United States
Environmental Protection
Agency
Air and Radiation
(ANR-445)
20A-4002.
Revised July 1990
&EPA Indoor Air Facts No. 3
Ventilation And Air Quality
In Offices
Introduction
Millions of Americans work in buildings with mechan-
ical heating, venulauon, 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 heat-
ing and air-condiuoning are relatively straightforward
operations, the more complex processes involved in
venulauon are the most important in determining the
quality of our indoor air.
While many of us tend to think of venulauon 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 in-
clude bringing in outdoor air, condiuoning and mixing
the outdoor air with some portion of indoor air, distri-
buting this mixed air throughout the building, and ex-
hausting 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 ai lower activity
levels. There are many potential sources of indoor air
pollution, which may singly, or in combination, pro-
duce other adverse health effects. However, the proper
design, operation and maintenance of the venubtion
system is essential in providing indoor air that is free of
harmful concentrauons of pollutants.
Sources of Indoor Air Pollution
sources over a wide area, and may be generated periodic-
ally 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 con-
tribute to building-related illnesses, which have clearly
identifiable causes, such as Legionnaire's disease.
HVAC systems that are improperly operated or main-
tained 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 imtauon. These
disorders lead to increased employee sick days and re-
duced work efficiency.
A committee of the World Health Organizauon
estimates that as many as 30 percent of new or re-
modelled buildings may have unusually high rates of
sick building complaints. While this is often tempo-
rary, some buildings have long-term problems which
linger, even after corTecuve 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
miugation 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.
Indoor air pollution is caused by an accumulation of con
taminants that come primarily from inside the building,
although some originate outdoors. These pollutants
may be generated by a specific, limited source or several
In the past, most buildings had windows that opened;
airing out a stuffy room was common practice. In ad-
dition, indoor-outdoor air pressure differences provided
ventilation by movement of air through leaks in the
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building shell. Today however, most newer office build-
ings arc constructed without operable windows, and
mechanical ventilation systems are used to exchange in-
door air with a supply of relatively cleaner outdoor air.
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 diox-
ide levels; carbon dioxide is a component of outdoor air,
but its excessive accumulation indoors can indicate in-
adequate vcnulauon. 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 Hcaung, Refrigerating, and Air-
Conditioning Engineers (ASHRAE) published its
"Standard 62-1989: Ventilation for Acceptable Indoor
Air Quality." This is a voluntary standard for "mini-
mum ventilation rates and indoor air quality that will be
acceptable to human occupants and are intended to avoid
advene 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
stales, through recently promulgated regulations, pend-
ing 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 prob-
lems 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 in-
door air quality. The closer such a source is to an ex-
haust however, the more effective the ventilation; local
exhaust vemilauon, e.g., a chemical fume hood, is
most effective. It is good pracuce 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 con-
ditioning needs (as in many variable air volume instal-
lations) may cause elevated indoor contaminant levels
and impair contaminant removal. Minimum ventilation
rates should be defined by air cleanliness and distribu-
tion, as well as temperature and humidity.
Distribution of air: Failure to maintain proper tem-
perature, humidity, and air movement in a building can
lead occupants to block supply registers if they emu air
that is uncomfortably hot or cold; this disrupts air flow
patterns. Placement of partitions or other barriers with-
in a space can also impair air movement. In addition,
locating air supply and return registers too close togeth-
er can result in an uneven distribution of fresh air and
insufficient removal of airborne contaminants. Precau-
tions 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 build-
ing, 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
(he building's ventilation system. The location of all
air supply vents must be carefully considered.
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•	Proportion ol 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 con-
tinuous 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
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 pro-
mote indoor air quality. If this is not done, ventilation
systems can become a source of contamination or be-
come clogged and reduce or eliminate air flow. Humid-
ification and dehumidification systems must be kept
clean to prevent the growth of harmful bacteria and fun-
gi. Failure to properly treat the water in cooling towers
to prevent growth of organisms, such as Leyionnella.
may introduce such organisms into the HVAC supply
ducts and cause serious health problems. Accumula-
tions of water anywhere in the system may foster harm-
ful biological growth that can be distributed throughout
the building.
Air Cleaners
Air cleaneremay be an important part of an HVAC
system, but cannot adequately remove all of the pol-
lutants typically found in indoor air. Air cleaners
should only be considered as an adjunct to source con-
trol and ventilation. Air cleaners that have a high fil-
ter 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 elec-
tronic air cleaner, and the ion generator. Mechanical fil-
ters, either flat or pleated, are generally effective at re-
moving particles; flat filters collect large particles and
pleated filters such as the high-efficiency particulate air
(HEPA) filters collect the smaller, respirable particles.
Electronic air cleaners and ion generators use an electron-
ic 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. Al-
though some of the devices which are designed to re-
move gaseous pollutants may be effective in removing
specific pollutants from indoor air, none are expected to
adequately remove all of the gaseous pollutants typical-
ly 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 in-
door air environment may substantially increase em-
ployee moral and productivity. Therefore, it is impor-
tant 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 de-
sign. Perform maintenance and inspections on a regular
basis, as prescribed by the manufacturer.
Record keening; Maintain records of all HVAC system
problems, as well as routine maintenance and inspec-
tion 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.
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Pollution control: Identify pollution sources.
Implement source removal or special ventilation tech-
niques (including restrictions on smoking).
Occupant activities: Eliminate practices which may
restrict air movement (e.g., furniture placement relative
lo 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 re-
visions 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.
Summary
•	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.
Additional Information
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 As-
sociation, or the following:
Indoor Air Division
US Environmental Protection Agency
Mail Code ANR-W5
401 M Street, SW
Washington, DC 20460
National Institute for Occupational Safely and Health
US Department of Health and Human Services
4676 Columbia Parkway (Mail Drop R2)
Cincinnati, Ohio 45226
Office of Building and Community Systems
US Department of Energy
CE-13, MS GH-068
1000 Independence Avenue, SW
Washington, DC 20585
Public Relations Office
American Society of Heating, Refrigerating, and
Air-Conditioning Engineers (ASHRAE)
1791 Tullie Circle, NE
Atlanta, GA 30329
Building Owners and Managers Association
International
1250 Eye Street. NW
Washington, DC 20005
Copies of this Fact Sheet and others in the Indoor Air
series are available from:
Public Information Center
US Environmental Protection Agency
Mail Code PM-21 IB
401 M Street, SW
Washington, DC 20460
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