United States
Environmental Protection
Agency
Air and Radiation (6609J)
402-F-94-003
Revised July 1990
PDA Ventilation and Air Quality
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in Offices
Fact Sheet
Introduction
Millions of Americans work in buildings with mechanical
heating, ventilation, and air-conditioning (HVAC)
systems; these systems are designed to provide air at
comfortable temperature and humidity levels, free of
harmful concentrations of air pollutants. While heating
and air-conditioning are relatively straightforward
operations, the more complex processes involved in
ventilation are the most important in determining the
quality of our indoor air.
While many of us tend to think of ventilation as either air
movement within a building or the introduction of outdoor
air, ventilation is actually a combination of processes
which results in the supply and removal of air from inside
a building. These processes typically include bringing in
outdoor air, conditioning and mixing the outdoor air with
some portion of indoor air, distributing this mixed air
throughout the building, and exhausting some portion of
the indoor air outside. The quality of indoor air may
deteriorate when one or more of these processes is
inadequate. For example, carbon dioxide (a gas that is
produced when people breathe), may accumulate in
building spaces if sufficient amounts of outdoor air are
not brought into and distributed throughout the building.
Carbon dioxide is a surrogate for indoor pollutants that
may cause occupants to grow drowsy, get headaches,
or function at lower activity levels. There are many
potential sources of indoor air pollution, which may
singly, or in combination, produce other adverse health
effects. However, the proper design, operation and
maintenance of the ventilation system is essential in
providing indoor air that is free of harmful concentrations
of pollutants.
Sources of Indoor Air Pollution
Indoor air pollution is caused by an accumulation of
contaminants that come primarily from inside the
building, although some originate outdoors. These
pollutants may be generated by a specific, limited source
or several sources over a wide area, and may be
generated periodically or continuously. Common sources
of indoor air pollution include tobacco smoke, biological
organisms, building materials and furnishings, cleaning
agents, copy machines, and pesticides.
Health Problems and Ventilation
Harmful pollutants from a variety of sources can
contribute to building-related illnesses, which have
clearly identifiable causes, such as Legionnaire's
disease. HVAC systems that are improperly operated or
maintained can contribute to sick building syndrome
(SBS); SBS has physical symptoms without clearly
identifiable causes. Some of these symptoms include dry
mucous membranes and eye, nose, and throat irritation.
These disorders lead to increased employee sick days
and reduced work efficiency.
A committee of the World Health Organization estimates
that as many as 30 percent of new or remodeled
buildings may have unusually high rates of sick building
complaints. While this is often temporary, some buildings
have long-term problems which linger, even after
corrective action. The National Institute for Occupational
Safety and Health reports that poor ventilation is an
important contributing factor in many sick building cases.
Controlling Indoor Air Pollution
Control of pollutants at the source is the most effective
strategy for maintaining clean indoor air. Control or
mitigation of all sources, however, is not always possible
or practical. Ventilation, either natural or mechanical, is
the second most effective approach to providing
acceptable indoor air.
In the past, most buildings had windows that opened;
airing out a stuffy room was common practice. In
addition, indoor-outdoor air pressure differences
provided ventilation by movement of air through leaks in
the building shell. Today however, most newer office
buildings are constructed without operable windows, and
mechanical ventilation systems are used to exchange
indoor air with a supply of relatively cleaner outdoor air.
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The rate at which outdoor air is supplied to a building is
specified by the building code. Supply rates are based
primarily on the need to control odors and carbon
dioxide levels; carbon dioxide is a component of outdoor
air, but its excessive accumulation indoors can indicate
inadequate ventilation. Supply rates, hereafter referred
to as ventilation rates, are commonly expressed in units
of cubic feet per minute per person (cfm/person).
Ventilation Standards and Building Codes
After achieving industry consensus in 1989, the
American Society of Heating, Refrigerating, and Air
Conditioning Engineers (ASHRAE) published its
"Standard 62-1989: Ventilation for Acceptable Indoor Air
Quality." This is a voluntary standard for "minimum
ventilation rates and indoor air quality that will be
acceptable to human occupants and are intended to
avoid adverse health effects." This standard applies to
all types of facilities, including dry cleaners, laundries,
hotels, dormitories, retail stores, sports and amusement
facilities, and teaching, convalescent and correctional
facilities. The specified rates at which outdoor air must
be supplied to each room within the facility range from
15 to 60 cfm/person, depending on the activities that
normally occur in that room.
