Figure 1. NAFA reports that while HEPA filters are rated by using a challenge of 0.3 micrometers, they are actually much more effective at even lower particle sizes.


The H1N1 “swine flu” virus has made headlines during its second pass through the United States’ population - including, finally and ironically, an American pig. Understanding transmission methods for H1N1 and influenza in general, and knowing which ventilation or filtration countermeasures could be useful, may spell the difference in the health of dozens or even hundreds of people in a facility during cold and flu season.

Let’s get one thing straight right off the bat: You cannot contract the H1N1 virus - aka, “swine flu” - by eating pork or pork products. In terms of human health, pigs are not the problem. In fact, not until last month did the USDA confirm the first-ever case of a U.S. pig catching the virus, that at the Minnesota State Fair where the local Pioneer Press reported that a few 4-H members also became ill. (So as far as we know, pigs may be referring to this disease amongst themselves as “Gangly Teenager Flu.”)

Nevertheless, as National Air Filtration Association (NAFA) president Bill Veeck says, even though “its projected impact and spread has been diminished from earlier announcements of a pandemic, it is still a serious illness and one that can cause death.”

What are organizations like the EPA, ASHRAE, and NAFA saying and doing about this twist to the usual cold and flu season? How are filtration manufacturers responding now that the disease’s fall wave is underway? Let’s have a look.

Fight the Flu with a Web

The EPA is currently hosting slides from a worthwhile presentation on the virus’ transmission and HVAC strategies, made by Steven Welty, CAFS, CIE, LEED® AP of Green Clean Air (Reston, VA) at the agency’s June meeting of the Federal Interagency Committee for IAQ. The full materials await at www.epa.gov/iaq/ciaq/influenza_presentation.pdf. Here are a few elements of interest that caught my eye.

Handwashing doesn’t fix everything. “No matter how sterile your hands are, you’ll still be fully exposed to airborne Influenza viruses entering and depositing into your lungs to cause disease.”

Location, location, location. Infectious droplet nuclei can circulate throughout buidings via HVAC systems, with the help of pressure differences between areas of the building, or via unsafe proximity of bathroom exhaust vents to fresh air vents.

Low absolute humidity is the enemy. “Viruses evaporate faster in low absolute humidity levels, thus creating more droplet nuclei,” and the condition also “allows droplet nuclei to stay airborne longer, as droplets do not absorb water weight which would cause them to fall to the ground.”

Your arsenal. Five weapons for killing or capturing and sterilizing the virus are high-MERV and/or HEPA filters, germicidal UV lights, magnetized air media filtration, cold plasma bipolar ionization, and photocatalytic oxidation.

Drop the exhaust. Due to toilet water aerosolization of viruses, bathroom ceiling exhaust fans can pull virions up into the breathing zone. Bathroom exhausts located a foot or less from the floor would increase health & safety by pulling them down and out.

Again, the presentation at that URL includes smuch more background, information, illustrations, and conclusions. I recommend it for personal general knowledge as well as professional enlightenment.

As For ASHRAE ...

The Society has published its Airborne Infectious Diseases Position Document Committee. You can find it at www.ashrae.org/aboutus/page/335. In a related release, ASHRAE president Gordon Holness said, “While the long-standing public health view is that influenza transmission occurs through direct contact or large droplets, newer data suggests it also occurs through the airborne route, meaning HVACR systems may contribute far more to transmission of the disease and, potentially, to reduction of that same transmission risk.”

The position paper examines the impact of ventilation on such diseases in general, issues associated with the flu, and what control strategies are available for implementation. Beyond the “arsenal” mentioned it above, it also mentions laminar flow and related tactics as appropriate for some medical and other applications.

It also explores the respective advantages of various types of ultraviolet (UV) strategies: “installation into ventilation ducts, irradiation of the upper zones of occupied spaces, and in-room irradiation after one occupant and before the next.”

Engineers might find particular reference value in the tables at the end of the paper. They detail diseases and related manifestations/at-risk populations (divided by whether a disease is transmitted by droplet and airborne transmission or not). A third table provides a quick cross-reference between occupancy types, HVAC strategies pertinent for each of those types, and research priority for each.

NAFA Knowledge

At this point, I’d like to quote NAFA president Veeck, whose input helps clarify the picture regarding specific types of filter media and their efficacy in this particular context.

“We at NAFA are currently writing a Position Paper on Airborne Infectious Diseases – not to compete with the ASHRAE paper by the same name, but to compliment issues either ignored or presented incorrectly, with emphasis on air filtration for the removal of particles from the air, including virally infectious particles.
“While most people do not believe that High Efficiency Particulate Air (HEPA) filters capture very small viral particles because they are below the filter test challenge of 0.3 micrometers, the air filtration industry and health care professionals know that HEPA filters do capture viruses and have been using them in healthcare facilities and equipment such as biological safety cabinets for decades. It is true that HEPA filters are rated by using a challenge of 0.3 micrometers; HEPA filters are much more effective at even lower particle sizes (Figure 1).

