Glossary

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A ·

Term	Definition
*Absorption*	The process of one substance entering into the inner structure of another.
*Abrasion*	The wearing away of a solid surface by friction.
*Abrasive Cleaners*	Products that clean through abrasive or scouring action.
*Acceptable Indoor Air Quality*	Air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction.
*ACGIH*	American Conference of Governmental Industrial Hygienists.
*ACH*	Air changes per hour
*Activated Charcoal*	A highly absorbent form of carbon used to remove odors and toxic substances from liquids or gases.
*Acute Exposure*	A single exposure to a toxic substance which results in biological harm or death; usually characterized as lasting no longer than a day.
*Acute Toxicity*	The ability of a substance to cause poisonous effects resulting in severe biological harm or death soon after a single exposure or dose. Any severe poisonous effect resulting from a short-term exposure.
*Adhesion*	Molecular attraction that holds the surfaces of two substances in contact.
*Adsorption*	The adhesion of a thin film of liquid or gases to the surface of a solid substance.
*Adverse Health Effect (occurrence)*	Any abnormal, harmful, or undesirable effect (occurrence) on the physical, biochemical, biological, or behavioral well-being of a person that results from being exposed to pollutants in the environment.
*Aerosol*	A suspended liquid or solid particle in a gaseous medium.
*AHU*	Air handling unit; a component of an HVAC system that includes the fan(s), filters, and coils to condition the air.
*AIA*	American Institute of Architects
*Air*	A mixture of gasses constituting a compressed fluid tied to the planet by gravitational attraction. Air is 79.0% nitrogen, 20.9% oxygen, and less than 0.1% a mixture of carbon dioxide, argon, helium, and hundreds of other gasses originating from natural and man-made sources.
*Air Changes Per Hour (ACH)*	Volume of air moved in one hour. One air change per hour in a room, home, or building means that all the air in that environment will be replaced in one hour.
*Air Cleaning*	An IAQ control strategy to remove various airborne particulates and/or gases from the air. The three types of air cleaning most commonly used are particulate filtration, electrostatic precipitation, and gas sorption.
*Air Cleaning System*	A device or combination of devices applied to reduce the concentration of airborne contaminants, such as microorganisms, dusts, fumes, respirable particles, other particulate matter, gases, and/or vapors in air.
*Air-Conditioning*	The process of treating air to meet the requirements of a conditioned space by controlling its temperature, humidity, cleanliness, and distribution.
*Air Exchange Rate*	Used in two ways: 1 ) the number of times that the outdoor air replaces the volume of air in a building per unit time, typically expressed as air changes per hour; 2) the number of times that the ventilation system replaces the air within a room or area within the building.
*Air Handling Unit*	For purposes of this program refers to equipment that includes a blower or fan, heating and/or cooling coils, and related equipment such as controls, condensate drain pans, and air filters. Does not include ductwork, registers or grilles, or boilers and chillers.
*Air Pollutant*	Any unwanted substance in air.
*Algae*	Simple rootless plants that grow in sunlit waters in proportion to how many nutrients are available.
*Allergen*	A chemical or biological substance (e.g., pollen, animal dander, or house dust mite proteins) that induces an allergic state or reaction, characterized by hypersensitivity.
*Allergen*	A substance that induces allergic reaction.
*Annoyance*	A general feeling of displeasure or adverse psychological reaction toward a source. Associated with disturbance, distress and frustration.
*ANSI*	American National Standard Institute
*Antimicrobial*	Agent that kills microbial growth. See "disinfectant," "sanitizer," and "sterilizer."
*Asbestos*	A naturally-occurring mineral fiber that can cause cancer.
*ASHRAE*	American Society of Heating, Refrigerating, and Air-Conditioning Engineers
*Asthma*	A condition marked by recurrent attacks of difficult or labored breathing and wheezing resulting from spasmodic contraction and hypersecretion of the bronchi. It is caused by exposure to allergens such as drugs, foods, environmental pollutants, or intrinsic factors.
*ASTM*	American Society for Testing and Materials
*Atmosphere*	A standard unit of pressure exerted by a 29.92-inch column of mercury at sea level and equal to 1000 grams per square centimeter.

