INDOOR AIR QUALITY ISSUES
Good building ventilation creates comfortable
and healthy indoor conditions. For thermal comfort ventilation,
indoor spaces must receive a sufficient quantity of outdoor air
that is warmed or cooled to satisfy human thermal comfort needs.
Comfort ventilation is assessed by measuring occupant perceptions
of indoor air quality, including their assessments of odors, thermal
conditions, and the adequacy of ventilation. For health ventilation,
indoor spaces must receive air that is free from hazardous chemical
or microbiological contaminants. Here, indoor spaces must receive
a sufficient quantity of outdoor air that has been filtered and
cleaned to create acceptable indoor air quality conditions. Health
ventilation is measured by comparing levels of indoor air pollutants
against occupational health standards, which usually are expressed
as threshold limit values (TLVs) or permissible exposure levels
(PELs) for air pollutants.
Ventilation standards gives outdoor air ventilation
rates for indoor spaces which should satisfy comfort and health
ventilation requirements and create acceptable indoor air quality.
Standards should define acceptable indoor air quality and require
that air is free from hazardous levels of contaminants and be
judged as satisfactory by most occupants. In the U.S.A. the ventilation
standard defines satisfactory indoor air quality as being air
that is free from contaminants at hazardous concentrations and
with which 80% of the building occupants are satisfied. Experiments
show that 20% of people dissatisfied air quality corresponds to
a steady state ventilation rate of about 12 cubic feet per minute
per person air quality or to a carbon dioxide concentration of
995 ppm for a non-smoking space (Iwashita, 1992), which agrees
well with the U.S. ASHRAE's criterion of 1000 ppm of carbon
dioxide for acceptable air quality. However, even in buildings
where ventilation system performance meets the current ASHRAE
standard one in five occupants may be complaining about climate
Several types of indoor air quality (IAQ)
problems can arise in buildings: complaints about IAQ; reports
of the sick building syndrome (SBS); toxic reactions from acute
or chronic exposures to contaminated air; and building-related
illnesses (BRIs). Toxic reactions from acute or chronic toxic
exposures can be verified by measuring concentrations of indoor
air contaminants. Episodes of BRI can be diagnosed because sufferers
develop measurable physiological changes and show clinical signs,
such as a high temperature. Symptoms of BRIs usually are similar
to those of other acute respiratory diseases and they persist
when the person is away from the building, only being alleviated
when the illness is treated or has run its course. BRIs often
indicate indoor air which is contaminated by microorganisms, and
again is objectively measurable. In both types of complaints remedial
action involves treating affected workers and removing or controlling
contaminant sources (Bardana, Montanaro and O'Hollaren,
1988). In buildings where the air is shown to be contaminated,
however, not all occupants will develop problems because various
non-environmental factors affect individual susceptibilities.
Complaints of poor IAQ and reports of SBS
usually are more perplexing to diagnose because results of IAQ
studies of buildings often fail to find highly contaminated air,
and in these cases simply increasing the ventilation rate may
not resolve IAQ complaints. The reasons for this lie in the research
findings that show that IAQ complaints and SBS are influenced
by various non-environmental variables, such as personal, occupational,
and psychological factors, which are thought to affect individual
sensitivities and susceptibilities to IAQ problems (Hedge, Erickson,
and Rubin, 1992, 1995, 1996). Understanding the role which these
various non-environmental variables can play invariably helps
to resolve IAQ problems.
PERCEIVED INDOOR AIR QUALITY
Perception of indoor air quality depends on
various sensory processes. For example, irritating air pollutants
arriving at the mucus membranes are detected by the receptors
for the general chemical sense, and the resulting sensations of
eye, nose, and throat irritation are indicators of poor indoor
air quality. Odors detected by the olfactory nasal mucosa also
can signal poor air quality.
However, sensitivity to irritants and judgements
of odor usually are the outcomes of relative and not absolute
perceptual processes. The perception of odors or irritants depends
on the intensity of stimulation of the sensory receptors relative
to background activity in the nervous system, called the signal/noise
ratio. Sometimes the sensory system will fail to detect a pollutant.
