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An Introduction to Indoor Air Pollution

Randall W. Whitesides, P.E.


Course Outline

The subject of indoor air pollution is not without some controversy. Indoor air quality is an evolving issue; it is important to keep informed about continuing developments in this area. This short course is not a detailed technical treatise on indoor air pollution; it is intended for Architects and Engineers who are interested in a general introductory overview of IAP, its various categories, probable causes, and suggested remedial actions.

A substantial portion of this course content is taken from U.S. GPO Publication No. 1994-523-217/81322 Indoor Air Pollution: An Introduction for Health Professionals, 1994. The publication was co-sponsored and placed in the public domain by the Environmental Protection Agency (EPA), the American Medical Association (AMA), the Consumer Product Safety Commission (CPSC), and the American Lung Association (ALA). The ability to reproduce this document, in whole or part, has been granted without the requirement for permission."

The overwhelming majority of the medical aspects, i.e. physiology, etiology, symptomology, and human physical diagnosis, contained in the GPO publication has been selectively and purposely excluded from this course content. This was done to limit the scope and focus to those aspects of IAP of greater interest to Engineers and Architects. Those students interested in viewing the unmodified original document should point their browser to: http://www.epa.gov/iedweb00/pubs/hpguide.html. Important references and additional health resources can be found at this URL.

This course includes a true-false quiz at the end.

Learning Objective

At the conclusion of this two hour course, the student will be familiar with the:

Course Content

INTRODUCTION

Indoor air pollution poses many challenges. This course offers an overview of those challenges, with patterns that point to particular agents and suggestions for appropriate remedial action.

Studies from the United States and Europe show that persons in industrialized nations spend more than 90 percent of their time indoors. For infants, the elderly, persons with chronic diseases, and most urban residents of any age, the proportion is probably higher. In addition, the concentrations of many indoor pollutants exceed those outdoors. The locations of highest concern are those involving prolonged, continuing exposure - that is, the home, school, and workplace.

Heavy industry-related occupational hazards are generally regulated. This course addresses the indoor air pollution problems that may be caused by contaminants encountered in the daily lives of persons in their homes, commercial establishments, and offices.

A few prominent aspects of indoor air pollution, notably environmental tobacco smoke and "sick building syndrome" have been brought to public attention.

Because of oil shortages and the resulting energy crises, the use of outdoor air for the purpose of general ventilation has been minimized. Additionally, the need for "energy efficient" buildings has resulted, in some instances, in the construction of nearly airtight structures. In earlier times, the use of outside air for normal ventilation had a diluting effect to indoor contaminants, lowering their concentrations. As buildings became self-contained envelopes, their occupants health complaints began to increase.

The course is organized according to pollutant or pollutant group. The student is cautioned that this is not an all-inclusive reference, but a necessarily selective survey intended to suggest the scope of the problem.

ENVIRONMENTAL TOBACCO SMOKE (ETS)

Background

Where allowed, environmental tobacco smoke is a major source of indoor air contaminants. The ubiquitous nature of ETS in indoor environments indicates that some unintentional inhalation of ETS by nonsmokers is unavoidable. Environmental tobacco smoke is a dynamic, complex mixture of more than 4,000 chemicals found in both vapor and particle phases. Many of these chemicals are known toxic or carcinogenic agents. Nonsmoker exposure to ETS-related toxic and carcinogenic substances will occur in indoor spaces where smoking is allowed or otherwise not prohibited. Today, commercial establishments and places of public assemble that allow indoor smoking are usually limited to bars and restaurants.

All the compounds found in "mainstream" smoke, the smoke inhaled by the active smoker, are also found in "sidestream" smoke, the emission from the burning end of the cigarette, cigar, or pipe. ETS consists of both sidestream smoke and exhaled mainstream smoke. Inhalation of ETS is often termed "secondhand smoking", "passive smoking", or "involuntary smoking."

The role of exposure to tobacco smoke via active smoking as a cause of lung and other cancers, emphysema and other chronic obstructive pulmonary diseases, and cardiovascular and other diseases in adults has been firmly established. Smokers, however, are not the only ones affected.

The U.S. Environmental Protection Agency (EPA) has classified ETS as a known human (Group A) carcinogen and estimates that it is responsible for approximately 3,000 lung cancer deaths per year among nonsmokers in the United States. Airborne particulate matter contained in ETS has been associated with impaired breathing, lung diseases, aggravation of existing respiratory and cardiovascular disease, changes to the body's immune system, and lowered defenses against inhaled particles.

