ASHRAE Journal - February 2023 - 25

COLUMN IEQ APPLICATIONS
existing energy rating schemes, and might be helpful to
those sensitive to specifi c contaminants.
To obtain a comprehensive picture of the IAQ in a
building it would be necessary to measure a range of
contaminants, but their individual concentrations may
be incomparable because of different health impacts
and time scales, and units; for example, radon (Bq/m3)
and particulate matter (µg/m3). One approach is to
convert the individual contaminant concentrations
into sub-indices, which may be a function of their
health risks, before they are aggregated into a single
index. The sub-indices may be weighted before
aggregation, but if the weights are determined
subjectively, and they are, then the fi nal metric is
meaningless. An example is the total volatile organic
compounds (TVOC) metric, which gives a single
number as its output, whereas others associate IAQ
with traffi c light colors or precious metals. They are,
however, all unable to show the change in harm when a
building transitions from one category to another.
Exposure limit values (ELV) are used in occupational
environments to prevent or reduce risks to health
from hazards, such as vibrations, by setting a
maximum quantity experienced over an exposure
time. This principle can be applied when measuring
the concentrations of a range of contaminants in a
building. The ratios of their maximum concentrations
to their respective ELV concentrations give a quick
indication of risk, where a ratio of <1 might be
acceptable but one approaching or exceeding unity
may be problematic. A problem is that it isn't clear
how a change in the metric, say by 10%, would affect
occupant health. This can only be done with knowledge
of the dose-response relationship.
ELVs are given by regulatory authorities for criteria
contaminants that are known to have a direct effect
on human health, but they don't agree with each
other. For example, the World Health Organization
and the U.S. Environmental Protection Agency give
wildly different ELVs for some contaminants, such as
PM2.5. If both organizations consider the same risk of
harm, they should agree. As it is, the selection of ELVs
is generally undocumented and subjective. A further
problem is that there are many criteria contaminants.
Prescribing lists of ELVs in standards is unwise
because a diagnostic procedure is required for each of
them, and time and cost constraints make enforcing
the list impossible. It makes more sense to identify
contaminants based on the dual conditions of being
harmful and commonly present in indoor air. Then
contaminants can be ranked by the harm they cause,
and the most harmful can be targeted for mitigation.
Disability-Adjusted Life-Years
Health-adjusted life years are measures of health over
time and give the weighted years a person or cohort
lives with a disease or disability. One is the disabilityadjusted
life-year (DALY), a measure of time where a
value of unity is one year of healthy life lost to some disease
or injury. DALYs are calculated as the sum of years
of life lost to premature mortality and morbidity in a
population for some negative health effect. Disability is
weighted by its effect on a person's life in general and
can account for mental illness. In the case of IAQ, the
burden of disease is a measurement of the difference
between the current health status of a population of
building occupants and an ideal situation where they all
live into old age, free of disease and disability. The DALY
has been used by the AIVC2 to prioritize indoor contaminants
found in houses for mitigation.
The DALY was used by the Lawrence Berkeley
National Laboratory3 to estimate the chronic harm
from exposure to airborne contaminants in dwellings.
To quantify harm, they followed two approaches:
one based on epidemiology and another based on
toxicology. They reviewed 77 studies reporting indoor
air contaminant concentrations in dwellings in the U.S.
and other countries whose populations have similar
lifestyles. They initially considered 267 chemical
contaminants in total and calculated the annual health
impact of each considering the total intake in dwellings
and other environments. The number of contaminants
was later reduced to 43, and the dose received in
dwellings for each of them was compared relative to a
no-dose scenario and weighted to the U.S. population.
They estimated that the most harmful contaminant
is particulate matter with a diameter of ≤2.5 microns
(PM2.5) by an order of magnitude. These particles
are small enough to bypass biological defenses and
are linked to chronic respiratory and cardiovascular
diseases and cancer. They also showed that secondhand
tobacco smoke and radon are important, but they can
Benjamin Jones, Dr.Eng., is an associate professor in the department of architecture
and built environment at the University of Nottingham in the U.K.
F E B R U A RY 2 0 2 3 ashrae.o rg ASHRAE JOURNAL
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ASHRAE Journal - February 2023

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