Lecture: Indoor Air Quality: Pollutants
Written by Ian Mawditt
January 2007
1. Introduction to indoor air quality
This lecture explores the complex and important topic of indoor air quality (IAQ),
focusing mainly on the effects in the home environment. The lecture will examine
the main aspects of IAQ, with a review of the key pollutants – the main cause of
poor air quality, and the health implications associated with them.
To begin, it is important to define, and to understand, the importance of air quality.
Definition of Indoor Air Quality
IAQ is a term used to describe the level of pollution of the air inside a confined
space, and can generally be satisfied by maintaining three fundamental
requirements for the human environment:
1. Hygrothermal conditions (i.e. temperature and humidity);
2. Normal concentration of respiratory gases;
3. Continuous dilution of pollutant concentrations to ‘acceptable’ levels.
Why is air quality important?
“Human beings need a regular supply of food and water and an essentially
continuous supply of air…. That all people should have free access to air and water
of acceptable quality is a fundamental human right”. (WHO 2000).
This statement by the World Health Organisation is a right that we take for granted
in the developed countries of the world. Most people are aware that, in developing
countries, this may not always be the case as food is often in short supply, and the
drinking water could be contaminated and possibly unfit for human consumption.
However, in developed countries, do many people really question the quality of the
air that we breathe? Perhaps they do outdoors, where they can relate to the
problems associated with traffic pollution, but not very many are concerned with the
potential problems indoors.
In the UK, outdoor air pollution is now routinely monitored from fixed sites around
the country. A summary of these results are reported daily by the media, but are
mainly related to traffic and industry emissions, which combined with the weather
predictions, may have an adverse effect on asthma sufferers. However, the air
inside buildings is not routinely monitored and, as a result, indoor air quality is often
overlooked, and little understood.
People expect that the indoor environment will not threaten their well-being, that it
will provide a respite from the pollution present in the outdoor air. Yet recent
research has found that the indoor environment may be much more polluted than
the outdoor environment, in some cases by factors of up to one hundred (Palmer et
al 2002). The sources of indoor pollution may vary a great deal from one building to
another, and depends upon the rate of emissions from the building fabric,
furnishings, heating and cooking activities, human metabolism and, the rate of
ventilation. The effects of pollution indoors can range from discomfort caused by
temperature extremes and odours, to fatality from exposure to pathogenic
organisms or toxic chemicals. As most people in the UK and other temperate
climates spend an average of 80-90% of their time indoors (WHO 1997), it is
imperative that the health implications associated with quality of the air inside our
homes and places of work are taken seriously.
Until recently, there has been little guidance relating to air quality standards inside
buildings in the UK. Over the past twenty years, numerous studies have been
undertaken, by expert groups across the world, in relation to the effects of individual
pollutants and pollutant mixtures. The cumulative outcomes of these studies have
assisted the collaborative development of international guidelines over recent years,
although much research is still required. The constants from the majority of these
studies relating to IAQ have been:
1. The need for source control (i.e. minimise pollutants entering the indoor space)
2. The effectiveness of pollution dilution resulting from air movement, or ventilation.
In March 2006, the UK government published their first guidelines relating to IAQ in
conjunction with ventilation. These guidelines are contained in the revised edition to
the Building Regulations, Approved Document F1 – Means of Ventilation, 2006
edition, and are discussed later.
What is in the air?
The air, or earth’s atmosphere, is one of the four classical elements – air, water,
earth and fire. It comprises a delicate mixture of naturally occurring gases as given
in table 1. Nitrogen, the main component of air is non-toxic, but cannot support life
on its own. Everyone needs the oxygen, present in the air, for breathing. Together,
the nitrogen and oxygen elements constitute over 99% of the air’s composition, with
the remaining 1% comprising argon and carbon dioxide, with only trace amounts of
other, mainly inert, gases.
