Indoor Air Quality has become the pollution-related health issue of the 90's. In recent years, the EPA has ranked poor Indoor Air Quality among the top five health risks caused by pollution.
Pollutants enter our bodies by ingestion (eating or drinking), by absorption through our skin, or by inhalation (breathing). Of course, of the three, only breathing is something we do continually. Studies indicate that we spend 90% of our time in an indoor environment, so, the quality of the indoor air we breathe is very critical to our health and well-being. Employers are finding that providing good indoor air quality promotes increased productivity and reduced lost time due to illness.

As the public becomes more aware of the health effects of poor indoor air quality, the demand for government regulation will increase. OSHA has proposed regulations aimed at promoting good indoor air quality for the workplace already. Municipalities around the U.S. have begun enacting ordinances requiring building owners and operators to control tobacco smoke in their restaurants, bars, and places where many people are in close proximity to one another.

LITIGATION AND ECONOMICS .... The Dollars and Sense
Until more definitive legislation regarding IAQ is enacted, the primary incentive to provide good quality indoor air is the possibility of litigation. The number of personal injury liability lawsuits due to poor quality indoor air is increasing. Settlements and awards have reached the $500,000 mark per plaintiff. Just the potential of this kind of litigation should be incentive for potential defendants to assure good IAQ in all buildings for which they are responsible.
Another benefit of providing clean indoor air is that the building interior and furnishings will be cleaner requiring less housekeeping and maintenance. In addition, a clean HVAC system operates more efficiently and requires less maintenance, reducing operational costs. All in all, providing good IAQ will improve the bottom line.

PARTICULATES Generally, airborne contaminants which affect the quality of the air can be divided into two groups:

  1. Particles: Pollen, Mold, and Dust
  2. Chemical Vapors, Gases and Odor

PARTICLES are matter that has a measurable size or diameter which is usually measured in microns: (1 micron=1 millionth of a meter or 1/25,000th inch). Most people cannot see particles smaller than I 00 microns. The human body has defenses which can protect against particles larger that 10 microns. Particles smaller than 10 microns can enter breathing passages and the lungs. Types of particles include:

  • Dust: Organic and Mineral
  • Textile Lint and Fibers
  • Bioaerosols: Pollen, Mold, Bacteria, Dust Mite and Roach fecal matter and body parts, Animal Dander and Dried Urine. Smoke: Tobacco, Welding

Odors, gases and chemical vapors are molecular compounds. Gases usually exist always as gases. Vapors are released by evaporation or off-gassing from liquids or solids containing those compounds. Some gases or vapors have odors associated with them, some do not. Some unpleasant odors are not particularly dangerous while some dangerous vapors or gases have little or no odor. Types of gases and vapors include:

  • Volatile Organic Compounds (VOC's)-released by solvents, petroleum-based products, synthetic materials, and mold. Tobacco Smoke-includes VOC's and combustion by-products.
  • Reactive Gases-acid vapors, sulfur dioxide, hydrogen sulfide, formaldehyde (emitted by pressed wood products and treated fabrics).
  • Ammonia-related to urine odors as found in day care nurseries and nursing homes.
  • Combustion by-products-carbon monoxide and oxides of nitrogen are the contaminants of concern.
  • (Note: Effective filtration methods for these contaminants are specialized and not usually found in air filtration systems used in typical residential, office, and light industrial applications).


  1. Eliminate the source, or substitute a material which emits less contamination. EXAMPLE: Prohibiting smoking in a building. Substitute a water-based adhesive for a solvent (VOC-based) adhesive. PROBLEM: A bar or bingo hall that prohibits smoking will lose customers.
  2. Isolate the source of contaminants. EXAMPLE: A designated room for smoking. A sealer applied on particle board to prevent formaldehyde off-gassing. PROBLEM: Smokers in a bingo hall may not want to be separated from their friends.
  3. Ventilate the building with outside air to dilute contaminants in the building and to exhaust them out of the building. PROBLEM: Outside air may be contaminated with vehicle exhaust or other contaminants. During hot or cold weather, this outside air will have to be cooled or heated resulting in increased utility costs. The ventilation requirement for a large number of smokers can be quite high. The increased heating and/or cooling costs can also be substantial. Often, the existing HVAC equipment cannot handle the increased thermal loads, so additional or larger equipment must be installed at additional costs.
  4. Filter the air in the building using filters appropriate for the contaminants present. Filters cannot remove all contaminants, so some outside air may be needed. The outside air should also be filtered. PROBLEM: While the HVAC system is the most logical place to install filters, the fans may not be able to overcome the resistance created by the filters. Stand-alone air cleaners are designed to work with special filters. They can be located at the contaminants source. Usually they can be operated continuously at a tower cost than the HVAC system.

