Subject : IAQ FAQ Part 2

5.3 Dust mites.

Dust mites are tiny (just barely visible to the naked eye under the right lighting) creatures which live on skin scale (tiny bits of flaked off skin). They live in materials such as carpeting, couches, and bedding where skin scale would tend to accumulate. They do not bite people. Their feces is highly allergenic; in fact more people are allergic to dust mite feces than to any other substance (around 30% of the U.S. population). When someone is allergic to "house dust" it is normally a dust mite allergy.

Dust mites require a certain amount of moisture to reproduce. Generally speaking, dust mite infestations occur at relative humidities higher than 45%. Keeping humidity levels down is therefore the ideal way to prevent such a problem. Few homes are designed, however, to be capable of controlling humidity.

In the U.S., the worst dust-mite infestations are normally in carpeting. For this reason, removal of wall-to-wall carpeting is often a recommended action (see also 5.3 and 6.1 for more reasons).

Other actions include covering of bedding in plastic sheeting, washing and drying of bedding at high temperatures.

Since it is the feces which is allergenic, a building can continue to be a problem even if there is no current infestation, unless a thorough cleaning (see 6.2) removes the bulk of the allergens.

Dust mites are not exclusively a problem of homes. A carpeted office with a humidity problem can also become infested.

It is possible to test for dust-mite allergens.

5.4 Mold.

Mold is nature's recycling mechanism. Microscopic spores (the reproductive cells of mold) are always floating in the air. When something dies, mold spores landing on it germinate, mold consumes it and recycles its organic materials.

There are hundreds of thousands of different types of mold, which vary in the types of food they prefer to consume, their ideal temperature and moisture conditions, etc. Some type of mold will consume virtually any type of hydrocarbon. That includes any sort of organic material, paints, many types of plastics, etc.

Somewhere around 10% of the U.S. population is allergic to mold of some type or many types. Its been said that for any type of mold, SOMEBODY is allergic to it. There has to be a certain amount of the mold in the air before someone allergic to it suffers a reaction, and the higher the concentration above that level, the worse the reaction is likely to be. Sometimes mold spore levels in the outdoor air can be sufficient to cause an allergic attack, particularly at certain times of the year (depending on seasons and climate in any particular locale). In addition, if mold is growing indoors, extremely high levels of mold spores can occur in the indoor air.

Many types of mold produce toxins (poisons) under certain conditions. The toxins are usually concentrated in the spores. Airborne spores may then affect people by contact (at least one type causes skin rashes) or by inhalation. The effects of toxic molds vary from relatively minor to very serious, including liver damage and immune system impairment.

Some types of mold can produce carcinogens (cancer causing chemicals). In fact, the most potent natural carcinogen known, Aflatoxin B1, is produced by a mold, Aspergillus flavus.

Molds are not capable of infecting people, unless they are already ill (opportunistic infections). Superficial infections are the exception to this (skin, nails).

5.5 Bacteria.

Bacteria also grow profusely when there is plenty of moisture present. In general, bacteria which grow in the environment do not grow well in the human body. The reason is the temperature difference. An organism that grows well at human body temperature (98.6 degrees Fahrenheit) probably won't do well at 70 degrees.

However, a large percentage of bacteria are toxic. These are the "Gram negative" bacteria. They contain a substance in their cell walls (endotoxin) which when inhaled in sufficient quantity can cause adverse health reactions, including fatigue, muscle aches, and upper respiratory symptoms. This is the main hazard of bacterial contamination.

5.6 How do you test for mold and bacteria?

You start by visually locating what appears to be mold growth, bacterial growth, or water damaged materials. A sample is then taken from the material and examined under a microscope by an environmental (not clinical) microbiology laboratory. They will confirm the presence of microbial growth and do a partial identification of the type of growth from the appearance of the microorganisms.

Air sampling is not recommended in most cases. It is relatively expensive, and can fail to identify a problem even though a serious problem exists. Therefore if a microbial contamination problem is suspected, a thorough inspection by someone who knows what to look for is vital.

