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Health Risks in Indoor Environment
Indoor air quality means the quality of the environment in an office or other building. A definition given by ASHRAE (American Society of Heating, Refrigerating and Air-conditioning Engineers, “Acceptable indoor air quality means air in which there are no known contaminants at harmful concentrations and air with which a substantial majority of the people exposed do not express dissatisfaction”. Indoor environments are highly complex and building occupants may be exposed to a variety of contaminants (in the form of gases and particles) for example:
 * Office machines
 * Cleaning products
 * Construction activities
 * Carpets and furnishings
 * Cigarette smoke
 * Water-damaged building materials,
 * Microbial growth (fungal / mould and bacterial
 * Other factors such as indoor temperatures, relative humidity, and ventilation levels can also affect how individuals respond to the indoor environment.

There are 5 common causes of pollution in the indoor environment:
 * Inadequate cleaning
 * Insufficient ventilation
 * Pollutants emitted inside the building
 * Contamination from outside sources
 * Biological contamination due to moisture problems

Chemical Pollution
Inorganic Chemical Pollution

Carbon Dioxide (CO2)

Carbon dioxide content in fresh air varies between 0.036% and 0.039%, depending on the location. Toxicity and its effects increase with the concentration of CO2, here given in volume percent of CO2 in the air: Due to the health risks associated with carbon dioxide exposure, the U.S. Occupational Safety and Health Administration says that average exposure for healthy adults during an eight-hour work day should not exceed 0.5%.
 * 1% can cause drowsiness with prolonged exposure.
 * At 2% it is mildly narcotic and causes increased blood pressure and pulse rate, and causes reduced hearing.
 * At about 5% it causes stimulation of the respiratory centre, dizziness, confusion and difficulty in breathing accompanied by headache and shortness of breath.
 * At about 8% it causes headache, sweating, dim vision, tremor and loss of consciousness.

Carbon Monoxide (CO)

Carbon monoxide is a colourless, odourless, and tasteless gas but is highly toxic. It combines with haemoglobin to produce carboxyhaemoglobin, which is ineffective for delivering oxygen to bodily tissues. A level of 50% carboxyhaemoglobin may result in seizure, coma, and fatality. In the United States, the OSHA (Occupational Safety and Health Administration) limits long-term workplace exposure levels above 50 ppm. In closed environments, the concentration of carbon monoxide can easily rise to lethal levels. The sources are all combustion devices, fireplaces, gas appliances, and tobacco smoking.

Nitrogen Dioxide (NO2)

Nitrogen dioxide is produced during combustion at high temperature from the combination of nitrogen and oxygen from air. It is an oxidising agent and is highly irritating to mucous membranes. Indoor sources of this gas are: Nitrogen dioxide is toxic by inhalation. However, as the compound is easily detectable by smell at low concentrations, inhalation exposure can generally be avoided. However if there is long-term exposure to NO2 at concentrations above 40–100 µg/m3 it may decrease lung function and increase the risk of respiratory symptoms.
 * Unvented gas appliances, such as gas stoves, kerosene heaters and fireplaces.
 * Smoking
 * Outdoor sources e.g. traffic, heat and power production, can also significantly add to indoor concentrations of NO2.

Sulphur Dioxide (SO2)

Sulphur dioxide is a colourless gas that is poisonous and can be detected at about 130µg/m3. Indoor concentrations of the gas are considerably lower than outdoor levels; this is due to the chemical reactivity of SO2 with surfaces and also the presence of neutralising ammonia generated by humans and animals. Sources of SO2 are mainly outdoors. It is a noticeable component in the atmosphere, especially following volcanic eruptions. Sulphur can also be removed from fuels prior to burning the fuel. This prevents the formation of SO2 because there is no sulphur in the fuel from which SO2 can be formed. Inhaling sulphur dioxide is associated with increased respiratory symptoms and disease, difficulty in breathing, and death. In 2008, the American Conference of Governmental Industrial Hygienists reduced the short-term exposure limit from 5 ppm to 0.25 ppm.

Ozone (O3)

Ozone is a pale blue gas that is present throughout the Earth’s atmosphere; it is an air pollutant with harmful effects on the respiratory systems of animals. It has many industrial and consumer applications. Most people can detect levels of about 0.01 μmol/mol of ozone in air because it has a very specific sharp odour that resembles chlorine bleach. Exposure of 0.1 to 1 μmol/mol produces headaches, burning eyes, and irritation to the respiratory passages. Even low concentrations of ozone in air are very destructive to organic materials such as latex, plastics, and animal lung tissue. Ozone can also be present in indoor air pollution, partly as a result of electronic equipment such as photocopiers, laser printers and UV lighting. Work environments where ozone is used or where it is likely to be produced are required to have adequate ventilation and detectors for ozone that will alarm if the concentration exceeds the permissible exposure limit (PEL).

