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Air Cleaners and Other Appliances To Keep Air Clean | Stemphylium species

Air Cleaners and Other Appliances For Keeping Air Clean

By Dr. Harriet Burge

Although it is entirely possible to design and construct buildings that provide clean air, many old buildings were not designed with clean air in mind, and many new buildings are either designed without consideration of air quality, or are constructed in ways that allow the intrusion of water, pests, and other air pollutant sources.

Because of increasing concerns about mold and other air quality concerns, many appliances are now on the market that claim to provide clean air, even in situations where sources are present. The question is do they work, and if so, how well?

In the first place, no amount of air cleaning is going to render a leaky moldy building acceptable for occupancy. The only solution to continuing water problems is to find the cause, fix it, and remove all existing mold growth. Given that water leaks have been repaired, then it is possible that free-standing appliances could prevent some mold growth (dehumidifiers), or remove residual spores as well as spores that might enter on peoples' clothes and from the outdoors (air cleaners).

Console dehumidifiers actually do work to lower humidity and may prevent condensation that might lead to mold growth. I would recommend dehumidifiers for anyone who does not have a bathroom or kitchen fan to remove vaporized water from cooking or bathing. I would also use a dehumidifier in any below-grade basement space. There are dehumidifiers on the market that can reduce humidity in an entire 1,000 square foot basement to below 40% and keep it there (e.g., the Santa Fe Rx sold by the Therma-Stor). With this kind of dehumidification, a basement will not be damp and moldy unless, of course, there is actual water intrusion.

Air cleaners present a more complex question. First, appliances that "ozonate" or "ionize" the air without actually capturing particles inside the units cannot be recommended. There are two general kinds of air cleaners that do capture particles from the air that passes through: fan driven filtration devices, and electrostatic precipitators which may or may not be fan driven.

Filtration devices use fans to force air through filters onto which airborne particles impact, thus being removed from the air stream. The efficiency of these devices depends on the particle collection efficiency of the filter (which is near 100% for the HEPA units) and on the rate at which air passes through the unit. The actual steady-state concentration of particles in the space during air cleaner operation also depends on the number and strengths of sources in the space. No air cleaner will keep all the spores out of the air in a room with the walls covered with mold. Nor will such a cleaner remove moldy odors. On the other hand, a high speed fan driven unit with a HEPA filter will reduce particle levels in a room with little or no mold to near zero very quickly, and will maintain relatively low levels providing the unit operates continuously and is properly maintained.

The principle problem with fan-driven air cleaners is the noise produced by the fan. Unfortunately, the better the filter, generally the more powerful the fan needs to be, and the more noise is produced. There is good data available documenting that people turn off air cleaners because of this noise, even in occupational spaces where the airborne particles are clearly hazardous (e.g., radioactive). No air cleaner will work if it is not turned on!

A relatively new air cleaner on the market today uses electrostatic precipitation to capture charged particles from air that is moved past the precipitating plates by a so-called "ionic breeze". Actually, the physics of the ionic breeze air movement has been known for more than 100 years. The corona discharge that charges particles so that they are attracted to the precipitating plates also ionizes the air, and the air ions also tend to move toward the plates. The amount of air movement generated by such a process depends on the voltage applied to create the corona discharge. Currently, available models move between 1.5 and 2 m3/minute. This is not as much as a high-speed fan will move, and it takes generally about 30 minutes for particles in an average size room to reach less than 1% of original concentrations. On the other hand, the units are silent, use little electricity, and do remove particles from the air.

In summary, fix water leaks and remove mold. Use dehumidifiers to limit condensation. For very sensitive people who can stand the noise, fan-driven air cleaners may be helpful. For those who do not need the fast cleaning provided by the fan-driven units, the silent Ionic Breeze sold by The Sharper Image can be used to reduce exposure to residual mold spores or those that seep in through cracks and on clothing.

The reader is strongly cautioned that none of these appliances substitute for good investigation and appropriate remediation of conditions allowing mold growth and removal of the mold itself.


Fungi of the Month VI: Stemphylium species

By Dr. Srivandana Kilambi

The genus Stemphylium, a dematiaceous (pigmented or colored) filamentous fungus, was first described in 1833 by Wallroth. To the naked eye colonies appear to be grey, brown, olivaceous brown or black in color and velvety or cottony in texture. Under the microscope the conidia (spores of the fungus) are single celled, pale to mid brown in color, both rough and smooth walled, oblong or sub spherical rounded at the tips with transverse and vertical septations and thickened scars at the base. Conidiophores (the spore producing structures) are identified by the presence of many vesicular swellings. The spores are dry and wind disseminated.

Pleospora is the sexual state of this genus (producing ascospores). Other synonyms include Epochniella, Fusicladiopsis, Soreymatosporium, Thyrodochium and Thyrospora. Approximately 20 species of Stemphylium are known.

Stemphylium is a ubiquitous fungus found mostly growing in outdoor environments. Indoors it is mostly found in dust as a part of the normal flux of outdoor particles. It is frequently isolated from soil, wood, paper, decaying vegetation, and air.

Stemphylium is generally considered to be both saprophytic (lives on dead organic matter) and pathogenic on plants. Studies related to the incidence of fungal spores at homes of allergic patients in an agricultural community, in association with local crops in California, showed a prevalence of Stemphylium spores along with Alternaria and Macrosporium during asparagus and strawberry harvesting time. From an agricultural point of view, Stemphylium acts as a leaf pathogen. Some species of Stemphylium are found to cause purple leaf blotch of leeks, leaf blight of garlic and a new disease in barley. In Oran Ankara, Turkey, the fungus was isolated from the plasters (inner surfaces) of prefabricated houses.

Stemphylium spores are distinctive and readily identifiable on both spore traps and tape lifts (direct examination), although young spores or spore fragments may be confused with other pigmented spores such as Ulocladium, Alternaria or Pithomyces.


This article was originally published on November 2004.