Captive Wind -- Part Two

This is the second part in a two part series on improving indoor air quality, which is a growing health problem in the United States. Part one (published in the May 2001 issue; under Archives) focused on air quality standards, contaminants of concern and exposure pathways. Part two will deal with an examination of air handling systems and how they can contribute to poor indoor air quality.

It was the wind that gave them life. It is the wind that comes out of our mouths now that gives us life. When this ceases to blow we die. In the skin at the tips of our fingers we see the trail of the wind, it shows us the wind blew when our ancestors were created. - Navajo Chant

Air Handling Systems -- Troubleshooting

In order to provide replacement or make-up air, a variety of systems are used to move air into and out of a facility. The basic systems rely on pressure differentials being created. A suction fan system is often used to create a partial vacuum. Through various intakes, air rushes in toward the lower pressure area. The side where the partial vacuum was created in an air handling system is called the suction side; the side where the air is being drawn into the system is called the supply side.

Various devices are used to provide equalization and appropriate airflow. American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) requirements include minimum air exchanges per hour for normal office type occupancy. When interior sources of industrial or commercial air pollutants are present, source reduction is usually the remedy of choice versus general ventilation to dilute both the source and source receiving areas.

The Common (Criteria) Air Pollutants

Designs are often complicated by the need to conserve energy and reuse interior air streams that have already been tempered (heated or cooled) and may have been humidified. Heat recovery may include systems to conductively channel heat from HVAC systems and service water heating, use of economizer cycles, mixing of reusable air with fresh air, and various forms of insulation.

Unfortunately, in an effort to reduce energy costs during the 1970s and thereafter, non-standard methods of energy conservation were used. The first step -- after identifying indoor air quality (IAQ) issues are of concern -- should therefore be a joint air quality study and mechanical system evaluation. IAQ studies should be conducted in conjunction with an evaluation of the current mechanical system usage and operation; maintenance may result in ineffective solutions to indoor air concerns.

The following illustrate just a few of the problems often identified in air handling systems:

  • Air intakes at ground level near loading areas where vehicles idle and back-up for loading and unloading, and/or traverse this area. Air intakes thus supply air to the system that is contaminated with diesel fumes and the products of incomplete hydrocarbon fuel combustion. These products of incomplete combustion may include carbon dioxides and carbon monoxide.
  • Adequate space is often not provided to access items that require maintenance such as filters, coils and drain pans, and strainers. These areas, in addition to accumulating the normal dust and dirt associated with air streams, may accumulate water through condensation events and become hospitable areas for mold and bacterial amplification. Biocide application without thorough mechanical cleaning of these areas and system alteration to preclude moisture accumulation often does not suffice. Biological amplification may then proceed to attendant ductwork, plenums and habitable spaces served by the system.
  • Renovation and facility or plant renovation activities may lead to unbalanced heating, ventilation and air-conditioning (HVAC) systems as ductwork and other air handling appurtenances are added. Positive and negative pressure areas within a building and within HVAC systems may become different from the design intent. This problem is especially dangerous where infection control, or chemical source reduction through dilution ventilation is required.
  • Fresh air intakes are permanently sealed by such means as welding plates to the intake faces, permanently closing dampers within ductwork or programming control systems to eliminate the fresh air intake option. Thus, buildings receive make up air only through doors being opened or seepage through construction materials (cracks in walls, up the sides of foundations to basement window casings with gaps). In addition to the potential for stagnant air, this situation encourages the infiltration of radon gas up the sides of foundations and into building structural gaps or openings.
  • Intake air for the general structure interior is being supplied by attic space air and/or sometimes even crawl space air. Obvious problems with air quality occur when air is supplied from damp crawl spaces frequented by rodents, or attic spaces frequented by birds and sometimes even bats. Even without animal habitation, degradation of building materials and water intrusion into these spaces surrounding habitable spaces can lead to indoor air problems associated both with particulates and biological growth (molds, bacteria). These problems can be present even if the only make up air supplied from the crawl spaces or attics is through cracks or other openings to these spaces.
  • Dirty air plenums and building spaces being used to supply air to HVAC systems. Plenums whether vertical or horizontal may contain chipping paints (lead, cadmium), accumulated dusts, and biological risk factors (spores, bacteria, animal droppings). Some plenums and building spaces are used as catch-alls for storage of a wide variety of real property. This real property may be in various stages of degradation and is often laden with soil particulate (dirt and dust). Paper materials and boxes so stored may contribute to biological growth and also the dispersal of cellulose fibers within these areas.
  • Air intake from tunnels or crawl spaces where sewage and water pipes are collocated. In a worst case scenario these spaces also contain delaminated asbestos mixed with leakage from sewers. Given that Hepatitis B and other biological organisms can remain pathogenic for weeks, these air supply areas may provide air laden with human pathogens.
  • Air intake for furnace blower systems at the base (floor) of the system and near condensate pans, stored chemicals, maintenance shops with wood and paint dusts, and general poor housekeeping debris situations.