Architectural/Engineering Considerations

While improved general ventilation of indoor spaces may decrease the odor of environmental tobacco smoke, health risks cannot be eliminated by generally accepted ventilation methods. Research has led to the conclusion that total removal of tobacco smoke - a complex mixture of gaseous and particulate components - through general ventilation is not feasible.

With regards to IAP, the most effective solution is to eliminate all smoking from the non-smoker's environment, either through smoking prohibitions or by restricting smoking to properly designed smoking rooms. These rooms should be separately ventilated to the outside.

Some higher efficiency air cleaning systems, under select conditions, can remove some tobacco smoke particles. Most air cleaners however cannot remove the gaseous pollutants from this source. And while some air cleaners are designed to remove specific gaseous pollutants, none is expected to remove all of them and should not be relied upon to do so.

When designing new projects, Architects and Engineers should take care to research any special local or municipal code requirements regarding indoor air quality as these may be more stringent than state or national building codes. Special items might include:

The 2004 version of ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, sets the minimum ventilation rates and other requirements for commercial and institutional buildings. The goal of the 2004 version, which contains 17 new addenda, is to provide language that is enforceable. Addendum 62n to this Standard describes ventilation rates that are based on the fact that building occupant's activities as well as the building contents can contribute to air pollution. It bases ventilation requirements on the number of occupants a space is expected to accommodate in addition to the space's floor area. Outside air flow rates are computed on a zone by zone basis by summing the components of occupancy, occupant's activities, and space make-up, such as furnishings. The procedure to calculate outdoor air intake rate is clearly presented in 62n. The procedure produces ventilation rates that can be measured for compliance verification.

The fact that EPA classifies ETS as a carcinogen simply means that there in no known safe minimum concentration of ETS. As such, no target concentration level can be ascertained and therefore no recommended ventilation rates for its mitigation can be prescribed. Addenda 62a and 62o unequivocally state that prescribed ventilation air flow rates apply only to spaces that do not contain environmental tobacco smoke.

Addendum 62g, which will specifically address ETS, is under preparation by ASHRAE. In the meantime, addendum 62n can be downloaded for free via the "standards addenda index" link at www.ashrae.com.

Addendum 62y is important because it provides air classifications for ventilation based on contaminants and odors.

PRODUCTS OF COMBUSTION

Background

Aside from environmental tobacco smoke, the major combustion pollutants that may be present at harmful levels in the home or workplace stem chiefly from malfunctioning heating devices, or inappropriate, inefficient use of such devices in individual residences. Incidents are largely seasonal. Another source may be motor vehicle emissions due, for example, to proximity to a garage (or a loading dock located near air intake vents).

A variety of particulates, acting as additional irritants or, in some cases, carcinogens, may also be released in the course of combustion. Although faulty venting in office buildings and other nonresidential structures has resulted in combustion product problems, most cases involve the home or non-work-related consumer activity. Among possible sources of contaminants: gas ranges that are malfunctioning or used as heat sources; improperly flued or vented fireplaces, furnaces, wood or coal stoves, gas water heaters and gas clothes dryers; and unvented or otherwise improperly used kerosene or gas space heaters.

The gaseous pollutants from combustion sources include some identified as prominent atmospheric pollutants -- carbon monoxide (CO), nitrogen dioxide (NO2), and sulfur dioxide (SO2).

The elderly, the fetus, and persons with cardiovascular and pulmonary diseases are particularly sensitive to elevated CO levels. Methylene chloride, found in some common household products, such as paint strippers, can be metabolized to form carbon monoxide. Nitrogen dioxide (NO) and sulfur dioxide (SO2) act mainly as irritants, affecting the mucosa of the eyes, nose, throat, and respiratory tract.

Design and Maintenance Considerations

Periodic professional inspection and maintenance of installed equipment such as furnaces, water heaters, and clothes dryers in laundry areas are recommended. Such equipment should be vented directly to the outdoors. In hotels, restaurants, and other places of public assembly, fireplace flues should be normal items of preventive maintenance that are regularly inspected, and cleaned if necessary. When designing kitchen facilities, exhaust fans should be exhausted to outside. When preparing equipment specifications, vented appliances should be used whenever possible.

The location of outside air intakes should be carefully planned to preclude the possibility for induction of exterior air pollutants. Addendum 62a of the 2004 version of ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, publishes specific requirements for outdoor air intake locations with respect to contaminant sources. The quality of outdoor air used for ventilation is addressed in addenda 62r, 62z, and 62af.

