We live in an era when our enemies can spread horrible airborne diseases that have been extinct in the field for decades, and loved ones can give us viruses that cause inevitable death. Nice world, but what can you do? You can sit in a cleanroom and wait for Armageddon or try to live a normal life, taking whatever precautions are available.

The role of hvac systems in spreading potentially harmful microbes is only beginning to be explored, but interest in the subject is high. What is intriguing is the possibility that the delivery systems could even be used to control, and even eliminate, the invisible threats in our homes and offices.

However, the potential for false claims and abusive practices lead the federal Environmental Protection Agency to take direct action last March to discourage the use of unapproved disinfectants, sanitizers, and other types of antimicrobial products during the cleaning of air ducts.

Marcia Mulkey, director of the EPA's Office of Pesticide Programs, issued a letter warning the agency has not determined whether such products are effective in promoting better indoor air quality, or if they pose potential risks to building occupants.

AK Steel's antimicrobial steel is said to reduce the growth of many molds, bacteria and fungi. Photo courtesy of AK Steel.

EPA 'particularly concerned'

According to the letter:

"We are particularly concerned because the agency (EPA) has not assessed the potential exposure and risks to building occupants or applicators from the use of these products in or on any surfaces that are part of hvacr systems in circumstances where the labels do not specifically authorize use in hvacr systems.

"Also, the agency has not assessed whether such products are efficacious when used in hvacr systems. Therefore, users cannot assume that EPA registration of these products reflects any conclusions about their safety or effectiveness in this situation.

"Even in circumstances where labels do list hvacr systems as a possible use, we are concerned that the agency has not received and reviewed adequate data to fully evaluate risks to building occupants or product efficacy in that use pattern.

"An additional source of concern arises because some pesticide products also bear labels which identify the product as hvacr 'cleaners,' which could further increase the likelihood that users incorrectly make pesticidal use of such products or make incorrect assumptions about the status of EPA review, evaluation, and conclusions about them.

"We recognize that it is important to address the labeling of these products, and we intend to work with pesticide registrants to assure that these product labels clearly communicate the uses which EPA has (and has not) authorized. We also expect to assure that appropriate evaluations of risk and effectiveness accompany any authorized uses in these systems."

(For the complete letter, visit the EPA Web site at www. epa.gov/oppad001/hvac.htm. EPA provides an antimicrobial hotline at (703) 308-0127; info_antimicrobial@epa.gov.)

Integrated products

While there are EPA-approved chemicals that can be applied during air duct cleaning that have shown some effectiveness, the industry's attention in the past year has been directed toward antimicrobial materials that are applied before the duct is even installed.

Perhaps the most intriguing substance is the "AgION" antimicrobial that is applied directly to the steel before it is even formed into products. The name AgION comes from the atomic symbol for silver - Ag - and describes the process by which ions from the silver separate, attack and kill microbes as they come into contact with it. The AgION antimicrobial compound is the flagship product of AgION Technologies, a Wakefield, Mass.-based biotechnology company involved in antimicrobial and materials research and development.

The company changed its name from HealthShield Technologies in late 2000 in response to EPA's scheduled plans to challenge trademarks and corporate names that expressed or implied public health claims for antimicrobial products. AgION is registered with EPA as an antimicrobial additive.

Although AgION Technologies does not to make health claims for its product, the company uses this slogan for its antimicrobial: "If this is on it, millions of bacteria aren't." It is assumed that removing millions of bacteria is a good thing.

According to the company, "We are now working with over 250 major corporations such as AK Steel, DuPont and Honeywell in the medical, consumer and industrial areas on a variety of applications for AgION antimicrobial compound - ranging from medical devices to sportswear - to create significant value added product and brand differentiation.

"AgION antimicrobial compound has been successfully and cost-effectively incorporated into fibers and fabrics, molded plastics, plastic films and coatings for metals, with proven effectiveness and safety. And our Upgrade Division can apply it to existing products."

AgION-coated steels can be used to create an array of medical equipment-from exam tables and countertops to equipment casings and instruments. Photo courtesy of AK Steel.


The Food and Drug Administration has recognized the AgION antimicrobial compound as an acceptable additive in all polymers which come in contact with food, and the National Sanitation Foundation has certified the compound for food contact and food zone applications.

A surprising number of recognizable brands now offer products with AgION, usually on an exclusive basis within their markets. Adidas uses it in athletic equipment, footwear, and apparel. Waterpik uses AgION in its personal health care and professional dental products.

