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GLOSSARY ‘I’ to ‘N’
IMPINGEMENT: As used in air-sampling, impingement refers to a process for the collection of particulate matter in which a particle containing gas is directed against a wetted glass plate and the particles are retained by the liquid. IMPINGEMENT FILTER: Any filter which removes particulate only when the particles hit (impinge on) the filter media. INCH OF WATER (IN. W.G.): A unit of pressure equal to the pressure exerted by a column of liquid water 1 inch high at a temperature of 39.2oF. INCHES OF WATER COLUMN: A unit used in measuring pressures. One inch of water column equals a pressure of 0.25 kPa (0.036 lb per sq in.). INDUCTION: The process of drawing room air into the projected air stream because of the velocity of the projected air stream (sometimes called aspiration). INFECTION: 1. The invasion of the body by germs that reproduce and multiply, causing disease by local cell injury, release of poisons, or germ-antibody reaction in the cells. 2. A disease caused by the invasion of the body by germs. INFECTIOUS: Capable of causing a disease in a susceptible host. INFILTRATION: Air leakage inward through cracks and interstices, and through ceilings, floors and walls of a space or building. INSECTICIDE: Any material or agent capable of killing insects. ION: An electrically charged atom. An atom that has lost one or more of its electrons is left with a positive electrical charge. Those that have gained one or more extra electrons are left with a negative charge. IONIZATION: The process whereby one or more electrons is removed from a neutral atom by the action of radiation. Specific ionization is the number of ion pairs per unit distance in matter, usually air. ISOTHERMAL: An adjective used to indicate a change taking place at constant temperature. JET VELOCITY: The average measured velocity of air passing between the fins. LAMINAR AIR FLOW: Streamlined airflow in which the entire body of air within a designated space moves with uniform velocity in one direction along parallel flow lines. LATENT HEAT: The heat required to change the state of a substance as in changing water to steam. LEGIONNAIRES' DISEASE: An acute bacterial pneumonia caused by infection with Legionella pneumophila and characterized by an influenza-like illness followed within 1 week by high fever, chills, muscle aches, and headache. Symptoms may include dry cough, inflammation of the membrane covering the lungs (pleurisy), and sometimes diarrhea. LOAD: The amount of heat per unit time imposed on a refrigerant system, or the required rate of heat removal. LOUVER: An assembly of sloping vanes intended to permit air to pass through and to inhibit transfer of water droplets. LOW LIMIT: The minimum desirable, or safe, temperature; the alarm given when the measured temperature drops below this selected temperature. LUMEN: The flux on one square foot of a sphere, one foot in radius, with a light source of one candle at the center that radiates uniformly in all directions. MANOMETER: An instrument for measuring pressures: especially a U-tube partially filled with a liquid, usually water, mercury, or light oil, so constructed that the amount of displacement of the liquid indicates the pressure being exerted on the instrument. MASS: The quantity of matter in a body as measured by the ratio of the force required to produce given acceleration, to the acceleration. MEAN RADIANT TEMPERATURE: The uniform surface temperature of a radiantly black enclosure in which an occupant would exchange the same amount of radiant heat as in the actual nonuniform space. MEDIUM: A nutrient-containing substance used for the growth and multiplication of microorganisms. MESOPHILE: An organism that grows optimally within the temperature range of 77oF to 104oF (25oC to 40oC). METABOLIC RATE: Rate of energy production of the body. Metabolism, which varies with activity, is expressed in met units in this Standard. One met is defined as 18.4 BTU/h ft2 (58.2 W/m2) which is equal to the energy produced per unit surface area of a seated person at rest. The surface area of an average man is about 19 ft2 (1.8 m2). MICROMETER (um): A unit of length that is 1/1X106 of a meter. MICRON: A unit of length, the thousandth part of 1 mm of the millionth of a meter. MICROORGANISM: A minute organism; microbes, bacteria, cocci, viruses, molds, etc., are microorganisms. MILLIGRAM (mg): A unit of weight in the metric system. One thousand milligrams equal one gram. MILLIGRAMS PER CUBIC METER (mg/m³): Unit used to measure air concentrations of dusts, gases, mists, and fumes. MILLILITER (mL): A metric unit used to measure volume. One milliliter equals one cubic centimeter. MINIMUM TRANSPORT VELOCITY, MTV: The minimum velocity which will transport particles in a duct with little settling; the MTV varies with air density, particulate loading, and other factors. MIXED AIR: The part of an HVAC system where the return air (RA) is mixed with the outside air (OF); the air resulting from this mixing. MODULATE: To control a damper or valve so that it may assume any position between full open and full closed, as well as these two positions. MODULATION: Of a control, tending to adjust by increments and decrements. MODULATING CONTROL: A mode of automatic control in which the action of the final control element is proportional to the deviation, from set point, of the controlled medium. MODULATING CONTROLLERS: Constantly reposition themselves in proportion to the requirements of the system, theoretically being able to maintain an accurately constant condition. MOLD: (1) A growth of fungi forming a furry patch, as on stale bread or cheese. See spore. A hollow form or matrix into which molten material is poured to produce a cast. MSDS: Material Safety Data Sheet MUCOUS MEMBRANES: Lining of the hollow organs of the body, notably the nose, mouth, stomach, intestines, bronchial tubes, and urinary tract. MULTIZONE: An HVAC system supplying air to two or more locations, each location having its own thermostat. The thermostat controls the delivered air temperature by controlling damper positions connected to a hot deck/cold deck. MULTISTAGE THERMOSTAT: A thermostat which controls multiple stages of auxiliary equipment for heating or cooling in response to a greater demand for heating or cooling. MUTAGEN: Any chemical or physical agent that causes a gene change (mutation) or speeds up the rate of mutation. MUTAGENIC AGENT: Any chemical substance or physical agent that iscapable of enhancing the frequency of detectable mutants within a population of organisms. MUTATION: A sudden, usually rare, change in the genetic code of an organism and results in a change in function that is inheritable. MYCOVIRUS: Viruses with a host-range specificity limited to the fungi. N.C.: Normally closed contacts of a relay. Contacts are close-circuited when the relay is de-energized. NEPHROTOXIN: A chemical which has a primary toxic effect on the kidneys. NEUROTOXIN: A chemical which has a primary toxic effect on the central nervous system. Styrene, mercury, carbon disulfide. N.O.: Normally open contacts of a relay. Contacts are open-circuited when relay is de-energized. NATURAL VENTILATION: The movement of air into and out of a space through intentionally provided openings, such as windows and doors, or through nonpowered ventilators or by infiltration. NIOSH: The National Institute for Occupational Safety and Health is a federal agency. It conducts research on health and safety concerns, tests and certifies respirators, and trains occupational health and safety professionals. NOISE CRITERIA CURVES (NC CURVES): Curves that define the limits which the octave band spectrum of a noise source must not exceed if a certain level of occupant acceptance is to be achieved. NOISE REDUCTION (NR): The difference between the average sound pressure levels of two spaces. Usually these two spaces are two adjacent rooms called, respectively, the source room and the receiving room. NORMALLY OPEN (OR NORMALLY CLOSED): The position of a valve, damper, relay contacts, or switch when external power or pressure is not being applied to the device. Valves and dampers usually are returned to a "normal" position by a spring. NOSOCOMIAL INFECTIONS: The type of infections that are acquired in hospitals. NUISANCE DUST: Have a long history of little adverse effect on the lungs and do not produce significant organic disease or toxic effect when exposures are kept under reasonable control.
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