The following methods of testing DO NOT WORK in investigating potential microbial contamination problems in commercial and residential environments:

1. Putting out petri dishes, in a room or in the ventilation system, for some period of time ("settle plates"), then culturing them to see what grows there. This may grossly underestimate or grossly overestimate the extent of a problem. In fact, its been shown that there is no relationship between the amount of growth and the amount of spores in the air.

2. Swabbing a surface, such as the inside of a duct, and culturing it and counting the number of "colony forming units" or CFU's of mold or bacteria. Again, this may claim to demonstrate a problem exists, when none exists, or it may overlook the existence of a serious problem completely. If test results from such a method rate each sample in terms of severity as "low", "moderate", "severe", realize that this evaluation is solely the opinion of the laboratory involved, and that nearly all environmental microbiologists would disagree with this evaluation.

Such methods were invented, and are validly used for, testing in certain types of facilities, including pharmaceutical manufacturing facilities.

5.7 Humidifiers.

Humidifiers are designed to produce moisture and so represent a major source of concern for microbial contamination. Some extremely serious disease outbreaks have been traced to humidifiers. It is recommended that humidifiers have their reservoirs emptied daily, that they be cleaned daily, and that they be disinfected every three days at a minimum. Only steam humdifiers should be used, never "cool-mist" or ultrasonic humidifiers.

5.8.What to do about water caused microbial problems.

Get rid of the excessive moisture and make sure it isn't going to happen again, or the problem will recur.

Once microbial contamination has taken hold in porous materials, they have to be disposed of. That would mean removing and disposing of carpeting, carpet padding, dry wall, etc. Wood that is contaminated can have the top surface planed off (1/4 inch or so), or it can possibly be disinfected if this can be done without ruining the wood. Contaminated paint on metal surfaces would have to be stripped.

Non-porous materials with mold growing on them can be cleaned and sanitized.

If the problem is serious or has gone on for a long time, there may be such an accumulation of mold spores or bacteria in the building that this will continue to adversely affect people even after the source of the problem is eliminated. In this case a special cleaning is required to remove the accumulations (see section 6).

5.9 What about Lysol?

Simply using biocides to try to kill a microbial contamination problem is rarely effective. For one thing, mold spores even if killed still cause the same harmful effects. A toxin in a mold spore is still toxic, and an allergenic spore is still allergenic, whether it is capable of reproducing or not.


6.1 Why the inside of a building should be clean.

Contaminates that affect air quality are either in the form of gases, or in the form of particles. Particles accumulate in dust on surfaces. Dust inside a building typically contains bacteria, various kinds of mold spores, fiberglass, and other irritating, toxic, and allergenic materials. The more dust, the more of these materials are present. Occupant activities stir up the dust which is then inhaled by them or lands on their skin or falls back out of the air, until the next time.

Numerous studies have demonstrated that the cleaner the air, the healthier it is. In fact, for every increase in the amount of dust in the air, there is a measurable increase in allergy and asthma attacks, emergency room visits, and deaths. This effect is measurable even at very low levels.

6.2 Ways to keep the air inside of a building clean.

There are basically three ways to keep the air inside of a building clean: Don't let contaminants in; filter them out of the air; and remove them from surfaces by cleaning.

If you don't bring outside air into the building, you won't bring in pollutants from the outside air. This usually isn't practical, but if you are next to a major highway, you can at least cut down on the amount of outside air you bring in during rush hours. There is, by the way, no such thing as a good smog day next to a major thoroughfare.

Using low-emitting source materials also means you never have pollutants there in the first place (see Section 7).

Filtration in the form of filters or air cleaners in a ventilation system, or room air cleaners, can be effective in removing particles. It takes a special kind of filter to remove gaseous contaminants. These are not usually economically feasible in commercial environments. In residential environments if you can get an air cleaner with more than 5 pounds of CPZ (carbon - permanganate - zeolite) filtration material it will be effective in reducing gaseous contaminant levels. (see section 6.3).

