Biological Contaminants

Most of us don't even want to think about bacteria, fungi, viruses, algae, insect parts, dead mice, and dust in the air we breathe. Yet these contaminants are all less common than human skin scales. We shed skin cells constantly from our skin and in our breath, and our environment is littered with our dead cells. It is estimated that a person sheds 40,000 biological particles containing bacteria per minute while sitting at a desk, and as many as 45 million per minute when exercising. The number of bacteria able to reproduce in an office environment is often in the range of 1000 colony-forming units per cubic meter.

Bacteria and fungi are present indoors and out, but office buildings provide an exceptionally favorable environment of high humidity and standing water in circulation and air-conditioning ducts, ceiling tiles, insulation, and even ice machines. These microorganisms release bioaerosols, which include tiny spores from molds and other fungi that float through the air and irritate skin and mucous membranes.

Mold in carpets eats skin scales, as do dust mites. Mold and dust mite excrement are two very common causes of allergies. Other biological particulates include

Figure 19-1 A dust mite in carpet.

pollens, spores, cat dander allergens, and finely ground food products like grains, coffee, and cornstarch. The protein in urine from rats and mice is a potent allergen. When it dries, it can become airborne.

Dust mites (Fig. 19-1) congregate where nutrients (dead skin cells) collect, in and around beds, bedding materials, in upholstered furnishings, in carpet, and in places of high human activity. They require at least 60 percent relative humidity to survive. A relative humidity of 30 to 50 percent is generally recommended for homes. Dust mites are common in both residential and commercial spaces.

Dust mites are relatively large, so they settle out of the air and usually live at floor level, only becoming airborne when the dust is disturbed. About 53 percent of allergic individuals are sensitive to household dust, and more than 37 percent are allergic to dust mite allergens. Dust mite allergens include enzymes in their feces, mite saliva, and the soluble proteins from mite body parts. Reactions include nasal inflammation, asthma, and itching, inflammation, and rash.

Nearly everything organic releases particles or microscopic bits of solid or liquid matter that can stay airborne for long periods of time. Larger particles are usually caught in the nose before they can reach the lungs. Pollen grains from weeds, grasses, and trees, which cause seasonal allergies for many people, are larger than ordinary dust particles, and can be filtered out mechanically. Most pollen grains are also hygroscopic, which means they vary in size and weight when they absorb water from humid air.

Particles less than 10 microns in diameter are known as respirable suspended particles or RSPs. (A hundred microns is about the diameter of a human hair.) When they get past the nose and invade deep into the lungs, they can cause coughing, wheezing, and respiratory tract infections. Respirable suspended particles can cause chemical or mechanical irritation of tissues, including nerve endings wherever they are deposited. They can affect respiration and aggravate cardiovascular disease. In addition, RSPs may have an impact on the immune system, and can cause changes in lung tissue, including cancer. They are linked to SBS, respiratory diseases, and asthma. They tend to affect preadolescent children, older people, and people with respiratory conditions most severely. Many people become increasingly sensitive to RSPs through repeated contact, resulting in allergic reactions.

It is often difficult to test for biological contaminants, as many of the specific test substances are not widely available, and the symptoms are varied and similar to those from other causes. Estimates of the impact of RSPs on building problems vary from 5 to 50 percent of sick building cases.

Biological contaminants need four things to grow in a building: a source, water, nutrients, and favorable temperatures. Contaminants arrive in buildings from outdoor air, and live in air-handling and humidification systems, and in building materials and furnishings. Building occupants, pets, and houseplants all contribute as sources. Water is provided by roof and plumbing leaks, vapor migration and condensation, houseplants, humidifiers, aquariums, and building occupants. Biological contaminants can eat dust, dirt, food, water, houseplants, dead plant tissue, building materials, and furnishings—almost anything you are likely to find in a building! They enjoy temperatures between 4.4°C and 37.8°C (40°F-100°F).

Biological contamination is often the result of inadequate preventive maintenance. The internal components of air-handling units, fan-coil units (FCUs), and induction units are seldom cleaned. Drain pans hold stagnant contaminated water that should be drained. Wet cooling coils and porous insulation collect dirt and debris, especially in air-conditioning systems.

Inaccessible, poorly designed mechanical systems defeat efforts at proper maintenance. Access doors to heat exchangers, air-handling units, and heat pumps may be in inaccessible locations over ceiling tiles. Air-handling units may be confined in small rooms or plenums. Fan-coil and induction units are often difficult to disassemble for cleaning. Locating an outdoor intake within 7.6 meters (25 ft) of a cooling tower or other unsanitary location allows microorganisms to enter the building. Whenever an area is flooded, cleanup must be thorough and prompt.

Moisture encourages the retention and growth of molds, fungi, viruses, and algae, and prime growth con ditions often exist in heating and cooling systems. Standing warm water, as in untreated hot tubs, air-conditioning drain pans, and humidifier reservoirs, can harbor hazardous bacteria. Dead mold and other biological contaminants don't always show up on tests, so diagnosis of problems can be difficult. Filters are rarely effective for bacteria, and evaporative humidifier filters can even harbor bacteria that eat cellulose and thrive in the warm, wet environment. Air-conditioning coils can hold skin cells, lint, paper fibers, and water, a perfect environment for mold and bacteria. Building air quality specialists tell horror stories of mold-covered mechanical systems supplying the air for an entire building.

Excessive humidity in occupied spaces encourages the growth of biological contaminants. Keeping the relative humidity below 70 percent discourages fungus, and below 50 percent minimizes condensation on cold surfaces during summer months.

