Originally Posted By: gromicko
This post was automatically imported from our archived forum.
THE ENVIRONMENTAL REPORTER
DEC 03/JAN 04
Section 1 Allergens
Section 2 Cooling Coil Drip Pans
Dear NACHI inspectors:
I hope that you are doing well and enjoying the holidays. We are sending the following information in the hope that you may find it helpful, interesting, or useful.
Sensitivity to indoor allergens poses a health problem to large segments of the population and is relevant from early childhood all the way through adulthood. Across the United States the number of people with asthma and allergies has increased dramatically. Asthma is the most common chronic illness among children in the United States, one of the most common chronic illnesses for all ages, and in the last few decades has been increasing in both severity and percentage of the population affected. Asthma occurs as a result of repeated inflammation of the airways related, in part, to exposure to both indoor and outdoor allergens. Sources of these allergens include pets (cats, dogs), pests (dust mites, cockroaches, mice), and mold spores. Children with combined sensitization to dust mite, cockroach and cat allergens have an increased risk of having more severe asthma. Reducing exposure to indoor allergens can help reduce the frequency and severity of asthma attacks in sensitized individuals as well as reduce the chances of developing asthma in susceptible individuals.
Where are these indoor allergens found?
Dust mites are ubiquitous in nature and are found in virtually every household. Mites prefer warm, moist surroundings, and thrive in mattresses and pillows, and in floor dust when humidity is high. Cockroach allergens are widely distributed in homes and schools. About 20% of homes with no evidence of cockroach infestation have significant levels of cockroach allergen in settled dust. The level of cockroach allergen in school dust is of concern because it may constitute an occupational risk to students, teachers and other school workers. Cat allergen is very sticky and can be found in high levels on walls and other surfaces within homes. Those who pet or handle cats or visit households with cats can easily carry cat allergen from home to home, office, school, etc. Carpeting, bedding, and upholstered furniture in homes serve as reservoirs for deposited dog allergen. Cat and dog allergen can remain airborne for long periods of time, in part because these allergens are associated to a significant extent with small particles less than five micrometers in diameter. Fungal (mold) spores, which are a natural part of the outdoor environment, also contain allergens. Some exposure to these spores is normal, but for sensitized people, exposure both indoors and out can lead to symptoms.
Why are allergens labeled as Der p1, Der f1, etc?
All plants and animals are assigned genus and species names by the scientific community. Allergens are named after the first three letters of the genus, followed by the first letter of the species, and finally by a number to separate the first allergen discovered from the second allergen discovered, etc. For example Der p1 designates the first allergen discovered in Dermatophagoides pteronyssinus, which is the scientific name for the European dust mite.
Where are these allergens produced?
Dust mite allergens are proteins that come from the digestive tract of mites and are found at high levels in mite feces. A dust mite fecal pellet is the size of a pollen grain and contains allergens (protein) called Der p1, Der f1 and Mite group 2. Cockroach allergens are produced in the gastrointestinal tract, saliva, feces and body parts of cockroach. As cockroaches die in a dwelling, their decomposing body parts become part of the environmental dust, which contains multiple allergens. One of the major cockroach allergens is Bla g2. The major cat allergen, Fel d1, is produced in cat sebaceous, salivary, and anal glands and is found on cat hair. Dog allergen, Can f1, is found in the dander (skin scales), pelt, hair and saliva, but not in the urine or feces of dogs. Mouse (Mus m1), and rat (Rat n1) allergens are present in the urine of these animals. Mold allergens are probably digestive enzymes present in spores or released from spores as they germinate. Very few of the many thousands of possible mold allergens have been characterized. Alt a1 is an allergen that is present in many Alternaria spores, as well as those of Stemphylium and other related genera. Cla h1 is one of the allergens present in the ubiquitous fungus Cladosporium herbarum. Asp f1 is an allergen produced by the medically important fungus Aspergillus fumigatus that causes infections in severely immunocompromised people.
How do I test for the indoor allergens?
