Airborne debris indoors (C) Daniel FriedmanIndoor Air Quality Improvements
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Best practices guide to indoor air quality:

Indoor Air Quality Testing, Diagnosis, and Remedies. Test & remove indoor air contaminants: gases, particles, odors, others.. These indoor air quality and health articles discuss in detail the steps needed to test, diagnose and improve indoor air quality in homes and commercial buildings.

Examples of topics we cover include air filters, allergens indoors, carpeting, Chinese drywall, house dust, unsafe gases found indoors, mold in buildings, odors, and building ventilation.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Indoor Air Quality - Best Practices for Improving Indoor Air in Homes

Indoor air particles of fiberglass and Pen Asp spore chains © D Friedman at

Here we provide detailed, un-biased advice on finding and correcting indoor air quality problems as well as advice on new construction details for a combination of low building energy cost and high indoor air quality.

This article series includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

Our page top photo shows that even the naked eye can see comparatively large airborne particles indoors. And our photo at left illustrates an indoor air particle sample dense with fiberglass, fungal hyphae, and Penicillium/Aspergillus spore chains - indicating a nearby mold contamination source.

But many indoor contaminants are simply too small to see, or are not particles at all but rather gases or chemicals.

See ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY for our full list of environmental hazard identification and remedy related to buildings

To find what you need quickly, if you don't want to scroll through this index you are welcome to use the page top or bottom SEARCH BOX to search InspectApedia for specific articles and information.

Overview of Indoor Air Quality Issues & Solutions

Photograph of toxic gas testing equipment in use (C) Daniel Friedman

As noted in Best Practices Guide to Residential Construction [link is to book information]:

Two trends have conspired to place significant stresses on the indoor environment over the past two decades.

First, houses are being built much tighter today than they were a generation ago, either deliberately by energy-minded builders or simply as a by-product of using modern building materials, such as plywood, DRYWALL, or INSULATION, and tight- fitting doors and windows.

Second, the number of synthetic building materials has rapidly expanded to include synthetic CARPETING, a wide variety of plastics, wood composites, adhesives, sealants, and finishes.

These, along with the wide variety of cleaning, personal care, and hobby products stored and used indoors provide most homes with an ample source of airborne chemicals, many of which have not been well studied, either alone or in combination with others.

Some leading indoor-air-quality advocates have referred to this unknown mix of airborne compounds as “chemical soup.”

Individuals with allergies, asthma, or strong chemical sensitivities were, like the proverbial canary in the coal mine, the first to call attention to the higher concentrations of chemicals that were building up in our new, tighter homes. While scientists had thoroughly studied the outdoor air in cities and indoor air in occupational settings, little was known about air quality in homes.

Indoor Air is Typically More Contaminated than Outdoor Air

Airborne debris indoors (C) Daniel Friedman

A growing body of scientific evidence has demonstrated that the air inside homes is typically more polluted than outdoor air, even in polluted urban areas. For example, the U.S. EPA team tudy of over 600 residents in seven cities in the 1980s found that exposure to toxic chemicals was much greater at home or at work than outdoors.

Compare our airborne dust photograph at left with the similar image at page top for two examples of the extreme range of airborne particle contaminants that may be present in a building.

Levels of about a dozen common organic pollutants were found to be two to five times higher inside homes than outside, regardless of whether homes were in rural or industrial areas.

And since the average person spends far more time indoors than outside, the study concluded that health risks from the indoor environment pose a greater risk to most people than outdoor air pollution.

Fortunately, as builders, designers, and homeowners, we potentially have much greater control over our indoor environment than out of doors.

Public health professionals and researchers both in the private sector and in state and federal agencies have identified the most significant threats posed by indoor air pollution, as well as a number of straightforward strategies that enable us to minimize or eliminate the health risks.

See INDOOR AIR QUALITY & HOUSE TIGHTNESS for a discussion of the relationship between air-tightness of a home and indoor air quality and for a description of the causes of variation in indoor air quality among similarly-constructed homes.

Acceptable Risk: Just How Clean Does Indoor Air Need to Be?

Remember, there is no environment— indoor or outdoor—that is 100% free of hazardous materials, many of which (like radon, asbestos, and airborne particulates) occur naturally in the environment. And while many of these substances have been studied extensively in the workplace, the effects of long-term exposure to the lower levels found in most homes are not well understood.

For some indoor air pollutants, like radon, scientists have a fairly precise understanding of the health effects and recognize that that no exposure level is safe. However, the cost of reducing the indoor radon level to zero (below outdoor levels) would be prohibitive for most people, so homeowners, health professionals, and regulatory agencies do their best to find a “cost-effective” goal that balances costs against perceived health risks.

In the absence of clear indoor air guidelines, and taking into account that all building projects have budget limitations, the goal of this chapter is to identify reasonable steps that builders and designers, and, in some cases, homeowners can take to produce a healthy indoor environment by eliminating or substantially reducing known hazards.

The emphasis will be on getting the greatest benefit for the least cost, starting with the most significant hazards.

How much an individual invests in clean indoor air is a matter of personal choice. Fortunately, with good planning, a great deal can be accomplished for a modest investment.

For individuals with special sensitivities to chemicals, dust, or biological materials such as INDOOR MOLD CONTAMINATION, the measures described here may not be adequate. A more comprehensive approach under the guidance of environmental health specialists is advisable.

Note: For a helpful discussion of just what constitutes "adequate venitlation", see Offermann, Francis (Bud) J., P.E., C.I.H., ASHRAE & Mark Nicas, Ph.D., MPH, C.I.H., USE WITH ADEQUATE VENTILATION ? [PDF], ASHRAE Journal, May 2018.