Table 1 – Composition of air (adapted from Lide 2002)
Gas
Symbol
Volume
Percent
Volume
Parts per million
Nitrogen
N2
78.084 %
7.81 x 105 ppm
Oxygen
O2
20.9476 %
2.09 x 105 ppm
Argon
Ar
0.934 %
9.34 x 103 ppm
Carbon Dioxide*
CO2
0.0367 %
367 ppm
Neon
Ne
0.001818 %
18.2ppm
Methane*
CH4
0.0002 %
2 ppm
Helium
He
0.000524 %
5.2 ppm
Gas
Symbol
Volume
Percent
Volume
Parts per million
Krypton
Kr
0.000114 %
1.1 ppm
Hydrogen
H2
0.00005 %
0.5 ppm
Xenon
Xe
0.0000087 %
0.09 ppm
Ozone*
O3
0.000004 %
0.04 ppm
Water Vapour*
H2O
0 to 4 %
0 to (4 x 104) ppm
* Denotes variable gas in the atmosphere, values are typical.
Both argon and carbon dioxide are non-toxic and non-reactive. In their respective
concentrations in the atmosphere, they do not pose any threat to life. Carbon
dioxide (CO2) gas is a product of both respiration and combustion. As a result, the
concentrations of this gas are constantly increasing due to the planet’s growing
population, and the activities of its inhabitants.
What is air pollution?
Since the Industrial Revolution, human activity has continuously changed the
composition of the air. In particular, CO2 levels have increased from 280ppm in the
early 19th century, to 367ppm today – its highest level for 160,000 years (Netcen,
2005). CO2 cannot be regarded as a pollutant due to its natural occurrence in the
air. However, the recent rapid increases in CO2 concentrations are largely
responsible for the increasing climatic temperatures associated with global
warming. The effects of climate change, CO2 levels, and the effect on human health
fall outside the scope of this lecture.
Human activity has also introduced new gases and substances into the
atmosphere. These extra gases and substances are known as air pollutants and
come from sources such as industry, power stations, and transport. Air pollution
from road transport is currently the main air quality problem in most cities. Gases
and particles released from exhausts can have serious effects on people’s health,
and cause damage to buildings. Some gaseous pollutants can react in the air to
form acidic chemicals, which eventually fall as acid rain, causing damage to both
the natural and built environment.
Pollutants generally fall into four main categories as illustrated in table 2.
Table 2 – Pollutant categories
Pollutant category
Example of substance
Typical source / cause
Inorganic gases
carbon monoxide; nitrogen
dioxide; ozone
combustion processes;
traffic emissions; reaction
with organic compounds
Organic gases*
volatile organic compounds;
formaldehyde
building products;
solvents; cosmetics
Non-biological
particles
n/a
combustion; road
pollution; industrial
sources; air-borne soil
and sand
Biological particles
dust / dust mites; mould;
pollen
naturally occurring
bacteria and organisms
*Organic gases are usually made up of carbon and hydrogen molecules.
2. Indoor pollutants – inorganic gases
Inorganic gaseous pollutants of interest in IAQ investigations are usually carbon
monoxide (CO) and nitrogen dioxide (NO2). Although not usually classed as a
pollutant, CO2 is listed in this category because it is classically used as a marker,
providing an indication of the adequacy of ventilation. Guidelines for exposure limits
to inorganic pollutants vary according to toxicity as listed in table 3.
Table 3 – Guideline values for classical substances (adapted from WHO 2000)
Substance
Guideline concentration value
Averaging time***
Carbon dioxide (CO2)
27000 (15000*)
9000 (5000**)
mg m-3 (ppm)
mg m-3 (ppm)
15 minutes
8 hours
Carbon monoxide
(CO)
100 (87.29)
60 (52.37)
30 (26.19)
10 (8.73)
mg m-3 (ppm)
mg m-3 (ppm)
mg m-3 (ppm)
mg m-3 (ppm)
15 minutes
30 minutes
1 hour
8 hours
Nitrogen dioxide
(NO2)
200 (0.106)
120 (0.064)
40 (0.021)
µg m-3 (ppm)
µg m-3 (ppm)
µg m-3 (ppm)
1 hour
8 hours
Annual
Ozone (O3)
120 (0.06)
µg m-3 (ppm)
8 hours
*Value from HSE 2005. ** Value from CIBSE
*** Averaging time is the duration of exposure according to toxicity, i.e. higher toxicity:
shorter exposure.
