Mold: Harmless Old Neighbor, or Pesky Troublemaker?

Sam Schell

March 1, 2003

In recent years mold has become a newsworthy discussion subject. And it’s not because you’re mad about the cost of throwing out a loaf of bread, because "the kids didn’t close the bread clasp again!" Instead, it’s because it has suddenly become TOXIC. A rising trend in "Sick Building Syndrome" claims has created a new awareness of the ancient creature known as mold. Table 1, ("Increased Media Attention," page 21) shows that the number of articles in the media related to toxic mold have more than doubled since 1998. And friends, these aren’t articles written by Betty Crocker on how to keep bread more fresh.

Anatomy of the Villain

Mold has been with us throughout the entire evolution of the human race. It’s estimated that mold has been in existence for more than 400 million years. The number of molds currently identified is in the range of 100,000 strong. Of that number, approximately 1,000 different types are found in the United States. The mold organism is closely associated with mildew, and both are classified as Fungi. Another well-known Fungi is the mushroom. The trait they all share is the lack of Chlorophyll, the substance that makes green plants green and allows them to produce food for the organism. This fact hints at the environment necessary for the growth and propagation of molds. The mold cycle of life is quite simple. To thrive, mold must:

  • Find a suitable living environment.
  • Grow and produce a colony.
  • Propagate offspring to begin the cycle again.

Molds aren’t hunter/gatherer types that prey on innocent victims. A mold is more of a nomad that drifts to a place that meets its basic needs. A spore begins the life cycle of mold. Mold spore is similar to a seed in normal plant life. The air transports the spore to a damp location, and once there the spore swells and grows, forming thread-like structures called hyphae. These threads form the basis of the mass that we see as mold. From these threads, roots and flowering stems grow to produce a spore case, which resembles the head of a pin. The mature spore case contains thousands of new spores that are released when the mature case breaks open.

What a Mold’s Suitable Living Environment?

Molds aren’t fussy about where they live as long as the basic necessities are met. These are:

  • water – high humidity and damp conditions are excellent
  • food source – any organic substance
  • comfortable temperature range – molds have a wide tolerance range

Water is an essential ingredient in the living quarters for molds. Without water, molds can’t sustain themselves. The mold life cycle begins when the mold spore is activated in water’s presence. Once activated, the mold needs a source of food. Unlike plant life, mold can’t produce their own food. Consequently they require a host source of food. The best description of the food relationship is opportunistic, such as Black Mold on Bread. Molds feed on any organic substances. As an example, paper is a product of wood, an organic substance that a mold spore recognizes as food. There are mold varieties that can live in all of the environment extremes on the planet, but the molds of concern are those that prefer the same environmental conditions that we prefer. An ideal temperature is the conditioned spaces of our dwellings. In short, if you can live there a mold spore can live there. Figure 1, (utility wall, upper right) shows the development of a mold colony behind the plumbing in a utility wall where all of proper conditions for the life cycle are available.

Inhospitable Environment

The active mold colony dies when the living conditions become inhospitable. Unfortunately this isn’t the end of the story, as the thousands of mold spores that were released from the mature colony will ensure that the mold returns. Mold spores have the ability to reach a dormant state when the living conditions become inhospitable. The mold spores’ dormant state can last for years, waiting for the proper conditions to return. Once living conditions improve, the life cycle begins again and we have the new mold colony. The mold colony prospers and produces new mold spores to begin the cycle again.

Why Does the Mold Problem Exist?

Why does the mold problem exist? This is a very complicated question with many possible answers, and all of them are correct to some degree. The first myth that needs to be crushed is the idea that we can eliminate the mold population. Mold was here before us and most probably will be here long after we are gone. In fact, every creature on the planet lives with some form of mold every day. Our world is a community of living and dead organisms sharing the same space. We have created conditioned spaces on earth that are very comfortable for us to occupy. Because these spaces are linked to the rest of the world through the ventilation system, personnel entrance and exit points, loading docks and a plethora of other outside connections, it’s impossible to have zero exposure to mold.

We require fresh air for our existence (a legal requirement of indoor air quality), necessitating the input of outside air. That air contains mold spores! Serving aboard a U.S. Navy submarine as a crewmember, I can tell you that after being submerged for many days and making our own oxygen without any exposure to the outside air, we still had mold. To date, no sailors have become sick or died from toxic mold.

If you take a close look at the current situation in the buildings we occupy, not only are they comfortable for us, they are also comfortable for a mold colony. In fact, it’s a virtual resort for the mold colony. We pay dearly to go on vacation at an all-inclusive resort that caters to our every need. We’re chauffeured to the resort, greeted warmly, given a comfortable suite to reside in during our stay and then provided with 24-hour food and drink services. These conveniences are available as long as we remain on the premises of the resort. Eureka, we have landed in paradise!

Thinking as if we’re a mold spore, let’s enter a modern building. The spore is drifting freely in the air and becomes entrained in the incoming makeup air for the building (chauffeured to the resort). As the spore enters the building, the temperature of the air is corrected to optimum conditions (greeted warmly and made comfortable). The spore settles in an area of the ventilation system, wall, duct or ceiling tile (comfortable suite). At this point the mold spore is still inactive, but now being a quality resort the availability of food and drink is delivered. Organic materials are readily available (food) and moisture is allowed to increase in the building area (drink) occupied by the mold. We have now have reached paradise. All this comes without any hunting or gathering on the mold’s part; it’s simply delivered just like a quality all-inclusive resort. The mold colony grows and a full bloom occurs, creating a very high population of mold colonies. The high concentration of mold colonies produces a high concentration of mold spores, and this is where the trouble begins. The alleged ill affects of mold concentrations in our environment are wide and ranging. Here’s a list of some of the common reported health effects:

  • burning eyes
  • headache
  • nausea
  • nose bleeds
  • allergic reactions
  • asthma
  • exhaustion
  • sinus infections

According to the Center for Disease Control and Prevention, "There are very few case reports that toxic molds inside homes can cause unique or rare health conditions ?The common health concerns from molds include hay-fever like allergic symptoms."

