In this article we will discuss about:- 1. Introduction to Indoor Air Pollution 2. Causes and Sources of Indoor Air Pollution 3. Changes in Indoor Air Quality 4. Cigarette Smoke 5. Respiratory Illness Control.
Introduction to Indoor Air Pollution:
In order to stay alive, a person has to inhale about 25000 breaths of air each day i.e., about 25 m3 of air per day. The air should be fresh and clean. As civilisation improved man has constrained his life to indoors and started living more and more indoors within the structures built by him. This led to the severe problem of ‘Indoor Pollution’. Man and several thousands of household products made by him pose a serious threat to indoor air quality. These products include cleaners, detergents, paints, air fresheners, disinfectants, insecticides etc.
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Indoor air pollution often leads to severe health hazards like irritation to the eyes, nose, throat, headache and most importantly the respiratory problems. The indoor pollution also leads to buildup of mental tensions leading to severe decrease in productivity among factory workers. Workers in polluted atmosphere are supposed to be subjected to severe fatigue than the workers in normal environment. Indoor environments often have higher levels of air pollutants than their surroundings in rural as well as urban areas.
Thus, indoor air pollution refers to the physical, chemical and biological characteristics of air in the indoor environment within a home, building or an institution or commercial facility. Indoor air pollution is a concern in the developed countries, where energy efficiency improvements sometimes make houses relatively airtight, reducing ventilation and raising pollutant levels. Indoor air problems can be subtle and do not always produce easily recognised impacts on health. Different conditions are responsible for indoor air pollution in the rural areas and the urban areas.
Causes and Sources of Indoor Air Pollution:
Improved building construction and insulation, including weather stripping, caulking and storm and thermopane windows, reduce infiltration and air exchange, which results in less air dilution and an increase in the concentration of indoor air pollution.
Inadequate ventilation and the recirculation of contaminated used air to save on energy costs for heating and cooling further aggravate the problem. Good practice would dictate that at least one-third of the recirculated air should be clean fresh air, even though this would increase energy costs, unless an air-to-air heat exchanger is used.
Household appliances, aerosol applications, cleaning products, pesticides, photo-copying machines (ozone), interior furnishings and building materials (formaldehyde and volatile organic compounds),tobacco smoke, dry cleaned clothing and radon may also contribute to the indoor air pollution problem. Noise might also be included.
Table 11.1 lists major pollutant/sources, specific contaminants and acceptable levels. The contaminants may be found in the new or rehabilitated home, office or other workplace; in the automobile, airplane or bus; or in the school, auditorium, indoor ice skating rink, restaurant, enclosed shopping center, commercial and public building, hospital and nursing home.
Most urban dwellers spend 16 hours a day and as much as 80 to 90 per cent of their time indoors. The primary types of indoor air quality problems are inadequate ventilation (52 per cent), contamination from inside the building (17 per cent), contamination from outside the building (11 per cent), microbiological contamination (5 per cent), contamination from building fabrics (3 per cent) and unknown (12 per cent).
Changes in Indoor Air Quality:
Human occupancy and activity vitiate air in occupied rooms and give a sense of discomfort to the occupants. The changes in air that take place in confined air in confined places are both chemical and physical.
The air becomes progressively contaminated by carbon dioxide and the oxygen content decreases due to metabolic processes. An average man at rest gives off 20 liter of carbon dioxide per hour. This may increase upto 65 liter during physical activity.
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In a mixed gathering comprising all age groups, the per capita output of CO2 is taken as 16 liters per hour. In addition to CO2, unpleasant odour arise from foul breath, perspiration, bad oral hygiene, dirty clothes and other sources.
By far the important changes that occur due to human occupancy are the physical changes.
These are:
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Rise in Temperature:
The indoor temperature tends to rise as a result of the emanation of body heat. A man at rest gives off approximately 400 B.Th.U. per hour. B.Th.U (British Thermal Unit) is the quantity of heat required to raise the temperature of one pound of water by 1°F (1 B.Th.U. = 252 calorie = 1050 Joule). Under conditions of physical exertion, the heat output may go upto 4000 B.Th.U. also.
There is an increase in relative humidity due to moisture evaporated from the skin and lungs. The exhaled air contains about 6 per cent of water vapour.
The exhaled air contains even micro-organisms in suspension. Unless the vitiated air is replaced by fresh air, it may adversely affect the comfort, health and efficiency of the occupants.
Cigarette Smoke:
Cigarette smoking is injurious to health-rather say ‘Cigarette Smoke is injurious to health’. 500 ppm i.e., 5,00,000 μg/m3 of carbon-monoxide for five minutes with frequent repetition may be a representative of cigarette smoking dose, 10-30 ppm of CO being an ambient air pollution problem. This may result in inactivation of upto 5 per cent of haemoglobin.
The presence of other pollutants also has a significant impact on the human. Similarly, the exposure to oxides of nitrogen present in cigarette smoke is about 100 ppm, whereas the average exposure to heavy air pollution over periods of about an hour will not exceed 1.5 ppm.
The other pollutants in cigarettes are carcinogens, aldehydes, tar, hydrogen cyanide, lead etc. with nicotine being the main pollutant entering the body. Filter cigarettes can remove them to a greater extent, but not upto a safer limit. Environment includes not only air, water or soil but also refers to the one created by one’s cultural habits i.e., drinking, smoking and eating behaviour. Smoking has been found to be responsible for development of high incidence of lung cancer. N-nitroso-compounds, hydrazine and polyaromatic hydrocarbons have been found to be cancer causing components in tobacco smoke.
Chewing of tobacco also brings carcinogens in contact of skin to cause different oral cancers. Children are more susceptible to the ill-effects of cigarette smoke and must be prevented from initiating smoking habits. It should be prohibited in all public places to prevent the passive smoking effects on innocent people.
