THE FUNGAL INFECTANT OF OUR AIR:
When I first got into this business of air conditioning, there were very few cases of this fungal contamination that were worth a lot of effort and/or eradication procedures. But today, it is a major problem. The more efficient the cooling systems, the tighter the homes, the more we get away from infiltrating 20% fresh air into the system, and the more we become dependent on air conditioned surroundings at home, at work and even at play, the greater becomes the problem. It must be dealt with or it will take over your cooling system and make it inoperative sooner or later.
Functionally, it restricts the air flow by clogging the cooling coils and blower blades. That causes the system to run more poorly, more costly and colder in the coil and ducts ( resulting in larger maintenance costs and compressor failures). This compounds its growth and the problem "snow balls". It loves this and grows faster. I don't yet know what will be the effect on our health.
I HAVE NOTICED SOME SIMILARITIES IN THE PLACES IT GROWS BEST:
IS THERE A TREATMENT PROCEDURE TO GET RID OF IT?
No! Not really. Not at this time. Nothing that is cost effective.
For those intently interested in more information on this fungal infestation I present the following article published by the 7th International Conference of Indoor Air Quality and Climate (INDOOR AIR '96) sent to me by Mr. Chin S. Yang. Ph.D. with P & K Microbiology Services, Inc.
Chin S. Yang, Ph.D.
P & K Microbiology Services, Inc., 1950 Old Cuthbert Road Unit L, Cherry Hill, New Jersey, 08034 USA
ABSTRACT
Nearly one thousand and two hundred bulk samples of fiber-glass air-duct liner (FGL) collected in 1994 & 1995 from the heating, ventilating, and air-conditioning (HVAC) system throughout the United States were analyzed for fungal contents. Occasionally, direct mounting and microscopic examination of FGL's were conducted. Because FGL is porous and often traps fiber and particles, including fungal spores, the recovery of fungi from FGL is not necessarily an indication of fungal colonization. The following criteria were used to dertermine if an FGL sample is colonized by fungi. They are: (1) fungal concentrations higher than 100,000 CFU/g, (2) no more than two dominant fungi detected, and (3) the presence of fungal hyphae and spores in FGL samples by direct microscopic examination.
Approximately 50% of the samples evaluated were considered to have fungal growth and colonization. Species of Cladosporium and Penicillium were the most frequently encountered colonizers. These two genera of fungi were often recovered from FGL samples taken from locations with high relative humidity, such as air ducts downstream from the coils and the blower, or buildings in humid geographical areas (such as Florida and Texas). FGL samples taken from locations where liquid water is often present, such as at cooling coils or drain pans, were dominated by high water activity fungi, such as Acremonium spp., Aureobasidium pullulans, Exophialaspp., Paecilomyes marquandii, Phoma spp., Rhodotorula spp., and yeasts.
Because the samples were collected from buildings with know indoor air quality complaints, the percentage of fungal colonization in FGL's may be biased. However, it is important to note that fungal colonization of FGL in the HVAC system can not be ignored.
INTRODUCTION
Fungal contamination in buildings and its impact on indoor air quality (IAQ) are well documented (1, 2, 3, 4). A recent review from the U.S. Public Health Service, Division of Federal Occupational Health, indicated that 1/3 of indoor air quality problems may be microbe related (5). There is also data from the State of Minnesota suggesting that microbial contamination is the primary IAQ concern in approximately 29% of the more than 150 buildings studied (6).
Fiber-glass liners (FGL) are commonly used for acoustical and thermal insulation inside the air handler and its associated air ducts. It is a very useful material for the described purposes. However, Morey and Williams (7, 8) suggested that fungal growth and amplification were likely to occur in soft, porous insulation materials. Fibrous glass insulation liners, were reported to be the primary source (92%) of microbial contamination in the Minnesota IAQ studies (6).
Since the mid-1980's, numerous FGL samples, taken in buildings throughout the U.S. and analyzed by the P&K Microbiology Services, Inc., were found to yield high fungal levels. They were often in pure growth, and were observed to have fungal growth and colonization. Soiled FGL's were the most common sources of fungal colonization. Statistics collected in 1994 & 1995 suggested that approximtely 50% of FGL taken for IAQ studies and examined by our laboratory were colonized by fungi. Direct microscopic examination was also used to reveal fungal hyphae colonizing glass fibers of FGL. Furthermore, insect parts, pollens, trichome (plant hairs), decayed leaves, and even dust mites have been seen in FGL samples. These organics are excellent nutrients for fungal growth. This article represents data collected in 1994 through 1995.