In the hvacr industry, Bosch incorporates AgION in its refrigerator inner walls and door linings. Mile High Equipment Co. of Denver, the manufacturer of "Ice-O-Matic" commercial ice making equipment, uses AgION in its Ice Series ice cube-makers.

Honeywell Consumer Products incorporates the antimicrobial compound into the manufacturing process for Honeywell and Duracraft humidifier filters to suppress the surface growth and migration of bacteria, mold, fungus, and algae.

AK Coatings Inc., a subsidiary of AK Steel Corp., says the EPA recently registered the use of its AgION antimicrobial steel compound in hvac systems. With the registration, AK Coatings said it has become the only supplier of coil-coated steels produced with an antimicrobial, antibacterial coating for use in commercial, industrial, and residential heating and cooling systems. The company said its coated steels are more economical than post-fabrication and post-installation antimicrobial paint systems.

Spiral duct-maker Lindab Inc. has formed an exclusive partnership with AK Coatings Inc. to manufacture round, nonresidential ductwork with AgION antimicrobial precoated steel.

Also entering into an agreement with AK Steel is Seal-Tite of Hillsboro, Ohio, known for its low-leakage duct, pipe, and fittings. The company's "Seal-Tite Rx" line is manufactured using galvanized steel pre-coated with an epoxy that includes AgION. The steel is coated under an agreement with AK Steel.

According to Seal-Tite, the antimicrobial agent won't wash out, and lasts as long as the coating is on the steel. The coating is said to provide resistance to fingerprints, watermarks, discoloration, and staining, and even protects against scratches less than 1/4 inch.

The product is designed for trunk duct and fittings, return air products, plenums, filter frames, drain pans, and pipe with a maximum operating temperature of 300 degrees F, company officials said.

How does it work?

According to AK officials, the AgION compound is a long-lasting, inorganic material that contains silver - a safe and natural antimicrobial agent that has proven successful in controlling the growth and spread of a broad range of microorganisms such as bacteria, mold, and mildew.

The compound has two key components working together to suppress the growth of microbes: silver ions, the active agent; and zeolite, which stores the silver ions and releases them.

When moisture is present, the zeolite acts as an ion pump to provide a controlled release of silver ions into the environment in exchange for sodium ions from the environment. As humidity increases, and the environment becomes ideal for bacterial growth and more silver ions are released. There is an upper limit to the release rate, even under very wet conditions.

The company said silver ions appear to have multiple ways of being effective against bacteria, although it said that "the exact mechanisms of action are not fully understood." It suggests three possible ways that it could work:

  • Silver ions are ingested by the microbe and destroy the cell wall of the microbe.

  • Silver interrupts the RNA replication process of the microbe, thereby preventing cell multiplication.

  • Through an oxidation process, silver ions cause cellular respiration to be blocked, effectively choking the microbe.

    For most types of bacteria, the treated surface will be virtually free of microbial contamination within three to four hours. The coating life depends on the application and surface wear.

    The silver zeolite powder is blended into an epoxy resin. The resin is applied to the steel by one of two methods: roll coating, and powder coating, where the resin is separated into a fine powder and is elecrostatically attracted to the steel.

    AgION is not intended as a substitute for good hygiene. Coated products still must be cleaned to ensure the surfaces will be free of destructive microbes.

    Potential downside?

    If AgION is effective against the growth of bacteria, does it present a danger by promoting a resistance to antibiotics? The company says that it "is highly unlikely that AgION promotes resistance."

    According to the company, both organic and inorganic substances are used to control microorganisms. Organic antimicrobials and biocides are carbon- or silicone-based compounds that include triclosan, Neosporin, and oral antibiotic drugs prescribed for an infection. Inorganic antimicrobials include chlorine compounds and elemental antimicrobials such as silver and copper.

    The mechanisms by which these substances control microorganisms are generally very different. Organic substances generally interact with one particular "site" in the organism using a single mechanism. Inorganic antimicrobials often attack organisms through several mechanisms that interact with fasci functions in the cell.

    Resistance occurs when a microorganism develops a mechanism to counteract the mechanism used by the antimicrobial. For example, resistance to penicillin was caused when certain strains of bacteria produced an enzyme that clipped the penicillin molecule in half, rendering it ineffective, AgION officials said.

    The probability of developing resistance to a single mechanism used by an antimicrobial is much higher than that of developing resistance to the multiple mechanisms employed by inorganic antimicrobials. Therefore, it is less likely that an organism will develop resistance to inorganic antimicrobials than to organic ones, according to the company.

    Since inorganic antimicrobials use very different mechanisms than those used by antibiotics, it is very unlikely that any resistance to inorganics will translate to resistance to therapeutic antibiotics, offcials added.