EVALUATING INDOOR AIR QUALITY
What can cause health problems in an office building?
1. Contaminants. Contaminants may come from inside or outside
the building. Indoor sources of contaminants include cigarette
smoke, renovation and remodeling materials, dirt, deteriorating
lining in the ventilation system itself, cleaning compounds, materials
that are used inside such as white-out, copy machines, laser printers,
pesticides, etc. Outdoor sources include car exhaust, pollen,
and industrial emissions from nearby buildings.
Any water leaks are also of concern because molds can find hospitable
growth conditions in damp carpet, wallboard or ceiling tile.
2. Ventilation. The other very important determinant of indoor
air quality ventilation. The ventilation system should bring fresh
air to all occupied spaces and remove contaminants that occur
in normal use. An evaluation includes determination of how much
fresh air is being provided and the quality of that fresh air.
It should address how well the distribution system is functioning
to ensure that all areas are getting adequate fresh air and feel
very stuffy much of the time. The air system must be balanced
and assure good mixing.
No evaluation is complete without a look at the fresh air intakes.
Is there really outside air entering the system or have louvers
been closed or blocked off. If the air is coming in, is it fresh
or is it potentially contaminated by nearby industrial discharge,
perhaps a loading dock where trucks idle or nesting birds some
other source of pollution.
Extensive and expensive measurement is not the way to go.
Sometimes measurements of carbon dioxide and total airborne hydrocarbons
(VOCs) are taken to help determine the adequacy of the ventilation
in maintaining good air quality. If the air circulation is poor
and the fresh air insufficient, carbon dioxide, which derives
primarily from people breathing, builds up. The carbon dioxide
is not itself hazardous, but is used as a marker of a lack of
fresh air and good ventilation. (Note that if only a few people
work in a large area, carbon dioxide may not be a good indicator
because there is not much breathing going on.) Additional measurements
of many different potential contaminants can be expensive and
add little information to the evaluation.
Carbon dioxide (CO2) Test results are almost always low when
compared to an OSHA standard that was set for industrial environments,
and is based on the potential toxic affects of the gas itself.
For example, the OSHA standard for carbon dioxide is 5000 parts
per million (ppm), but it is recognized that when indoor levels
rise above 700-800 ppm, building occupants report discomfort.
Carbon dioxide is often the only useful measure taken and can
provide useful information if done properly.
Odors Your nose can be an important qualitative measurement device.
For example, if vehicle exhaust enters the building carbon dioxide
(as well as carbon monoxide) levels will increase. Vehicle exhaust
is accompanied by an odor which people are quick to recognize
and complain about. Smoking contributes to both carbon dioxide
and total hydrocarbons levels in the air.
Total volatile hydrocarbons can be measured as an indication
of the overall adequacy of the ventilation. This test would pick
up traces of cleaning chemicals, perfumes, exhaust, paints, art
materials, cigarette smoke, carpet glues, etc. As with carbon
dioxide, OSHA standards for industrial environments for many of
these same hydrocarbons found in trace levels in office air are
several hundred times higher. There is no national standard for
the indoor environment, either office or school. For the Scandinavian
countries a level of less than 0.5 mg/m3 is recommended although
often exceeded. VOCs are not routinely measured as measurements
vary considerably with method of used and type of concurrent activity.
If a source is obvious, steps should be taken to reduce it rather
than measure it.
Particulates, airborne dust particles, are a common problem in
office and school environments. Potential sources of particulates
in the air include old and/or dirty carpeting, paper dust, chalk,
outside dirt that gets tracked in, and other dirt from habitation
and work. If ventilation filters are overloaded or breached, or
some part of the structure (sometimes the insulation of the ductwork)
deteriorates, the ventilation system itself can become a source
of contamination. It is not unusual for construction dust to get
into the ventilation system. Systems designed with an open return
plenum are especially susceptible.
If the filters are changed regularly and the system is intact
and functions well, routine cleaning of the duct work should not
be necessary. Evidence of dirt around the air supplies on the
ceiling indicates an excess of room dirt that is caught there
by static electricity caused by the air flowing. It is not due
to dirt in the ductwork itself.
3. BIOAEROSOLS. Levels of airborne mold or bacteria or their
by-products are sometimes measured. The most common measurement
is of viable airborne mold levels, the spores that will grow if
they out on a agar petri dish. These results have NOT been shown
to correlate with symptoms. Mold is always present in indoor as
well as outdoor air and varies tremendously both seasonally and
from place to place. A visual inspection for evidence of water
damage, a history of leaks, or chronic dampness is often more
useful than measurement in determining the potential for mold.
For comfort good temperature control and relative humidity levels
between 30 and 50 % are recommended. Levels below 30% indicate
air that may be dry enough to be irritating to mucous membranes.
Air that is too humid, RH greater than 60%, may cause moisture
to form and mold to grow.
In most cases, a few simple measurements and a close look at
the environment and ventilation system provides enough information
about what kinds of changes need to be made to improve the air
quality. This kind of qualitative investigation points the way
to improving the air quality and the health of the workers in