- By Martha Boss
- Dec 01, 2000
The term Indoor Air Quality (IAQ) is somewhat of a misnomer, since all air originates as exterior air. The implication to the term IAQ is that air is changed once being brought indoors. The history of these changes provides some clues as to our current IAQ problems.
Originally IAQ was determined by the quality of the fire inside a cave and the air movement within a cave. Until the advent of ducted heating systems, nothing had really changed. The source of heat was interior to a space and provided heat to that space.
The sources of moisture and available food may make ductworks hospitable locations for the vegetation of mold/fungi spores.
With the addition of fans, blower housings and ductwork, air was carried back and forth between living spaces. In some cases, plenums were used instead of ductwork. However, prior to the advent of central air conditioning, ductwork carried only exterior air and air treated so as to be heated. This air stream may have been mixed in certain proportions to approximate cooling events (cool exterior air mixed with heated duct air), still cooling as in central air conditioning systems was not occurring.
Air conditioning systems
Air conditioning systems function by taking the air stream and alternately condensing and expanding the air volume. This phenomenon is parallel to the reverse occurrence within the air conditioning unit itself. As the coolant mix takes heat from ducted room air, the coolant mix heats and expands and the ducted air cools and compresses. The cool ducted room air is then sent to living spaces and absorbs heat from the room and room occupants.
The coolant mix is piped to cooling towers or exterior fan units. In these cooled atmospheres the coolant mix releases heat to the cooling tower/fan unit atmosphere -- thus the coolant becomes compressed and is ready for recirculation.
Ductwork - heat exchange and mold
If the ductwork is alternately used to carry heated and then cooled air, the same condensation phenomenon occurs within the ductwork. When the heated air is cooled, moisture is released within the duct work interior. Bringing cool make-up air into a heated duct system can have similar effects.
If the ductwork has a liner, the liner can become wetted through the condensation event. Fiberglass liners can become wetted and through successive use, vents also may loft. This lofting may provide areas where both entrained airstream particulate and moisture can accumulate.
The sources of moisture and available food may make ductworks hospitable locations for the vegetation of mold/fungi spores. Vegetation is the process whereby the mold/fungi spores begin growing as mulicellular structures. The mulicellular structures are termed colony-forming units and ultimately can bear new spores. Once this process occurs in ductwork, additional spores enter the ductwork air stream and can then further populate other duct areas or hospitable locations within the rooms serviced by the ductwork. This process, whereby additional growth and dissemination of spores occurs, will amplify the number of colony forming units and is termed amplification.
Spores may or may not remain viable in the air streams. Even the non-viable spores may cause sensitization reactions in some individuals. The viable spores, however, are the biological structures that amplify risk. This risk can be quantified in terms of colony forming units detected in the air stream, and various air-sampling devices are available to provide information as the number of colony forming units/meter cubed. All ultimately rely on microscopy (for viable and non-viable spores and vegetative pieces) and/or incubation on agar strips. The agar can be laced with various nutrients to screen out certain biologicals. This screening may be required to eliminate overgrowth of aerobic bacteria that would interfere with the mold/fungi cultures.
How much is too much?
The quantitation of biological contamination is a very difficult endeavor. The method of spore collection and the analytical routine both play a part in determining the strength or quantitation numbers. This disparity in numbering events is one reason biological risk numbers akin to the Permissible Exposure Limits (PELs) have not been accomplished to date.
CDC's investigation suggests that one of the causes of infant pulmonary hemorrhage may be toxins from the indoor mold in the infants' environment.
In 1994, Review of Quantitative Standards and Guidelines for Fungi in Indoor Air was published to detail the various quantitative standards used internationally. This work was supported by a cooperative agreement with the U.S. Environmental Protection Agency (EPA) (Award #CR 822641-01-0) and by a training grant in Environmental Health Sciences (Grant #2 T³2 ES07155; Program Director Armen R. Tashjian) through the National Institute of Environmental Health Sciences. The publishing authors were Carol Y. Rao and Harriet A. Burge, Harvard School of Public Health, Department of Environmental Health, Boston, Mass., and John C.S. Chang, EPA - Air Pollution Prevention and Control Division, National Risk Management Research Laboratory, Chapel Hill, N.C. Lack of funding has since resulted in lack of further quantitation studies by these researchers. This review stated that only one city, New York, had developed quantitation numbers. The New York City Department of Health developed these numbers as guidelines
on assessment and remediation of Stachybotrys atra in indoor environments based on a 1993 panel discussion. The concern for Stachyobotrus atra is reflected in the following excerpt from the Centers for Disease Control and Prevention's pamphlet, Important Facts about: Pulmonary Hemorrhage (September 1996):
EPA and CDC believe it is important to recognize the symptoms of pulmonary hemorrhage and to avoid exposing infants to indoor molds. CDC would also like to continue the investigation and identify other possible cases. While we do not want to create undue alarm or misstate the possible relationship between infant pulmonary hemorrhage and Stachybotrys atra, public awareness of the symptoms and causes of pulmonary hemorrhage could save lives.