Organic Chemical Pollution
Organic compounds involved in the generation of indoor air problems can be genotoxic, toxic, irritant and/or odorant. Some organic compounds can occur at concentrations which are several orders of magnitude below known effect levels and therefore not able to be measured accurately.

Volatile Organic Compounds (VOCs)

Volatile organic compounds (VOCs) are organic chemicals that have a high vapour pressure at room-temperature conditions. Many VOCs are dangerous to human health or cause harm to the environment. VOCs are regulated by law, especially indoors, where concentrations are the highest. VOCs are typically not acutely toxic, but instead have compounding long-term health effects. Long-term exposure to VOCs in the indoor environment can contribute to sick building syndrome. In offices, VOC results from new furnishings, wall coverings, and office equipment such as photocopy machines. Good ventilation and air-conditioning systems are helpful at reducing VOC emissions in the indoor environment. Many VOCs are potent narcotics and cause the depression of the central nervous system; some can also cause irritation of the eyes and respiratory tract. Studies also show that leukaemia and lymphoma can increase through prolonged exposure to VOCs in the indoor environment.

Formaldehyde (HCHO)

Formaldehyde is a colourless gas with a characteristic pungent odour. Formaldehyde is used extensively in the woodworking and cabinet-making industries. Other sources in the indoor environment are from: Formaldehyde is highly toxic to all animals, regardless of method of intake. Ingestion of as little as 30 ml of a solution containing 37% formaldehyde has been reported to cause death in an adult. Water solution of formaldehyde is very corrosive and its ingestion can cause severe injury to the upper gastrointestinal tract. On 10 June 2011, the US National Toxicology Program described formaldehyde as a known carcinogen.
 * Cigarette smoking
 * Combustion processes
 * Urea-formaldehyde resins
 * Insulation (UFFI)
 * In hospitals it is used as a disinfectant or preservative.

Polynuclear aromatic hydrocarbons (PAH)

Polynuclear aromatic hydrocarbons (PAH) are potent atmospheric pollutants that consist of fused aromatic rings. Naphthalene is the simplest example of a PAH. PAHs occur in oil, coal, and tar deposits, and are produced as by-products of fuel burning. As a pollutant, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic. PAHs are also found in cooked foods. Studies have shown that high levels of PAHs are found, for example, in meat cooked at high temperatures such as grilling or barbecuing, and in smoked fish. In addition to their presence in fossil fuels they are also formed by incomplete combustion of carbon-containing fuels such as wood, coal, diesel, fat, tobacco, and incense. The only toxic effect known by exposure to some PAHs is that they are carcinogenic.

Physical Factors
Particulate Matter

Combustion sources are leading generators of fine mode particles, which contain organic and inorganic material. Sprays and cooking aerosols may also contribute. Tobacco smoke can be a significant source of indoor particles and these are especially hazardous due to their chemical composition, they are inhalable and remain airborne for hours after smoking stops. The particles can deposit in different areas within the body depending on particle aerodynamic diameter: fine particles deposit mainly in the thoracic region whereas coarse particles deposit mostly in the nasopharyngeal region.

Asbestos

Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. Indoor asbestos concentrations can be higher than outdoor concentrations. Indoor asbestos dust originates from insulation materials, asbestos plasters etc. The inhalation of asbestos fibres can cause serious illnesses, including malignant lung cancer, mesothelioma and asbestosis. This is most common among the miners of asbestos, since they have the longest exposure to it. The European Union has banned all use of asbestos and extraction, manufacture and processing of asbestos products.

Man-made mineral fibres (MMMF)

Man-made vitreous fibres (MMVF) are fibres manufactured from glass, natural rock or other minerals. They are widely used as asbestos substitutes but can cause mechanical irritation of the skin. Carcinogenic effects have been found under high occupational exposure.

Radon (Rn)

Radon is a reactive noble gas. Only Radon-222 reaches to significant indoor concentrations. When radon and its decay products are inhaled the radiation dose to lung tissue is primarily alpha-particles. Main source of radon is the soil; small doses could also come from water or outdoor air. It is known to be a human carcinogen, inhalation of radon and its decay products can cause lung cancer.

Biological Factors
Biological particles which affect indoor air quality are: Allergens produced by dust mites and pets are the most important cause of disease in atopic individuals. People exposed to biological agents may develop allergic problems:
 * Mites
 * Pets
 * Fungi
 * Bacteria
 * Rhinitis with hay fever symptoms
 * Asthma
 * Humidifier fever
 * Extrinsic Allergic Alveolitis
 * Atopic allergic dermatitis