas such as mail rooms, reception areas, etc.
Media is low density fiberglass that traps airborne particles through polarization.
Maintenance
merely requires periodic changing of media – probably 2 to 4 months
intervals depending on the application.
Bulb life is approximately 1 year of continuous operation
Call for more information: 1-888-872-5838 or 1-866-276-9958
JOY environmental
3328 Holloman Road
Falls Church, VA 22042