No filter will be very effective if large amounts of contaminants are allowed in from outside, if surfaces in the interior of the building are allowed to be excessively dirty, or if there are major sources of contaminants in the building.

Cleaning of the interior of the building is a very effective way to reduce levels of particulates in the air. Routine housekeeping or janitorial cleaning is rarely effective enough, especially with fabrics such as carpeting, chair and couch seats, and partitions. These materials can absorb huge amounts of dirt and yet still look clean. Nevertheless, disturbing the materials releases invisible clouds of dust.

Its best to have no wall-to-wall carpeting at all. Residential type (deep pile) carpeting is hopeless. Even regular excellent vacuuming with HEPA filtered vacuum cleaners, and frequent cleaning is still fighting a losing battle. Also carpet cleaning often causes more problems than it solves; if the carpeting stays wet too long it'll grow mold; if not carefully done it'll leave soap residue in the carpet that'll cause problems.

6.3 Types of filters.

The following are the main types of filters. These are found in central heating and air conditioning systems, and also in room air cleaners, and some types in vacuum cleaners. Sometimes, especially in room air cleaners, there is more than one type in the machine.

The typical furnace filter is a one or two inch thick (or less) flat panel filter. These filters are very ineffective. Basically, they only remove the very largest particles, which don't have any health effects anyway. They are there to protect the equipment, not the people.

A type of filter called a "passive electrostatic" filter is highly promoted as effective in removing allergens and dust from the air. This is mainly hype. They are somewhat more effective than the ordinary flat panel filter when they are clean; they quickly become less effective as they get dirty and soon are less effective than even an ordinary flat panel filter. Their main advantage is they are washable so you don't have to keep throwing them out and buying new ones. But they must be kept clean. The advertising for them that promotes figures such as "95%" is misleading. This is the percentage of dust removed by weight, which is almost all in the heaviest particles. Such filters are classed technically as "low efficiency impact filters".

"Pleated" filters are much more effective. These are "medium efficiency" filters and do remove a significant amount of the smaller, more harmful particles. They come in various thicknesses, with the thickest ones - 6, 8 or 12 inches thick - being very effective. However, the system has to be capable of handling them. Some systems don't have enough "oomph" to push the air through the filter, or there is no place to fit such a filter in the system.

Electronic air cleaners are powered filters that remove particles by electrically charging them and attracting the charged particles to an oppositely charged plate. They get their power from the main electrical supply of the building. They are very effective when clean, but efficiency drops as they get dirty. Also you have to make sure they are working properly; if they look fine but aren't working you have no filter in your system.

HEPA (high efficiency particle air) filters were developed originally for the nuclear industry. They remove at least 99.97% of particles of a very small size. In short, virtually nothing gets through them.

All the above filters remove only particles from the air. The most common type of filter for removing gases is activated charcoal. These will remove many - but not all - gaseous contaminants from the air. There is also "CPZ", charcoal with two other materials that remove more gases from the air. But the charcoal or CPZ has to be thick enough to be effective. Nearly all filters of this type sold to the public do not have enough material to be effective, except possibly at reducing odors somewhat. In one study of room air cleaners, the only one that was really effective at removing gases from the air had about 15 pounds of CPZ in it.

6.4 More about filters and air cleaners.

Filters in central ventilation systems should be the most efficient that the system can handle. Even then, they won't do anything if the fan isn't running on the system. Since many people use their systems only a portion of the time, that makes room air cleaners often a better choice for filtration.

If you have chosen a room air cleaner of good efficiency, it may still do no good at all. It has to process enough volume of air. There is a rating system, "CADR" or clean air delivery rate which can be used to judge whether the air cleaner is large enough for your intended use. Manufacturer's typically state these in terms of the number of times per hour the device will clean the air in a given size room.