The following key points are adapted from the CDC brochure Important Facts about Pulmonary Hemorrhage and the January 17, 1997 issue of CDC's Morbidity and Mortality Weekly Report:
Pulmonary hemorrhage is bleeding in the lungs. Symptoms include coughing up blood and nosebleed. If you notice these symptoms in your infant, get medical attention immediately. It can be fatal in infants under one year of age.
While research continues about this rare but deadly disease, CDC's investigation suggests that one of the causes of infant pulmonary hemorrhage may be toxins from the indoor mold in the infants' environment. These toxins may irritate the lining of the infant's lungs and weaken developing blood vessels, eventually leading to pulmonary bleeding. In addition, CDC indicates that exposure to tobacco smoke in addition to this indoor mold may increase an infant's risk of pulmonary hemorrhage.
The mold suspected to be associated with pulmonary hemorrhage is Stachybotrys atra. Stachybotrys is black or green-black and has a slimy appearance. This mold grows primarily on materials such as wood and wood based products, paper or other cellulose products which have become and remain wet. It is not typically found in dry or humid locations or on bread, shower tiles, plastic, vinyl, concrete or ceramics.
For these reasons, the number indicative of contamination, according to New York City, is one colony-forming unit per meter cubed of Stachyobotrus atra.
On the other end of the spectrum, thousands of colony forming units of other mold types may be acceptable and are common in exterior environments. The current guidelines range somewhere between one and 500 colony forming units per meter cubed for most mold/fungi, with a level of 200 colony forming units per meter cubed being the limit of acceptability for molds such as Aspergillus niger. However, levels higher than this may be acceptable when exterior air has higher levels during events such as Fall vegetation rotting. This limit is not applicable to immune compromised or sensitized populations.
So what's the mystery?
The mystery -- as we consider our Heating Ventilation and Air Conditioning Systems -- may center on questions such as: is that black dust we see around our supply vents soot, Aspergillus niger, some other mold, dirt/soil particulate from outside or recirculated dirt from failed filter banks?
Such questions may not be easily answered. Room and building occupants may suffer needlessly if one or the other causation is assumed when, in fact, the IAQ problems originate from other causes. A common example is to assume that very black particulate seemingly deposited in circular patterns around supply vents is soot. Often this pattern is associated with Aspergillus and thus mold growth should always be considered in these cases.
Overgrowth of mold colonies in attic locations may look like ooze running from the attic area. This ooze is actually dead mold and decaying vegatative structures. Thus, ooze instead of particulate may be the indication of mold problems. These areas may not yield viable molds if sampled directly, and a very real biological problem will be missed.
Sampling, either via contact or air sampling devices -- where airborne viable spores are collected, yields the crop of mold or fungi when incubated. Both the morphology and the number of the mold or fungi colony forming units will be taken into consideration.
In trying to eliminate these problems, building owners may try duct steam cleaning, filter removal and vacuuming. All of these methods, if used incorrectly, can result in further potentiating the amplification of molds.
Keep asking questions
When IAQ problems develop, keep asking questions. The old adage, "If it looks like a duck and walks like a duck -- it is a duck," is true. If you think you have IAQ problems, you probably do. However, identifying them may not be simple.
Be sure to consider how your heating system and cooling system is cycling. Ask if you have the potential for trouble as hot and cool air are exchanged. If so, investigate whether mold growth is occurring in ductwork, filtration units or on room surfaces. At the same time, investigate the other IAQ parameters such as volatile chemicals, air movement and humidification and dispersal of particulates (heavy metals, asbestos, radon-laced soils). Try not to consider too limited a scenario or you may miss the cause of the IAQ problem and thus incorrectly diagnose a cure.
| Avoiding Stachyobotrus
Fix all leaks and eliminate water sources associated with the mold growth. Clean hard surfaces with a solution of bleach and water (11/2 cups of bleach per gallon of water); make sure to ventilate the area when using chlorine bleach (note: do not add detergents which contain ammonia to the solution of bleach and water - toxic fumes could result). Some experts suggest that persons performing the cleanup wear filter masks and gloves to avoid contact with the mold. Let the bleach and water mixture sit for 15 minutes and then dry the area thoroughly. Porous materials that are wet and cannot be thoroughly cleaned and dried should be discarded, as they
can remain a source of mold growth.
Martha Boss, CIH, CSP, is Risk Management Group Leader at URS in Omaha, Neb. She can be reached via e-mail at firstname.lastname@example.org.
This article originally appeared in the 12/01/2000 issue of Environmental Protection.