Let’s cut to the chase. The infectious range for anthrax has been estimated at 6,000 to 8,000 spores/cu m of air. This means the hvac system — when properly maintained, given better filtration, increasing the number of air changes, and getting accessories like in-duct UV lighting — can be quite effective at reducing the total number of spores.

The bad news, of course, involves all those hvac systems that are not properly maintained; whose coils are dirty enough to breed and feed an army of anthrax; and whose mechanical rooms are too easily accessible.

“Biological contamination through the hvac is not a good way to kill people, but a great way to scare the pants off ’em,” said Forrest Fencl, president of Steril-Aire (Cerrito, CA), maker of UVC lights. “We’re part of an overall control strategy.”

Contractors need to evaluate some product claims cautiously, especially those stating that they can completely eradicate a contaminant. Other firms are taking steps to provide accurate information.

Bob Baker, chairman and ceo of BBJ Environmental Solutions, Inc. (Tampa, FL), said he has received numerous calls asking if the company’s products are effective against anthrax. “What these people are really asking is, ‘Can I use your products to protect myself against anthrax or some other biological terrorist attack?’ That question is more precise and the answer is complex.

“We know that air-delivery systems are one of the most effective ways to spread these deadly organisms,” he told his sales staff. “Let’s look at a case that has been in the news — the staff member at the publishing building in Boca Raton, Florida.

“It is believed that this man opened an envelope containing anthrax spores while sitting at his desk (spores were found on his computer keyboard). Such spores are very light and opening the envelope no doubt caused some of them to become airborne. He inhaled some of these, which eventually led to infection and death.”

Would application of one of BBJ’s products have protected the man in this case? Frankly, no, said Baker. “If, as we suspect, his exposure was from the airborne spores from the envelope, he still would have become infected and died.”

But keeping coils sanitary — through cleaning and the application of chemicals and/or UV lights — is part of a system-wide approach, which can prevent spores from amplifying in the hvac system.

Bioterrorists could release spores into the outside air intakes or return air duct of a building. This is where filters would hopefully catch many of them — but has the filter been changed recently? Has loading separated the filter from the screen, allowing air to blow past unfiltered? If it’s a bag type, is the bag blown out?

If the spore-contaminated airstream moves through the air handler, additional spores would stick to the moist surfaces of the cooling coil. “If the surfaces are clean and treated with a growth-inhibiting treatment,” said Baker, “the spores would most likely be washed down the drain along with the condensate water and would not be able to germinate.”

UV lights can also be installed just downstream of the cooling coil, said Fencl. However, he cautions that the system needs to be applied properly. Let the manufacturer help.

If spores or a virus introduced in this manner are caught by the filters and not allowed to grow on the coils, “There is a fair chance that not enough spores would remain in the airstream to cause infection,” said Baker.

Filter Upgrades

Most buildings could stand to have their filters upgraded. How-ever, make sure that you don’t create airflow resistance that the mechanical system can’t handle.

“To be effective, this must be an air distribution system that takes outside air in through the filter and pushes this filtered air back out through the leak paths in the building — thus the HEPA system creates a slight positive overpressure in the facility,” states a Camfil Farr (El Segundo, CA) bulletin.

“Such building positive pressure creates a balloon effect that helps keep contaminated air from entering the building. HEPA units that merely cleanse the recirculation air would provide little protection against anthrax-laden air that is sucked into your facility, unless an area is provided with complete positive overpressure protection.”

But a HEPA filter may not be necessary or advisable. Charlie Seyffer, U.S. market manager for Camfil Farr, advised contractors to “Use the highest efficiency filter that will balance with the system. In some cases, an 85% [MERV 14] filter can be just as effective as a 95% hospital-grade filter if you increase the number of air changes.”

According to Camfil Farr, typical commercial buildings with constant-volume systems operate at six to eight air changes per hour; vav systems may operate as low as two to three air changes per hour. “During incidences of infectious control…increasing air changes can reduce the number of infectious airborne contaminants. If the system has a fan ‘on’ switch for constant flow volume, you can increase the number of air changes per hour by moving this switch to on.”

A critical note for service contractors: “Bacteria feeds on other bacteria,” said Seyffer. “If a building becomes infected, the filter must be discarded and handled as hazardous waste.” Wear respirators and gloves when handling potentially contaminated filters; bag and seal them before disposal, and mark the bags as hazardous waste, Seyffer advised.

UV Lights, Cleanliness

UV light manufacturers such as Steril-Aire have long dealt with bacteria in hospital settings. “We know that high-efficiency filters will drop the circulating numbers,” the company said, “but totally depending on filters and a typical air-conveyance system to prevent infection has had its pitfalls.”

“UV light will kill anthrax,” said Fencl. It will also deactivate viruses, he said. “However, the average guy can’t design an infectious disease control system.”

This company is one of many that have been working feverishly to keep up with the public’s demands. “We’re now working with companies to design their mailrooms to isolated areas with outdoor air that can go to negative pressure,” Fencl said. Some mailrooms are looking into lab-type fume hoods under which mail would be opened.

Fencl said that the best point for UV light installation is “in the air system, where all the air can pass by. We recommend downstream of the coil, facing the coil.” Maintenance should be performed annually.

BBJ’s Baker is a strong advocate of strenuous coil cleaning and a strict maintenance program. “If filtration is absent or poorly maintained so there is bypass,” he said, “most or all of the spores would pass the filtration stage. Spores passing through and onto a dirty coil with accumulated organic material on the surfaces might be trapped on those surfaces and not likely to be washed down into the drain.

“Eventually, if conditions allowed, many of the spores would germinate and amplify into a high concentration of live organisms that would eventually produce more spores. As the friction of passing air increased, more and more of the accumulated contamination would erode from the coil surfaces and be carried into the occupied space.”

Do the necessary cleaning, Baker advised. “Do it better than you ever have before.”

Publication date: 10/29/2001