MATERIALS AND METHODS
Bulk FGL samples were collected by industrial hygienists conducting indoor air quality (IAQ) studies in the continental United States. A typical sample was 25 cm² (5 cm X 5 cm) approximately 1 cm deep section taken from interior FGL insulation of selected air handlers and air ducts. It was cut with a sharp razor blade or knife and placed in a clean plastic bag. Express shipping couriers were usually used to deliver the samples to the laboratory.
Upon receipt in the laboratory, a 0.10 to 0.25 gram sub-sample, taken from the air-stream side of the sample, was weighed, suspended in sterile distilled water, vortexed for 30 seconds, diluted serially, and inoculated onto 2% malt extract agar (DIFCO Laboratories, Detroit, MI) plates. All samples were incabated at 25°C and characterized in ten days. The characterization included enumeration of fungal colonies and identification of all fungi. Fungal colonies are identified to genus or to species using keys and descriptions in several reference books (9, 10, 11, 12). Fungal concentration in the sample was calculated and presented in colony forming units per gram (CFU/g).
Some samples were also examined directly under a stereo-microscope and a compound microscope. Glass fibers were removed directly with a pair of forceps or with sticky tape, mounted with biological dyes, and examined under a compound microscope at 100, 200, or 400X magnifications. The two biological dyes used were cotton blue in lactic acid and 0.1% phloxine in alcohol, glycerin, and distilled water (13, 14). In addition to fungal characterization, various particles and fibers (other than glass fibers) were identified and noted. Close attention was paid to fibers and dust particles of organics, which may become a nutrient source for fungal growth and colonization.
RESULTS
A total of 1,194 bulk FGL samples were analyzed for fungal contents. 578 of the 1,194 samples (48.4%) were determined to have fungal colonization. The determining criteria were: (1) fungal concentrations higher than 100,000 CFU/g, (2) no more than two dominant fungi detected, and (3) the presence of fungal hyphae and spores in FGL samples by direct microscopic examination. The majority of the samples with fungal colonization yielded concentrations greater than 1,000,000 CFU/g, some as high as 10,000,000 CFU/g. Fungal concentrations, however, may not directly reflect the extent of colonization. Higher fungal concentrations were likely to be related to the availability of moisture for active fungal growth during the cooling season.
Two distinct fungal populations were observed to colonize FGL. The primary group of fungi were the species of Cladosporium, primarily C. cladosporioides, C. herbarum and C. sphaerospermum, followed by Penicillium species. Various species of Penicillium are known to grow at a moderately high water activity between 0.90 and 0.85 (15, 16, 17). The second group of fungi included Acremonium spp. (slimy-spored), Aureobasidium pullulans, Exophiala spp., Paecilomyces marquandii, Phoma spp., Rhodotorula spp., Sporobolomyces spp., and yeasts. Fusarium spp. were occasionally detected. Because samples were taken by outside industrial hygienists, exact sample locations within the HVAC system were not known. It was not known whether the FGL samples were exposed to high relative humidity or to frequent wetting by condensate water. Samples with Cladosporium and Penicillium colonization were believed to be collected from areas of consistently high relative humidity. Many fungi in the second group are known to grow at high water activity (Aw > 0.90-0.95) or moist/wet conditions (17, 18, 19, 20). The samples were suspected to be taken from areas where frequent wetting of FGL was likely to occur. These areas included drain pans and cooling coils.
Approximately 5% of the total samples were examined by direct optical microscopy. Fungal hyphae and spores were visible on glass fibers removed from samples that were considered to have fungal colonization. Cladosporium, as in the culture analysis, was the dominant fungus identified. Penicillium conidiophores and spores and yeast cells were also occasionally observed.
