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IAQ Glossary A


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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 thermally acceptable.

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ACGIH: The American Conference of Governmental Industrial Hygienists; association supports or produces TLV List, Industrial Ventilation Manual, Bioaerosol documents.

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 with sound.

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.

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 of times.

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 or system.

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 of oxygen.

AEROSOL: A gaseous medium containing suspended particles.

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 consolidation.

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 suspended particulates.

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 conditioned space.

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 together.

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 reused therein.

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 the system.

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 unacceptable.

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 transfer.

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, and lubricants.

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 respiration.

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 dust particle.

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 bronchial asthma.

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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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