This information begs us to ask the question, "Have we created our own problem?" That answer is YES. Mold didn’t cause the mold problem – it’s merely the effect of the cause.

How Do We Identify the Cause?

The solution is simple. Examine the cause and eliminate it. With buildings, we have created a resort environment for the propagation of mold, so why wouldn’t it flourish? Common sense says that to reduce the concentration of mold to an acceptable level, we must change environmental conditions. Remember, we can’t eliminate mold, only reduce it. Without a resort in which to flourish, the mold colonies will not blossom, and mold spore levels will return to normal. At first glance it’s a simple solution, but upon further investigation we have very complicated requirements. Looking at our building envelopes we see that there are many factors affecting the building envelope. To begin the troubleshooting process, we need to start with the life cycle of the mold and its needs. Mold needs water, food, and environment in the building envelope. To put out a fire you must eliminate any one of the main ingredients and the fire is extinguished. In our case, the same logic applies to the elimination of the mold blossom. Let’s examine the facts:

  • Water – Humans in a building envelope provide moisture through the normal biological process of living. We perspire, producing moisture, and our legally required fresh air makeup provides additional humidity.
  • Food – Many of the common building materials are organic based materials. In addition, a little know fact is dust that’s contained in a building is 70 percent to 80 percent dead human skin from the occupants (also viewed as food by the mold).
  • Environment – This is simple; if it’s nice for you to live there, it’s nice for the mold!

Suddenly elimination of something seems to be impossible. Looking closely at the problem, we see that logically we can’t change the environment and make it inhospitable for humans, so that removes that option. Changes in building products are occurring all the time, with fewer use of organic-made materials. However, as long as people are in the building, a relatively plentiful food source exists. Finally, we must have humidity in the makeup air, and the only humans that don’t perspire aren’t with us anymore. What is the possible solution?

How Do We Fix the Causes?

There’s not a simple, "one size fits all" solution to the mold growth problem. A combination of strategies starting from the engineering of the building envelope, working through construction and finally careful operation and maintenance provides the best results. The initial solution is to manage the water and humidity in the building to minimize the available sites for mold spores to land, creating prosperous colonies. This action will significantly reduce the amount of mold present. By comparing the graphs of the water damage (Table 2, "Texas Water Damage," page 21) and mold claims (Table 3, "Texas Mold Claims," above) in Texas, a clear parallel can be noted. There are many ways of managing the water in a facility, starting from the design and working through the construction to the day-to-day operation. A simple example of a corrective action is in the plumbing of the drain pans in the air-handling units. The pan drain should be of the "P-trap type" to ensure that an air seal is provided during air handler operation. Without the proper water seal in the trap, the water in the drain pan is lifted out of the drain by inrushing air and allowed to enter the ventilation system. Once inside the ventilation system, the duct liner is wetted and the mold life cycle can begin. At a recent visit to a casino, all of the trap drain lines from the rooftop heating and cooling units inspected were incorrectly piped, allowing unconditioned air into the air handler and the entrainment of water into the ventilation systems. In severe instances, the water can combine with the airborne dust, creating a blockage of airflow through the coil from the mold colonies growing on the coil (See Figure 2, "evaporator coil mold," page 22).

Proper maintenance of the ventilation systems will also reduce the ability of mold colonies to proliferate. There are chemically available biocides designed to prevent the mold growth in the drain pans of the air handlers, but this is only a first step. Simple actions like keeping ventilation filters changed and minimizing unfiltered air leakage to the ventilation systems reduce mold’s available food supply.

Improperly sized equipment can result in mold colonies blooming. Examples of this include oversized air conditioning equipment and humidifiers. The excess capacity of a humidifier or improper location can result in excess wetting of building envelope systems. Oversized air conditioning equipment short cycles and results in a lower temperature (dry bulb) in the building envelope, but insufficient (wet bulb) dehumidification, which also results in wetting of building envelope systems. HVAC technicians call this "damp cave syndrome" (in other words cool and wet, mold paradise).

Engineered systems such as insulation should be properly specified and meet the realistic needs of the environment, considering all facets of the building envelope, not just the energy conservation. Use of a vapor barrier, when appropriate, can significantly reduce the mold colony formation and bloom. Figure 3 ("wallpaper," page 20), shows the reaction of vinyl wallpaper applied to a building insulation system without a vapor barrier. The vinyl wallpaper acted as the vapor barrier and the drywall paper and insulation materials became the colony’s food source.

So What Is the Solution?

Simply stated, "Too much of anything, even a good thing, is bad." This statement holds true in the mold community. We need to strive to understand and prevent the excessive growth of mold colonies in our building envelopes. To accomplish this, all aspects of the building envelope and its systems must be reviewed. Remember, mold isn’t the enemy. Without it, soils would become infertile because there would be no waste breakdown, certain foods such as Roquefort and Blue Cheese wouldn’t mature, and many, many people would be very ill without penicillin. Mold was here before us and will remain long after us. Remember, mold did not create the mold situation, we did; thus we can fix it.