Subject : IAQ FAQ Part 1

This article is a compilation of frequently asked questions about Indoor Air Quality (IAQ).

Its author is:

Richard R. Byrd
Director of Indoor Air Quality Investigations
Machado Environmental Corp.
Glendale, Calif. USA

Note: As are all FAQs, this is an evolving document. This is particularly true in the field of indoor air quality, where there are few hard facts and many questions unanswered. Where it exists, this FAQ expresses the consensus of scientific opinion. Where it does not, it should be understood, this FAQ is an expression of the opinion of the author. Suggestions, comments, additions, corrections, raves and flames are cheerfully solicited.


1. General/ Introduction.
2. Sick building syndrome (SBS), building related illness (BRI), and multiple chemical sensitivity (MCS).
3. Legionnaire's disease.
4. Carbon Monoxide poisoning.
5. Bioaerosols and water problems.
6. Air cleaners, air filters, and cleanliness.
7. VOC's (volatile organic compounds) - carpets, particle board, remodels, etc.
8. Fiberglass and other man-made mineral fibers.
9. Lead, radon, and asbestos.; industrial chemical exposures; etc.
10. Ventilation systems.
11. IAQ professionals.
12. Standards, regulations, guidelines, legal issues.
13. Bibliography.
14. Organizations.
15. Acknowledgments, legal notices, etc.


1.1 What is Indoor Air Quality?

Indoor Air Quality (IAQ) refers to the effect, good or bad, of the contents of the air inside a structure, on its occupants. Usually, temperature (too hot or too cold), humidity (too dry or too damp), and air velocity (draftiness or motionlessness) are considered "comfort" rather than indoor air quality issues. Unless they are extreme, they may make someone unhappy, but they won't make a person ill. Nevertheless, most IAQ professionals will take these factors into account in investigating air quality situations.

Good IAQ is the quality of air which has no unwanted gases or particles in it at concentrations which will adversely affect someone. Poor IAQ occurs when gases or particles are present at an excessive concentration so as to affect the satisfaction or health of occupants.

In the minor instances, poor IAQ may only be annoying to one person. At the extreme, it could be fatal to all of the occupants of a structure.

It is important to note that the concentration of the contaminant or contaminants is crucial. Potentially infectious, toxic, allergenic, or irritating substances are always present in the air. There is nearly always a threshold level below which no effect occurs.

1.2 What is the relationship between indoor and outdoor air quality (pollution)?

No building is perfectly sealed and so the air inside ultimately originates outside. Air pollution present in the outdoor environment will therefore enter into the building as well. Generally, pollutants present in the outdoor environment are present at a somewhat lower concentration than outside (probably 10 to 90% in most cases). There are several reasons for this. Some pollutants are absorbed by materials in the building. Others deteriorate or react chemically and so disappear. Still others may be filtered out by the ventilation system. Also as it takes some time for the outdoor air to enter in quantities, there may be a delay from the time a contaminant appears outdoors, to when it becomes a problem indoors. Smog from outdoors reaches its peak indoors some time after the outdoor peak.

Outdoor contaminants may be present indoors at a sufficient concentration to affect the occupants. Examples are pollen and mold spores from outdoors causing hay fever and allergies indoors; and high smog levels affecting occupants inside a building. Incidentally, there is no such thing as a good smog day close to a major highway (expressway/freeway).

1.3 How common are IAQ problems?

According to the World Health Organization, approximately 30% of all commercial buildings have significant IAQ problems. Similar estimates have been made by others. I am unaware of any similar estimates in regards to residences.

1.4 How serious are IAQ problems?

The vast majority of IAQ problems are relatively minor. This means that occupants may suffer health effects such as cold or flu-like symptoms. In the case of workplaces, some individuals may miss some work days, and productivity will be affected. Serious and/or permanent health effects are much rarer, however they do occur, as in the case of Legionnaire's disease outbreaks.

1.5 State of current knowledge.

IAQ is a new field in many ways. Much of the current knowledge is less than 20 years old, and there is a great deal that is not known about it. In fact, it is safe to say that far more is unknown than is known about the field at this time. Even experts cannot come up with a definite answer in every situation.

1.6 Types of pollutants.

Air quality is affected by the presence of various types of contaminants in the air. Some are in the form of gases. These would be generally classified as toxic chemicals. The types of interest are combustion products (carbon monoxide, nitrogen dioxide), volatile organic compounds (formaldehyde, solvents, perfumes and fragrances, etc.), and semi-volatile organic compounds (pesticides). Other pollutants are in the form of particles. These include bioaerosols (mold spores, pollen, viruses, bacteria, insect parts, animal dander, etc.); soot; particles from buildings, furnishings and occupants such as fiberglass, gypsum powder, paper dust, lint from clothing, carpet fibers, etc.; dirt (sandy and earthy material), etc.

