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Indoor Air Quality (IAQ) deals with the content of interior air that could affect health and comfort of building occupants. The IAQ may be compromised by microbial contaminants (mold, bacteria), chemicals (such as carbon monoxide, radon), allergens, or any mass or energy stressor that can induce health effects. Often it is perceived that outdoor air is polluted, but indoor air is acceptable. Scientific studies illustrate the falsity of this perception, and, in fact, indoor air is often a greater health hazard than the corresponding outdoor setting.

Techniques for analyzing IAQ include collection of air samples, collection of samples on building surfaces and computer modelling of air flow inside buildings. The resulting samples can be analyzed for mold, bacteria, chemicals or other stressors. These investigations can lead to an understanding of the sources of the contaminants and ultimately to strategies for removing the unwanted elements from the air.

Risk Assessment

Radon

Radon is an invisible, radioactive atomic gas that results from radioactive decay of some forms of radium that may be found in rock formations beneath buildings or in certain building materials themselves. Radon is probably the most pervasive serious hazard for indoor air in the United States and Europe, probably responsible for tens of thousands of lung cancer deaths per annum. There are relatively simple tests for radon gas, but these tests are not commonly done, even in areas of known systematic hazards. Radon is a very heavy gas and thus will tend to accumulate at the floor level. Building materials are actually a signicant source of radon, but very little testing is done for stone, rock or tile products brought into building sites. The half life for radon is 3.8 days incicating that once the source is removed, the hazard will be greatly reduced within a few weeks.

Molds and other Allergens

These biological agents can arise from a host of means, but there are two common classes: (a) moisture induced growth of mold spore colonies and (b) natural substances released into the air such as animal dander and plant pollen. Moisture buildup inside buildings may arise from water penetrating compromised areas of the building skin, from plumbing leaks or from ground moisture penetrating a building slab. Especially in the absence of light and with lack of air circulation, mold colonies can propagate on surfaces and eventually enter the air. In a situation where there is visible mold and the indoor air quality may have been compromised a mold inspection and/ or mold remediation may be needed. Through an inspection one should be able to determine the presence or absence of mold, which can cause allergic reactions and respiratory effects; there are some varieties of mold that are toxic in nature. Indoors, mold growth can be inhibited by keeping humidity levels between forty and sixy percent.

Carbon Monoxide

One of the most acutely toxic indoor air contaminants is carbon monoxide (CO), a colorless, odorless gas that is a byproduct of incomplete combustion of fossil fuels. Common sources of carbon monoxide are tobacco smoke,space heaters using fossil fuels, defective central heating furnaces and automobile exhaust. Improvements in indoor levels of CO are systematically improving from increasing numbers of smoke-free restaurants and other legislated non-smoking buildings. By depriving the brain of oxygen, high levels of carbon monoxide can lead to nausea, unconsiousness and death.

Legionella

Legionellosis or Legionnaire's Disease is caused by a waterborne bacterium, which is probably the most common serious health threat to building interiors, since mortality is high in infected patients. The number of instances of this disease is higher than commonly understood. The bacterium itself thrives on warm moist substrates and hence is usually associated with a plumbing misdesign or malfunction.

Asbestos Fibers

The U.S.Federal Government and some states have set standards for acceptable levels of asbestos fibers in indoor air. Many common building materials used before 1975 contain asbestos, such as some floor tiles, ceiling tiles, taping muds, pipe wrap, mastics and other insulation materials. Normally significant releases of asbestos fiber do not occur unless the building materials are disturbed, especially by sanding, drilling or building remodelling. There are particularly stringent regulations applicable to schools and residences. Inhalation of asbestos fibers over long exposure times is associated with increased incidence of lung cancer.

Carbon Dioxide

Carbon dioxide is a surrogate for indoor pollutants that may cause occupants to grow drowsy, get headaches, or function at lower activity levels. To to eliminate most Indoor Air Quality complaints, total indoor carbon dioxide must be reduced to below 600 ppm. NIOSH considers that indoor air concentrations of carbon dioxide that exceed 1,000 ppm are a marker suggesting inadequate ventilation (1,000 ppm equals 0.1%). ASHRAE recommends that carbon dioxide levels not exceed 1,000 ppm inside a space. The UK standards for schools say that carbon dioxide in all teaching and learning spaces, when measured at seated head height and averaged over the whole day should not exceed 1,500 ppm. The whole day refers to normal school hours (i.e. 9.00am to 3.30pm) and includes unoccupied periods such as lunch breaks. Canadian standards limit carbon dioxide to 3500 ppm. OSHA limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes.

Mechanical engineering issues

A basic way of measuring the helath of indoor air is by the frequency of effective turnover of interior air by replacemnent with outside air. In the UK, for example, classrooms are required to have 2.5 outdoor air changes per hour. In halls, gym, dining, and physiotherapy spaces, the ventilation should be sufficient to limit carbon dioxide to 1,500 ppm.

The use of air filters can trap some of the air pollutants. ASHRAE recommends that at least Air Filters with a Minimum Efficiency Reporting Value, MERV, of 6 be used upstream of any wet-surface devices, such as air conditioning and/or dehumidifying coils. Air filters are used to reduce the amount of dust that reaches the wet coils. Dust can serve as food to grow molds on the wet coils and ducts.

In order to avoid wet ducts and ducts with nearly 100% Relative Humidity, %RH, ducts and dampers can be arranged so that a fan draws air through the cooling coil, and mixes some 'by pass air'. The 'by pass air' is warmer than the air leaving the cooling coil. This arrangement is used at some schools 'roof top units' to lower the %RH in the supply air duct and in the space (rooms be cooled) without using energy in at reheat coils:

1. Minimum Outside Air Damper 2. Outside Air Damper 3. Return Air Damper 4. Cooling Coil 5. Reheat Coil 6. By Pass Damper and duct connected to the return air 7. Fan

Moisture management and humidity control requires operating HVAC systems as designed. Moisture management and humidity control conflict with efforts to try to optimize the operation to conserve energy. For example, Moisture management and humidity control requires systems to be set to supply Make Up Air at lower temperatures (design levels), instead of the higher temperatures used sometimes used to conserve energy.

The "dew point temperature" is an absolute measure of the moisture in air. Some facilities are being designed with the design dew points in the lower 50's degrees F, and some in the upper and lower 40's degrees F. Some facilities are being designed using desiccant wheels with gas fired heater to dry out the wheel enough to get the required dew points. On those systems, after the moisture is removed from the make up air, a cooling coil is used to lower the temperature to the desired level.

There is a need to keep buildings under positive pressure to help Moisture management and humidity control work properly.

Institutional Roles

The topic of IAQ has become popular due to the greater awareness of health problems caused by mold and triggers to asthma and allergies. Awareness has also been increased by the involvement of the Environmental Protection Agency. They have developed an "IAQ Tools for Schools" program to help improve the indoor environmental conditions in educational institutions (see external link below).

A variety of scientists work in the field of indoor air quality including chemists, physicists, mechanical engineers, biologists, bacteriologists and computer scientists. Some of these professionals are certified by organizations such as the American Industrial Hygiene Association, American Indoor Air Quality Council, Indoor Environmental Institute, Indoor Air Quality Association, and the Indoor Environmental Standards Organization. AIHA and A2LA both offer laboratory accreditation programs that relate to indoor air quality.

External links

Health | Health risks | Air pollution | Building biology | Industrial hygiene

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Indoor air quality".

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