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INDOOR AIR QUALITY IMPROVEMENT GUIDE
AIR CLEANER PURIFIER TYPES
AIR FILTER CLEANER EFFECTIVENESS
Air Filtering Strategies
Air Pollutants, Health Effects
Air Pollutants, Common Indoor
Air Pollutants, Finding & Reducing
BACKDRAFTING HEATING EQUIPMENT
BLUE vs YELLOW COMBUSTION FLAMES
BUY PRODUCTS for MOLD & ALLERGY CONTROL
CABINETS & COUNTERTOPS
CARPETING & INDOOR AIR QUALITY
CHINESE DRYWALL HAZARDS
COMBUSTION APPLIANCE CONTAMINANTS
EMERGENCY RESPONSE, IAQ, GAS, MOLD
FIRE & SMOKE ODOR REMOVAL
FIREPLACE & WOODSTOVE CONTAMINANTS
Formaldehyde Gas Hazard Reduction
GAS CONCENTRATIONS in AIR
GAS EXPOSURE EFFECTS
GAS EXPOSURE LIMITS & STANDARDS
Gases, Quick Guide to Indoor
INDOOR AIR HAZARDS TABLE
INDOOR AIR QUALITY IMPROVEMENT, KEY STEPS
INDOOR COMBUSTION PRODUCTS & IAQ
LEAD EXPOSURE HAZARDS INDOORS
GAS CONCENTRATIONS in AIR
GAS LP & NATURAL GAS SAFETY HAZARDS
LP & Natural Gas Pressures
METHANE GAS SOURCES
Natural Gas Combustion Products
ODORS, Smells, Gases in buildings
PARTICLES in INDOOR AIR, CHART
PESTICIDE EXPOSURE HAZARDS
RADON HAZARD TESTS & MITIGATION
UREA FORMALDEHYDE FOAM INSULATION, UFFI
URETHANE FOAM Deterioration, Outgassing
VENTILATION, EXHAUST ONLY
VENTILATION, WHOLE HOUSE STRATEGIES
VOCs VOLATILE ORGANIC COMPOUNDS
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.
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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.
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
Overview of Indoor Air Quality Issues & Solutions
As noted in Best Practices Guide to Residential Construction:
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, 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
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. EPATEAM study 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.
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.
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 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
and at CARBON MONOXIDE WARNING.
Long-Term Health Effects of Exposure to Indoor Pollutants
Some of the most toxic substances in our homes, such as lead, 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 by-products have 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, 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?
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
Daniel Baxter (firstname.lastname@example.org) or
Larry Wayne (email@example.com)
For mold or general environmental dust samples also contact our backup
EMS lab is a very large and competent network of labs offering a wide range of services
InspectAPedia.com 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.
Continue reading at INDOOR AIR QUALITY IMPROVEMENT, KEY STEPS or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: is an indoor mold spore count of 29,100 and 689 Aspergillus harmful?
Is an indoor spore count of 29,100 and a raw count of 689 of Aspergillus a harmful level? My daughter has moved into an apartment we feel has a heavy musty odor of mold and we are concerned. We had testing done and we are having trouble understanding the test results. Thanks! - Willie 8/13/2011
Willie the interpretation of a spore count, given the huge variability from moment to moment of indoor particle levels, has meaning mostly if interpreted by an expert who also has actually inspected the building. I have no trust in "raw" indoor airborne particle counts - I'm not even sure what your report means by that number, but in any event, we need to know not just how many of particle x there are in a building but how big a percentage of all particles they form.
When you have some idea what your "mold tester" was up to, then the article titled MOLD CONTAMINATION LEVELS
In my OPINION whomever you paid should not just have thrown a lab report over the wall to you - they owe you something for their fee, no?
At MOLD / ENVIRONMENTAL EXPERT, HIRE ? we include some criteria for helping decide when further investigation for a hidden mold contamination problem is in order.
Question: the air quality in our house is causing breathing issues with everyone - the mold inspector didn't see a problem and recommended an air exchange unit
The air quality in our house is causing breathing issues with everyone in the house. A certified mold inspector just looked at our house and saw no water issues nor mold issues. Our dehumidifier in the basement needs to be emptied 3x a day. She suggested replacing the humidifier with an air exchange system like Humidex. Is that a reasonable step to take or should we get some other inspector in? - Barbara 8/16/11
Reply: dilution of contaminated air versus finding and removing the contaminant is the question?
Barbara, the swap out of a portable dehumidifier to an air to air exchange unit would be expected to add outdoor fresh air into the home, perhaps diluting an indoor contaminant, irritant, or pollutant. It's not an unreasonable suggestion ("how-to" advice is at VENTILATION, BALANCED), but it begs the question.
If no one has diagnosed a problem in the home no one knows what's wrong or what needs to be fixed, so we don't know if there is not something more harmful, or urgent, that should be corrected. You could wear a HEPA filter respirator while indoors too, and might feel better if the problem in indeed due to indoor air particles, but still no one would know what problem to address in the home.