1.7 How indoor air affects people.

You remember I said the state of the research is incomplete? So don't expect a total answer on this one as it is not known. Some air contaminants are toxic; they affect the body as a poison. Pesticides and lead fall into this category. Odorous substances may be toxic, or may be only annoying, but might still scare someone into having a physical reaction. Some substances are irritants, such as fiberglass. Some are carcinogenic, e.g., asbestos, and some of the chemical constituents of soot. Some substances - chemical as well as biological - are allergenic and will trigger allergy or asthma attacks in susceptible individuals.

The most common health effects from poor indoor air quality are upper respiratory irritation (eyes, nose, sinuses, throat), headaches, fatigue, and allergic reactions.

1.8 Tobacco smoking.

One of the most important IAQ subjects is going to get very little attention in this FAQ: tobacco smoking. Tobacco smoke is recognized as carcinogenic and a cause of increased heart disease to those who inhale it - whether as the smokers themselves or as second-hand smoke.

In buildings in which tobacco smoking is permitted, the level of particles in the air is commonly 5 or 10 times higher than it would be if there were no smoking occurring. High dust levels are un-healthful in and of themselves. There are also many toxic chemical constituents of cigarette smoke.

Despite the tobacco industry claims, this is not controversial. Since tobacco smoking, yea or nay, is totally under the control of occupants - well, need I say more?

In commercial buildings where smoking is allowed only in dedicated smoking lounges, it is essential that they be properly ventilated. Air from the room must be exhausted under sufficient pressure so it doesn't migrate into other areas. It must also be exhausted in a way that it doesn't get pulled back into the building from outside. If smokers go outside they must not smoke in front of outside air intakes or doorways where their smoke will be sucked into the building.

1.9 How can you tell if you have an indoor air quality problem in a building?

The usual clue is that people feel ill while inside the building, and the symptoms go away shortly after leaving the building, or sometimes, when away for the building for a period of time (as on weekends away from work, or a vacation).

This doesn't necessarily work in cases of BRI (sections 2.3, 2.4), where it may take medical testing and investigation of the building to determine whether the building is the source of the problem.

1.10 What should you do if you suspect you have an indoor air quality problem?

Look over this FAQ. Find the material most related to what seems to be going on. In most cases there are suggestions as to things that can checked in to. Some of these can be checked by anyone; others require an expert (medical doctor, HVAC service company, IAQ investigator, etc.).

1.11 How do you choose an IAQ consultant?

If necessary, hire an IAQ consultant to investigate the building. Be forewarned: There is currently no license, degree, certification, or training that will guarantee getting a competent job of investigation done. Check out references, make sure the person has done similar work before. For more information, see section 11.



2.1 What is SBS?

Sick building is the condition of a building in which more than 20% of the occupants are suffering from adverse health effects, but with no clinically diagnosable disease present. It is the condition of the building; not of the occupants. The 20% figure is arbitrarily set as there will always be SOME individuals complaining about adverse health effects associated with occupancy of a building. However, if the figure is 20% or more, it is considered that there must be some determinable cause which can be remedied.

The symptoms reported most often include headaches, stuffed or runny nose, sneezes, sore throat, eye irritation, fatigue, and muscle aches.

It is important to note that there is no medically recognized disease involved in these cases. The symptoms may be annoying, may cause lost production and missed work days, but there is no serious or permanent adverse health effect involved.

This is the most common indoor air quality problem in a commercial building, and common it is indeed. It is generally agreed that 30% of all commercial buildings in the U.S., for example, suffer from SBS, and that the expenses in terms of medical costs and lost production are in the tens of billions of dollars per year in the U.S. alone.

2.2 What causes SBS? How do you deal with it?

The causes of SBS are still uncertain. Amongst the causes postulated, and for which some evidence exists, include man- made mineral fibers (MMMF), macromolecular organic chemicals (large size molecules produced by living things, such as protein molecules), volatile organic compounds (VOC's), and many others. Studies have shown that SBS is far more likely to occur in a building which has air-conditioning then in one which is naturally ventilated (operable windows). Buildings with air- conditioning that have an inadequate supply of fresh air are far more likely to suffer from SBS than those whose fresh air supply satisfies current standards.

Most experts feel that SBS is due to long-term exposure to low levels of a combination of contaminants. The level of each contaminant present may be far below any level at which a recognized health effect occurs, but the combination of numerous chemicals and particles at such levels then has the effect known as SBS. Research on this is at an early stage but tends to support this hypothesis.

Some psychologists have claimed that SBS is 100% psychological in origin, but this is clearly not true. The true percentage is probably closer to 5%. Women are far more likely to complain of symptoms than men, as are employees who are dissatisfied with their jobs, under stress, or in work circumstances where they have little control over their jobs. Rarely, complaints may be a part of a phony Worker's Compensation claim or lawsuit.

