Anti-microbial Effectiveness

Position Statement on Anti-microbial Fabric Ducts:

Some fabric duct suppliers offer their permeable polyester impregnated with a silver salt to yield an "anti-microbial" characteristic. However, it is Fabric Duct Systems’ premise that this “feature” is more of a competitive barrier than an effective measure to eliminate microbial pollutants!

Pre-filter selection and monthly maintenance are more of a contributor to indoor air quality than downstream anti-microbial measures. Filters that are not changed regularly can become a bed for fungal growth, sometimes allowing particles or microorganisms to be distributed within the building. When filters become clogged, the fans use more energy to operate and move less air. If the filters are an inexpensive, low-efficiency type that becomes clogged and then “blows out,” the coils then accumulate dirt, causing another increase in energy consumption.

Secondly, relying on the fabric duct to become a "secondary filter" for microbes, rather than on the primary fan filtration/maintenance, will cause dirt to build up in the fabric ducts and thus become more contaminated with molds. This necessitates more frequent laundering, as well as increasingly inefficient air distribution and resulting higher energy costs. There is no evidence that microorganisms that lodge downstream within the filters or the fabric ducts are inhibited or killed. Antimicrobial materials must come in physical contact with microbes in order to be effective. Unless the microbes are filtered out onto the fabric, the usefulness of an antimicrobial fabric treatment is questionable. There are no DYNAMIC testing methods to evaluate the effectiveness of an antimicrobial finish using an air stream to expose the fabric to the microbes. Existing test methods employ a STATIC procedure where the tested fabric is in long term contact (hours) with the microbe(s).

Thirdly, and most importantly, many microbes are microscopically smaller than the weave of the fabric and will blow right through the open portions of the woven threads! Molecule size is measured in angstroms (1/10,000,000,000 of a meter). Microbes are, in general, 1,000 to 10,000 times smaller than a fine dust particle and thus will pass through the finest particle filters as well as the fabric weave!   

Direct contact is required for an anti-microbial agent to destroy microorganisms. Dust buildup on the inside of a fabric duct tends to further inhibit direct contact.

If an application DEMANDS anti-microbial protection, install high output UV-C lights downstream from the coiling coil. The high output UV-C lamps will also sterilize the coils and/or the humidification pads without using chemicals.

All things considered, Fabric Duct Systems DOES supply an antimicrobial polyester for those specifications demanding it, however, we cannot justify the value added cost or effectiveness of this feature.

Please review the attached articles for particle size comparison and more charts and articles:

Anti-Microbial Laboratories

For more information on anti-microbial textiles, please read the article attached below. It was written by Benjamin D. Tanner, Ph.D. - President, Antimicrobial Test Laboratories, and was originally published in the AATCC Review. It is posted here with written permission from the publisher.