Air toxics and indoor air quality in Australia

State of knowledge report
Environment Australia, 2001
ISBN 0 6425 4739 4

Part B: Indoor air quality

Overview of indoor air quality

6.1 Introduction

The 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 NHMRC3.

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.1

6.2 Indoor air pollutants

Tables 6.1 and 6.2 present information on the pollutants detected indoors (Table 6.1) and common reasons for poor indoor air quality and potential sources of indoor air pollutants (Table 6.2). Chapter 7 will discuss the broad categories of indoor pollutants and their sources in more detail.

Whether a pollution source causes an indoor air quality problem or not will depend on a number of factors, including the nature of the contaminant, the rate of emission from the source, and the ventilation rate of the building (DEST 1996). That is, it will depend on the intrinsic hazard of the pollutant and the level of exposure to that pollutant.

Table 6.1: Pollutants detected in indoor environments
Acetic acid Ethylbenzene Pesticides
Acetone Formaldehyde Phenol
Asbestos n-Hexane Propane
Benzene Lead Radon
Butane Legionella Respirable suspended particles
Butyric acid Limonene Semivolatile organic compounds
Camphene Methanol Sulfates
Carbon monoxide Methyl chloroform Sulfur dioxide
Chloroform m-Methylethyl benzene Tetrachloroethylene
p-Dichlorobenzene Methyl ethyl ketone Toluene
1,2-Dichloroethylene Microbials Total suspended particles
Dichloromethane (methylene chloride) Nicotine Total volatile organic compounds
Diethylketone Nitrogen dioxide 1,1,2-Trichloroethane
n-Decane Nonanal 1,2,3-Trimethyl benzene
Dust mites n-Nonane 1,2,4-Trimethyl benzene
Environmental tobacco smoke Ozone, photochemical oxidants Volatile organic compounds
Ethanol PCBs m-,o- and p-Xylene
Ethyl acetate Pentane

Source: Adapted from Brown (1996), EPA Victoria (1993) and ANZEC (1990).

Indoor air quality is influenced by two major components: the amount and quality of outdoor air getting in, and indoor sources of emissions. The influence of outdoor air quality on indoor air quality depends on the air exchange rate; this varies with climate, lifestyle and building design (Bofinger 1999). Kim et al (1996), in tracking the levels of individual airborne compounds, identified indoor/outdoor ratios between 0.7 and 1.3 during the day, and ratios of 0.5 and 1.7 at night. Ando et al (1996) concluded that concentrations of suspended particle matter and PAHs in indoor air increased in proportion to those in the outdoor air. Suspended particulate matter and PAHs were selected because they are indicators of vehicle exhaust and coal combustion.

Table 6.2 lists some of the contributing factors to poor indoor air quality found in the United States, and highlights the importance of ventilation in many reported cases of poor air quality in indoor environments. This table shows that inadequate ventilation was primarily responsible for health complaints in over half of the buildings investigated by the US National Institute of Occupational Safety and Health (NIOSH) health hazard evaluations. Overall, it shows that United States buildings studied were often not adequately ventilated. Whether this was the prime cause of the complaints and could be remedied was not determined.

Table 6.2: Common factors associated with indoor air pollution
Contributing factor to indoor air quality Percentage of cases
Inadequate ventilation 52
Contamination from inside the building 16
Contaminants brought in from outside the building 10
Microbiological contaminants 5
Building material contamination 4
Cause not determined 13

Source: Information adapted from Indoor Environmental Quality Guidance and Reference Manual by Martin 1998 with reference to studies by NIOSH. More information on health effects and occupational exposure limits for various chemicals can be found at 

6.3 Health effects as a result of exposure to pollutants

The health impacts resulting from exposure to individual chemical substances in building materials are not well understood. Many chemicals present in indoor air environments have not been evaluated thoroughly and little is known about their long-term health effects (Meek 1991). 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 typically involve multiple contaminants (Ng 1999).

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.2

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:

6.4 Sensitive sections in the community

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). Allergic responses to indoor air pollutants are discussed in more detail in Section 7.4.2.