Carbon dioxide
Carbon dioxide (CO2) is a dense and odourless gas produced by combustion and
biological metabolism. Accordingly, concentration levels in the indoor environment
are usually higher due to space heating, cooking and occupant activity. Carbon
dioxide is naturally present in the air at concentrations of approximately 367ppm in
clean air (table 1). However, a study in Paris by Widory (2003), demonstrated that
concentrations could increase to 950ppm or higher in dense urban environments.
The Chartered Institute for Building Services Engineers (CIBSE) have published
maximum recommended limits for indoor CO2 concentrations of 5000ppm for an 8hour period (table 3), although they suggest that between 800 and 1000ppm is an
indicator of adequate ventilation (CIBSE 2001). Therefore, the relationship between
the indoor concentration and rates of ventilation become increasingly important in
areas where there are high outdoor concentrations of CO2.
According to Liddament (1996), it is strictly the difference between indoor and
outdoor carbon dioxide concentrations that provide a measure of metabolic impact.
An understanding of the metabolic emission rates is useful in the design of a
building, and its ventilation system, when the occupants are the dominant source of
pollution. The rate of emission of metabolic CO2 is well defined and is related to the
level of activity. Typical production rates are given in table 4.
Table 4 – Energy production and emission rates of CO2
(adapted from BS 5925:1991)
Activity (adult male)
Metabolic rate (watts)
CO2 production rate (l/s)
Sedentary work
100
0.004
Light work
150-300
0.006-0.012
Moderate work
300-500
0.012-0.02
Heavy work
500-650
0.02-0.026
Very heavy work
650-800
0.026-0.032
Whilst carbon dioxide, on its own, is not harmful to human health, a build-up in a
room can lead to a feeling of stuffiness, and can impair concentration. Elevated
levels of CO2 in a confined space will lead to an increase in the rate of respiration.
Only in exceptional circumstances is it present in sufficient amounts to be a danger
to health (Möhle G et al 2003). It is primarily for these reasons, and that it is
relatively simple to measure, that CO2 has traditionally been used as a marker to
determine sufficient rates of ventilation. In IAQ investigations, measurement of CO2
concentrations can give valuable information, particularly when it is used as a proxy
for other indoor contaminants. CIBSE recommend (CIBSE 2001), ventilation rates
should be capable of maintaining between 800 and 1000ppm CO2. In most
situations this should effectively dilute other, more serious, pollutants to safe
concentration levels.
Carbon monoxide
Carbon monoxide (CO) is a toxic gas produced during the burning of fuel, and is a
significant indoor pollutant, known to cause accidental death and severe damage to
health (DoH 2004). It is colourless and odourless, and therefore undetectable by
our olfactory system (our ability to smell). It is dangerous because it displaces
oxygen from the haemoglobin, reducing the blood’s ability to deliver oxygen to the
essential organs and tissues in our bodies. In sufficient concentrations, CO will form
carboxyhaemoglobin (Crump et al 2002), which will eventually lead to asphyxia and
ultimately death. The physical symptoms that will be experienced by a person
exposed to CO vary with the level of exposure, and are summarised in the table 5.
The level of exposure is expressed as the percentage of haemoglobin that has
been converted to carboxyhaemoglobin (COHb).
Table 5 – Human health effects of exposure to carbon monoxide
(adapted from DOH 2004)
Carboxyhaemoglobin %
Symptom
0-10
None
10-20
Tightness across forehead
20-30
Headaches
30-40
Severe headache, weakness, dizziness, nausea
and vomiting
40-50
Collapse, increased pulse and respiratory problems
50-60
Coma, intermittent convulsions
60-70
Depressed heart action, death possible
70-80
Weak pulse, slowed respiration, death likely
> 80
Death in minutes
The amount of COHb in the blood is influenced by the following factors:




the concentration of carbon monoxide in the inhaled air;
the duration of exposure to carbon monoxide;
degree of activity of the person being exposed to carbon monoxide;
individual susceptibility.
