State of knowledge report
Environment Australia, 2001
ISBN 0 6425 4739 4
Part B: Indoor air quality (continued)
This section examines various indoor environments and the likely pollutants to which occupants may be exposed. The divisions are in some cases a little arbitrary, as many pollutants and sources are common to a range of indoor environments and have little to do with the purpose for which the building is used. A case in point is formaldehyde emissions from the use of pressed-wood panels in mobile homes. This applies equally to mobile offices of similar construction and design.
Pollutants may originate from outdoor air, building construction materials, furnishings, appliances and equipment, and from the activities of the occupants. Table 9.1 shows potential exposure to some common pollutants. The relative contribution of the various sources of indoor air pollutants will be unique to any particular building. To avoid unnecessary duplication in this chapter, pollutants and their sources are discussed primarily under the type of building in which they are most likely to be a significant issue.
More detailed information on the pollutants mentioned in this chapter can be found in Chapter 7.
Indoor air quality in the home is of special importance because it is where we spend the greatest proportion of our time. The home is also the indoor environment in which occupants are most likely to be able to address at least some of the causes of poor indoor air quality. Conversely, people are less likely to be able to control the ingress of pollutants from the outdoor air than they are in other buildings. Homes mostly rely on natural ventilation, while larger buildings are more likely to have mechanical ventilation systems that can filter out some pollutants.
VOCs and formaldehyde are significant indoor air pollutants in the home because they occur in a wide range of building products, such as pressed-wood panels, paints, adhesives and sealants. Studies have found that occupants are exposed to much higher levels of VOCs and formaldehyde for 6–12 months after building construction or renovation. A recent CSIRO study of 27 Melbourne homes (Brown 2001) found that VOC concentrations in established homes were approximately four times higher than outdoor levels, and considerably higher still in new homes. About 150 000 new houses and other residential buildings are constructed each year in Australia, so many occupants are exposed to these very high levels of VOCs.
|Environment||Percentage of the day||Common pollutants||Major sources|
|Home||57||Formaldehyde||New building products unflued gas appliances|
|Nitrogen dioxide, carbon monoxide||Unflued gas appliances|
|Allergens||House dust mites|
|Benzene, 1,3-butadiene, particles, carbon monoxide||Vehicle exhaust (attached garage or near busy road)|
|Environmental tobacco smoke||Occupants who smoke|
|Work||14||Formaldehyde||New building products|
|VOCs, ozone, particles||Office equipment|
|Legionella bacteria||Cooling towers|
|Shopping||2||Benzene, 1,3-butadiene, particles, carbon monoxide||Vehicle exhaust (enclosed carpark or busy road)|
|Legionella bacteria||Cooling towers|
|Recreation||18||Environmental tobacco smoke||Occupants who smoke|
|Legionella bacteria||Cooling towers|
|Benzene, 1,3-butadiene, particles, carbon monoxide||Vehicle exhaust (enclosed carpark or busy road)|
|Transit||5||Benzene, 1,3-butadiene, particles, carbon monoxide||Vehicle exhaust (in slow moving traffic)|
VOC = volatile organic compound.
Percentages are for total time spent in that environment, which may include an outdoor component. Common pollutants relate to indoor environments only.
Levels of VOCs and formaldehyde in caravans and mobile homes tend to be higher than for conventional homes because they are more likely to contain pressed-wood products and to have low air infiltration rates (Brown 1997). Some 160 000 Australians, or 0.9% of the population, were residing in caravans and mobile homes at the 1996 census, although this figure includes both permanent residents and holidaymakers who were staying in such accommodation on census night.
House dust mites, a major source of allergens, are of greatest significance in the home, where they live in mattresses, furniture and carpets. House dust mite faeces, which readily become airborne, contain an allergen that affects humans. In Australia, house dust mite allergen concentrations have been found to be 20–40 times higher in homes than in public buildings (Mahmic and Tovey 1998).
Pets are a common source of allergens in the home. In particular, allergens from cats can produce a strong allergic reaction. Allergens are found in cat saliva and are transferred to the fur during grooming. When the saliva dries and falls off the hairs, these allergens readily become airborne. Cat hair itself is also an allergen source.
Overseas studies have shown cockroach allergy to be very common, but little is known about the relative importance of cockroach allergens in Australia.
Exposure to pesticides in the home may arise from the infiltration of termiticides used to treat foundations, from pesticide treatments applied inside the house, in roof cavities or in subfloor areas, or through the use of consumer pesticide products inside the home. Residues from the past use of organochlorine termiticides such as chlordane may persist in the soil beneath buildings for many years. More information on the effects of pesticides on indoor air quality can be found in Chapter 7.
Environmental tobacco smoke is of particular importance in the home, which is one of the diminishing number of indoor environments where smoking is permitted without specified ventilation requirements or other restrictions.