Health Effects of Indoor Air Pollutants

Indoor air pollutants at high levels can cause acute illness, while lower levels may lead to health problems only after years of exposure. In the case of certain carcinogens, such as radon, health professionals believe that a single exposure could lead to health problems many years later (although the greater the total exposure over time, the greater the risk).

While the effects of some pollutants are well understood, for others further research is needed to determine what concentrations and types of exposure will impair health. Also, it is important to bear in mind that different people react very differently to indoor pollutants.

Even in the absence of definitive studies on every pollutant, there is little disagreement that reducing exposure to volatile organic compounds, combustion gases, radon, common allergens, and other indoor pollutants is a worthwhile goal for all homeowners and particularly vital for the very young or for those with allergies or respiratory problems.

[See MOLD RELATED ILLNESS for an extensive list of occupant-reported illnesses related to mold and other indoor contaminants.]

Short-Term Health Effects of Exposure to Indoor Pollutants

High levels of indoor pollutants can cause immediate symptoms after one or more exposures. The symptoms may look like those of a cold or virus, including irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue.

These effects are usually short-term and reverse quickly once the person leaves the building or the pollutant is identified and eliminated. Short-term exposures can also trigger asthma episodes and lead to other serious allergic responses, including hypersensitivity pneumonitis and humidifier fever, both of which may first appear as flu-like symptoms.

For many pollutants, the exposure level at which symptoms first appear is highly variable. Key factors include a person’s age, preexisting medical conditions, and his or her individual sensitivity to the chemical or biological compound in question.

For example, MOLD, or POLLEN, or INSECT FRAGMENTS, or INSECT FECALS=, and ANIMAL DANDER or PROTEINS (dander, etc.), elicit a range of allergic reactions in some, while others are unaffected.


Also, the level at which formaldehyde elicits symptoms ranges from as little as .04 ppm to as much as 5.0 ppm (parts per million), depending on an individual’s sensitivity.

To complicate matters, people can develop sensitivities to both biological and chemical pollutants at any point in their lives, possibly from repeated exposures to low levels of the substance.

See COMBUSTION AIR REQUIREMENTS for additional details about the requirement for combustion air.

COMBUSTION AIR for TIGHT BUILDINGS explains how to provide outside combustion air for tight buildings.

See COMBUSTION GASES & PARTICLE HAZARDS for an explanation of the dangers of inadequate combustion air.

See COMBUSTION PRODUCTS & IAQ for the relationship between fuel burning appliances and building indoor air quality. More about carbon monoxide - CO - is



Long-Term Health Effects of Exposure to Indoor Pollutants

Some of the most toxic substances in our homes, such as LEAD, or ASBESTOS, and RADON, can under some circumstances cause long-term irreversible damage to health. Many types of air pollutants increase the frequency and severity of asthma attacks.

COMBUSTION BYPRODUCTShave been linked to reduced lung function in developing children. Some health problems, including certain cancers, have long latency periods and may show up years after exposure to a pollutant such as tobacco smoke or radon.

There is also ample evidence that some materials, such as FORMALDEHYDE GAS, are “sensitizers,” which can cause a person to become hypersensitive after years of low-level exposure.

Whether indoor air quality contributes to other chronic health problems, such as heart disease, respiratory diseases, and cancers (other than lung cancer from radon and secondhand smoke), is unclear; but there is evidence that all major internal systems can be strained and become symptomatic as a result of poor indoor air quality.

-- Adapted with permission from Best Practices Guide to Residential Construction.

Collecting & Testing Building Dust Samples for Indoor AIr Quality Assessment

Reader Question: how can I collect a dust sample for lab analysis to screen for problem particles?

This expert-recommended mold test kit is easy, inexpensive, and
accurate *IF* you sample from a representative spot and *IF* you use a competent mold analysis laboratory!

Can you tell me the best procedure for getting a dust sample analyzed to see if there are indications of mold, insects, pollen, small fiberglass particles, or other indoor irritant particles? - Maurice 2/5/2010

I am looking through the site so that I can follow the suggested steps to test a dust sample from my apartment. Can you recommend a lab to send it to? Thank you. - Peggy Sissleman 6/15/2011


Please see DUST SAMPLING PROCEDURE where we describe when, where, & how best to collect a sample of settled dust from a representative building surface.

Just about any forensic microscopy lab, including many of the labs who accept mold test samples, should be able to examine your dust to let you know what particles are dominant and whether or not the dust contains clues suggesting that further building investigation is needed.

Dust samples are also useful to track down annoying or apparently unusual quantities of indoor dust to its probable source. For example we may examine a settled dust sample as well as a snip of carpeting fiber or a sample of building insulation to determine if that carpet or insulation is the source.

Watch out: keep in mind that while airborne particles are a key component in IAQ investigations, particle analysis will not detect irritating or hazardous gases, VOCs, odors, etc.

Reader Question: where can I mail building dust samples for analysis?

30 Oct 2014 Maria said

Where can I mail dust samples to see what they contain - Maria



You can use any environmental test lab - to avoid any possible conflict of interest, please do not send dust samples to our own forensic lab.

For environmental or forensic investigative support and lab work, you can use any forensic lab provided you first check that their area of expertise matches your needs.

For strange particle analysis, building dust analysis, fiberglass particle screening, mold contaminant screening contact these expert forensic microscopists

For mold or general environmental dust samples also contact our backup is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information for the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.


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