ASHRAE Journal - March 2013 - 47

Q

Why is that?
In our experience, people tend to reduce their rate of work until they are
again able to achieve an acceptable error
rate.

Q

What aspects of mental work are affected?
fected?
In general, tasks that require concentration (clear thinking and symbolic
manipulation), memory and original
thought.3,5,6

Q

Are all kinds of performance affected
to
to the same extent?
Most mental work involves concentration and is likely to be similarly affected.

Q

What are the exceptions?
Excessive concentration can impair
recognition memory and creative thinking, so as moderate warmth leads to
lowered arousal, it can paradoxically
improve the performance of work that
includes such tasks.

Q

Does low relative humidity (RH) affect
performance?
performance?
Not always, although levels below
15% RH were found to impair visual
acuity and the performance of tasks requiring continuous acquisition of visual
data, which are both crucial in process
control, driving, piloting an airplane and
work with PCs.7

Mechanisms

Q

How do raised temperatures affect
performance?
performance?
Raised temperatures have been found
to increase end-tidal CO2 (ETCO2) is an
indicator of mild “acidosis,” which is an
increase in the concentration of CO2 in
the blood) and to decrease oxygen saturation in blood (SpO2), both of which are
likely to be detrimental for mental work.6

Q

How does poor air quality affect performance?
formance?
Poor air quality may lead to mild
acidosis, exactly as raised temperature
does, because it has been found to reduce CO2 emission from occupants.8 If
so, this may be why both factors have
March 2013

such similar effects. Satish, et al.,9 have
recently shown that increasing the ambient CO2 concentration artiﬁcially can
decrease performance, suggesting that
ambient CO2 may have to be regarded as
a pollutant instead of as an indicator of
low outdoor air supply rate.

Magnitude

Q

What is the magnitude of the negative
tive effects of the indoor environment on
performance?
For adults, up to 5% in the laboratory,3 up to 10% in the ﬁeld.2 For schoolchildren, over 20%.4

Q

Is work in transportation environments
similarly
similarly affected?
It would seem so. Driver vigilance
was found to be reduced by up to 30%
by warmth in ﬁeld intervention experiments lasting only one hour.10

Q

What are the estimated costs of allowing
lowing poor IEQ to reduce performance?
As staff costs per unit of ﬂoor area
exceed operating costs by 100:1, the effects observed are seldom negligible.1

would have been predicted from laboratory experiments.2,5 This may be because
laboratory experiments use paid subjects,
who tend to exert more effort in the course
of a necessarily brief laboratory exposure
to poor indoor environmental quality than
they would routinely at a workplace.

Q

Why do some laboratory experiments
show
show no effects on performance?
If subjects are highly motivated they
can sometimes maintain performance
during short exposures to poor indoor
environmental quality. Negative effects
on fatigue may then be found instead.
Additionally, some studies may have
missed the subtle changes in performance that are caused by slightly suboptimal indoor environmental conditions.

Q

Do performance tests really predict
productivity?
productivity?
Logically, yes. Although environmental effects on component skills have yet
to be validated as predictors of overall productivity, call-center results use
“bottom-line” measures of the call volume achieved in practice,2,5 and schoolwork is what children do in school.4,11,12

Q

Q

Q

Q

Surely, children are less affected than
adults
adults because they are young and
healthy?
We have found that their performance
is more affected, not less. We believe
that this is because children in school,
by deﬁnition, are doing work that is new
to them, while adult workers are usually
very familiar with the work they do and
are better able to cope with environmental effects that make their work more
difﬁcult.
Is factory work likely to be less affected
fected by thermal and IAQ effects than
office work?
We believe not, as most workers in
modern factories have to interact with
computers, just as ofﬁce workers do.

Methodology

Q

Does laboratory research really predict
dict what happens in practice?
Many ﬁeld studies have found that the
negative effects of poor working conditions are greater in real workplaces than

Do field intervention experiments prepre
dict
dict what happens in practice?
Yes. Field intervention experiments
examine directly what does happen in
practice, often over periods of several
weeks or even months. Tests of year-end
educational attainment have been found
to support predictions based on shortterm intervention experiments in classrooms.4,11
Can experiments of limited duration
predict
predict what happens in practice?
It depends on the length of exposure.
Most continuous work is, in fact, performed in periods lasting less than ﬁve
hours, followed by a break, and even
laboratory experiments may include
ﬁve-hour exposures.

Q

Does a decrease in the performance
of
of schoolwork indicate reduced learning?
Not proven. But surely schoolwork is
assumed by teachers to promote learnASHRAE Journal

47
ASHRAE Journal - March 2013

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