Carpets are recognised as a major contributor to indoor particulate pollution in homes and office buildings. Dust in carpets is usually controlled by the use of vacuum cleaners, but conventional vacuum cleaners can reduce indoor air quality. This is because they rely on bag filters, which allow smaller, more harmful particles to escape into the air. If their drawing capacity is inadequate, they can also lead to dust particles accumulating in carpets. The efficiency of a vacuum cleaner depends on the design of its motor and the type of filter it uses.
Na et al (2000) tested eight vacuum cleaners for emissions of total suspended particles. The study found that a high-performance vacuum cleaner using a HEPA filter in combination with a cyclonic design motor was the best performing of the models used. It removed more than 70%, or 8.48 g/m², of dust from the carpet surface (twice as much as the others tested). This model also had the lowest exhaust emission, averaging around the levels of total suspended particles found in the surrounding air (35 µg/m³ compared with 34 µg/m³), five times less than the highest-emitting vacuum cleaner (172 µg/m³).
The growth of fungi, in particular moulds, is favoured by the presence of damp surfaces, which are commonly found in poorly ventilated bathrooms and other wet areas in the home. Moulds produce large numbers of spores which are allergens and may also cause lung infections or be toxic.
As part of their education and information campaign, EPA Victoria proposed the ‘ideal house’. As an illustration, an ideal house that kept some of the major contaminants to a minimum would have the following features:
- it would be built on land that had minimal levels of radon emissions;
- it would be designed to allow natural ventilation of around 1.5 air changes per hour in all weather conditions, while maintaining a comfortable temperature and relative humidity of 50% or less;
- it would be constructed of natural wood products or brick, with no reconstituted wood-based panels used in construction or furnishings;
- joinery would be done without the use of solvents and caulking compounds;
- surfaces would be finished with low-emission coatings (eg zero-VOC paints, based on comparisons of manufacturers' material and safety data sheets);
- heating and cooking appliances would be maintained correctly and operated with local exhaust ventilation and venting outdoors;
- no asbestos, or other materials containing respirable fibres, would be used; and
- no tobacco smoking would take place, and any wood-burning heater would be fully enclosed, with effective draught and no leaks in the flue.
The features of the ‘ideal house’ include the qualities that are recognised widely as best practice when addressing indoor air quality.
Indoor air quality in schools is considered as a separate issue in this report because over many years children spend many hours per week at school, in an indoor air environment which neither they nor their parents control directly. Schools, for the purpose of this report in the context of indoor air quality, are taken to include daycare centres.
Children are smaller and have a higher metabolic rate than adults, so they breathe in more air per unit body weight and are more susceptible generally to the effects of indoor air pollutants. This is an important factor in any consideration of levels of indoor air pollutants in schools.
The factors affecting indoor air quality in schools are generally the same as for other buildings, but some are particularly relevant.
There is considerable variation in the design of school buildings throughout Australia, according to their location, size and age. The materials used in their construction and furnishings vary, as do the rate and type of ventilation. These variations mean that the relative importance of factors affecting indoor air quality varies from school to school; nonetheless it is useful to identify some factors.
Unflued gas heaters, associated with high levels of nitrogen dioxide in indoor air, continue to be used in some Australian schools. In 1990 the NSW Department of School Education instituted a major program to rectify gas leaks and introduce heaters that emitted low levels of nitrogen oxides (but were still unflued) in all government schools (Brown 1997). More information on this program is in Section 7.2.1. Currently, Victoria is the only State that formally requires gas heaters to be flued to the outside air.
Chemicals used in schools include cleaning products, and those used in art, craft and science courses, all of which are potential sources of indoor air pollutants.
Brown (1998b) reported that VOC problems had been encountered in a portable classroom that had been renovated with new paint and carpet. For three years afterwards both teachers and students complained of headaches, nausea, sore throats and increased use of asthma medication in the classroom. Even after three years, the total VOC level was 550 mg/m³, which was in excess of the NHMRC2 air quality goal of 500 mg/m³.
A study by Smede et al (1997) suggested that the indoor air quality (including VOCs and formaldehyde) of the school environment was important and could affect asthmatic symptoms. The study also concluded that exposure to indoor pollutants, including VOCs, affected perception, even at the low concentrations normally found indoors in nonindustrial buildings. Other authors have inferred that the ability to learn is reduced during exposure and concluded that VOCs may affect sensory responses, eye physiology and performance (Kjaergaard et al 1990).
Most schools are not air conditioned, relying instead on natural ventilation, which aids the dispersion of pollutants that originate within the building, at least in warmer weather when windows are open. In cooler weather, when windows are likely to be closed, ventilation rates in schools that rely on natural ventilation are likely to be lower than for air conditioned schools. Where there are significant outdoor sources of air pollutants, such as in schools located near major roads, high ventilation rates are likely to diminish air quality by allowing a greater influx of air pollutants from outdoors.