Contamination of the central air system and lack of proper ventilation create breeding conditions for microorganisms. Incorrectly specified building and interior materials or finishes provide homes for bacteria and fungi. For example, carpet that is not resistant to moisture can become wet in the wrong location and harbor microorganisms.

Fungus particles and dust mites grow in basements, damp carpets, bedding, fabrics, walls, ceilings, and closets. Covering beds and upholstery with barrier cloth and increasing ventilation can contain them. Borax treatments can retard fungus. Many types of bacteria and fungi produce toxic substances called endotoxins as byproducts of their metabolic processes.

Microorganisms become airborne by attaching to dust particles suspended in the air by activity nearby. Dust control, air sterilization, and carefully designed ventilation systems can help. Operating rooms may require special downdraft ventilation. The air supplied to nurseries for premature babies or to laboratories is sometimes sterilized with ultraviolet (UV) light in the ductwork, although this system is difficult to maintain. Air from high infection risk areas, like medical treatment and research areas, is normally isolated from the air supply for uninfected areas. The safety precautions taken include increasing outside air supplies, avoiding air movement from one room into another, and specifying cleaning of recirculated air.

In the 1960s, a group of American Legion members at a convention in a hotel suddenly began to die of a mysterious malady, which became known as Legionnaire's disease. This fatal respiratory illness was eventually traced to the bacterium Legionella growing in an improperly maintained HVAC system. Legionella grows in cooling towers and plumbing systems, and on other surfaces within water-containing systems. Most people have been exposed to Legionella, which is present in about a quarter of fresh water samples, but it rarely causes disease except under certain indoor conditions and in susceptible human hosts. Legionnaire's disease is a progressive, potentially fatal form of pneumonia that infects only about 5 percent of those who inhale droplets of water with the bacteria. Fifteen percent of those infected die of the disease. Pontiac fever is a two- to three-day-long flu-like illness also caused by Legionella that infects 95 percent of exposed individuals.

Legionnaire's disease continues to cause periodic deaths in poorly maintained buildings, including the Ford Motor Co.'s Cleveland Casting Plant, which was temporarily closed after an outbreak in 2001. The air-conditioning system in the new aquarium in Melbourne, Australia, was reported in 2000 to have spread the bacteria responsible for a deadly outbreak of Legionnaires' disease. Two women died, eight people were in critical condition, and 66 people were confirmed to have the disease.

Pseudomonas is responsible for humidifier fever or humidifier lung, and produces flu-like symptoms with fever, chills, difficulty breathing, muscle aches, and malaise when toxins produced by microbes are distributed through the air. The water reservoirs of humidified heating systems, air-conditioning units, cool-mist humidifiers, and evaporative air coolers can harbor pseudomonas. Humidifier fever symptoms emerge 4 to 12 hours after exposure, and then subside. Humidifier lung can cause permanent, potentially fatal changes in lung tissue with continual exposure.

Fungi are plantlike organisms that lack the chlorophyll needed for photosynthesis, and include molds, mildew, and yeasts. Mildew is a fungus that appears as a thin layer of black spots on a surface; you may see it on your shower curtain. Fungi live on decomposed organic matter or living hosts, and reproduce by spores. Some spores are dry, and can become airborne. Others are slimy, and it is these that create mold-infested building materials or furnishings implicated in SBS. They will grow on almost anything, including glass, paint, rubber, textiles, electrical equipment, mineral wool, or fiberglass duct lining materials, and the substances that hold buildings together. Molds grow where there is moisture or a relative humidity over 70 percent, often from water damage from leaks in pipes or floods or from condensation on walls and ceilings. Synthetic carpets containing large amounts of dust make excellent mold environments, especially after water damage. Spores in air-conditioning systems may contribute to SBS.

Mycotoxins are digestive by-products of fungi. Some are helpful, like penicillin, while others, like aflatoxin, are carcinogens. Some mycotoxins become toxic in combination with other substances. Fungi emit VOCs, creating a distinctive odor that is often the first indication of their presence. Ethanol is one common VOC emitted by fungi, and enhances the toxic and irritant effects of other VOCs. Exposure to fungi spores, myco-toxins, and VOCs can result in allergic reactions, which are usually hard to test for, and other immune system disorders and toxic reactions.

Free-living amoebas are microscopic protozoa that can form dormant cysts when food isn't available and hide away until times of plenty. Amoebas are implicated in some BRIs. In addition, bacteria that have been eaten by amoebas can stay alive, and are thus protected from disinfectants like chlorine. Viruses are submicroscopic organisms that reproduce in living hosts, and that can cause disease. Blue-green algae and green algae are one-celled microscopic organisms that grow in fresh or salt water and sunlight. They can be dispersed through the humidification and HVAC systems from areas of standing water.

Installing and using exhaust fans that are vented to the outdoors in kitchens and bathrooms, and venting clothes dryers outdoors can reduce moisture and cut down on the growth of biological contaminants. Ventilate the attic and crawl spaces to prevent moisture buildup. If using cool mist or ultrasonic humidifiers, clean appliances according to manufacturer's instructions and refill with fresh water daily. Thoroughly clean and dry water-damaged carpets and building materials, within 24 hours if possible, or consider removal and replacement.

Keeping the building clean limits exposure to house i( dust mites, pollens, animal dander, and other allergy-causing agents. As an interior designer, avoid specifying room furnishings that accumulate dust, especially if they cannot be washed in hot water. Using central vacuum systems that are vented to the outdoors or vacuums with high-efficiency filters may also be of help. Do not finish a basement below ground level unless all water leaks are patched and outdoor ventilation and adequate heat to prevent condensation are provided. Operate a dehu-midifier in the basement if needed to keep relative humidity levels between 30 and 50 percent.

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