A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
ABATEMENT: the reduction or removal of a contaminant.
ABSOLUTE PRESSURE: Air at standard conditions
(70 degrees F air at sea level with a barometric
pressure of 29.92 in. Hg.) exerts a pressure of
14.696 psi. This is the pressure in a system when
the pressure gauge reads zero. So the absolute
pressure of a system is the gauge pressure in
pounds per square inch added to the atmospheric
pressure of 14.696 psi (use 14.7 psi in environmental
system work) and the symbol is "psia".
ABSORBENT: A material which, due to an affinity
for certain substances, extracts one or more such
substances from a liquid or gaseous medium with
which it contacts and which changes physically
or chemically, or both, during the process. Calcium
chloride is an example of a solid absorbent, while
solutions of lithium chloride, lithium bromide,
and ethylene glycols are liquid absorbents.
ABSORPTION: A process whereby a material extracts
one or more substances present in an atmosphere
or mixture of gases or liquids accompanied by
the material's physical and/or chemical changes.
ACCEPTABLE AIR QUALITY: Air in which there are
no known contaminants at harmful concentrations
and with which a substantial majority (usually
80%) of the people exposed do not express dissatisfaction.
ACCEPTABLE THERMAL ENVIRONMENT: An environment
that at least 80% of the occupants would find
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ACGIH: The American Conference of Governmental
Industrial Hygienists; association supports or
produces TLV List, Industrial Ventilation Manual,
ACH: Air Changes Per Hour The complete
replacement of air inside an area. An office or
space that has its total air volume replaced in
the time period of one-hour experiences one air
change per hour.
ACOUSTIC, ACOUSTICAL: Containing, producing,
arising from, actuated by, related to, or associated
ACTION LEVEL: Term used by OSHA and NIOSH to
express the level of toxicant that required medical
surveillance, usually one half the PEL.
ACTIVATED ALUMINA: A form of aluminum oxide used
as a desiccant for gases, or as a carrier for
potassium permanganate being used as a gas chemisorber.
ACTIVATED CARBON: A form of carbon capable of
removing certain gases from air; also known as
ACTIVATED CHARCOAL: Charcoal is an amorphous
form of carbon formed by burning wood, nutshells,
animal bones, and other carbonaceous materials.
Heating it with steam to 800-900 C activates charcoal.
During this treatment a porous, submicroscopic
internal structure is formed which gives it an
extensive internal surface area. Activated charcoal
is commonly used as a gas or vapor adsorbent in
air-purifying respirators and as a solid sorbent
in air sampling.
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ACTUATOR: A controlled motor, relay or solenoid
in which the electric energy is converted into
a rotary, linear, or switching action. An actuator
can effect a change in the controlled variable
by operating the final control elements a number
ACUTE: Health effects which show up a short length
of time after exposure. An acute exposure runs
a comparatively short course.
ACUTE EXPOSURE: Severe biological harm/death
from a single or short-term exposure to a toxin.
ACUTE TOXICITY: A substance so poisonous as to
cause severe biological harm or death soon after
a single exposure or dose.
ADIABATIC PROCESS: A thermodynamic process during
which no heat is added to, or taken from, a substance
ADJUSTED DRY-BULB TEMPERATURE (tadb): The average
of the air temperature (ta) and the mean radiant
temperature (tr) at a given location. The adjusted
dry bulb temperature (tadb) is approximately equivalent to operative temperature (to) at air
motions less than 80 fpm (0.4 m/s) when tr is
less than 120F (50oC).
ADMINISTRATIVE CONTROLS: Methods of controlling
employee exposure by job rotation, work assignment,
or time periods away from the hazard.
ADSORBATE: the material that is removed from
the air stream by contact with an adsorbent.
ADSORBENT: A material which has the ability to
cause molecules of gases, liquids, or solids to
adhere to its internal surfaces without changing
the adsorbent physically or chemically. Certain
solid materials, such as silica gel and activated
alumina, have this property.
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ADSORPTION: The action, associated with the surface
adherence, of a material in extracting one or
more substances present in an atmosphere or mixture
of gases and liquids, unaccompanied by physical
or chemical change. Commercial adsorbent materials
have enormous internal surfaces.
ADBORBTION ISOTHERM: a measurement of adsorption
at a particular temperature determined by varying
the amount of adsorbent used.
AEROBE: Microorganisms that require the presence
AEROSOL: A gaseous medium containing suspended
AGGLOMERATION: Implies consolidation of solid
particles into larger shapes by means of agitation
alone, i.e., without application of mechanical
pressure in molds, or between rolls, or through
dies. Industrial agglomeration usually is implemented
in balling devices such as rotating discs, drums,
or cones; but it can occur in a simple mixer.