“Even filters of lower minimum efficiency reporting values (MERV) capture viral particles because of the filtration principle of diffusion. In 2003, NAFA was part of a study done by the EPA that showed several different air filters’ abilities to remove viral particles in one pass. For example, using an MS2 viral phage dispersed as a micrometer-sized polydispersed aerosol, a clean MERV 6 filter (typical filter found in commercial and residential applications) had an efficiency of 25%, and when loaded with dust, an 83% efficiency.

“Influenza is spread by several means, and the respiratory route is but one. We do know that air that contains more particles provides an opportunistic environment for the spread of viral particles by the respiratory route. We also know that particles and viruses can be removed from an airstream in one pass with higher levels of air filtration. Therefore, air filtration is one good method of helping prevent the spread of viruses in the environment.”

Review NAFA’s collection of info and related links at www.nafahq.org.

Manufacturing Response

Companies specializing in filtration are predictably seeing an increase in inquiries. In addition, one particular product segment that has seen an uptick in interest ever since the spring’s first H1N1 wave is UVC.

Meredith Stines is the president/CEO of American Ultraviolet (www.americanultraviolet.com). Recalling the different ways one can attack this problem with UVC mentioned in the ASHRAE position paper, his company’s TB series and Corner mount series fixtures are designed for upper room sterilization, while its CC and DC series are designed for installation on cooling coils and inside of air ducts to eliminate airborne particles.

Stines reports that “Our customers - which are nursing homes, hospitals, other health care facilities, and schools - are concerned over the outbreak and uncertain which way to go because of all the different opinions that have been presented.”

In response to what Stines terms general concern about product availability should the situation worsen, American Ultraviolet has increased its inventories to prepare for a maximum-demand scenario. Recognizing that an upswing in interest today translates to an upswing in web traffic, the company has also updated its website to provide as much information as it can find to better educate the consumer.

Sanuvox Technologies (www.sanuvox.com) also responded to increased public interest. Sanuvox Technologies manufactures UV air sterilization systems which are installed into the ductwork and designed to sterilize the biological contaminants as they pass through the UV system. Sanuvox also manufactures mobile decontamination units and standalone HEPA filter / UV air sterilization systems designed to destroy biocontaminants while trapping particles down to .3 microns in size.

The manufacuturer has stated that its technology can “destroy the influenza virus, including those that fall into the family of Orthomyxoviridae. These include type A, type B, and type C influenza viruses. The World Health Organization has confirmed that these cases are a never-before-seen version of the H1N1 strain of the influenza type A virus.”

Sanuvox’ in-duct system is designed “to maximize exposure time between the air and the UV germicidal energy.” The company reports that its portable standalone UV air sterilization unit has been tested by McGill University in Montreal, achieving a destruction rate of 90% for tuberculosis while operating in the Montreal Chest Hospital’s sputum induction room.

Steril-Aire’s (www.steril-aire.com) line of high-output UVC Emitters™ is also “designed to destroy microorganisms including flu and other viruses, bacteria and mold,” according to the company’s president and chairman, Robert Scheir, Ph.D. He specifies that these systems are typically installed on the supply side of the system, downstream from the cooling coil and above the drain pan.

In testing performed by RTI International on behalf of the EPA and National Homeland Security Research Center, Steril-Aire’s single-ended UVC Emitters delivered 99% airborne inactivation efficiency on the test virus (MS2 bacteriophage), +99.96% on vegetative form of bacteria, and 96% on spore form of bacteria.

Like the others, Steril-Aire has seen an increase in related business, “particularly in the health care and school sectors,” as well as also being approached as an industry authority for general consumer information.

Scheir also directs readers to the independent series of EPA reports about the aforementioned testing, providing some benchmark data for various UVC devices. Inspect highlights of that study at www.epa.gov/NHSRC/news/news100406a.html.

Parting Tips

Let’s conclude with some flu-fighting tips sent along from Trane. Check for clogged drains and eliminate pooled water. Consider a higher-efficiency filter, but only if your fan system can handle the resistance change. Consider timing filter replacements according to pressure drop, rather than the calendar. Wear cut-resistant gloves when performing filter or damper maintenance. Check exhaust fans in restrooms; especially for small fans, dirt can accumulate and reduce effectiveness.

And remember, it’s not the BBQ plate that will get you - although it might be person coughing or sneezing at the next table over. How does takeout sound? ES