Indeed there are many hazardous air pollutants that we cannot
detect, such as carbon monoxide and radon gases. Sometimes our
sensory systems can cause us to imagine that we
are being or have been exposed to a hazardous pollutant, when
this is not the case, and people can show psychogenic illness.
Psychogenic illnesses can arise because the sensitivity to irritation
and odors is not fixed but varies between people and changes over
time and with beliefs about the potential hazard. For example,
to a person who likes a particular fragrance, a high concentration
of that fragrance may be desirable, while for another person who
dislikes the same fragrance the same exposure may be highly unpleasant.
Also, for the same person, the perceived intensity of an odor
which is being emitted at a constant rate also varies with time
because of sensory adaptation processes, and consequently odor
judgements made immediately upon entering a room are more intense
than odor judgements made 30 minutes later. Immediate odor judgements
have been suggested as a metric for determining perceived indoor
air quality in buildings (European Concerted Action, 1992). It
is not clear whether this approach is sufficient because judgements
of what are desirable and undesirable odors are influenced by
personal preferences and beliefs.
Unpleasant odors do not necessarily indicate
hazardous indoor air and the absence of odors does not necessarily
signify healthy air because many pollutants, like carbon monoxide,
carbon dioxide, and airborne microorganisms have no odor. Field
research also shows that thermal comfort variables, such as air
temperature and air movement, affect perceptions of stale and
stagnant air. Experiments show that judgements of acceptability
correlate better with the percentage of dissatisfied people than
judgements of odor intensity. Acceptability ratings change with
air temperature (from 68 deg F to 79 deg F - about 20 deg C to 26 deg C), and the higher the air
temperature the lower the acceptability of perceived air quality
THE SICK BUILDING SYNDROME
Cases of the SBS typically report vague symptoms
which cannot be objectively measured, and sufferers usually show
no clinical signs of illness. SBS symptoms include headache, lethargy,
eye, nose and throat irritation, breathing problems, and skin
irritation (World Health Organization, 1983). SBS symptoms are
linked to building occupancy because they get better on leaving
the building. IAQ surveys of sick buildings often fail to find
pollution problems, even though complaints are chronic and symptom
prevalence among occupants is high with up to 80% of workers reporting
at least one symptom (Wilson and Hedge, 1987). In newly constructed
or recently remodelled spaces, reports of SBS can be acute and
temporary, typically dissipating within 6 months. Many of these
symptoms are thought to stem from acute exposure to volatile organic
compounds (VOCs) emitted from new building materials, paints,
furniture, and finishes, although research evidence for this remains
inconclusive. In permanently "sick" buildings, a high
symptom prevalence can persist for several years and exposure
to VOCs emissions from new materials cannot explain symptoms.
Moreover, concentrations of indoor air pollutants invariably are
low. Never the less, poor IAQ is suspected as the cause of symptoms
because these are alleviated when sufferers are away from the
Buildings with a high prevalence of SBS cases
are labelled "sick" buildings, although there is no
standardized method for gauging symptom prevalence and no agreement
on the criteria which can discriminate between "sick"
and "healthy" buildings. Regrettably, there
is no consensus on the number, pattern, severity, or frequency
of symptoms which define an SBS case, on how to measure symptoms,
over what time period, or even what symptoms should be measured.