CO is mainly non-reactive in the atmosphere, which means that concentration
levels are directly proportional to emissions (Sherman et al 2003). It is produced
mainly as a result of incomplete combustion of carbon containing fuel – vehicles
being a major source of emissions (DoH 2004).
According to the Department for the Environment, Food and Rural Affairs (DEFRA)
road transport is responsible for 69% of CO emissions in the UK (DEFRA 2003a).
However, studies by the Institute for Environment and Health (IEH) have found that
whilst outdoor concentrations have an influence on indoor concentrations, the major
determinants inside buildings are smoking and malfunctioning heating and cooking
appliances (IEH 2001).
Nitrogen dioxide
Nitrogen dioxide (NO2), along with the other nitrous oxides, is formed naturally and
is part of the natural nitrogen cycle, necessary for organic growth. However, various
human activities produce NO2 in concentrations that constitute atmospheric
pollution (Spengler et al. 2000). Similar to carbon monoxide, NO2 is formed as a byproduct of the combustion process in which air is used as the oxidant.
Consequently, emissions tend to be intermittent. Sources of NO2 include gas
cookers, open fires, oil and gas boilers, gas tumble-driers, and tobacco smoke.
Externally, the main source of NO2 is from car emissions, which may enter a
building.
Although not poisonous like CO, NO2 is a respiratory irritant, particularly in children.
A report by the Institute for Environment and Health (IEH 1996) suggests that about
70% of a person’s exposure to NO2 occurs in the home, usually where gas cookers
are used. A previous study by Coward et al. (2001), found that NO2 concentrations
in UK houses were highest in kitchens and lowest in bedrooms. They also found
that outdoor concentrations were similar to indoor levels, except in homes without
gas appliances. The main source was gas cooking and heating and they deduced
that indoor surfaces partly absorb some of the NO2, hence why bedrooms tended to
be lower. NO2 is clearly an important pollutant, and often features in IAQ surveys.
Ozone
Ozone is a naturally occurring gas that is created, and exists, in the stratosphere
(the atmospheric layer approximately 10km above ground level). At this altitude,
ozone provides essential protection for our existence: by absorbing potentially
harmful ultra-violet radiation from the sun, which can cause skin cancer and
damage to vegetation (CAS 1998). However, ozone is a highly reactive oxidising
agent: at low atmospheric levels (often referred to as ground level ozone), it is a
pollutant and can have an adverse effect on human health. Acute health effects of
ozone may include eye/nose irritation, respiratory problems and airway
inflammation (Defra 2003b).
Ground level ozone is a secondary pollutant: that is, it is not directly emitted, but
formed from organic compounds and oxides of nitrogen in the presence of sunlight
(Sherman et al 2003). This means that ozone concentrations are strongest in urban
areas during the daylight hours, and do not persist at night. It is not usual for ozone
to be a problem indoors, although it can rapidly react with airborne organic
compounds to form chemical gases, which may collectively have a greater health
impact than ozone (Weschler 2000). However, as this is a relatively unusual
occurrence, ozone does not usually form part of IAQ studies.
Sulphur dioxide
Sulphur dioxide (SO2) is a colourless gas with a pungent smell, and is directly
emitted from the combustion of sulphur-containing fuels, such as oil and coal.
According to DEFRA, approximately 85% of UK SO2 emissions originate from
power stations and industrial sources. Externally, SO2 levels are closely monitored
because it is a respiratory aggravator, particularly amongst asthma sufferers, and
because of the damage it causes to the environment. However, according to Crump
(2002), levels of SO2 have not been reported in any large-scale IAQ survey of UK
homes. This is due mainly to the decline in use of coal as a domestic fuel. As with
ozone, SO2 does not normally form part of IAQ investigations.
