Biological Contaminants

Table of Contents:

Heating, ventilation, and air conditioning systems and humidifiers can be breeding grounds for biological contaminants when they are not properly cleaned and maintained. They can also bring biological contaminants indoors and circulate them. Biological contaminants include bacteria, mold and mildew, viruses, animal dander and cat saliva, mites, cockroaches, and pollen. There are many sources for these pollutants. For example, pollens originate from plants; viruses are transmitted by people and animals; bacteria are carried by people, animals, and soil and plant debris; and household pets are sources of saliva, hair, and dead skin (known as dander).

Available evidence indicates that a number of viruses that infect humans can be transmitted via air. Among them are the most common infections of mankind. Airborne contagion is the mechanism of transmission of most acute respiratory infections, and these are the greatest of all causes of morbidity.

The primary source of bacteria indoors is the human body. Although the major source is the respiratory tract, it has been shown that 7 million skin scales are shed per minute per person, with an average of four viable bacteria per scale [3]. Airborne transmission of bacteria is facilitated by the prompt dispersion of particles. Infectious contact requires proximity in time and space between host and contact and is also related to air filtration and air exchange rate.

Although many important allergens—such as pollen, fungi, insects, and algae—enter buildings from outdoors, several airborne allergens originate predominately in homes and office buildings. House dust mites, one of the most powerful biologicals in triggering allergic reactions, can grow in any damp, warm environment. Allergic reactions can occur on the skin, nose, airways, and alveoli.

The most common respiratory diseases attributable to these allergens are rhinitis, affecting about 15% of the population, and asthma, affecting about 3%-5% [3]. These diseases are most common among children and young adults but can occur at any age. Research has shown that asthma occurs four times more often among poor, inner-city families than in other families. Among the suspected causes are mouse urine antigens, cockroach feces antigens, and a type of fungus called Alternia.

Hypersensitivity pneumonitis (HP), characterized by shortness of breath, fever, and cough, is a much less common disease but is dangerous if not diagnosed and treated early. HP is most commonly caused by contaminated forced-air heating systems, humidifiers, and flooding disasters. It can also be caused by inhalation of microbial aerosols from saunas, home tap water, and even automobile air conditioners. Humidifiers with reservoirs containing stagnant water may be important sources of allergens in both residential and public buildings.

Some biological contaminants trigger allergic reactions, while others transmit infectious illnesses, such as influenza, measles, and chicken pox. Certain molds and mildews release disease- causing toxins. Symptoms of health problems caused by biologicals include sneezing, watery eyes, coughing, shortness of breath, dizziness, lethargy, fever, and digestive problems.

Attempts to control airborne viral disease have included quarantine, vaccination, and inactivation or removal of the viral aerosol. Infiltration and ventilation play a large role in the routes of transmission. Because many contaminants originate outdoors, attempts to reduce the ventilation rate might lower indoor pollutant concentrations. However, any reduction in fresh air exchange should be supplemented by a carefully filtered air source.

Central electrostatic filtration (as part of a home’s forced-air system) has proven effective in reducing indoor mold problems. Careful cleaning, vacuuming, and air filtration are effective ways to reduce dust levels in a home. Ventilation of attic and crawl spaces help prevent moisture buildup, keeping humidity levels between 30% and 50%. Also, when using cool mist or ultrasonic humidifiers, one should remember to clean and refill water trays often, since these areas often become breeding grounds for biological contaminants [6].

Monitoring Methods

Methods and instrumentation for measuring IAQ vary in their levels of sensitivity (what levels of pollutant they can detect) and accuracy (how close they can come to measuring the true concentration). Instruments that can measure low levels of pollutant very accurately are likely to be expensive and require special expertise to use. Some level of sensitivity and accuracy is required, however, to ensure that data collected are useful in assessing levels of exposure and risk.

In choosing methods for monitoring IAQ, a tradeoff must be made between cost and the levels of sensitivity, accuracy, and precision achieved in a monitoring program. Required levels for each pollutant are based on ranges found in residential buildings. In providing detailed information concerning specific methods or instruments, emphasis is placed on those that are readily available, easy to use, reasonably priced, and that provide the required levels of sensitivity and accuracy.

Methods to monitor indoor air fall into several broad categories. Sampling instruments may be fixed location, portable, or small personal monitors designed to be carried by an individual. These samplers may act in an active or passive mode. Active samplers require a pump to draw in air. Passive samplers rely on diffusion or permeation.

Monitors may be either analytical instruments that provide a direct reading of pollutant concentration or collectors that must be sent to a laboratory for analysis. Instruments may also be categorized according to the time period over which they sample. These include grab samplers, continuous samplers, and time-integrated samplers, each of which is briefly described below. Additional details are available in Part I, Chapter 8.

  • 1. Grab sampler. Collects samples of air in a bag, tube, or bottle, providing a short-term average.
  • 2. Continuous sampling. Allows sampling of real-time concentration of pollutants, providing data on peak short-term concentrations and average concentrations over the sampling period.
  • 3. Time-integrated sampling. Measures an average air concentration over some period of time (active or passive), using collector monitors that must be sent out for analysis, and cannot determine peak concentrations.

More details regarding monitoring methods for specific indoor air pollutants can be found in the 1AQ Handbook [3].

CosaTron is just one example of a company that produced mechanical air-cleaning devices. The patented CosaTron system has been handling IAQ successfully in thousands of installations for over 25 years. CosaTron is not a filter that ionizes air. It cleans the air electronically, causing the submicron particles of smoke, odor, dirt, and gases to collide and adhere to each other until they become larger and airborne and are easily carried out of the conditioned space by the system air flow to be exhausted or captured in the filter. Mechanical air devices such as this one improve IAQ so much that outside air requirements can be reduced significantly [7].


  • 1. U.S. EPA. Environmental Progress and Challenges. EPA’s Update, August 1988.
  • 2. Taylor, J. Sampling and Calibration for Atmospheric Measurements. Philadelphia, PA: ASTM Publication. 1987.
  • 3. Mueller Associates, Inc. Indoor Air Quality Environmental Information Handbook: Building System Characteristics. Mueller Associates, Baltimore, MD, 1987.

4. Theodore, L. and Dupont, R. R. Environmental Health and Hazard Risk Assessment: Principles and Calculations,

  • 5. Cox. J. E. and Miro, C. R. EPA, DOE, and NIOSH address IAQ problems, ASHRAE Journal, 10, July 1993.
  • 6. Burke, G., Singh, B., and Theodore, L. Handbook of Environmental Management and Technology. Hoboken. NJ: John Wiley & Sons, 2000.
  • 7. Four proven solutions for IAQ! ASHRAE Journal, 2, March 1993.
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