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GLOSSARY ‘A’
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 which at least 80% of the occupants would find thermally acceptable. 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 which 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 which required medical surveillance, usually one half the PEL. ACTIVATED CHARCOAL: Charcoal is an amorphous form of carbon formed by burning wood, nutshells, animal bones, and other carbonaceous materials. Charcoal becomes activated by heating it with steam to 800-900 C. 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. 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. 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. 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. 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 used to remove airborne impurities such as dusts, gases, vapors, fumes, and smoke. 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 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, EXHAUST: Air removed from a space and not reused therein. AIR, MAKEUP: Outdoor air supplied to replace exhaust air and exfiltration. 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, 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. 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. ALGAE: A minute fresh water plant growth which forms a scum on the surfaces of recirculated water apparatus, interfering with fluid flow and heat transfer. 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. 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. 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. 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 which 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. AQUEOUS: Pertaining to water AROMATIC: Applied to a group of hydro carbons and their derivatives characterized by presence of the benzene nucleus (molecular ring structure). ARRESTANCE: A filter's ability to remove a coarse dust particle. A-SCALE: A filtering system that has characteristics which 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. 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. Certain drugs must not be used by persons with asthma. 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. 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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