View as PDF - CIBSE Journal

contaminant. ETS is a mixture of particles
that are emitted from the burning end of a
cigarette, pipe, or cigar, and smoke exhaled
by the smoker. Smoke can contain any of
more than 4,000 compounds, including
carbon monoxide and formaldehyde (see
below). More than 40 of the compounds
are known to cause cancer in humans or
animals, and many of them are strong
irritants. ETS is often referred to as
‘secondhand smoke’ and exposure to ETS is
often called ‘passive smoking’.
Polycyclic aromatic hydrocarbons
PAH is an organic class of compounds
containing just carbon and hydrogen
released from burning of fossil fuel and
biomass for both room heating and cooking.
The cooking food itself will emit PAHs but
the greatest indoor influence is ETS. There
is a strong connection between PAHs and
lung cancer.
Volatile organic compounds
VOCs are chemical compounds that have
a carbon (organic) basis and evaporate
readily into the air at room temperature.
The presence of VOCs is commonly
associated with an odour; however, this is
not always the case – all can be harmful.
There are thousands of different VOCs
produced and used daily, examples being
Benzene, Formaldehyde, Methylene,
Napthalene, Toluene, and
Ethylene glycol. Many are
not anthropogenic (manmade).
Radon
A radioactive gas formed
by the disintegration of
radium, radon occurs
naturally, especially in
areas over granite, and is
measured in Becquerels
(a measure of radioactive
decay) per cubic metre
of air (Bq/m 3 ). Once produced, radon
moves through the ground to the air above.
When radon undergoes radioactive decay
(it has a half-life of four days), it emits
ionizing radiation in the form of alpha
particles. It also produces short-lived decay
products (progeny), some of which are
also radioactive. Unlike radon, the progeny
are not gases and can easily attach to dust
and other particles. Radon is strongly
associated [6] with lung cancer. The Health
Protection Agency recently announced that
it was introducing a ‘target level’ of 100
54
Figure 1: Table of
recommended
exposure levels for
some substancesa
Bq/m 3 , to reflect international guidance
from the International Commission for
Radiological Protection [7] . The ingress
of radon may be reduced by appropriate
building details effectively trapping the gas
by a gas-impermeable sheeting (plastic)
and venting the trapped gas away from the
occupied areas.
Other inorganic gases
These include the following:
Ozone (O3) concentrations are generally
lower at urban locations than at rural
locations. This is due to the destruction
of O3 by nitric oxide
(NO) that is emitted by
vehicles. O3 levels are
usually higher during
the spring and summer
months because of more
movement from the
upper atmosphere and
more sunlight, which
allows O3-forming
chemical reactions to
occur more rapidly. O3
can have a characteristic
sharp odour when
at very high concentrations, such as that
associated with photocopiers and laser
printers.
Carbon monoxide (CO) is an odourless,
colourless gas that interferes with the
delivery of oxygen in the blood to the rest of
the body. It is produced by the incomplete
combustion of fuels.
Carbon dioxide (CO2) is also a colourless,
odourless gas. It is produced when any
carbon-based material used for fuel
(coal, oil, wood, etc.) is burned, as well as
by tobacco smoke, human and animal
Carbon dioxide is
often measured
when trying to
determine the
indoor air quality of
a building as it can
provide an indication
of the number of
occupants
Guidelines for limiting amounts of selected substances in air
Averaging time By volume By mass
Benzene 1 year 5 ppb 16 µg.m -3
Carbon monoxide
15 min 86 ppm 100 mg.m -3
30 min 52 ppm 60 mg.m -3
1 hour 26 ppm 30 mg.m -3
8 hours 10 ppm 12 mg.m -3
Formaldehyde 30 min 80 ppb 100 µg.m -3
Nitrogen dioxide
1 hour 150 ppb 300 µg.m -3
1 year 21 ppb 42 µg.m -3
Ozone 8 hours 60 ppb 120 µg.m -3
PM10 24 hours - 50 µg.m -3
Toluene 1 week 68 ppb 260 µg.m -3
respiration. Vehicles and industrial
equipment, and burning fuel for power are
some of the major contributors to CO2 in
the air.
CO2 is not generally found at hazardous
levels in an indoor environment, and it is
often measured when trying to determine
the indoor air quality of a building as it
can provide an indication of the number
of occupants. If the levels of CO2 are
high, it is assumed that there may not be
adequate ventilation to that area, which
in turn may allow for the build up of
other environmental contaminants. For
a ‘standard’ room occupation a rate of
8 l/s fresh air per person would mean
that the levels would rise 600 ppm CO2
which, when added to the normal outdoor
CO2 of 400 ppm, gives an internal CO2
concentration of 1000 ppm – this is unlikely
to provide any discomfort
Nitrogen oxides (NOx) arise from
combustion and vehicles (including garden
equipment), together with hydrocarbons,
reacting to produce nitrates and, with the
assistance of sunlight, ozone. They have
been shown to affect the respiratory tract of
humans and increase the susceptibility to
infections.
Sulphur dioxide (SO2) is produced in
various industrial processes. Coal, oil and
petrol combustion generates sulphur
dioxide. It irritates the human respiratory
tracts and the effects are felt very quickly –
within 10 or 15 minutes.
Mould and fungal spores
Moulds produce tiny spores that waft
through the indoor and outdoor air
continually. When mould spores land on a
damp spot indoors, they may begin growing
CIBSE Journal April 2011 www.cibsejournal.com