The standing assumption was that end point filtration took care of all of the above problems. Filters initially were flat filter media. With time, these filtration systems have become more geometric with pleating and layering of filters. The currently accepted filtration dynamics assumption is that filter loading increases the filter efficiency up to the failure point. However, as the failure point is approached, the weight of the filter media causes the filter to pull away from the supportive framework and breakthrough of particulate then occurs. Thus, the timing of filter replacement becomes an imperative.

These filter systems -- when maintained and monitored -- may do a very good job of filtering most air particulates of one micron and above. Smaller particulates, gases, fumes, vapors and mists either go readily through the filter media, or in some cases partially through, and may contribute to filter failure. If standing moisture is an issue, biological and chemical reactions may ensue within the filter membrane and throughout lined ductwork. The original intent of air handling unit and ductwork lining -- to abate noise -- may thus be supplanted, as these linings also become repositories for biological and chemical risk agents.

Filter systems may become the final resting-places for rodents, birds, various insects and spiders. Initial entry may be through broken air intake systems or failed ductwork. Often residual moisture in condensate pans and near coils is an attractant for rodents, and mice or rat populations may flourish in these environments. Upon death, the rotting and necrotic tissues of these animals contribute a host of unpleasant and potentially toxic gases to the air stream; as well as biological amplification sites.


Often the essence of IAQ problems lies in a singular phenomenon -- lack of sanitation. Since the air handling systems are often invisible to us; we tend to forget that the air we breathe did not magically appear in the room. Most air handling systems, even if inspected by normal maintenance means, are inaccessible for visual observation along ductwork and plenum runs. Telescopic, fiber optic and/or camera scoping of these systems is sometimes the only means to determine levels of contamination.

The original engineering concept for the HVAC system may have been that filtration and air flow velocity were sufficient to keep the system dry, and with the exception of the filter beds -- free of contaminant. As this concept fails either through intended changes in the system, or system break down -- increased vigilance to maintenance may be required.

Unfortunately, some systems cannot be rendered dry and other systems cannot be adequately cleaned. However, for those systems where debris and stored extraneous materials can be easily removed, these actions may substantially increase air quality and reduce the necessity for end point filtration as the sole guarantor of a clean air stream.

More complicated sanitation methods may require chemical and mechanical cleaning and/or mechanical encapsulation of dirty system. Chemical and particulate out-fall from these sanitation events may also be of concern if the HVAC system being treated cannot be partitioned (shut down, separated by critical barriers) during the chemical application or mechanical cleaning event.

Cause and Effect

Now we begin to find both a starting point and solutions to our IAQ problems. The need is real with the World Health Organization (WHO) estimating that in India and in sub-Saharan Africa respectively, as many as 500,000 children die per year of respiratory problems often exacerbated by the burning of fossil fuels in interior locations (www.who/int/peh). In more developed counties, asthma rates and respiratory diseases in children are also on the rise. Adults suffer with workplace, medical center and residential areas, in some cases, providing sub-standard air quality. All of course further acerbated by environmental ambient air quality that may be sub-standard.