[NOTE: Color fonts and underlining added by James' A/C Co. for emphasis]
Dirt and dust in the FGL samples, upon microscopic examination, contained a variety of identifiable fibers and particles. In a few samples, taken from buildings in Florida and Texas, skeletons of dust mites mixed with fungal mycelia of Cladosporium were observed in the microscopic preparations. In addition to fungal spores, pollen particles, cellulose fibers, synthetic fibers, plant hairs (trichome), decayed leaves, insect parts, and organic matter were often detected. Cellulose fibers and synthetic fibers probably come from indoor sources. Pollen particles, trichome, decayed leaves, and insect parts most likely originate outdoors (14). Many of these were organics and could be nutrients for fungal growth and colonization. The presence of pollen particles, trichome, decayed leaves, and insect parts strongly suggests that the filtration system used in the HVAC was insufficient to remove them from the incoming airstream.
DISCUSSION
The fungi identified from these samples are known to be able to grow at relatively low temperature (17, 18). The operating temperature of cooling coils in the U.S. is usually designed for 11-18°C (or 52-65°F). Newer designs are often operated at a higher temperature for energy conservation. Fungal colonization of FGL was frequently observed near cooling coils and within 3 meters downstream of the cooling coils (6). Temperatures, within these areas, were expected to be near or slightly higher than the operating temperature. High relative humidity, just downstream of the cooling coils, helped promote fungal growth. Fungi that are able to grow at relatively low temperature are expected to grow well near the cooling coils.
Water and moisture play an inportant role in fungal growth and colonization. Fungi, including many commonly found indoors, are known to grow at a wide range of water activity (15, 16, 17). Exophiala species, Rhodotorula, Fusarium, and yeasts are indicator fungi of a high water activity (Aw >0.90-0.95)(17). In addition, Acremonium spp., Aureobasidium pullulans, Paecilomyces marquandii, and Phoma sp., were reported to be contaminants in water from humidifiers (19). This agrees with our assessment that FGL's in areas of the HVAC system, subjected to frequent wetting, support growth and colonization of fungi of high water activity. Cladosporium and Penicillium appeared to grow better in areas where there was high relative humidity but not wetting.
A substantial portion (48.4%) of the samples examined strongly indicated the occurrence of fungal colonization, particularly those that were soiled and used in high relative humidity and wet conditions. It is recommended that FGL should be used in such a way that dusts and dirt are not trapped in the porous material so that fungal colonization cannot occur. FGL should also not be used in areas of the HVAC system where frequent wetting may occur. Exterior insulation is one possible solution. Ductwork can be quiet and energy efficient without relying on interior fibrous glass liners. Some U.S. manufacturers of air handling equipment have sealed interior fibrous glass liners with smooth plastic or galvanized sheet metal. This is likely to protect the insulation material from becoming soiled and colonized by fungi. Flex-duct, which is insulated with fibrous glass, has a smooth interior plastic liner. Flex-duct, has been used for many years without significant concerns of fungal contamination.
The evaluated FGL samples were taken for IAQ evaluations and from buildings with known IAQ complaints. Therefore, the percentage of fungal colonization in FGL's may be biased. It is nevertheless important to note that the relationship between IAQ and fungal colonization of FGL's in the HVAC system can not be ignored or overlooked (7, 8).
FGL is a very useful material for acoustical and thermal insulation and has been widely used in the U.S. for interior insulation of the HVAC system. A number of organic fibers and dust particles were identified from deposits found on FGL. The presence of these fiber and dust deposits is indicative of a poor filtration system which allows for fungi to grow and thrive. Upgrading of filtration efficiency is likely to reduce accumulation of organic fibers and dusts, and hence reduce the possibility of heavy fungal colonization.
A new industry of air duct cleaners has been firmly established over the last few years in the U.S.A. Biocides (chlorine-releasing chemicals) and sealants containing antifungal chemicals (such as zinc oxide and borates, and antimony trioxide and decabromodiphenyl oxide) designed to combat fungal colonization in the HVAC system have been registered with the U.S. Environmental Protection Agency for use in treating and coating FGL. FGL coated with anti-fungal compounds has also been marketed in the U.S.A. It is, however, prudent for the manufacturers and users of FGL to re-engineer the material to be suitable for use in the HVAC system.
REFERENCES
Also see lots of information from the U.S. EPA, Office of Air and Radiation.