Standard 62-1989 is a voluntary standard, which means
that it becomes enforceable only after a state or locality
adopts the standard in its building code. Furthermore,
most current building codes pertaining to ventilation are
standards only for the way buildings in a particular
jurisdiction must be designed: they are not enforceable
standards for the way the buildings are operated. A few
states, through recently promulgated regulations,
pending legislation, labor agreements and other
mechanisms, are working to apply existing design codes
and standards to building operations.
Ventilation System Problems and Solutions
The processes involved in ventilation provide for the
dilution of pollutants. In general, increasing the rate at
which outdoor air is supplied to the building decreases
indoor air problems. The other processes involved in
ventilation however, are equally important. Buildings with
high ventilation rates may suffer indoor air problems due
to an uneven distribution of air, or insufficient exhaust
ventilation. Even in a well-ventilated building there may
be strong pollutant sources which impair indoor air
quality. The closer such a source is to an exhaust
however, the more effective the ventilation; local exhaust
ventilation, e.g., a chemical fume hood, is most effective.
It is good practice to provide separate exhaust systems
in areas where copy machines or solvents are used.
Providing localized exhaust for these specific sources
can result in a reduction of the amount of overall building
exhaust ventilation necessary.
As was mentioned earlier, an HVAC system that is
properly designed, installed, operated, and maintained
can promote indoor air quality. When proper procedures
are not followed, indoor air problems may result. Some
common problems, and their solutions, are discussed
below.
• System Design
Intermittent air flow: Designs that specify HVAC system
operation at reduced or interrupted flow during certain
portions of the day in response to thermal conditioning
needs (as in many variable air volume installations) may
cause elevated indoor contaminant levels and impair
contaminant removal. Minimum ventilation rates should
be defined by air cleanliness and distribution, as well as
temperature and humidity.
Distribution of air: Failure to maintain proper
temperature, humidity, and air movement in a building
can lead occupants to block supply registers if they emit
air that is uncomfortably hot or cold; this disrupts air flow
patterns. Placement of partitions or other barriers within
a space can also impair air movement. In addition,
locating air supply and return registers too close together
can result in an uneven distribution of fresh air and
insufficient removal of airborne contaminants.
Precautions must be taken to maintain comfortable
thermal conditions and proper placement of supply and
return registers, and furnishings.
Building supply and exhaust locations: Air supply vents
that are installed too close to building exhaust vents re-
entrain contaminated exhaust air into the building,
increasing indoor pollution. Placement of supply vents
near outdoor sources of pollution, such as loading
docks, parking and heavy traffic areas, chimneys, and
trash depots, provides a pathway for contaminants into
the building's ventilation system. The location of all air
supply vents must be carefully considered.
• Proportion of Outdoor Air
To dilute and eventually remove indoor contaminants,
HVAC systems must bring in adequate amounts of
outdoor air. However, because it is costly to heat cold
winter air and to cool hot summer air, some building
engineers reduce or eliminate the amount of outdoor air
brought into the system during hot and cold spells; this
allows contaminated air to accumulate inside, causing
pollutant concentrations to increase. Therefore, a
continuous supply of fresh air must be provided.
• Periods of Operation
An HVAC system that begins to operate after building
occupants have arrived, or shuts off before the end of
the work day can cause an increase in building-and
occupant-generated pollutant levels. Similarly, if the
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system is off during periods of non-occupancy (e.g., at
night and on weekends) building-generated pollutants
may accumulate. Therefore, the ventilation system
should be turned on several hours prior to occupancy,
and shut down only after occupants have left.
• Maintenance
HVAC systems must be properly maintained to promote
indoor air quality. If this is not done, ventilation systems
can become a source of contamination or become
clogged and reduce or eliminate airflow. Humidification
and dehumidification systems must be kept clean to
prevent the growth of harmful bacteria and fungi. Failure
to properly treat the water in cooling towers to prevent
growth of organisms, such as Legionnella, may
introduce such organisms into the HVAC supply ducts
and cause serious health problems. Accumulations of
water anywhere in the system may foster harmful
biological growth that can be distributed throughout the
building.
Air Cleaners
Air cleaners may be an important part of an HVAC
system, but cannot adequately remove all of the
pollutants typically found in indoor air. Air cleaners
should only be considered as an adjunct to source
control and ventilation. Air cleaners that have a high filter
efficiency and are designed to handle large amounts of
air are the best choice for use in office buildings.