No filter or air cleaner will do much good if there are doors or windows open (bringing in new air faster than you can clean it) or if the interior of the building is filthy or has a major source of contaminants, such as an active mold growth problem.

Also room air cleaners should blow out the top, not out the bottom, where they will blow dust out of the carpet or surface they sit on. Such a setup can actually increase the amount of allergens in the air.

6.5 Vacuum cleaners.

Ordinary vacuum cleaners pick up dirt from a carpet, filter out the larger, harmless particles, and throw a majority of the harmful allergenic, irritating, and toxigenic particles into the air. If you don't breathe them before they settle out of the air, you then have the chance to try again next time.

Some vacuum cleaners promoted as "allergy" vacuums don't do any better than an ordinary vacuum cleaner. The "Rainbow" vacuum falls into this category. This vacuum uses water to filter out debris, but apparently the finer particles go right through the water inside air bubbles.

Other "allergy" vacuums are very good. Two brands that are generally reliable are Miele and Kirby. Any HEPA filtered vacuum cleaner will be effective in actually removing unhealthful particles.

Other things being equal, a vacuum with more suction will remove more material and one with a beater brush (agitator head) will remove more material than one that doesn't have one. Central vacuum cleaners are relatively good because they tend to be more powerful, and anything they don't filter out is normally blown outside.

If you don't have a good quality vacuum cleaner and can't afford one, use a canister with a long hose and put the canister outside.

Better yet, get rid of your wall-to-wall carpeting.


7.1 What are volatile organic compounds (VOC's)?

VOC's are a broad class of chemicals which contain carbon atoms and which are either gases, or if liquids, tend to give off high levels of vapor at normal temperatures. Gasoline and common solvents are typical examples.

7.2 What kinds of problems do they cause, and how common are they?

VOC's give off high levels of vapors, so one is likely to inhale significant amounts of them. Many VOC's are toxic. And VOC's are extremely common. Any time you apply a material which is intended to dry out, there are almost always VOC's present. Paint, white out, paint stripper, almost any kind of cleaner fall into this category. Plastics are manufactured with VOC's, as are many other materials.

Many new materials therefore give off relatively high levels of VOC's. As time goes by, in days or weeks, sometimes months, the emission rate eventually becomes very low. This phenomenon is the source of the "new" odor - new car, new furniture, etc.

It is probably not common for serious health problems to occur from VOC exposure, except under unusual circumstances. Minor effects are very common. Who hasn't gotten dizzy or a headache from inhaling some chemical? There is the (serious) phenomenon of "multiple chemical sensitivity" (sections 2.5, 2.6).

7.3 Carpets and IAQ.

In the last few years there has been a lot of controversy about carpets as a cause of IAQ problems. This began with an incident in the EPA headquarters building in Washington, D.C., where a number of employees became ill following some renovations including installation of new carpeting.

Following this incident, a laboratory put some mice in a chamber with a piece of carpet. The mice died.

Studies are still going on, and this is an area of profound disagreement. One claim is that 25% of all new carpeting is toxic; another claim is that no harmful effects have been found from carpeting at all.

Certainly, new carpeting and the adhesive used to glue it down do off-gas (give off) VOC's, and the levels should be minimized. It is a good practice to have new carpeting unrolled in a warehouse for a couple of weeks prior to installation. Also use relatively low-emitting, non-toxic mastics.

A major problem with carpeting is the wonderful job it does of accumulating dirt and hiding it. It is virtually impossible to do a good job of cleaning deep pile carpeting, and anyone with allergies should simply not have wall-to-wall carpeting in their home.

Improper cleaning of carpeting can result in mold growth (if it remains wet too long) or other problems (as if too much of the cleaning chemicals remain in the carpet afterwards).

7.4 Mobile homes, particle board, and formaldehyde.

One VOC that should be considered by itself is formaldehyde. Individuals can become sensitized to it and thereafter experience adverse reactions (mainly respiratory effects) at extremely low. There are by the way, other VOC's for which this same type of effect can occur (for example, "MDI", produced when polyurethane foam cures).

