By Bob Baker

It sometimes seems that mold growth is all we hear about today. It is a major factor in Indoor Air Quality. This is because it represents a major comfort issue and probably is a threat to our health when excessive. Unfortunately, we do not know how much is "excessive" due to the lack of completed research. As a result, many people tend to panic if there is any level of indoor mold growth.

The result is that there is a lot of discussion and debate. Some of the questions being asked include:

• What kinds of mold are of most concern?
• What about spores and allergies?
• What about VOCs put of during growth?
• What about toxic cell parts?

One of the most frequently asked sets of questions revolve around where, when and why mold grows in the indoors and how can we prevent that growth? The purpose of this article is to discuss those questions and provide some useful information to people who want to minimize mold growth for themselves or others.

Mold (more accurately "fungi" of which mold is only one example) can use almost anything as food. They thrive on a wide variety of surfaces so it is difficult if not impossible to control growth by depriving them of food. One strategy is to chemically alter or protect surfaces so they are less friendly to growth. There are products such as BBJ MicroBiocide that will provide such protection. Our purpose in this article is to look at other factors influencing growth; the primary of which is moisture (water). Water is necessary to almost all mold growth and removing moisture is an often-recommended control strategy. It does not take very much moisture for mold to grow but if the environment can be kept free of excessive moisture (whatever that is) mold is unlikely to be a problem. Unfortunately, that is far from simple.

Sources of water

Water can enter a building when there are leaks in the roof, walls, or windows. Keeping those in good repair will eliminate those sources as long as the building is properly designed. Breaking pipes and floods are more of a challenge. Those are significant events and unless the resulting water is not removed quickly (within 24-48 hours) there is likely to be significant mold growth in places that were wet. These are obvious sources of water and following leak repairs, the building and furnishings should be dried out, cleaned thoroughly, and inspected for any residual mold growth.

More complex is mold growth associated with moisture that condenses out of the air. All air contains moisture. The moisture holding capacity of air is dependent on temperature. Warmer air can hold more moisture and cold air can hold less moisture. As air cools (loses heat) it is able to hold less moisture. Engineers and physicists have constructed a chart called the Psychrometric Chart which graphically illustrates the temperature moisture relationships of air and assists in the design of moisture control systems.

Dewpoint

As air cools, it will reach a temperature at which it begins to give up moisture. This is known as the dewpoint temperature. As an example, if room air at 50% relative humidity (RH) and a temperature of 75 degrees F were suddenly cooled to 55 degrees, it would be at dewpoint and would give up moisture until it lost enough moisture content to be below the dewpoint. This explains why in very cold weather and in a room that has low humidity, you often see moisture condensing on windows. The cold surface of the window removes enough heat from the air immediately adjacent to the glass to lower its temperature to dewpoint.

Mold grows all year

We often associate mold growth with hot, humid conditions that are normal in the southern costal areas or in the summer in other areas of the country. This is because the air under such conditions contains a lot of moisture and it is easier to achieve dewpoint with fairly small temperature changes. For example, if temperature is 90 degrees and RH is 90% dewpoint will be reached when air temperature falls below 87 degrees. Under such conditions condensation of water and associated mold growth is an ever-present possibility.

Under the right conditions, however, mold growth supported by moisture condensing out of the air is just as possible in the coldest climates. Take the example of a building that is at 75 degrees and 20% relative humidity. Under those conditions, the air temperature would have to fall to 32 degrees to reach dewpoint which is a large temperature change. If the temperature outside is below 0, it is very possible that air near a conductive surface such as a window would lose enough heat to reach that temperature and lose moisture. That is the reason we often see mold growing on a windowsill in the winter. Likewise, the same air circulating in an air duct running through an unheated area would be subject to condensation and air leaking into an un-insulated wall cavity could become cold enough for moisture to condense out.

Ironically, mold problems associated with moisture condensation related to extreme temperature differentials are very common in cold climates all year. In such areas good insulation and sealing of buildings is necessary both for energy saving and prevention of mold growth. Even a small leak of frigid air meeting warm inside air can lead to significant growth of mold. The primary mold control strategy in northern areas is building design and construction. This is part of the reason that construction costs in southern areas are generally lower.

HVAC systems provide significant opportunity for mold growth in all climates and at most times of the year. This is because they circulate the room air and are designed to change the psychrometric properties of the air moving through them. As a result, the circulated air is often at dewpoint and considerable moisture is deposited on heat exchange surfaces and elsewhere in the system. Leaks and unconditioned outside air can lead to even more moisture and associated growth. Supplemental strategies to inhibit growth are necessary to assure growth free operation.

Mr. Baker's field of expertise is the control of contamination in air-conditioning and ventilating systems by mold, mildew and bacteria. He writes and speaks frequently about the efficacy, legal risks, and regulatory issues involved in various control strategies. He serves on ASHRAE Technical Committee TC 2.3, TC 2.4, TC 9.8, and Sampling of Airborne Particulate Concentration in Commercial and Residential Buildings GPC 17P. He also serves as a member of ASTM D22.06 (Indoor Air Quality) and is on the Board of Directors of the Indoor Air Quality Association and the Florida Public Health Foundation. Because HVAC applications encompass new uses from an U.S. EPA regulatory standpoint, Mr. Baker works closely with the EPA and industry groups, including serving as the chair of the IAQ committee of the Consumer Specialty Products Association, to help formulate policy in this area.

Bob Baker is Chairman and CEO of BBJ Environmental Solutions, Inc., a company specializing in providing clean air through environmentally responsible products, such as BBJ MicroBiocide , BBJ Micro Coil Clean , "FreshDuct Odor Eliminator ", and BBJ Mold and Mildew Remover™ as well as the revolutionary new Power Coil Clean™. For additional information, Mr. Baker can be reached at (800) 889-2251 or through the company web site at http://www.bbjenviro.com.