2.3 What is BRI?

Building Related Illness or BRI is the general term for a medically diagnosable illness which is caused by or related to occupancy of a building. Examples include Legionnaire's disease if caught from a building's cooling tower; carbon monoxide poisoning from a malfunctioning water heater; etc.

2.4 What causes BRI? How do you deal with it?

The causes vary with the disease. In addition to any appropriate treatment for the disease, elimination of the source of the problem is essential and may be the only thing required to eliminate the disease.

2.5 What is MCS?

Multiple Chemical Sensitivity (MCS), which has also been called Environmental Illness (EI) and "20th century disease" is a condition of an individual who is sensitive to chemicals (by inhalation, ingestion, or contact) to a point where he suffers adverse health effects from exposure to even extremely low levels of a variety of chemicals.

It is controversial whether MCS is a genuine medical condition. Not much research has been performed yet though the U.S. EPA is currently beginning a project to investigate it.

The AMA has recently stated that alleged cases of MCS should be taken seriously and the person receive a complete medical work-up.

2.6 What causes MCS? How do you deal with it?

Again, this is controversial. One study claimed to demonstrate that MCS doesn't exist and is really a manifestation of mental illness. However, the study was flawed. One hypothesis is that MCS usually begins with exposure to a single chemical and then spreads, that it is caused by a common physiological reaction to chemicals in general. Some recent work has tended to support this notion. This hypothesis suggests that the same mechanism that causes SBS, will, in the extreme, cause MCS.

Individuals with extreme cases of MCS may not be able to work in a normal work environment and may have to live in specially constructed environments which are ultra-low emitting of chemicals - having hardwood floors, no carpeting, plastics, etc.

There are physicians specializing in treating MCS cases, who may be known as "Clinical Ecologists".


3.1 What is Legionnaire's disease?

Legionnaire's disease is a form of pneumonia caused by a bacterium, Legionella pneumophilia. It was first discovered following an outbreak at an American Legion convention in a Philadelphia hotel in 1976. However, after the organism was isolated, some earlier pneumonia outbreaks were investigated and it was verified that earlier cases had occurred.

Legionnaire's disease has an attack rate of about 5%, meaning about 5% of those exposed will contract the disease, and a mortality rate of around 15%, meaning about 15% of those who contract the disease will die of it. In total, then, a bit under 1% of those exposed will die from the disease.

3.2 How is it transmitted?

The bacterium which causes Legionnaire's disease is normally present at low levels in potable water supplies. Under the right conditions (particularly moderately hot water temperatures, from about 90 to 130 degrees Fahrenheit, and in the presence of nutrients), its population may greatly increase. If droplets of contaminated water get into the air and are inhaled by a susceptible individual, he may contract the disease.

Amongst the recognized sources of infection are air-conditioning cooling towers, and shower heads. There have been documented cases of individuals being infected by droplets from a cooling tower on top of a building which they were merely passing by. Probably most cases outside of hospitals are caught from the shower head in one's home.

3.3 How common is it, and who gets it?

Contrary to popular belief, Legionnaire's disease is a common disease. There are estimated 25,000 deaths per year in the U.S. from it. Most cases are never diagnosed as being Legionnaire's disease, but are simply recognized as a case of pneumonia.

It is believed that most cases of Legionnaire's disease are caught in hospitals.

Another common misconception is that anyone and everyone is at risk. Legionnaire's disease is an "opportunistic infection", meaning that it attacks individuals who are already ill or in generally poor health. The original incident involved a group of primarily older men who were heavy drinkers and smokers. It has been established that smoking and above-average consumption of alcohol are risk factors (make it more likely one will contract) for Legionnaire's disease.

3.4 What to do if you suspect you have it.

First of all, if you don't have Pneumonia, you don't have Legionnaire's disease. If you do, there is a blood test for exposure to Legionella which can be performed by many clinical microbiology laboratories. Your doctor can easily get this done.

3.5 What is Pontiac fever?

Pontiac Fever is a flu-like illness caused by the same bacterium as Legionnaire's disease. It is self-limiting (people get well on their own in a few days) and no one knows why some infections manifest as the one disease and some as the other.

3.6 What preventative maintenance actions should be followed to prevent Legionnaire's disease outbreaks?

Hot water heaters should be maintained at the intended temperature, above 130 degrees Fahrenheit. Mixed hot and cold water holding tanks should not be used.

Proper cooling tower maintenance is essential. This involves regular use of biocides, periodic cleaning of cooling towers, and periodic testing of water for biocide and bacterial levels. Due to a recent court case, standard of care now requires periodic testing of cooling tower water specifically for Legionella.

3.7 When do public health authorities get involved in cases of Legionnaire's disease?

Since Legionnaire's disease is really rather common, it takes evidence of an outbreak to interest public health authorities. An example would be multiple cases with indications of a common source, such as two people who work at the same facility.