· B ·

Term	Definition
*BAQ*	Building Air Quality
*BRI*	See "Building-Related Illness
*Bacteria*	Microscopic living organism.
*Baghouse Filter*	A large fabric bag used to eliminate intermediate and large particles. It operates like a vacuum cleaner bag, allowing air and smaller particles to pass through it, while entrapping larger particles.
*Biocide*	Any poison that kills a living organism.
*Biodegradability*	The ability of an organic material to break down or change into a natural substance such as water or carbon dioxide.
*Biodegradable*	Able to break down or decompose rapidly under natural conditions.
*Biological Contaminants*	Agents derived from or that are living organisms (e.g., viruses, bacteria, fungi, and mammal and bird antigens) that can be inhaled and can cause many types of health effects including allergic reactions, respiratory disorders, hypersensitivity diseases, and infectious diseases. Also referred to as "microbiologicals" or "microbials."
*Bioremediation*	The management of microorganisms.
*BOCA*	Building Officials and Code Administrators
*BOMA*	Building Owners Management Association
*Breathing Zone*	Area of a room in which occupants breathe as they stand, sit, or lie down.
*Buffer Action*	A substance's resistance to a change in pH.
*Building Envelope*	Elements of the building, including all external building materials, windows, and walls, that enclose the internal space.
*Building-Related Illness*	Diagnosable illness whose symptoms can be identified and whose cause can be directly attributed to airborne building pollutants (e.g., Legionnaire's disease, hypersensitivity pneumonitis).

· C ·

Term	Definition
*Carbon Dioxide (CO₂)*	A colorless, odorless, nonpoisonous gas which results from fuel combustion and human activity indoors. Elevated levels of CO₂ indicate ineffective ventilation indoors.
*Carbon Monoxide (CO)*	A colorless, odorless, poisonous gas which results from incomplete combustion.
*Carcinogen*	A substance that can cause or contribute to cancer.
*Caustic*	Able to burn, corrode, dissolve, or eat away other substances.
*Caustic Soda*	Sodium hydroxide, a strong alkaline substance used as the cleaning agent in some detergents.
*CAV*	See constant air volume.
*Ceiling Plenum*	Space below the flooring and above the suspended ceiling that accommodates the mechanical and electrical equipment and that is used as part of the air distribution system. The space is kept under negative pressure.
*Central AHU*	See "Central Air Handling Unit."
*Central Air Handling Unit*	For purposes of this document, this is the same as an AHU, but serves more than one area.
*CFM*	Cubic feet per minute. The amount of air, in cubic feet, that flows through a given space in one minute.
*Chemical Cleaning*	Cleaning by using a chemical instead of mechanical or abrasive cleaning.
*Chemical Disinfection*	Disinfection by using chemicals instead of heat and other physical, electrical, or radioactive methods.
*Chemical Mixture*	Any combination of two or more substances.
*Chemisorb*	To take up and hold, usually irreversibly, by chemical forces.
*Chlorinated Solvents*	Organic solvents containing chlorine atoms. Examples include methylene chloride, perchloroethylene and 1,1,1 trichloroethylene used as cleaning agents.
*Chronic Exposure*	Long-term exposure lasting several weeks to a lifetime.
*Chronic Toxicity*	The ability of a substance to cause long-term poisonous human health effects.
*Cinogenic*	Able to induce a cancer response at the cellular level.
*Cleaning*	The process of removing unwanted substances and putting them in their proper place.
CO	Carbon monoxide.
*CO₂*	Carbon dioxide
*Coagulation*	A joining together of particles that settle out in waste water. Lime, alum, and iron salts induce the clumping of particles.
*Combustion*	Burning or rapid oxidation accompanied by a release of energy.
*Commissioning*	Start-up of a building that includes testing and adjusting HVAC, electrical, plumbing, and other systems to assure proper functioning and adherence to design criteria. Commissioning also includes the instruction of building representatives in the use of the building systems.
*Concentration*	The quantity of one constituent dispersed in a defined amount of another.
*Conditioned Air*	Air that has been heated, cooled, humidified, or dehumidified to maintain an interior space within the "comfort zone." (Sometimes referred to as "tempered" air.)
*Constant Air Volume System*	Air handling system that provides a constant air flow while varying the temperature to meet heating and cooling needs.
*Contaminant*	Any physical, chemical, biological, or radioactive substance that can adversely affect air, water or soil.
*Corrosion*	Action or effect of eating away gradually. This can occur through oxidation, the action of strong acids, or caustic alkali.
*Corrosive*	A chemical agent that reacts with a surface, causing it to deteriorate or wear away.
*Crawl Space*	The area beneath floors that provides access to utilities and other services. Other options are basements and slabs on grade.
*Cubic Feet per Minute (CFM)*	A measure of the volume of a substance flowing through air within a fixed period of time. Indoors, it is the amount of air measured in cubic feet that is delivered and exchanged in one minute.