Benjamin Franklin remarked over 200 years ago, "I closed up my house, and I became sick. I opened my windows, and I became well." That premise is still substantially true, provided the environmental air source is not too contaminated with industrial/agricultural chemicals, or native spores and pollens. Thus, in seeking cause and effect, we must always consider our starting air source and at the very least -- not make this air stream less breathable in our air handling systems and environs.

We must always remember the wisdom of the Navajo Chant - that the finite wind that blows through us becomes part of us.

The Common (Criteria) Air Pollutants


  • Ground-level ozone is the principal component of smog.
  • Source - chemical reaction of pollutants, VOCs and NOx.
  • Health Effects - breathing problems, reduced lung function, asthma, irritates eyes, stuffy nose, reduced resistance to colds and other infections, may speed up aging of lung tissue.
  • Environmental Effects - ozone can damage plants and trees; smog can cause reduced visibility.
  • Property Damage - damages rubber, fabrics, etc.

VOCs* (volatile organic compounds)

  • Smog-formers.
  • Source - VOCs are released from burning fuel (gasoline, oil, wood coal, natural gas, etc.), solvents, paints, glues and other products used at work or at home. Cars are an important source of VOCs. VOCs include chemicals such as benzene, toluene, methylene chloride and methyl chloroform
  • Health Effects - In addition to ozone (smog) effects, many VOCs can cause serious health problems such as cancer and other effects.
  • Environmental Effects - In addition to ozone (smog) effects, some VOCs such as formaldehyde and ethylene may harm plants.
  • All VOCs contain carbon (C), the basic chemical element found in living beings. Carbon-containing chemicals are called organic. Volatile chemicals escape into the air easily.
  • Many VOCs are also hazardous air pollutants, which can cause very serious illnesses. EPA does not list VOCs as criteria air pollutants, but they are included in this list of pollutants because efforts to control smog target VOCs for reduction.
  • Nitrogen Dioxide (One of the NOx)

  • Smog-forming chemical.
  • Source - burning of gasoline, natural gas, coal, oil etc. Cars are an important source of NO_2.
  • Health Effects - lung damage, illnesses of breathing passages and lungs (respiratory system).
  • Environmental Effects - nitrogen dioxide is an ingredient of acid rain (acid aerosols), which can damage trees and lakes. Acid aerosols can reduce visibility.
  • Property Damage - acid aerosols can eat away stone used on buildings, statues, monuments.
  • Carbon Monoxide (CO)

  • Source - burning of gasoline, natural gas, coal, oil.
  • Health Effects - reduces ability of blood to bring oxygen to body cells and tissues; cells and tissues need oxygen to work. Carbon monoxide may be particularly hazardous to people who have heart or circulatory (blood vessel) problems and people who have damaged lungs or breathing passages.
  • Particulate Matter (PM-2.5); (dust, smoke, soot)

  • Source - burning of wood, diesel and other fuels, industrial plants, agriculture (plowing, burning off fields), unpaved roads.
  • Health Effects - nose and throat irritation, lung damage, bronchitis, early death.
  • Environmental Effects - particulates are the main source of haze that reduces visibility.
  • Property Damage - ashes, soots, smoke and dusts can dirty and discolor structures and other property, including clothes and furniture.
  • Sulfur Dioxide

  • Source - burning of coal and oil, especially high-sulfur coal from the Eastern United States; industrial processes (paper, metals).
  • Health Effects - breathing problems, may cause permanent damage to lungs.
  • Environmental Effects - SO2 is an ingredient in acid rain (acid aerosols), which can damage trees and lakes. Acid aerosols can also reduce visibility.
  • Property Damage - acid aerosols can eat away stone used in buildings, statues, monuments.
  • Lead

  • Source - leaded gasoline (being phased out), paint (houses, cars), smelters (metal refineries), manufacture of lead storage batteries.
  • Health Effects - brain and other nervous system damage; children are at special risk. Some lead-containing chemicals cause cancer in animals. Lead causes digestive and other health problems.
  • Environmental Effects - Lead can harm wildlife.

  • This article originally appeared in the September 2001 issue of Environmental Protection, Vol. 12, No. 9, p. 51.

    This article originally appeared in the 09/01/2001 issue of Environmental Protection.