BIOLOGICAL AIR POLLUTANTS

Background

Biological air pollutants are found to some degree in every home, school, and workplace. Sources include outdoor air and human occupants who shed viruses and bacteria, animal occupants (insects and other arthropods, mammals) that shed allergens, and indoor surfaces and water reservoirs where fungi and bacteria can grow, such as humidifiers. A number of factors allow biological agents to grow and be released into the air. Especially important is high relative humidity, which encourages dust mite populations to increase and allows fungal growth on damp surfaces. Mite and fungus contamination can be caused by flooding, continually damp carpet (hotel, motel, and seaside resort living units near swimming pools for instance), inadequate exhaust of restrooms, or kitchen-generated moisture. Appliances such as humidifiers, dehumidifiers, air conditioners, and drip pans under cooling coils (as in commercial refrigerators), support the growth of bacteria and fungi.

Components of mechanical heating, ventilating, and air conditioning (HVAC) systems may also serve as reservoirs or sites of microbial amplification. These include air intakes near potential sources of contamination such as standing water, organic debris or bird droppings, or integral parts of the mechanical system itself, such as various humidification systems, cooling coils, or condensate drain pans. Dust and debris may be deposited in the ductwork or mixing boxes of the air handler.

A disease associated with indoor air contamination is Legionnaires' Disease, a pneumonia that primarily attacks exposed people over 50 years old. The agent, Legionella pneumophila, has been found in association with cooling systems, whirlpool baths, humidifiers, food market vegetable misters, and other sources, including residential tap water.

Another class of agents that may cause disease related to indoor airborne exposure is the mycotoxins. These agents are fungal metabolites, like from mold, that have toxic effects ranging from short-term irritation to immunosuppression and cancer. Mycotoxins are contained in some kinds of fungus spores, and these can enter the body through the respiratory tract.

Engineering and Maintenance Considerations

Fresh air ventilation is an important factor in contagion control. The transmission of airborne infectious diseases is increased where there is poor indoor air quality. Evidence is increasing that inadequate or inappropriately designed ventilation systems in health care settings or other crowded conditions with high-risk populations can increase the risk of exposure. Unfortunately, many building systems are not equipped for the introduction of outside (fresh) air. Properly installed and maintained ultraviolet irradiation, particularly of upper air levels in an indoor area, is a useful means of disinfection in health care facilities.

A summary of actions could be:

VOLATILE ORGANIC COMPOUNDS

Background

At room temperature, volatile organic compounds are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals (e.g., formaldehyde, benzene, perchloroethylene), some of which may have short- and long-term effects. Concentrations of many VOCs are consistently higher indoors than outdoors. A study by the EPA, covering six communities in various parts of the United States, found indoor levels up to ten times higher than those outdoors -- even in locations with significant outdoor air pollution sources, such as petrochemical plants.

A wide array of volatile organics is emitted by products used in home, office, school, and arts/crafts and hobby activities. These products, which number in the thousands, include:

Many of these items carry precautionary labels specifying risks and procedures for safe use; some do not.

Formaldehyde has been classified as a probable human carcinogen by the EPA. Urea-formaldehyde foam insulation (UFFI), one source of formaldehyde used in home construction until the early1980s, is now seldom installed, but formaldehyde-based resins can be components of finishes, plywood, paneling, fiberboard, and particleboard, all widely employed in mobile and conventional home construction as building materials (subflooring, paneling) and as components of furniture and cabinets, permanent press fabric, draperies, and mattress ticking.

Pesticides sold for household use, notably impregnated strips, and foggers or "bombs", which are technically classed as semivolatile organic compounds, include a variety of chemicals in various forms. Exposure to pesticides may cause harm if they are used improperly. However, exposure to pesticides via inhalation of spray mists may occur during normal use. Exposure can also occur via inhalation of vapors and contaminated dusts after use (particularly to children who may be in close contact with contaminated surfaces).

Possible Remedial Engineering

Ventilation should be increased when using products that emit volatile organic compounds, and meet or exceed any label precautions. Open containers of unused paints and similar materials should not be stored within maintenance shops or office spaces.

Formaldehyde is one of the best known volatile organic compound (VOC) pollutants, and is one of the few indoor air pollutants that can be readily measured. Identify, and if possible, remove the source if formaldehyde is the potential cause of the problem. If not possible, reduce exposure: use polyurethane or other sealants on cabinets, paneling and other furnishings. To be effective, any such coating must cover all surfaces and edges and remain intact.

When preparing project specifications, design professional should review local or municipal codes to apprise themselves of any special or site specific prohibitions on building material types or protective coatings.

AIRBORNE LEAD AND MERCURY VAPOR

Background

Most technical professionals are aware of the threat of lead (Pb) toxicity, particularly its long-term impact on children in the form of cognitive and developmental deficits which are often cumulative and subtle. Such deficits may persist into adulthood. According to the American Academy of Pediatrics, an estimated three to four million children in the U.S. under age six have blood lead levels that could cause impaired development, and an additional 400,000 fetuses are at similar risk.