Air cleaners include the simple furnace filter, the
electronic air cleaner, and the ion generator. Mechanical
filters, either flat or pleated, are generally effective at
removing particles; flat filters collect large particles and
pleated filters such as the high-efficiency particulate air
(HEPA) filters collect the smaller, reparable particles.
Electronic air cleaners and ion generators use an
electronic charge to remove airborne particles; these
devices may also produce ozone, a lung irritant. All air
cleaners require periodic cleaning and filter replacement
to function properly.
In addition to removing particles, some air cleaners may
remove gaseous pollutants; this is possible only if the air
cleaner contains special material, such as activated
charcoal, to facilitate removal of harmful gases. Although
some of the devices which are designed to remove
gaseous pollutants may be effective in removing specific
pollutants from indoor air, none are expected to
adequately remove all of the gaseous pollutants typically
present in indoor air. Information is limited on the useful
lifetime of these systems; they can be expensive and
require frequent replacement of the filter media. (For a
more detailed discussion of air cleaners, read Indoor Air
Facts No. 7, Residential Air Cleaners.)
Economic Considerations of Air Quality
It is generally agreed that poor indoor air can adversely
affect employee health and productivity. These costs to
industry have been estimated to be in the "tens of
billions of dollars per year" (Report to Congress on
Indoor Air Quality, 1989). Improvements in the indoor air
environment may substantially increase employee moral
and productivity. Therefore, it is important to include
indoor air quality controls in operation, maintenance, and
energy conservation strategies.
Resolving Air Quality Problems
Building managers and tenants must work together to
improve indoor air quality; areas to address include:
HVAC system operation and maintenance: Operate
the ventilation system in a manner consistent with its
design. Perform maintenance and inspections on a
regular basis, as prescribed by the manufacturer.
Record keeping: Maintain records of all HVAC system
problems, as well as routine maintenance and inspection
activities. Document the nature of complaints concerning
the indoor air environment, as well as steps taken to
remedy each complaint. These records may be useful in
solving future problems.
Pollution control: Identify pollution sources. Implement
source removal or special ventilation techniques
(including restrictions on smoking).
Occupant activities: Eliminate practices which may
restrict air movement (e.g., furniture placement relative
to air vents).
Building maintenance activities: Increase ventilation
rates during periods of increased pollution, e.g., during
painting, renovation, and pesticides use; schedule use of
pollutant sources to minimize the impact on indoor air
quality.
Ventilation standards and codes: Keep abreast of
revisions to ventilation standards and building codes
affected by those standards.
Energy conservation: Reexamine energy conservation
practices with regard to indoor air quality considerations,
employee health, and productivity costs.
Identify areas for follow-up.
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Summary
Additional Information
An HVAC system that is properly designed, installed,
maintained, and operated is essential to providing
healthful indoor air; a poorly maintained system can
generate and disperse air pollutants.
Control of pollutants at the source is the most
effective means of promoting indoor air quality.
An adequate supply of outdoor air is essential to
diluting indoor pollutants.
In the absence of adequate ventilation, irritating or
harmful contaminants can build up, causing worker
discomfort, health problems and reduced
performance levels.
Ventilation rates specified in most local building
codes are design standards only, and therefore are
not enforceable for insuring healthful indoor air
quality after the system begins to operate.
Air cleaning is an important part of an HVAC system,
but is not a substitute for source control or
ventilation. All air cleaners must be properly sized
and maintained to be effective.
An objective evaluation of indoor air quality,
employee health, and productivity costs should be
included when considering energy costs and energy-
saving strategies.
For more information on topics discussed in this Fact
Sheet, contact your state or local health department,
non-profit agency such as your local American Lung
Association, or (possibly one of) the following:
National Institute for Occupational Safety and Health
US Department of Health and Human Services
4676 Columbia Parkway (Mail Drop R2)
Cincinnati, Ohio 45226
www.cpsc.qov/niosh/homepaqe.html
Office of Building and Community Systems
US Department of Energy
CE-13, MSGH-068, 1000 Independence Avenue, SW
Washington, DC 20585
www.eere.enerqv.gov
Public Relations Office
American Society of Heating, Refrigerating, and Air-
Conditioning Engineers (ASHRAE)
1791 Tullie Circle, NE,
Atlanta, GA 30329
www.ashrae.org
Building Owners and Managers Association (BOMA)
International
1201 New York Ave, NW
Washington DC 20005
www.boma.org
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