Emissions from flooring have been associated with poor indoor air quality in schools as illustrated in the case study by Ball (2000), shown in Box 9.1
In 1993, at Ravenshoe State School in Queensland, seamless flooring was laid in an area adjacent to classrooms and offices. This type of flooring comprises an epoxy resin base and a polyurethane sealing coat. It is laid wet and then cures to form a hard surface.
The flooring was laid in an area adjacent to classrooms and offices, which remained occupied at the time. Offensive odours were reported during and after the work was carried out. Attempts by the flooring contractor to remedy the problem were unsuccessful and the flooring was eventually removed. Again, adjacent areas remained occupied while the removal was carried out. The building was eventually evacuated and was not reoccupied till 1996.
In January 1994 the same flooring was laid by the same contractor in a new school at Herberton. Complaints of odours and ill health followed and the school was closed in May 1994 after staff refused to continue working there.
The Queensland Department of Public Works Built Environment Research Unit investigated and found that the solvents xylene and isobutyraldehyde were responsible for the odours. Much of the problem was attributable to incorrect application of the product. The epoxy base had been overthinned with xylene, and insufficient drying time had been allowed between coats. Solvents trapped in the flooring then evaporated over a long period of time. This was made worse by poor ventilation in the classrooms.
The problems encountered at Ravenshoe and Herberton, and in other Queensland schools, were compounded by the way in which the complaints were initially investigated. Testing was initially carried out by the manufacturer and workplace health and safety inspectors, but the results were compared to occupational exposure standards, which was not appropriate in the circumstances. This led to the finding that emissions were within acceptable limits, which caused further concern to the community.
A medical evaluation by Dr Roscoe Taylor concluded that it was highly unlikely that there was an increased possibility of long-term, delayed health risks for the majority of the exposed population, but noted that there were incidents of chemical sensitivity, worsening respiratory problems and other complaints.
Source: Ball (2000).
Typically, buildings that are affected by ‘sick building syndrome’ are office buildings. Large office buildings are usually ventilated mechanically, and inadequate ventilation is a major potential factor contributing to poor indoor air quality (see Section 8.3).
Some pollutant sources may particularly affect indoor air quality in offices compared to other buildings – for example, office equipment such as photocopiers and printers. These have been shown to emit respirable particles, ozone and a range of VOCs at various levels depending on the age of the appliance and the condition of its operation (Brown 1996b). Office furnishings may also have significant effects on indoor air quality. The impact of other factors, such as building construction materials, use of cleaning products and influx of outdoor pollutants, will vary from building to building.
More information on indoor air quality in the office may be found in Sections 10.3, 10.4 and 10.6.
Hospitals and nursing homes, like schools, merit special consideration because hospital patients and nursing home residents are either ill or old and infirm. Poor indoor air quality can be expected to have a greater adverse health effect on such people than on those who are strong and healthy.
Hospitals use a broad range of chemicals in medical and laboratory procedures; some of which may impact on indoor air quality.
Hospitals and nursing homes have a particular need to ensure that their premises are kept clean so as to prevent the spread of infection. Cleaning is likely to be carried out more frequently and more thoroughly than in other buildings and the cleaning products used may be more concentrated. Cleaning and sterilisation practices are, therefore, significant potential sources of indoor air pollutants in these institutions.
The boundary between goals for indoor air and occupational exposure standards has become blurred in buildings that act as one person's workplace and another's public place (for example, shopping malls). Indoor air goals must consider somewhat different factors and risk levels from those in the work environment.
Aircraft passengers and crew breathe the air provided through the aircraft's ventilation system, often for long periods of time. They do not have the opportunity to seek out fresh air should they wish, and may suffer discomfort and adverse health effects if air quality is poor. Several potential sources of pollutants exist. Low ventilation rates can lead to cabin air becoming stale (ie. build up of carbon dioxide). Outside air drawn into the ventilation system may be contaminated with engine oils and hydraulic fluids. Residues from pesticide treatments applied in the cabin may remain in the air.
Concerns about aircraft air quality have seen proposed new legislation introduced into the United States Congress in June 2001.1· If enacted, the Aircraft Clean Air Act of 2001 would impose certain obligations on air carriers. Carriers would be required to disclose mechanical and maintenance records to complainants affected by poor cabin air. Carriers would have to provide information on the chemical constituents of products used in the maintenance, operation or treatment of aircraft. The Act would also require the Federal Aviation Administration to commission a study to determine the cabin oxygen levels necessary to protect health of occupants.
2 On 19 March 2002, the National Health and Medical Research Council rescinded its publication "Ambient Air Quality Goals and Interim National Indoor Air Quality Goals". The Council has made this publication available on its Internet Archives site as a service to the public for historical and research purposes only.
The publication is available at: http://www.nhmrc.gov.au/publications/synopses/eh23.htm
The Internet Archives site also contains the following statement made by the National Health and Medical Research Council:
Rescinded publications are publications that no longer represent the Council's position on the matters contained therein. This means that the Council no longer endorses, supports or approves these rescinded publications.
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