Lead poisoning via ingestion has been most widely publicized, stressing the roles played by nibbling of flaking paint by infants and toddlers. Airborne lead, however, is also a worrisome source of toxicity. Airborne lead outdoors, originating chiefly from gasoline additives, has been effectively controlled since the 1980s through regulation at the federal level. Much of this lead may still remain in the soil near heavily trafficked highways and in urban areas, however, and could become airborne at times. It may enter dwellings via windows and doors, and contaminated soil could possibly be tracked inside.

Additional sources of airborne lead include art and craft materials, from which lead is not banned, but the U.S. Consumer Product Safety Commission (CPSC) requires its presence to be declared on the product label if it is present in toxic amounts. Significant quantities are found in many paints and glazes, stained glass, as well as in some solder. Hazardous levels of atmospheric lead have been found at police and civilian firing ranges. Repair and cleaning of automobile radiators in inadequately ventilated premises can expose workers to perilous levels of airborne lead. The use of treated or painted wood in fireplaces or improperly vented wood stoves may release a variety of substances, including lead and other heavy metals, into the air.

While old paint has been the most publicized source of airborne heavy metal (i.e., lead), new paint has emerged as a concern as well. A 1990 report detailed elevated levels of mercury in persons exposed to interior latex (water-based) paint containing phenylmercuric acetate (PMA). PMA was a preservative that was used to prolong the product's shelf life.

Initial action by the U.S. Environmental Protection Agency resulted in the elimination of mercury compounds from indoor latex paints at the point of manufacture as of August 1990, with the requirement that paints containing mercury, including existing stocks originally designed for indoor use, be labeled or relabeled "For Exterior Use Only". As of September 1991, phenylmercuric acetate is forbidden in the manufacture of exterior latex paints as well. Latex paints containing hazardous levels of mercury may still remain on store shelves or in homes where they were left over after initial use, however.

Maintenance and Engineering Considerations

Wet-mop and wipe furniture frequently to control lead dust. Have professionals remove or encapsulate lead containing paint; individuals involved in this and other high exposure activities should use appropriate protective gear and work in well-ventilated areas. Do not burn painted or treated wood.

When preparing project specifications, design professional should review local or municipal codes to apprise themselves of any special or site specific prohibitions on building material types or protective coatings. While not a major contributing factor to IAP, the recent controversy over the use of CCA treated wood is an indication of how readily a particular well based building product can become problematic. Chromated copper arsenate, or CCA, is a chemical compound mixture containing inorganic arsenic, copper and chromium that has been used for wood preservative uses since the 1940s.

SICK BUILDING SYNDROME

Background

The term "sick building syndrome" (SBS), first employed in the 1970s, describes a situation in which reported symptoms among a population of building occupants can be temporally associated with their presence in that building. Typically, though not always, the structure is an office building.

Generally, a spectrum of specific and nonspecific complaints are involved. Typical complaints are:

The key factors are commonality of symptoms and absence of symptoms among building occupants when the individuals are not in the building. Sick building syndrome should be suspected when a substantial proportion of those spending extended time in a building (as in daily employment) report or experience acute on-site discomfort.

Design and Maintenance Considerations

There has been extensive speculation about the cause or causes of SBS. Poor design, maintenance, and/or operation of the structure's ventilation system may be at fault. The ventilation system itself can be a source of irritants. Interior redesign, such as the rearrangement of offices or installation of partitions, may also interfere with efficient functioning of such systems.

The location of HVAC return air grilles influence the air flow pattern through the building and their improper location can exacerbate the creation of naturally occurring localized recirculation zones. The short-circuiting of conditioned supply air due to improper return air grille location can result in a limited volumetric flow to some occupied spaces.

Another theory suggests that very low levels of specific pollutants, including some discussed in the preceding pages, may be present and may act synergistically, or at least in combination, to cause health effects. Humidity may also be a factor: while high relative humility may contribute to biological pollutant problems, an unusually low level -- below 20 or 30 percent -- may heighten the effects of SBS. Other contributing elements may include poor lighting and adverse ergonomic conditions, temperature extremes, noise, and psychological stresses that may have both individual and interpersonal impact.

Appropriate persons -- employer, building owner or manager, building investigation specialist, if necessary state and local government agency medical epidemiologists and other public health officials -- should undertake investigation and analysis of the implicated building, particularly the design and operation of HVAC systems, and correct contributing conditions. Persistence on the part of individual(s) and health care consultant(s) may be required to diagnose and remediate the building problems.