ASHRAE standard 52.1-1992 is used to measure the performance of most filters used in HVAC systems and air cleaning systems. Besides measuring air flow resistance, two filtration performance measurements can be made depending on the type of filter. The dust weight arrestance test indicates how well a filter captures larger, heavier particles (greater than 10 microns). It is used to evaluate panel filters used in HVAC systems and as pre-filters in air cleaners. These filters usually are not very effective on fine dusts and smokes (less than 8-10 microns). The dust spot efficiency test indicates how well a filter captures small particulates (.3-6 microns) such as fine dusts and smokes. It is usually used to evaluate pleated filters, bag filters and electronic filters. Military standard 282 (not an ASHRAE standard) measures the percentage removal of 0.3 micron particles of D.O.P. smoke. These are very high efficiency filters. A high efficiency particulate air filter (HEPA) is 99.97% efficient using this test. By comparison, a 95% dust spot filter is about 65% D.O.P.
Pre-filters are used in air cleaners to filter lint, dust, and other large particles. Usually a flat panel or a 1-2 inch pleat is used. Minimal performance should be at 80-90% arrestance. Better Pre-filters are at least 30% dust spot efficient. Frequent changing of disposables or cleaning of reusable filters prolongs the life of the main filter.
The Main Filter removes fine particulates. The minimum efficiency should be 60% dust spot. If tobacco smoke is a concern, the minimum efficiency should be 95% dust spot. Special air cleaning requirements may call for a 95% D.O.P. or 99.97% D.O.P. HEPA filter.
Final Filters are used when a high level of air cleanliness is required. Often a 950/%-99.97% D.O.P. filter is used after a 60%95% dust spot filter. This configuration protects the more costly final filter
Adsorbent Filters are used to remove odors, chemical vapors, and gases. No mechanical or electronic filter can remove these contaminants. The adsorbent material most often used is activated carbon or charcoal. It is capable of removing over 200 different odors, vapors, or gases. Carbon is primarily used to filter organic odors, solvents, volatile organic compounds (VOC's), and tobacco smoke. Carbon filters are available in three types:

  1. Polyester pad (1/4"-3/8" thick) with carbon powder bonded to the fibers. For light to medium duty filtration. May also be used as a pre-filter.
  2. Carbon Web (1 "-2" thick) has carbon granules suspended in a non-woven fiber matrix. Good for medium duty requirements and where high air flows are needed.
  3. Granular carbon panels and cells are available in 1 " and 2" depths. They are used for relatively high contamination levels or when longer filter life is desired. However, these filters are restrictive to air flow.

Potassium Permanganate is used for gases and vapors like formaldehyde, hydrogen sulfide, and sulfur dioxide. It is impregnated in small alumina spheres. The contaminant is adsorbed onto the sphere and chemically reacts with the potassium permanganate. New, unexposed spheres are purple. As the reactions take place, they turn gray or brown. When all of the spheres have changed color, they are no longer active and cannot remove the contaminant.
Zeolite is a natural mineral which adsorbs ammonia and related odors.
Type 5 is a proprietary material which adsorbs and chemically reacts with acid vapors, chlorine, flourine, bromine, and iodine. Color changes from yellow to white.

ACH's(Air Changes Per Hour)
The rate at which air in a room is cleaned (called air changes per hour, or ACH), is critical to an air cleaning system installation. If the air cleaner is too small or if there are not enough air cleaners, the air may not be cleaned to an acceptable level. The following procedure will help determine the air flow needed in cubic feet per minute, or CFM. Once the CFM required is determined, the size or quantity of air cleaners can be determined.

First, select a contaminant level and required air exchange rate, for example:

  • Nuisance dust lint - 15 minutes (4 ACH)
  • Light odor, chemical - 10 minutes (6 ACH)
  • Moderate odor, chemical, tobacco smoke - 8 minutes (8 ACH)
  • Heavy odor, chemical, tobacco smoke - 6 minutes (10 ACH)

Next, determine room volume:

  • Volume = length x width x height

Determine CFM required to clean the room:

  • CFMREQ = Volume/Air Exchange Rate

Select an air cleaner with an output equal to or greater than CFM required. If the CFM required is much greater than available system output, multiple units may be required. To determine the number of air cleaners required:
Number of Systems = CFMREQ / CFM per system
NOTE: System CFM will be affected by the filter configuration used. Make sure you select the appropriate filters for the contaminants you wish to control. On ducted systems, CFM can be affected by friction loss caused by duct and grilles. However, most, ducted layouts will not cause a significant loss of CFM.

Effective air cleaning requires air pattern management: using the clean filtered air coming from the system supply grill(s) to push the contaminants to the system return grill(s) where the dirty air is drawn into the air cleaner to be filtered. Proper location of the air cleaner is important to achieving good air pattern management. It is necessary to know the HVAC air flow patterns in the room. The air cleaning system air flow must not be against the HVAC system air flow; it should go with it.

Another technique for controlling airborne contaminants involves slightly pressurizing or depressurizing a room.

EXAMPLE 1: An inspection room in a dusty factory must be kept clean. Dust cannot come into the room when the door is opened to enter or leave. SOLUTION: An air cleaning system can be installed so that most of the air it draws in comes from outside of the inspection room. All of the filtered air is supplied to the room. Since more air is introduced into the room than is drawn out, it will be under positive pressure relative to the factory. Clean air will leak out (exflltration) rather than dirty air leak into the room (infiltration). When the door is opened, air will move out of the room, keeping dust out.

EXAMPLE 2: A small room contains a label printing machine. Chemical vapors, odor, and fine ink droplets drift through an open doorway into the next room. A door cannot be installed because of the HVAC air flow. SOLUTION: An air cleaning system can be installed so that the return (where filtered air is drawn into the system) is in the printer room. The system supply (where filtered air comes out) is located in the adjacent room near the doorway. since air is drawn out of the printer room through the air cleaner return and there is no supply, the printer room will be under negative pressure relative to the adjacent room. Air movement at the doorway will be into the room, so contaminants released by the printing process cannot drift into the adjacent room.