3. Indoor pollutants – organic compounds
There are several hundred varieties of organic chemical compounds present in the
indoor air (ECA 1989). These comprise a complex mixture of many individual
chemical substances of varying volatility and toxicity. Most individual compounds
are present in the air at very low concentrations, although the World Health
Organisation has published concerns about the effects of simultaneous multiple
exposure to these compounds on human health (WHO 1989).
Volatile organic compounds
Volatile organic compounds (VOCs) represent the largest group of indoor air
pollutants. Derived mainly from petrochemicals, VOCs release vapours at room
temperatures in a process known as ‘off gassing’. Their presence indoors is a result
of emissions from sources such as people, buildings, furnishings, and consumer
products. They are also present because of outdoor, airborne pollutants entering
the building through ventilation and infiltration (Crump et al 2002). Understanding
the levels of VOCs in the indoor air is important because concentrations can exceed
external levels by factors of up to one hundred (Palmer et al 2002), potentially
posing a risk to human health.
In 1987, a working group on organic indoor air pollutants, convened by the World
Health Organisation (WHO 1989), devised a means for determining organic
compounds according to their volatility or boiling point ranges. As illustrated in table
6, VOCs are only one of a group of the chemical compounds present in the air. The
boiling points shown in the table are not an indication of the toxicity of the
compound range, but are used to determine the most appropriate sampling
methods as indicated in the table (WHO 1989).
Table 6 – Classification of Organic Indoor Pollutants
(adapted from WHO 1989)
Description
Abbreviation
Boiling point
range (°C)
Sampling methods
typically used in
field studies
Very volatile (gaseous)
organic compounds
VVOC
<0 to 50-100
batch sampling,
adsorption on
charcoal
Volatile organic
compounds
VOC
50-100 to
240-260
adsorption on
Tenax®, graphitised
carbon black or
charcoal
Semi-volatile organic
compounds
SVOC
240-260 to
380-400
adsorption on PUFC
or XAD-2D
Organic compounds
associated with
particulate matter
POM
>380
collection on filters
VOC is now the most common term for the definition of any organic compound
occurring in the indoor air under normal environmental conditions (Crump et al
2002). Many of the compounds emitted from construction materials over time
(weeks or years) tend to be within the VOC range (table 6). This is mainly because
the very volatile organic compounds (VVOC) range evaporates rapidly due to their
lower boiling points. Virtually any material in a building has some potential for
containing organic compounds, which can evaporate from its surface and get into
the air.
VOCs typically detected in indoor air mostly belong to nine groups of compounds as
shown in table 7 (ECA 1994). Most of the compounds are used as solvents and can
be found in a wide range of products within the home. An expert group convened by
the European Commission under the name European Collaborative Action (ECA)
on Indoor Air Quality and its Impact on Man, categorises the sources of VOCs into
three groups (ECA 1994):



building-related materials, furniture or other inventory;
human beings as themselves, or human activity-related sources;
outdoor sources, mostly air pollution by motor vehicles, the contribution of
which to indoor air pollution is mediated and modulated by ventilation.
Table 7 – Chemical structures of VOCs most frequently detected indoors
and typical representatives (from ECA 1994)
Chemical structure
Frequently detected compounds
alkanes
n-hexane, n-decane
cycloakanes and alkenes
cyclohexane, methyl-cyclohexane
aromatic hydrocarbons
benzene, toluene, xylenes, 1,2,4trimethylbenzene
halogenated hydrocarbons
dichloromethane, 1,1,1-trichloroethane,
trichloroethene, tetrachloroethene, 1,4dichlorobenzene
terpenes
limonene, alpha-pinene, 3-carene
aldehydes
formaldehyde(1), acetaldehyde(1), hexanal
ketones
acetone, methylethylketone
alcohols, alkoxyalcohols
isobutanol, ethoxyethanol
esters
ethylacetate, butylacetate, ethoxyethylacetate
not a VOC – see formaldehyde section.
(1)
According to Crump (2002), building-related emissions are likely to be the most
prevalent compounds, and the potential causes of poor indoor air quality. Almost
any material in a building has the potential to off gas organic compounds into the
air, including metals and other non-porous materials (Tucker 2000). Sources inside
the home cover a wide range of materials: from low emitters, such as metals which
absorb pollutants, through to high emission rate materials such as cleaning spirits.