There is also no agreement on the criteria for classifying a building
Investigations of IAQ and the SBS usually
use unstandardized, self-administered questionnaires to gauge
the prevalence of symptoms and IAQ complaints. Many of these questionnaires
are biased, ambiguous, badly scaled, and poorly designed. Self-reports
of symptoms and complaints are subjective judgements which can
be influenced by a diverse range of psychological factors, such
as recall and response scale biases. Recall bias occurs because
we have an imperfect memory of events, such as how often IAQ problems
have occurred or symptoms have been experienced in the past. Recall
bias is influenced by differences in questionnaire design, such
as whether question responses involve checking a list of named
IAQ problems and SBS symptoms, or are open-ended questions. Research
on prescribed drug use shows that recall is significantly higher
when patients are given specific drug names rather being asked
to name the drugs being taken, even though all patients were on
similar medication regimes (Mitchell et al., 1986). In IAQ studies
some questionnaires have used open-ended questions, for example,
the NIOSH questionnaire used in health hazard investigations,
while others have listed specific problems. Poorly designed response
scales can cause response scale bias. Categorical scales with
labels such as "always", "often", "sometimes"
or "rarely" are ambiguous labels and can be interpreted
differently by different respondents and investigators. Likewise,
symptom labels such as "shortness of breath" convey
different meanings to people, some interpret this as meaning slow,
labored breathing, while others interpret this as rapid, shallow
breathing (Pennebaker, 1982).
Questionnaires usually collect data on workers'
perceptions of environmental conditions and health over extended
periods of time, such as one month, 3 months, 1 year, whereas
measures of environmental conditions seldom are taken over such
extensive periods. Moreover, such measurements normally are not
taken for each individual location in a building. Thus, it is
perhaps not surprising that little association between self-reported
symptoms and measured IAQ has been found.
OTHER PSYCHOSOCIAL INFLUENCES ON IAQ COMPLAINTS AND THE SBS
Because we cannot directly sense many indoor
air quality hazards, such as airborne bacteria, or colorless,
odorless and toxic gases, we rely on beliefs and imagination to
help us to anticipate and avoid invisible hazards. These same
belief and imagination processes also change how we interpret
internal bodily sensations. Belief and imagination processes work
to influence what we create or choose as hypotheses to explain
what we believe to be happening in the environment and inside
our bodies. Once we believe that the air we are breathing contains
a colorless, odorless, yet noxious pollutant which causes eye
irritation, we will selectively attend to eye sensations for confirmation
of exposure, and unconsciously we even may behave to create this
information, by rubbing our eyes more frequently than normal thereby
increasing irritation sensations. Such behaviors are, for example,
quite common. If a person thinks about how itchy his/her nose
is, they will eventually scratch it. If a person thinks about
mites and fleas crawling over their body, they will eventually
experience sensations of itchy skin and want to scratch. At musical
concerts audience members are more likely to feel the urge to
cough when they hear others coughing. At comedy shows audience
members are more likely to start laughing when they hear others
laughing. These contagion effects are very powerful. Studies of
medical students have shown that 70% of freshman students believe
they have developed the symptoms of diseases being studied (Pennebaker,
1982). Similar processes influence all perception, including a
worker's perception of indoor climate conditions.
SBS symptoms also are percepts affected by
the same cognitive processes which influence all other aspects
of perception (Pennebaker, 1982). Reports of nasal congestion
depend on whether people are told to focus their attention on
nasal congestion, which increases reports of nasal stuffiness,
or to focus attention on free breathing, which decreases reports
of nasal congestion under precisely the same environmental conditions
(Pennebaker and Skelton, 1981). Building occupants frequently
cannot accurately identify what is causing symptoms which they
are experiencing. Symptoms like headache, for example, can be
caused by poor IAQ, inadequate lighting, pressure of work, noisy
work conditions, and so on. Building occupants therefore must
rely on personal beliefs about what is causing the sensations
which they are experiencing. Sometimes the imagination of some
building occupants can create a climate of panic hysteria that
results in a major incident in which the building may even be
evacuated because of a suspected IAQ problem.
Mass psychogenic illness
Mass psychogenic illness (MPI), or mass hysteria,
refers to "the collective occurrence of a set of physical
symptoms and related beliefs among two or more individuals in
the absence of any identifiable pathogen" (Colligan and
Murphy, 1982). Social psychological processes of contagion, where
complaints and symptoms spread from person to person, and convergence,
where groups of people develop similar symptoms at about the same
time, underlie MPI. Environmental events, like an unpleasant odor,
can trigger contagion and convergence processes, and occupants
who cannot readily identify what has triggered their symptoms
often attribute these to any visible environmental changes, such
as installation of a new carpet, or invisible agents, such as
a "mystery bugs". MPI symptoms include headache, nausea,
weakness, dizziness, sleepiness, hyperventilation, fainting, and
vomiting, and occasionally skin disorders and burning sensations
in the throat and eyes (Colligan and Murphy, 1982; Olkinuora,
1984; Boxer, 1985, 1990).
