The National Health and Medical Research Council NHMRC defines indoor air as any non-industrial indoor space where a person spends a period of an hour or more in any day. This can include the office, classroom, motor vehicle, shopping centre, hospital and home.
Historically, indoor air quality has been addressed to varying degrees by the health, occupational health and safety and environment agencies of government. Such agencies have also drawn on advice from the NHMRC.
It is important to make certain that our indoor air quality is of a sufficient standard to ensure the adequate protection of human health and well being. This is particularly the case as Australians may spend 90% or more of their time indoors. Further, it is generally accepted that poor indoor air quality can result in health problems, which may carry a substantial cost burden. The CSIRO estimates that the cost of poor internal air quality in Australia may be as high as $12 billion per year (Brown 1998b).
Despite the long periods we spend indoors, relatively little research has been done on the quality of air in our homes, schools, recreational buildings, restaurants, public buildings and offices or inside cars. In recent years, comparative risk studies performed by the US EPA and its Science Advisory Board have consistently ranked indoor air pollution among the top five environmental risks to public health.
Common Indoor Air Pollutants…
Whether a particular source of pollution causes indoor air quality problems depends on a number of variables including the nature of the contaminant, the rate of contaminant emission from the pollution source, the ventilation rates of the structure, and the HVAC system. That is, it will depend on the intrinsic hazard of the pollutant and the level of exposure to that pollutant. A number of common indoor air quality contaminants are listed in Table 1:
Table 1: Common Indoor Air Quality Pollutants
|Butane||Legionella||Respirable suspended particles||Butyric acid|
|Limonene||Semivolatile organic compounds||Camphene||Methanol|
|Sulfates||Carbon monoxide||Sulfur dioxide||Chloroform|
|m-Methylethyl||benzene||p-Dichlorobenzene||Methyl ethyl ketone|
|Toluene||1,2-Dichloroethylene||Microbials||Total suspended particles|
|Nicotine||Total volatile organic compounds||Diethylketone||Nitrogen dioxide|
|Environmental tobacco smoke||Ozone, photochemical oxidants||Volatile organic compounds||Ethanol|
What Causes Indoor Air Problems?
Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants.
What are the Common Sources of Pollutants?
There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution.
The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted.
Some sources, such as building materials, furnishings, and household products like air fresheners, release pollutants more or less continuously. Other sources, related to activities carried out in the home, release pollutants intermittently. These include smoking, the use of unvented or malfunctioning stoves, furnaces, or space heaters, the use of solvents in cleaning and hobby activities, the use of paint strippers in redecorating activities, and the use of cleaning products and pesticides in house-keeping. High pollutant concentrations can remain in the air for long periods after some of these activities.
Why is Ventilation Important?
If too little outdoor air enters a building, pollutants can accumulate to levels that can pose health and comfort problems. Unless they are built with special mechanical means of ventilation, buildings that are designed and constructed to minimize the amount of outdoor air that can “leak” into and out of the building may have higher pollutant levels than other buildings. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a building, pollutants can build up even in buildings that are normally considered “leaky”.
How Does Outdoor Air Enter a Building?
Outdoor air enters and leaves a building by: infiltration, natural ventilation, and mechanical ventilation. In a process known as infiltration, outdoor air flows into the building through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors. In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind. Finally, there are a number of mechanical ventilation devices, from outdoor-vented fans that intermittently remove air from a single room such as an office, bathrooms or kitchen, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the building. The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and pollutant levels can increase.
What are the Health Effects of Poor Indoor Air Quality?
The health effects of exposure to individual chemical substances in building materials are not well understood and are only recently becoming subject to wide spread study. Many chemicals present in indoor air environments have not been evaluated thoroughly and little is known about their long-term health effects. Even less understood are the health effects from constant exposure to mixtures of chemicals (Pollak 1993). Little is known on interactions (antagonistic, synergistic or additive) arising from mixtures of chemicals, even though indoor exposures usually involve multiple numbers of contaminants.
Human health responses to multiple physical and psychological factors in the indoor environment are very individual, complex and often not well defined. There is general knowledge about the qualitative relationship between exposure and health end points, but in quantitative terms information is often very limited (Morawska and Moore 1999).
The occupants of buildings with poor indoor air quality can suffer from severe effects (asthma, allergic response, cancer risk) to mild and generally non-specific symptoms. Some health effects may show up years after exposure has occurred or only after long or repeated periods of exposure, and thus can be characterised as long-term health effects. These effects, which include respiratory diseases and cancer, can be severely debilitating or fatal. Long-term health effects are associated with indoor air pollutants such as radon, asbestos, and environmental tobacco smoke.
The incidence of these health effects has not been investigated systematically in Australia. However, several studies have found that mechanically ventilated office buildings often fail to meet current ventilation guidelines or have occupants who experience the indoor air to be stuffy and a cause of headache, drowsiness and irritancy (Brown 1997).
