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Odors
and Odor Thresholds
Introduction
It is not always possible to have an "odor-free"
environment. Early on, it became apparent to building
managers that no one can ventilate buildings with
enough outside air to get rid of all odors. There
are always going to be some type of odors; the key
is keeping odors to a minimum and making sure they
are appropriate for the setting. For example, it would
not be good if an office smelled like a crowded locker
room. However, odors are also very subjective. What
may be pleasant to one person may be offensive to
another; odors are rarely neutral. For example, people
may wear perfumes and colognes to appear attractive
to others. However, some may become physically sick
from these scents.
The perception of odor is one of the most important
factors triggering complaints about the indoor environment.
If the air smells "stuffy" or unpleasant,
the number of people upset with the quality of air
in a building can range between 15 and 40% even with
good ventilation rates and a high efficiency filter
system. Sometimes the sensory systems of some people
can cause them to imagine that they are being or have
been exposed to a hazardous pollutant. This belief
(psychogenic illness) can often trigger similar reactions
in others and is most common in workplaces where there
are odors and poor working relationships between workers
and management.
Odor itself is not a good indication if something
is hazardous. Some dangerous chemicals have no odor
(carbon monoxide) or what some would consider a pleasant
odor (vinyl chloride), while some safe substances
may have a very offensive odor. Other substances may
cause what is called
"nasal fatigue." This is when your nose gets to the point when it can no longer smell
the odor any more. The odor is not gone; you just
cannot smell it.
Odor
Threshold
For some chemicals odor thresholds have been determined.
Though this will not tell you if a chemical is hazardous
or not, it might give an indication of how much of
a chemical is present. To get these limits, there
is a panel of people with no nasal or sinus problems
who indicate when they can first begin to smell a
particular chemical. Then these numbers are averaged
for the panel members to get the odor threshold. For
example, ammonia, which has a very strong odor, has
an odor threshold, of 17 ppm. The recommended exposure
limit for ammonia is 25 ppm. Therefore, you may smell
it before you reach a concentration that could be
dangerous to you. However, you cannot always rely
on odor. For example, carbon tetrachloride may cause
cancer. It has a recommended exposure limit of 2 ppm
but an odor threshold of 140 to 584 ppm—by the time
you can smell it, you are way past what is considered
safe. In addition, some things like carbon monoxide
do not have an odor, so you cannot rely on that. Natural
gas does not have an odor either though many utility
companies add sulfur odorant to it so it can be detected
before it reaches dangerous levels.
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