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). Currently, there is no widely accepted test of physiological function that correlates with MCS symptoms (Cullen 1987; Health Council of the Netherlands 1999 in DHAC 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.

6.5 Goals for indoor air quality

Australia's National Health and Medical Research Council (NHMRC) has recommended interim national indoor air quality goals3 for a number of common indoor air pollutants (see Appendix D and Table 6.3 below). In addition, various international bodies have recommended indoor air quality goal concentrations for specific pollutants, generally on a health-related basis. Table 6.4 summarises these and compares them with the goals determined by the NHMRC.

Table 6.3: Interim national indoor air quality goals recommended by the National Health and Medical Research Council3
Pollutant Goals for maximum permissible levels of pollutants in aira Measurement criteria Comments
µg/m³ ppm
Carbon monoxide (CO) 10 000 9 8-hour average not to be exceeded more than once a year This is not a threshold limit value
Formaldehydeb 120 0.1 Not to be exceeded For dwellings and schools
Lead 1.5 3-month average  
Ozone 210 0.10 Maximum hourly average not to be exceeded more than once a year  
170 0.08 Four hour average  
Radonb 200 Bq/m3 Annual mean Action level
Sulfates 15 Annual mean  
Sulfur dioxide (SO2) 700 0.25 10-minute average Levels may not be low enough to protect the most sensitive individuals
570 0.20 Hourly mean  
60 0.02 Annual mean  
Particles 90 Annual mean  
Total volatile organic compounds 500 Hourly average A single compound shall not contribute more than 50% of the total

a At 0° C and 101.3 kPa.
b Final NHMRC goals.
– = no goals set in those units

Source: NHMRC (1996).

Table 6.4: Comparison of indoor air quality guideline concentrations for pollutants
Indoor air pollutant Goal concentrations (µg/m³ unless specified)
NHMRC3 (1993) (indoor) Health and Welfare Canada (1987) (residential) Norwegian Health Directorate (NHD) (1990)a (indoor) WHO (1987)b (indoor)
Asbestos Source control Carcinogen
Synthetic mineral fibres No free fibres
Radon 200 Bq/m³ (1y)d 800Bq/m³ (1 year) 200–800 Bq/m³ Carcinogen
Environmental tobacco smoke Prohibited
Respirable suspended particles TSP90 (1 year) PM100 (1 hour) 40 (8 hours) 100
Legionella 2.5
House dust mite 1 g/g Der p 1e
Microbes No pathogens or odour
Formaldehyde 120 (ceiling)d 60–120 100 60
VOC TVOCs 500 (1 hour)d
VOC 250 (1 hour)d
Irritants, TVOCs 400 Some VOCsc
Nitrogen dioxide Review 480 (1h) 200 (1 hour) 400 (1 hour)
Carbon monoxide 9 ppm (8 hours) 11 ppm (8h) 9 ppm (8 hours) 9 ppm
Carbon dioxide 3500 ppm 1000 ppm (max) 1000 ppm
Ozone 240 (1 hour) 240 (1h) 150 (1 hour)
Sulfur dioxide 700 (1 hour) 1000 (5 min)
Lead 1.5 (3 months) 0.5–1.0
Mercury 1.0 (1 year)
Relative humidity (%) 30–80

a Values averaged over 24 hours unless specified.
b Short-term exposure averages.
c 1,2 dichloroethane 700, dichloromethane 3000, styrene 800 (70 odour), tetrachloroethylene 5000, toluene 8000 (1000 odour).
d Final goals for radon and formaldehyde; level of concern for volatile organic compounds (VOCs) and total VOCs (TVOCs); other goals are interim goals using ambient air gas.
Der p 1 is the allergen specific to Dermatophagoides pteronyssinus.
Bq = becquerel;
PM100 = particulate matter (less than 100 micrometres in diameter).
– = no goal set.


1 US EPA Targeting Indoor Air Pollution, available at 

2 The US EPA's approach to indoor air quality and progress is found in Targeting Indoor Air Pollution, available on the internet at 

3 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: 

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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