Subsequently, organic compounds are an important pollutant in IAQ surveys.
Examples of typical sources are given in table 8.
Table 8 – Examples of Hazardous VOC Sources (adapted from Tucker 2000)
Compound
Indoor sources
acetaldehyde
floor materials, machine lubricants, wood
products
benzene
furnishings, paints, varnishes, wood products,
plastics tobacco
chloroform
fabrics, pesticides, soft furnishings
ethylbenzene
insulation products, polystyrene, paints,
varnishes, plastics, photo-copiers
formaldehyde
floor materials, insulation products, paints,
varnishes, fibre-board, chip-board, tobacco
tetrachloroethylene
caulks, sealants, dry-cleaning
toluene
adhesives, caulks, sealants, paint, thinners,
dyes, cosmetics, inks
Formaldehyde
Although an organic compound, formaldehyde (HCHO) is not chemically classed as
a VOC because of its low boiling point range of –19.5°C (refer to table 6 for boiling
point ranges). The emission rate in the indoor environment therefore depends
strongly on temperature and humidity. HCHO is the simplest and most common of
the aldehydes range. At normal ambient room temperatures, it is colourless gas
with a pungent suffocating odour (ECA 1990).
Indoor formaldehyde is emitted from a wide range of sources, including tobacco
smoke, combustion gases from gas appliances, disinfectants, water based paints,
and paper products (WHO 1997). The most common form of formaldehyde is urea
formaldehyde (UF) resin – the cause of significant indoor pollution due to its wideranging use. UF is used as the bonding agent in the production of particleboard,
such as MDF and chipboard, plywood sheets, and UF foam insulation. The
concentration that occupants are exposed to indoors depends on factors including
the potency of formaldehyde-emitting products, the age of the material (emissions
decrease over time), the extent of their use, and the local ventilation conditions.
Health effects of organic compounds
Health effects caused by the exposure to organic compounds are diverse. Some
are known carcinogens, whilst others merely cause odorous irritation. The potential
effects of some common individual VOCs found indoors are listed in table 9, and
can be categorised in one of the following three main health outcomes (WHO
1997):



odour and other sensory effects such as irritation;
mucosal irritation and other morbidity caused by systemic toxicity;
genotoxicity (damaging to DNA) and carcinogenicity
Human beings have different degrees of sensitivity to individual VOCs: previous
studies on irritancy caused by exposure to mixtures (Mølhave et al 1993) have lead
to proposals for IAQ guidelines to consider total VOC (TVOC) concentrations. The
TVOC approach is considered the most practical indicator for locating VOC sources
in buildings (WHO 1997). In 1997, an expert group devised guidelines for
monitoring TVOCs in indoor air quality investigations (ECA1997), which is still used
as a protocol for sampling.
Table 9 – Neurotoxic effects of VOC commonly found in indoor air
(adapted from WHO 1997)
Chemical
Effects
acetaldehyde
eye, skin, respiratory irritation, nasal tumours
benzene
central nervous system depression, vertigo,
convulsions, spasms, leukaemia
chloroform
kidney tumours
ethylbenzene
fatigue, vertigo irritability, organ weight increase
formaldehyde
bronchitis, ulcers, irritation, potentially lung
cancer
tetrachloroethylene
central nervous system depression, kidney
effects, impaired balance, headaches
toluene
memory loss, visual disturbances, decreased
reaction time, tremors, impaired balance
Specific guidelines relating to TVOC exposure have only recently been introduced
in the UK in the form of the revision to Building Regulations AD F. A limit of 300 µg
m-3 has been recommended, based upon the outcomes from studies, published in
the ECA report, which are summarised in table10.