On occasion, however, the word agglomeration has
been used to describe the entire field of particulate
AIHA: American Industrial Hygiene Association.
AIR, AMBIENT: The air surrounding an object.
AIRBORNE MICROORGANISMS: Biologically active
contaminants suspended in the air either as free-floating
particles surrounded by a film or organic or inorganic
material, or attached to the surface of other
AIR CHANGES: A method of expressing the amount
of air movement into or out of a building or room
in terms of the number of building volumes or
room volumes exchanged.
AIR CLEANER: A device that actively removes impurities
from the air, including forced air filtrations
systems and electronic air cleaners. Air cleaners
may be in-duct systems, which are added to HVAC
systems to treat the air stream, or standalone
room units. Effectiveness of these units depends
on the combination of their efficiency and their
airflow rate (i.e., clean air delivery rate)
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AIR CONDITIONING: The process of treating air
so as to control simultaneously its temperature,
humidity, cleanliness and distribution to meet
the comfort requirements of the occupants of the
AIR CONDITIONING UNIT: A piece of equipment for
the treatment of air so as to control, simultaneously,
its temperature, humidity, cleanliness and distribution
to meet the requirements of a conditioned space.
AIR CONDITIONING, UNITARY: An evaporator, compressor,
and condenser combination; designed to be assembled
AIR CONTAMINANT: an airborne chemical or particulate
that reduces the acceptability.
AIR DENSITY: (also WEIGHT DENSITY). The weight
of air in lbs per cubic foot. Dry standard air
at T = 70 degrees f, bp = 29.92 inch Hg has a
density of 0.075 lbs/cu ft.
AIR DIFFUSER: A circular, square, or rectangular
air distribution outlet, generally located in
the ceiling and comprised of deflecting members
discharging supply air in various directions and
planes, and arranged to promote mixing of primary
air with secondary room air.
AIR, DRY: Air without contained water vapor.
AIR EXCHANGE RATE: The rate of airflow moving
through a space, usually expressed in terms of
room volume units per unit of time, i.e., (room)
air changes per hour.
AIR, EXHAUST: Air removed from a space and not
AIR HANDLING UNIT (AHU): the part of the HVAC
system responsible for moving air, which may also
clean, heat, or cool the air.
AIR, MAKEUP: Outdoor air supplied to replace
exhaust air and exfiltration.
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AIR MONITORING: The sampling for and measuring
of pollutants in the atmosphere.
AIR, OUTDOOR: Air taken from the external atmosphere
and, therefore, not previously circulated through
AIR PURIFYING RESPIRATOR: Respirators that use
filters or sorbents to remove harmful substances
from the air.
AIR QUALITY STANDARD: a government-mandated regulation
that specifies the maximum contaminant concentration
beyond which health risks are considered to be
AIR, RECIRCULATED: Air removed from the conditioned
space and intended for reuse as supply air.
AIR, REHEATING OF: In an air conditioning system,
the final step in treatment, in the event the
temperature is too low.
AIR, RETURN: Air removed from a space to be then
recirculated or exhausted.
AIR, SATURATED: Moist air in which the partial
pressure of the water vapor is equal to the vapor
pressure of water at the existing temperature.
This occurs when dry air and saturated water vapor
coexist at the same dry-bulb temperature.
AIR, STANDARD: Dry air at a pressure of 29.92
in Hg at 69.8oF temperature and with a specific
volume of 13.33 ft.3/lb.
AIR, SUPPLIED RESPIRATOR: Respirator that provides
a supply of breathable air from a clean source
outside of the contaminated work area.
AIR, SUPPLY: That air delivered to the conditioned
space and used for ventilation, heating, cooling,
humidification, or dehumidification.
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AIR, VENTILATION: That portion of supply air
which is outdoor air plus any recirculated air
that has been treated for the purpose of maintaining
acceptable indoor air quality.
AIR WASHER: A water spray system or device for
cleaning, humidifying, or dehumidifying the air.
ALDEHYDES: a group of highly reactive organic
compounds that contain the common group CHO (carbon-hydrogen-oxygen),
such as formaldehyde.
ALGAE: A minute fresh water plant growth that
forms a scum on the surfaces of recirculated water
apparatus, interfering with fluid flow and heat
ALIOHATIC HYDROCARBONS: A class of organic compounds
with characteristics similar to aromatic compounds.
Sources include petroleum products (such as gasoline),
paint, and adhesives.
ALKALI: A compound that has the ability to neutralize
an acid and form a salt. Example: sodium hydroxide,
referred to as caustic soda or lye. Used in soap
manufacture and many other applications. Turns
litmus paper blue.
ALKANE: One of a group of saturated aliphatic
hydrocarbons present in many waxes, polishes,
ALLERGIC ILLNESS: an illness caused by an allergen,
usually upon second exposure. Although often associated
with biological substances, certain chemicals
may also trigger allergic diseases.