Formaldehyde is given off at quite high rates by what is called "medium density particle board", which is frequently used in mobile home (and some other home) sub-flooring, and in cabinetry and the like. Since its toxic properties have become well known, manufacturers now make the stuff so it emits at much lower levels. Nevertheless, this material is of concern and individuals sensitive to formaldehyde can suffer serious health effects from living in a home in which lots of it was used.

7.5 New construction, remodels, and renovations.

Most of the problems with VOC's are connected to new construction and remodels. Besides using low-emitting materials, ventilation should be adjusted during the course of a remodel, and following a remodel or new construction. During the remodel, areas being worked on must be isolated so air doesn't flow from them to other areas of the building. This is done by shutting off returns and exhausting air directly from the construction areas to the outside of the building.

In new buildings or following a remodel, the amount of fresh air supplied to the building should be increased to compensate for the higher than normal levels of VOC emissions. In fact, one authority recommends supplying 100% outside air for the first six months.


8.1What is it?

Fiberglass is simply strands of glass. The form of it known as glass wool, which is made of fine (small diameter) strands, is used as an insulating material and is the most commonly used insulating material in buildings, found in walls, ceilings, and ventilation systems. It is a part of a larger class of materials called man-made mineral fibers (MMMF) which include rock wool and slag wool, made from fine strands of molten rock and slag respectively.

8.2 Is fiberglass a carcinogen?

This is still an open question. The U.S. and German governments have it classed as a possible carcinogen. While more research is needed, it is certainly not in the same class as asbestos. It seems likely that workers in plants manufacturing fiberglass may suffer slightly elevated cancer levels.

8.3 Medically recognized effects.

Fiberglass is medically recognized as an irritant to skin, eyes, and upper respiratory systems. Rashes, sinus headaches, coughing, conjunctivitis are common effects of exposure to large quantities.

8.4 Sources.

As noted above, fiberglass is commonly found in buildings as insulation. Large quantities can be released into the air during remodels. Ceiling tiles usually contain fiberglass, and high levels can be released, for example, if an earthquake knocks tiles down. Fiberglass particles can also filter down from above ceilings. But probably the most major source of fiberglass contamination in buildings is the ventilation systems. Nearly all ventilation systems have fiberglass exposed to the air stream. It eventually breaks down and blows out.

8.5 How to tell if there is a problem.

If there are epidemics of eye irritation, fiberglass is one of the first suspects. If you can look up at a supply vent and see pieces of fiberglass caught in the vent, there's a problem. Also, if people come into an office in the morning and find debris on desks below vents, this is usually fiberglass.

8.6 How to deal with a fiberglass problem.

Fiberglass inside ventilation systems should be sealed, or better yet replaced with a non-fiberglass insulation. Fiberglass insulation in attics and walls should be covered in paper, foil, or best, plastic. Also pressure relationships should be maintained so air goes into the wall or attic, not out of it into occupied spaces.

If fiberglass or fiberglass bearing dust has to be disturbed in a remodel, it should be moistened to keep down the dust, and the area isolated (see section 7.5).

If an area is heavily contaminated with fiberglass in the dust, it may have to be vacuumed using HEPA filtered vacuum cleaners to cure the problem.


9.1 How come you haven't said anything about lead, radon, or asbestos?

And I'm not going to. These substances have some things in common: They all cause long-term effects, not acute effects; the effects are very serious (lung cancer and mental retardation, for example); they are all the subject of considerable government intervention; and they all require considerable expertise and special licensing to deal with competently ("don't you try this at home").

The one exception to this is home radon kits which you can buy and use yourself to find out if you have a problem. They are widely available and easy to use. Otherwise, if you have a concern about one or more of these subjects, hire an expert.

9.2 What if I think I'm being exposed from (the chemical plant next door; the landfill on which my house was built; etc.)?

Same answer. Hire an expert to evaluate it.