As an initial measure, the development of tobacco related diseases can be reduced by using ‘less harmful cigarettes’ made up of less tar containing tobacco. Smoking should be prohibited in offices, universities, all educational institutions, aircraft, trains, buses, theatres, cinema halls etc. There should be a ‘No Smoking Day’ throughout the nation once a week to create anti-smoking awareness amongst people.
The display of advertisements regarding the sale of cigarettes and other tobacco products at prominent public places like railway stations, hospitals and educational institutions should be banned. It should be noted that every day about 1500 crores of cigarettes are burnt in the world and that about 6 lakhs people die because of smoking in India alone.
The effects of cigarette smoking are more important than the effects of air pollution, as far as lung cancer or chronic pulmonary diseases are concerned. But when both factors are present it has a more detrimental effect. Thus cigarette smokers are at unusual risk, if they live in areas with substantial air pollution and the effects of air pollution on chronic pulmonary diseases are more likely to occur in cigarette smokers.
It was observed that smokers in their twenties suffered from chronic diseases three times as often as non-smokers. Cigarette smoke causes a delay in recovery from acute virus infections of the respiratory tract, perhaps because it reduces ciliary action required to cleanse the air ways.
Respiratory Illness Control:
The following guidelines should be followed to minimise respiratory illness:
1. Promptly and permanently repair all external and internal leaks in the heating, ventilation and air- conditioning system (HVAC).
2. Maintain relative humidity below 70 per cent in occupied spaces and in low-air-velocity plenums. (At a higher level of humidity, the germination and proliferation of fungal spores are enhanced.)
3. Prevent the accumulation of stagnant water in cooling-deck coils of air-handling units through proper inclination and continuous drainage of drain pans.
4. Use steam rather than recirculated water as a water source for humidifiers in HVAC systems; however, such steam sources should not be contaminated with volatile amines.
5. Replace filters in air-handling units at regular intervals. (These should have at least a moderate efficiency rating—50 per cent or more—as measured by the atmospheric-dust spot test and should be of the extended-surface type; prefilters, e.g., roll type, should be used before passage over the higher efficiency filters.)
6. Discard, rather than disinfect carpets, upholstery, ceiling tiles, and other porous furnishings that are grossly contaminated.
7. Provide outdoor air into ventilation systems at minimum rates per occupant of at least 20 ft3/min in areas where occupants are smoking and at least 5 ft3/min in non-smoking areas.
These activities should be considered in ongoing preventive maintenance programmes. The usual method of air purification by washing and filtration is relatively inefficient in removing bacteria or viruses from used air, although it can be effective in removing dust and other airborne particles.
Electrostatic air precipitator units and special air filters effectively reduce indoor particulates. Central vacuum cleaning systems are very effective for the removal of dust and other particulates without re-suspending the finer particles indoors.
Proper venting is the removal of all the products of combustion through a designated channel or flue to the outside air with maximum efficiency and safety. Gravity-type venting relies largely on having the vent gases inside the vent hotter (thus lighter) than the surrounding air. The hotter the vent gases, the lighter they are and the greater their movement up through the vent. Thus, in order to keep the vent gases hot so that they may work at maximum efficiency, proper installation and insulation are necessary.
Factors that prevent proper venting are abrupt turns; downhill runs; common vents to small, uninsulated vent pipes; conditions that cause backdrafts; obstructions in the flue or chimney to which a furnace, heater, or stove is connected such as birds’ nests, soot and debris, broken mortar and chimney lining, and old rags; and unlined masonry chimneys.
Stained and loose paper or falling plaster around a chimney is due to poor construction. A masonry chimney will absorb a great deal of the heat given off by the vent gases, thus causing the temperature in the chimney to fall below the dew point. The high moisture in vent gases condenses inside the chimney, forming sulphuric acid.
This acid attacks the lime in the mortar, leaching it out and creating leaks and eventual destruction of the chimney. Therefore, it is necessary to line a masonry chimney with an insulating pipe, preferably terracotta flue lining.
Figure 11.4 shows chimney conditions apt to result in backdrafts. The flue or vent should extend high enough above the building or other neighbouring obstructions so that the wind from any direction will not strike the flue or vent from an angle above the horizontal. Unless the obstruction is within 30 ft. or unusually large, a flue or vent extended at least 3 ft. above flat roofs or 2 ft. above the highest part of wall parapets and peaked roof ridges will be reasonably free from downdrafts.
To ensure proper venting as well as proper combustion, sufficient amounts of fresh air are required, as shown in Fig. 11.4. An opening of 100 to 200 inch2 will usually provide sufficient fresh air under ordinary household conditions; this opening is needed to float the flue gases upward and ensure proper combustion in the fire box. Proper venting and an adequate supply of fresh air are also necessary for the prevention of carbon monoxide poisoning or asphyxiation.
The connection (breeching) between the furnace or stove and chimney should be tight fitting and slope up to the chimney at least 1/4 inch/ft. Chimneys are usually constructed of masonry with a clay tile flue liner or of prefabricated metal with concentric walls with air space or insulation in between and should be Underwriter’s Laboratories approved. All furnaces and stoves should be equipped with a draft hood, either in the breeching or built into the furnace or stove, as required, for proper draft (Fig. 11.4).
Before making any vent installations or installing any gas- or oil-fired appliances, consult the building code and the local gas or utility company. Standards for chimneys, fireplaces, and venting systems, including heating appliances and incinerators, are given by the National Fire Protection Association, building codes.
Portable kerosene heaters are a fire hazard and since they are not vented, emit dangerous gases into a room. Their sale and use should be prohibited. The concentrations of carbon dioxide, nitrogen dioxide and sulphur dioxide emitted into a room usually greatly exceed ambient air standards.