Building-related illness (BRI) is a clinically diagnosed illness directly related to indoor exposure (eg lung disease, cancer). ‘Sick building syndrome’ is a subset of BRI that comprises an excess of chronic symptoms. Raw (1992) summarised sick building syndrome symptoms as:
- irritated, dry or watering eyes (sometimes described as itching, tiredness, smarting, redness, burning, difficulty wearing contact lenses);
- irritated, runny or blocked nose (sometimes described as congestion, nosebleeds, itchy or stuffy nose);
- dry or sore throat (sometimes described as irritation, oropharyngeal symptoms, upper airway irritation, difficulty swallowing);
- dryness, itching or irritation of the skin, occasionally with rash (or specific clinical terms such as erythema, rosacea, urticaria, pruritis, xeroderma); and
- headache, tiredness or lethargy.
Significant proportions of the population have a greater sensitivity to pollutants. These commonly include newborns, young children, the elderly, heart patients, those with bronchitis, asthma, hayfever or emphysema, and smokers. These population sectors will be at greatest risk from pollutant exposures and, according to the Allergy, Sensitivity, Environmental Health Association (1998), deserve ‘special consideration’. The higher risk to children is a result of their higher metabolic rate, higher intake of airborne pollutants and lower resilience, resulting in a two to four times higher absorption rate (Gilbert and Black 2000).
A study conducted by EPA Victoria in 1993 concluded that allergic diseases are important in both morbidity and mortality in Australia. Most asthmatics are allergic, and allergy is the single greatest risk factor for asthma. The most common allergens for asthmatics are mites (about 80%), cats (37%), ryegrass pollen (31%) and Fungus alternaria (16%). Many other allergens are important in particular circumstances (eg cockroaches, silverfish, carpet beetles, dogs, mice, horses and many different plants, including weeds and trees).
There is evidence that some individuals suffer from multiple chemical sensitivity (MCS), although some medical bodies dispute the existence of this effect (Collins 1993; Brooks 1992; Hodgson 1993 in Brown 1997). MCS is described as an acquired, chronic disorder that is sometimes associated with an episode of high exposure to one or more toxic substances, or to low-level exposure over longer periods of time. It is argued that people with MCS tend to react severely to everyday exposures to commonly used chemicals (perfumes, tobacco smoke, pesticide formulations, cleaning fluids, paints, and industrial chemicals) at doses far below those which generally cause harmful effects to the majority of the community (Immig 2000).
Exposure to environmental toxics (not necessarily airborne) has been suggested as one of a number of factors which may be associated with attention deficit hyperactivity disorder, attention deficit disorder and, to a lesser extent, chronic fatigue syndrome. However, the causes of these disorders are poorly understood, and it is not currently possible to make any definitive statements about their possible links to airborne pollutants.
How can you improve your Indoor Air Quality?
1. Source Control
Usually the most effective way to improve indoor air quality is to eliminate individual sources of pollution or to reduce their emissions. Some sources, like those that contain asbestos, can be sealed or enclosed; others, like gas stoves, can be adjusted to decrease the amount of emissions. In many cases, source control is also a more cost-efficient approach to protecting indoor air quality than increasing ventilation because increasing ventilation can increase energy costs. In order to determine the exact sources of pollution, an indoor air quality consultant should be engaged to conduct an assessment of the building and to determine the following:
a) The concentration and composition of the pollutant;
b) The source of the pollution; and
c) What can be done to cost effectively eliminate or reduce the pollutant.
2. Ventilation Improvements
For most indoor air quality problems, source control is the most effective solution.
Another approach to lowering the concentrations of indoor air pollutants in your building is to increase the amount of outdoor air coming indoors. Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Opening windows and doors, operating window or attic fans, when the weather permits, or running a window air conditioner with the vent control open increases the outdoor ventilation rate. Local office, bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located and also increase the outdoor air ventilation rate.
It is particularly important to take as many of these steps as possible while you are involved in short-term activities that can generate high levels of pollutants – for example, painting, paint stripping, heating with kerosene heaters, cooking, or engaging in maintenance and hobby activities such as welding, soldering, or sanding. You might also choose to do some of these activities outdoors, if you can and if weather permits.
Advanced designs of new homes are starting to feature mechanical systems that bring outdoor air into the home. Some of these designs include energy-efficient heat recovery ventilators (also known as air-to-air heat exchangers).
3. Air Cleaners
There are many types and sizes of air cleaners on the market, ranging from relatively inexpensive table-top models to sophisticated and expensive whole-house systems. Some air cleaners are highly effective at particle removal, while others, including most table-top models, are much less so. Air cleaners are generally not designed to remove gaseous pollutants.
The effectiveness of an air cleaner depends on how well it collects pollutants from indoor air (expressed as a percentage efficiency rate) and how much air it draws through the cleaning or filtering element (expressed in cubic feet per minute). A very efficient collector with a low air-circulation rate will not be effective, nor will a cleaner with a high air-circulation rate but a less efficient collector. The long-term performance of any air cleaner depends on maintaining it according to the manufacturer’s directions.
Another important factor in determining the effectiveness of an air cleaner is accurately determining the strength of the pollutant source. Table-top air cleaners, in particular, may not remove satisfactory amounts of pollutants from strong nearby sources. People with a sensitivity to particular sources may find that air cleaners are helpful only in conjunction with concerted efforts to remove the source.
Over the past few years, there has been some publicity suggesting that houseplants have been shown to reduce levels of some chemicals in laboratory experiments. There is currently no evidence, however, that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices. Indoor houseplants should not be over-watered because overly damp soil may promote the growth of microorganisms which can affect allergic individuals.