ASBESTOS AND RADON

Background

Asbestos and radon are among the most publicized indoor air pollutants. Both are known human carcinogens. Their carcinogenic effects are not immediate but are evident only years, even decades, after prolonged exposure.

Once widely used in structural fireproofing, asbestos may be found predominantly in heating systems and acoustic insulation, in floor and ceiling tiles, and in shingles in many older houses. It was formerly used in such consumer products as fireplace gloves, ironing board covers, and certain hair dryers.

When asbestos-containing material is damaged or disintegrates with age, microscopic fibers may be dispersed into the air. Over as long as twenty, thirty, or more years, the presence of these fibers within the lungs may result in asbestosis (asbestos-caused fibrosis of the lung).

Radon is the second leading cause of lung cancer, following smoking. Radon is an odorless, colorless, tasteless inert gaseous element, which occurs naturally from the radioactive decay of radium atoms, found in soils and rocks throughout the world. Radium is a decay product of uranium. Radon in turn breaks down into radon decay products, short-lived radionuclides. These decay products, either free or attached to airborne particles, are inhaled, and further decay can take place in the lungs. Soil gas is considered the most important contributor of radon, with decreasing levels of contribution from outdoor air and building materials.

It is the emission of high-energy alpha particles during the radon decay process that increases the risk of lung cancer. While the risk to underground miners has long been known, the potential danger of residential radon pollution has been widely recognized only since the late 1970s, with the documentation of high indoor levels.

When radon decay products are inhaled and deposited in the lungs, the alpha emissions penetrate the cells of the lung lining. Energy deposited in these cells during irradiation is believed to initiate the process of carcinogenesis.

The EPA estimates that as many as six million homes throughout the country have elevated levels of radon. Since 1988, EPA and the Office of the Surgeon General have recommended that homes below the third floor be tested for radon.

Maintenance and Inspection Considerations

Products and materials containing asbestos are not necessarily so labeled. Construction professionals or state or local environmental agencies may inspect and analyze suspect materials. The National Academy of Building Inspection Engineers' (NABIE) Standards of Practice lists the requirement for observation, reporting, and evaluation of suspected asbestos containing materials and evidence of UFFI. Manufacturers of particular products may also be able to supply information.

The risk of disease depends on exposure to airborne asbestos fibers. Average levels in buildings are low, and the risk to building occupants is therefore low.

Removal of asbestos is not always the best choice to reduce exposure. The EPA requires asbestos removal only in order to prevent significant public exposure and generally recommends an in-place management program when asbestos has been discovered and is in good condition.

With regards to radon, short term testing is the quickest way to determine if a potential problem exists, taking from two to ninety days to complete. Low-cost radon test kits are available by mail order, in hardware stores, and through other retail outlets. Corrective steps include sealing foundation cracks and holes, and venting radon-laden air from beneath the foundation. Professional expertise should be sought for effective execution of these measures.

Site selection and evaluation with particular regard to subsurface geology are paramount for new structures for which below grade occupancy is planned.


Additional Resources

To Learn More About Indoor Air Quality

U.S. Environmental Protection Agency
Office of Radiation and Indoor Air
Indoor Environments Division (6609J)
Arial Rios Building
1200 Pennsylvania Avenue, N.W.
Washington, DC 20460
(202) 564-9370
(202) 565-2038/39 (fax)

Indoor Air Quality Information
Clearinghouse (IAQ INFO)
P.O. Box 37133
Washington, DC 20013-7133
1 (800) 438-4318
(703) 356-4020 (local)
(703) 356-5386 (fax)
E-mail: IAQINFO@aol.com

The student may be interested in investigating the following texts, publications, and magazine articles to gain a more detailed understanding of certain specific aspects of Indoor Air Pollution:

Responding to Indoor Air Quality Problems, Naumann, Keith and Doug Lamecker, Heating/ Piping/Air Conditioning magazine, July 1998.

IAQ: An Environmental Factor in the Indoor Habitat, Burroughs,H.E. Barney, Heating/ Piping/Air Conditioning magazine, February 1997.

Room Air Circulation: The Missing Link to Good Indoor Air Quality, Kelly, Roy, Heating/ Piping/Air Conditioning magazine, September 1995.

U.S. Environmental Protection Agency, U.S. Public Health Service, and National Environmental Health Association. Introduction to Indoor Air Quality: A Reference Manual, EPA-400-3-91-003, 1991.

U.S. Environmental Protection Agency, Office of Air and Radiation. Indoor Air Facts No. 4: Sick Building Syndrome, revised 1991.



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