ALLERGY: An abnormal response of a hypersensitive
person to chemical and physical stimuli. Allergic
manifestations of major importance occur in about
10 percent of the population.
AMBIENT: Surrounding, as the atmosphere, especially
the outdoor environment.
AMBIENT AIR: The air surrounding a building.
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ALPHA PARTICLE: A small electrically charged
particle of very high velocity thrown off by many
radioactive materials, including uranium and radium.
It is made up of two neutrons and two protons.
Its electric charge is positive.
ALVEOLI: Tiny air sacs of the lungs, formed at
the ends of bronchioles; through the thin walls
of the alveoli, the blood takes in oxygen and
gives up its carbon dioxide in the process of
ANAEROBE: An organism that does not require molecular
oxygen for growth.
ANAEROBIC BACTERIA: Any bacteria that can survive
in partial or complete absence of air.
ANECDOTAL DATA: The information drawn from individual
case experience as opposed to controlled studies.
ANEMOMETER: An instrument for measuring the velocity
of a fluid.
ANSI: The American National Standards Institute
is a voluntary membership organization (run with
private funding) that develops consensus standards
nationally for control and stability of action
by a prime mover.
ANTIBIOTIC: A chemical substance, excreted by
microorganisms or synthetically produced, that
has the capacity to inhibit or kill bacteria when
applied in dilute solutions.
ANTIGEN: Any substance (usually foreign) that,
when introduced into the body of an animal, will
stimulate the formation of specific antibodies.
ANTIPARTICLE: A particle that interacts with
its counterpart of the same mass but opposite
electric charge and magnetic properties (e.g.,
proton and antiproton), with complete annihilation
of both and production of an equivalent amount
of radiation energy. The position and its antiparticle,
the electron, annihilate each other upon interaction
and produce gamma rays.
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AQUEOUS: Pertaining to water
AROMATIC: Applied to a group of hydrocarbons
and their derivatives characterized by presence
of the benzene nucleus (molecular ring structure).
ARRESTANCE: A filter's ability to remove a coarse
ASHRAE: American Society of Heating, Refrigerating,
and Air conditioning Engineers. The trade association
that provides information and sets standards for
the industry. The organization has committees
and task groups devoted to pollutants, filtration
technology, ventilation requirements, indoor air
modeling, and operations and maintenance.
ASHRAE STANDARD 62-1989 (OR 62-89): a ventilation
guide, developed by an interdisciplinary ASHRAE
committee, that specifies minimum ventilation
rates needed to provide air quality that is deemed
acceptable by 80% of building occupants and in
which there are no harmful concentrations of known
contaminants; also known as Ventilation
Standard for Acceptable Indoor Air Quality.
A-SCALE: A filtering system that has characteristics
that roughly match the response characteristics
of the human ear at low sound levels (below 55
dB Sound Pressure Level, but frequently used to
gauge levels to 85dB). A-scale measurements are
often referred to as dB(A).
ASPECT RATIO: In air distribution outlets, the
ratio of the length of the core opening of a grille,
face, or register to the width. In rectangular
ducts, the ratio of the width to the depth.
ASPERGILLUS: a genus of fungal species common
in both indoor and outdoor air, many of which
are potential human pathogens; aspergillas fumigatus
and A. niger can cause asthma-like allergic reaction,
as well as an opportunistic infection in individuals
undergoing antibacterial or anti fungal therapy
(to which they are resistant)
ASPIRATION: Production of movement in a fluid
by suction created by fluid velocity.
ASTHMA: A lung disorder. It is marked by attacks
of breathing difficulty, wheezing, coughing, and
thick mucus coming from the lungs. The episodes
may be started by breathing foreign substances
(allergens) or pollutants, infection, vigorous
exercise, or emotional stress. Treatment includes
getting rid of the cause if possible. Sprays or
wideners of the bronchi taken by mouth, and steroid
drugs are also used. Persons with asthma must
not use certain drugs. For example, some of the
drugs for treating circulatory disease (beta-adrenergic
drugs), barbiturates, and narcotics. Repeated
attacks often result in shortness of breath (emphysema)
and permanent obstructive lung disease. Also called
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ATMOSPHERIC PRESSURE: The pressure exerted in
all directions by the atmosphere. At sea level,
mean atmospheric pressure is 29.92 inches Hg,
14.7 psi, 407 inches w.g., or 760 mm Hg.
ATTENUATION: The sound reduction process in which
sound energy is absorbed or diminished in intensity
as the result of energy conversation from sound
to motion or heat.
AUDIBLE SOUND: Sound containing frequency components
lying between 20 and 20,000 Hz.
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