MPI reactions probably arise from the interaction
of pre-existing poor physical environment conditions (poor ventilation,
poor lighting, excessive noise), stressful work conditions (tedious
work, poor organizational climate, poor labor-management relations),
disposition differences among individuals (gender differences,
differences in anxiety levels), with the occurrence of a triggering
event (bad odor), followed by inappropriate management response
to the perceived threat. Studies of MPI typically find a similar
sequence of events leading to the incident.
People diagnosed as suffering from multiple
chemical sensitivity or environmental illness are thought to be
extremely susceptible to environmental agents. However, this susceptibility
also can be influenced by psychological factors. Research suggests
that for many sufferers the symptoms which they report are comparable
to those of one or more commonly recognized psychiatric disorders,
such as mood disorders, affective disorders, and anxiety disorders
(Black, Rathe, and Goldstein, 1990).
Influences of Environmental Stress
Apart from finding that IAQ complaints and
the SBS are significantly more prevalent in the air-conditioned
than naturally ventilated offices (Hedge, 1984; Robertson et al.,
1985; Burge et al., 1987; Hedge et al., 1989; Mendell & Smith,
1990; Zweers et al., 1992; Mendell, 1993), there has been comparatively
little research linking these problems to actual exposures to
indoor air pollutants. Studies have found that environmental stress
plays a significant role in the occurrence of problems. The extent
to which physical environment stressors create strain and adverse
health effects depends on the characteristics of exposed individuals
and there ability to cope with these stressors (Hedge, 1989).
IAQ complaints and SBS symptom reports often arise from the effects
of diverse environmental and non-environmental factors which stress
the body and, depending on individual coping abilities, these
can increase the personal strain which is experienced. This personal
strain in turn can alter a person's sensitivity to environmental
irritants or possibly even directly cause some of the SBS symptoms.
Research on office workers has shown that
although workers usually believe their symptoms were caused by
prevailing environmental conditions, typically there is no correlation
between these conditions, such as daily variations in temperature
and humidity, and their reports of SBS symptoms, such as dry nose/nasal
congestion complaints. However, SBS symptoms are often correlated
with stress levels (Morris and Hawkins, 1987). Occupational factors
(job level, hours of computer use, job stress, job satisfaction,
handling of carbonless copy paper, photocopying), psychological
factors (perceptions of control, perceptions of ambient conditions,
perceptions of comfort), personal factors (gender), and organizational
factors (public sector versus. private sector buildings), influence
the prevalence of SBS symptoms among office workers (Hedge, 1988;
Hedge et al., 1989; Skov et al., 1989). In a study of almost 4,500
office workers in air-conditioned office buildings perceived indoor
quality, computer use, gender, job satisfaction, and job stress
have been shown to significantly influence the number of SBS symptoms
reported by workers (Hedge, Erickson and Rubin, 1992, 1995, 1996).
Research shows that IAQ problems and reports
of the SBS generally are not caused simply by exposure to poor
IAQ, but rather they occur because of the combined effects of
various physical environment and non-environmental factors. IAQ
complaints and the SBS are the outcome of complex processes, initiated
by a set of stressful multiple risks which create personal strain.
Most studies of IAQ complaints and the SBS
have found that there is good evidence that personal, psychological,
and occupational variables also affect reports of IAQ complaints
and health symptoms. Brooks and Davis (1992) summarize 3 sets
of factors that appear to be common to most indoor air quality
problems: the presence of point sources of pollution, the presence
of a susceptible population, and inadequate ventilation. By studying
and addressing all 3 sets of factors satisfactory climate conditions
and healthful indoor air quality can created in any building.
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