The issue seems to be dampness (not to the touch) from the concrete. When I am away from the home and no one is tending to the dehumidifier constantly the surface mold develops on items conducive to mold growth--certain wood items, baseboards behind bookshelves, cardboard boxes or clothes directly on the concrete floor and the like. My house is on a wooded lot, which is nice and cool in the summer, but may contribute to the general dampness in the basement. Is this still sounding like an air to air exchange unit would be helpful? We are also considering cutting down a tree or two overshadowing our house. Members of the home are seriously affected by the air quality. Would you recommend hiring an expert inspector like Greg Brown or try the air to air exchange unit? (Thank you for your assistance!) - Barbara 8/17/11
If you are seeing indoor mold growth there is an indoor humidity problem. All mold is everywhere, all the time. So when indoor conditions are right, depending on the particular indoor surface - what it's made of - some mold spores find it a nice place to begin colonization.
Question: My vinyl floor smells like B.O. and is making me sick
Hi, hopefully you can help,
The [smelly vinyl] floor is Permastone by Tarkett and it was tested by the Resilient Floor Covering Institute and given a floor score as being environmentally sound and complies with California's volatile organic compound emissions criteria. Maybe that was after mine was manufactured.
Amanda, vinyl flooring outgassing of VOCs usually diminishes rapidly in the days right after installation; outgassing and odors may also be from the adhesive or mastic used to install the floor, not the flooring itself. But yours is the first report we've had of an odor associated with "BO" or body odor.
Also see these articles:
Question: are pressure treated materials toxic to breathe?
I need to know if pressure treated materials are toxic to breath , and how do you get rid of the smell on the pressure treated materials. I have tried sealers[Bin Shellac] and added ventilation under the home .I have 6 by 14 pressure treated beams under the house supporting the main floor. Please advise - Paul MacGregor 3/26/12
What and where are your pressure treated materials. Odor complaints from treated lumber are not something we have heard reported before. How did you determine the odor source?
However Paul, if you are talking about sawdust from construction during building of a structure that uses pressure-treated lumber, modern pressure treated lumber typically uses borate salts rather than the more toxic CCA (that contained copper arsenate - an arsenic compound) in older lumber.
Nevertheless, sawdust in general is a respiratory irritant that should be avoided by wearing a proper respirator - we'd recommend a HEPA respirator worn while sawing or sanding treated or any other wood.
Details about the types of wood preservative treatment, health concerns, & working with treated lumber are
Question: indoor air contaminants include gases & microbes
(May 20, 2011) Manish K. Verma said:
Here the normal concentration of the contaminants like gases, microbes should be mentioned.
Thank you for the suggestion Mannish, see the table just above.
Question: soft water in a dehumidifier
(Feb 6, 2014) Anonymous said:
I use water soften by auqa pur in my dehumidifier and it puts a salt dust in the air and covers my furniture, is this harmful?
Really? a dehumidifier removes moisture from building air. More likely you are discussing a humidifier - a device to add humidity to building air.
Please see HUMIDITY CONTROL & TARGETS INDOORS
Question: office flooded, IAQ complaints
(July 24, 2014) Josie said:
Our office was recently flooded due to a plumbing mishap. Because of the water, the walls had to be torn apart, insulation removed & replaced, drywall & studs replaced. The repairs are still ongoing. Anytime I'm in the office now, after about an hour my throat gets itchy, my tongue tingles & itches, I develop a cough, nausea and headache. Could the repairs, open/disturbed insulation, etc be the cause of these new symptoms? thanks for your time.
Josie it is possible that the extent of demolition and cleaning were inadequate. Some simple measurements of what is in the indoor dust may be helpful.
Also see FIBERGLASS HAZARDS
Question: office smells rotten
(Sept 11, 2014) Lee Bryant said:
Our office smells like there is something "rotten" and it is usually in the mornings. It seems to not be as bad as the day passes.
Lee in the More Reading links above, beginning at
we provide suggestions for tracking down odor sources.
11/30/2014 Glen de Valk said:
Last May we replaced our central air unit in our 2400 sq.ft. home in Sarasota, FL. It was replaced with the same size unit that had been in place for over 20 years (3.5 tons) and cooled and dehumidified very well. However, the new unit does not dehumidify the air regardless where temp. is set and keeps the humidity level no lower than 60% and as high as 72% when we raise the thermostat to our comfort level around 75 degrees. We had an independent inspection of the system done and detected that the air humidity at the registers was 83-85% when the unit was running; when the compressor shuts off and the fan runs for a pre-set 90 seconds more, the humidity level goes to 100%. The installer cancelled the 90 second period of running but the humidity level still stays at 82-85% coming out of the registers and around 60 to 65 % at the returns. The house was also thoroughly tested for plumbing leaks, etc. and there are none. The A/C contractor thought the 3.5 ton unit was too big and replaced it with a 3 ton unit so it would run longer cycles. That made absolutely no difference in dehumidification. The contractor seems to be at a loss to cure it. Please advise. Thanks.
Glen, please see your question and our reply in the article at DEHUMIDIFICATION PROBLEMS
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Technical Reviewers & References
prices, have already updated their building codes to the 2001 version. Some states and cities, such as Phoenix, are now going further by leapfrogging the 2001 edition and enacting part or all of the 2004 edition instead."