3.8 How does one test for Legionella in the environment?

This is done by taking water samples from suspected contaminated sources. There is a very specific test, which is done by only a handful of laboratories. We recommend using Pathcon Laboratories, Norcross, Georgia, who will advise on methods of sampling, etc.


4.1 What is it?

Carbon monoxide is a colorless, odorless gas which is a normal product of combustion. When carbon containing materials burn in air, complete combustion results in CO2 - carbon dioxide. Any incomplete combustion - and perfect combustion is impossible - results in creation of carbon monoxide.

Carbon monoxide, inhaled, combines in the blood stream with hemoglobin - the oxygen carrying chemical in red blood cells. Unfortunately, once combined, it doesn't let go very easily, and puts that hemoglobin out of action for quite some time. If enough carbon monoxide is inhaled, too much of the hemoglobin is tied up, and the person suffers adverse health effects, up to and including death.

4.2 What are the symptoms?

The most well known symptoms of carbon monoxide poisoning are headaches and nausea, but long term moderate exposure can cause other symptoms, including flu-like symptoms.

4.3 How does it happen?

Any process resulting in incomplete combustion gases entering occupied spaces can cause carbon monoxide poisoning. It depends on the concentration of carbon monoxide in the gases; the volume of combustion gases; and the length of time over which this occurs.

The most common sources are combustion engines (automobiles, gas-powered lawn mowers, etc.) and fumes from water heaters, gas stoves, unvented heaters, and furnaces. Unhealthful levels of carbon monoxide have been measured at tractor pulls and in ice-skating rinks (from the Zamboli ice making machines).

Any of these devices when improperly installed, adjusted, or dirty, can vent much higher levels of carbon monoxide than usual. That means that any exhaust fumes getting into the occupied spaces are going to have that much more carbon monoxide in them than usual.

Various causes can bring the fumes into an occupied space. In a tightly constructed home, a bathroom exhaust fan can reverse the flow of air in a water heater flue - sucking the fumes down the flue to replace the air it is exhausting from the interior of the home.

4.4 What to do if you suspect you have it.

If you suspect a serious case of carbon monoxide poisoning is occurring, GET OUT OF THE BUILDING IMMEDIATELY. Very high levels of carbon monoxide can kill in a few minutes. So first, get out; second, call the fire department to come measure the carbon monoxide levels inside the building.

In suspected cases of carbon monoxide poisoning, the blood can be tested for the level of COHb - the chemical formed of hemoglobin and carbon monoxide.

Of course, if carbon monoxide poisoning is verified, the cause of the problem must be found and eliminated before re-entering the building.

4.5 How to prevent it.

Ensure that any combustion appliances are professionally installed, and are maintained and operated according to manufacturer's directions.

Don't idle cars in enclosed garages - even with the garage door open.

Don't use a stove or oven as a heater and don't use unvented kerosene or other heaters inside the home.

Have your home inspected by a qualified inspector who will look for and test for potential carbon monoxide problems.

4.6 Are carbon monoxide monitors useful?

Carbon monoxide monitors are useful, though I would not use them as a substitute for preventive actions listed above. They have been a problem due to the tendency of them to go off on bad smog days. The standard for these is just now changing (October 1995) to prevent this.

Carbon monoxide monitors operate cumulatively; if they go off you don't know if you are being exposed to a long-term, moderate, non-lethal level or a situation immediately dangerous to life. So when they go off, you get out of the house immediately. See 4.4 above.

Also - carbon monoxide is scary, because it's colorless and odorless - a "silent killer" so to speak. But realize that fatalities are rare; there are only a couple hundred deaths per year from carbon monoxide in the U.S. To put things in perspective, that makes riding a bicycle far more of a hazard.


5.1 What are bioaerosols?

A bioaerosol is something airborne which is a living thing; was living; or was a product of something living. Examples are viruses, bacteria, mold spores, algae, yeasts, protozoa, pollen, dust mite allergens, cat allergens, dog allergens, cockroach parts, rodent hairs and excrement, pigeon excrement, etc. All of these listed, by the way, can affect people's health.

5.2 How moisture contributes to IAQ problems.

Many IAQ problems begin with moisture problems: rain leaks, floods, or excessive humidity. When this occurs, explosive growth of dust mite, mold, bacteria, and other micro-organisms can occur.

Many people are allergic to dust mites and mold. Some molds and bacteria are toxigenic (capable of being poisonous). Rarely, molds and bacteria growing in the environment can also be infectious.

While it is normal for such things to exist in the environment, under excess moisture conditions the levels can become extremely high inside a building.

In order to prevent growth of microorganisms in large numbers, water problems need to be dealt with rapidly. One study demonstrated that if porous materials (such as carpeting, wallboard, or ceiling tiles) get wet and remain wet for more than 3 days, the chances of mold growth are nearly 100%.