Dust samples for indoor allergens can be collected using a dust cassette or by using a vacuum cleaner. A filter or an 8 square inch bed linen can be placed between the hose and the attachment of a vacuum cleaner to collect the dust. Approximately 150 mg of dust, about a teaspoon, should be collected. The dust sample should be placed in a Ziploc bag and sent to the laboratory for analysis. Indoor allergen analysis, especially dust mite allergen analysis, is time sensitive. Samples should be sent to the laboratory as quickly as possible after sampling. Keep the samples cool (place them in refrigerator until shipping) and ship them using a cold pack or in a cooler to prevent growth of dust mites and deterioration of the allergens.
How are the samples processed in the lab?
It varies somewhat from laboratory to laboratory. We use operating procedures brought to us by Dr. Harriet Burge of the Harvard School of Public Health, and adapted from the protocols that they follow for dust mite, cockroach, cat, mouse, rat, and mold allergens. The analysis is an ELISA methodology that uses monoclonal antibodies. Values are expressed as micrograms or units of allergen per gram of dust.
How do I interpret the results?
A level of 2.0 micrograms of dust mite allergen per gram of dust is the generally recognized threshold for sensitization and symptom development among susceptible individuals. Cat allergens can range from less than 1 microgram to greater than 3,000 micrograms per gram of dust and levels in the range of 1?8 micrograms of Fel d1 per gram of dust is considered to pose a significant risk for sensitization. It has been shown that children who were exposed to the cockroach allergen Bla g2 at a level of 1 unit per gram or higher demonstrated skin sensitivity to and children who were exposed to more than 5 U/g of Bla g2 were sensitized. Sufficient evidence is not yet available for establishing threshold risk levels for dog, mouse, or mold allergens. Detectable levels of dog or mouse allergens may indicate unusual exposure. Mold allergens are ubiquitous, and unusual exposure levels will have to be documented before accurate interpretation will be possible.
Cooling Coil Drip Pans
We have been asked whether people should be concerned about water in cooling coil drip pans and, consequently, thought the following information may be useful.
When humid air passes over chilled cooling coils, water condenses and drips through the coils into a collection pan, from which it continuously drains. Problems with these systems may occur when this water collects and becomes stagnant either on the coils or in the drip pan. When standing water is present, a biofilm will develop. This biofilm is composed of bacteria and fungi that are embedded in a slimy matrix. Other organisms such as amoebae and algae may also occupy this comfortable growth site, feeding off the accumulated organic material.
Because this is a slimy layer, one might think that the organisms are unlikely to ever become airborne. This is not true. Organisms are released into the water, and the drops falling from the cooling coil, or wind from the fans create bubbles, each of which contains some of these organisms. The bubbles actually scavenge particles (including bacteria and spores) so that the concentration in the bubbles is higher than that in the water itself. Once in the air, these bubbles dry down into droplet nuclei and are readily transported downstream into the ventilation system. In addition to these particles, the organisms growing in the biofilms produce volatile organic compounds (odors) that are readily carried with the ventilation air into the occupied space.
Another problem that water in drip pans may cause results from the locally high relative humidity near the drip pan, and the fact that the fast moving air stream may pick up liquid droplets that impact onto downstream surfaces. The combination of high local humidity and deposition of droplets may be enough to allow fungal growth on the surfaces.
What can be done about these problems?
First, all drip pans should drain continuously, and should never contain standing water. This means that the drain must be the lowest point in the drip pan, and be connected to drain plumbing.
Second, systems should be operated such that the coils are continuously washed by water so that biofilms are slow to develop. There is some evidence that germicidal ultraviolet light will reduce the chances of growth on cooling coils.
Third, porous insulation should be avoided close to cooling coils. It should be noted, however, that water droplets will not travel far before evaporating, so that only the first few feet of ventilation system surfaces are at risk of becoming wet.
Fourth, biocides will not fix the problem of non-draining drip pans. Organisms embedded in biofilms are relatively resistant to biocides, and continue to grow and produce odoriferous compounds. Also, biocides are likely to enter the ventilation air and be delivered to occupant breathing zones.
Again, we hope that you are enjoying the holidays and are doing well. We also hope that you found the above useful or interesting and, as always, we welcome any feedback. Please let us know if you have any questions, comments, or suggestions.
With warmest wishes,