Table 10 – Guidelines for acceptable TVOC concentrations
(adapted from ECA 1997)
Author
Concentration
(µg m-3)
Comment
National Health and
Medical Research
Council (Australia)
500
no single compound should contribute
>50%
<200
comfort range
200-3000
multifactorial exposure
3000-25000
discomfort
>25000
toxic
300
target guideline value
no single compound should exceed
10% of target value
<200
target values of indoor climate
<300
intermediate air quality
<600
minimum requirement
<400
advisable for residential air
Mølhave, L
Seifert, B
Finnish Society of
Indoor Air Quality
and Climate
Japanese Ministry
of Health, Labour
and Welfare
4. Indoor pollutants – particles
Airborne particulate pollution can be found everywhere. Non-biological particulate
sources range from natural volcano activity through to artificial sources such as
asbestos and insulation products. They are also created from combustion
processes, for instance diesel engines and tobacco smoke (Fogarty 2000).
Biological particulates are equally abundant, and include pollen, bacteria, moulds
and dust mites.
The health effects relating to biological and non-biological particles are diverse.
They can range from mild respiratory discomfort through to asthma attacks and
serious respiratory failure. Some non-biological particles, such as asbestos and
silicate, are known carcinogens that have been responsible for thousands of
deaths.
Particulates are clearly an important area of concern. However, sampling
particulates does not normally form part of a standard indoor air quality
investigation, unless there are particular concerns (Crump 2002). This is mainly due
to the complexity, and therefore cost of the analysis, particularly for biological
particles. Analysis of samples involves an in depth laboratory study to physically
count and identify the particles at a microscopic level.
5. Radon
Radon is a naturally occurring radioactive gas resulting from the decay of uranium,
found in all soil and rocks. It accounts for almost 50% of our recommended total
annual radiation dosage, and prolonged exposure can increase the risk of lung
cancer (HPA 2006). According to the World Health Organisation, radon is the
second highest cause of cancer after smoking (WHO 2000).
Radon gas emitted from the soil disperses quickly outside, but can enter a building
through gaps and cracks in the structure (Samet 2000), where it can accumulate if it
is not adequately vented. However, concentration levels depend upon geological
conditions, which are well mapped by the Health Protection Agency (HPA).
According to the HPA, concentration levels inside UK homes are fairly low and need
only be assessed in areas where the geology is known have high levels of radon
(Miles 2005). It should be borne in mind that negative pressures induced on
houses, as a result of ventilation, may potentially give rise to radon concentrations
indoors. This area requires further research.
6. Temperature, humidity and air movement
The hygrothermal conditions have an affect on the rate of emission and activity of
pollutants. Combined with air movement, these factors also play a key role in our
overall well-being, or thermal comfort, inside buildings. Cumulatively, they are linked
to symptoms associated with sick-building syndrome (SBS) and building related
illness (BRI). Temperatures inside buildings are dependent upon outside
temperatures, heat losses and gains, and the heating installation. Humidity depends
on moisture generation from breathing, washing, cooking and bathing. Ventilation
provides air for breathing, although excess ventilation can cause draughts, affecting
our thermal comfort.
These factors, jointly, have an influence on the indoor air quality, and on the overall
perception of air quality (Fang 1998). Pollution emissions from people and building
materials increase when temperature and humidity increase. Therefore, knowledge
of these conditions inside a building will provide valuable information about the
building’s environmental performance. Table 11 shows the temperature ranges as
recommended by the Chartered Institute for Building Services Engineers (CIBSE
2002). To many people these temperatures would seem high and it would be wise
to use them cautiously.
Table 11 – Recommended winter dry resultant temperatures for dwellings
(adapted from table 3.1, CIBSE 2002)
Room
Temperature range (°C)
bathrooms
26-27
bedrooms
17-19
hall/stairs/landing
19-24
kitchen
17-19
living room
20-23
toilet
19-21
N.B Dry resultant temperature combines air and mean radiant temperatures into a
single index temperature. For indoors (low air velocities), this is typically
represented as follows:
Where: tc is the dry resultant temperature
tai is the internal air temperature
tr in the internal radiant temperature
In well-insulated buildings that are predominantly heated by convective means, the
difference between the air and mean radiant temperatures (and hence between the
air and dry resultant temperatures) is often very small.
It is the combination of high temperatures and humidity, coupled with low air
movement that will provide the ideal conditions for mould growth and the cultivation
of bacteria. The effects of relative humidity are listed in table 12 below. The table
summarises the description of effects on people and buildings according to Crump
(et al 2002), and coincides with the recommendation in BS 5250:2002 (BS 2002) for
an upper limit of 70% to prevent mould growth.
Table 12 – Effects of relative humidity
(adapted from Crump et al 2002)
Relative humidity
Effect
less than 30%
drying of the mucous membranes of the upper
respiratory track
30 to 60%
unlikely to cause discomfort at normal temperatures
35 to 40%
adequate to prevent mite proliferation in winter, but
difficult to maintain
greater than 70%
mould growth likely
7. IAQ and the Building Regs. – Approved Document F1
For the very first time, the UK government have taken a step to introduce standards
for IAQ. Approved Document F1, Means of Ventilation, was revised in April 2006 to
bring in a range of new measures to govern ventilation standards. Part of the new
performance criteria is that the ventilation system in a building should provide
pollution control. This is a significant step, although it is not enforced by statute.
One of the reasons for this is the difficulty in maintaining effective pollution dilution
at the time of building completion (i.e. when the BCB issue a completion certificate).
At this stage, the building will be full of high-rate emissions associated with the
drying-out and the ‘newness’ of the fabric and furnishings of/within a building.
The targets recommended are in accordance with guidance given by the WHO, and
are limited to CO, NO2 and TVOCs. Table 13 summarises the criteria adopted in the
revised ADF1.
Table 13 – Performance criteria for dwellings
(adapted from ADF1 2006)
Substance
Carbon Monoxide
(CO)
Nitrogen Dioxide
(NO2)
Total Volatile Organic
Compounds (TVOC)
Guideline concentration value
100 (87.29)
60 (52.37)
30 (26.19)
10 (8.73)
mg m-3 (ppm)
mg m-3 (ppm)
mg m-3 (ppm)
mg m-3 (ppm)
288 (150) µg m-3 (ppb)
40 (21) µg m-3 (ppb)
300 µg m-3
Averaging time
15 minutes
30 minutes
1 hour
8 hours
1 hour
Long-term
8 hours
7. Conclusion
The topic of indoor air quality is by no means a new one. However, our
understanding of its importance is now being realised, given the rapid rise of
respiratory illnesses – a factor associated with polluted areas (cities). The key
pollutants: CO, NO2 and TVOCs are now frequently monitored in many workplaces
and public buildings. This may be more to do with the litigious nature of our society
than any revisions the Building Regulations may bring about.
Clearly the most toxic: carbon monoxide must be addressed, as exposure to this
gas will quickly result in death. There is almost no excuse in today’s society for CO
deaths to be considered accidental. CO production can be limited/eliminated
through good maintenance of combustion appliances and through ventilation. It can
also be easily detected. NO2 is not so easy to detect, but its presence indoors can
be effectively limited by the occupant. The main concern is the unknown nature
associated with VOCs, and the combined effect that these may have on health in
the long-term. Detection of VOCs is extremely complex, not least because many
thousands of new compounds are created every single day.
We all have a responsibility for the quality of our environment. Architect, designers,
engineers, local authorities, building owners and occupants all have a role to play to
ensure that the indoor environment will sustain healthy living. Much more research
is required in the field of IAQ, particularly the ‘cocktail effect’ that combinations of
pollutants have on our health, and the reactions that these cocktails may have with
other gases present in the air to produce new pollutants. IAQ is of particularly high
importance now that we live and work in air-tight buildings. The need to conserve
energy should never compromise health and therefore ventilation will play a key
role to ensure that energy-efficient buildings are healthy!
The key principles for maintaining good IAQ are:




to limit contaminant sources (use natural material as preference to synthetic)
to dilute contaminants by ventilation (open windows or designed ventilation)
to regularly clean the indoor environment to prevent dust build-up and
bacteria growth
to remove contaminants by transpiration (houseplants)
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