· D ·

Term	Definition
DA	Distribution apportionment; the relationship between the proportion of the outside air (OA) quantity being delivered to portion a building and the proportion of the people in the building that are actually located in that portion of the building.
*Dampers*	Controls that vary airflow through an air outlet, inlet, or duct. A damper position may be immovable, manually adjustable, or part of an automated control system.
*DDC*	Direct digital control.
*Decibel (DB)*	A unit of sound measurement. Sound doubles in loudness for every 10 decibels.
*Decomposition*	The breakdown of matter by bacteria and fungi.
*Degreaser*	A chemical such as soap, solvents, alkali, or detergent that dissolves and helps remove greases and oils.
*Depressurization*	A condition that occurs when air pressure inside a structure is lower than air pressure outside.
*Dessicant*	A chemical agent that absorbs moisture.
*Detergent*	1. Synthetic washing agent that helps remove dirt and oil. Some contain compounds that kill bacteria or encourage algae growth. 2. A chemical composition that cleans.
DI	DI distribution integrity; the relationship between the outside air (OA) quantity entering the HVAC equipment and the OA that actually gets delivered to the building occupants.
*Diffusers and Grilles*	Components of the ventilation system that distribute and diffuse air to promote air circulation in the occupied space. Diffusers supply air and grilles return air.
*Digestion*	The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants.
*Dilution*	A concentration made less concentrated by adding gas or liquid.
*Dilution Ventilation*	Dilution of contaminated air with uncontaminated air in a general area, room, or building for the purpose of health hazard or nuisance control.
*Disinfectants*	One of three groups of antimicrobials registered by EPA for public health uses. EPA considers an antimicrobial to be a disinfectant when it destroys or irreversibly inactivates infectious or other undesirable organisms, but not necessarily their spores. EPA registers three types of disinfectant products based upon submitted efficacy data: limited, general or broad spectrum, and hospital disinfectant.
*Disinfection*	A chemical or physical process that kills pathogenic organisms.
*Disposal*	Final placement or destruction of wastes.
*Dissolved Solids*	Disintegrated organic or inorganic material contained in water.
*Dose*	The amount of exposure undergone at one time.
*Dust*	An air suspension of particles (aerosol) of any solid material, usually with particle size less than 100 micrometers.

· E ·

Term	Definition
*Ecology*	The relationship of living things to one another and their environment.
*Ecosystem*	The interacting system of a biological community and its environmental surroundings.
*Electrostatic Precipitator (ESP)*	An air-pollution control device that removes particles from an air stream. The ESP imparts an electrical charge to particles causing them to adhere to metal plates inside the precipitator.
*Emission*	Pollution discharge from a source.
*Emulsion*	Two or more liquids that do not dissolve in each other but are held in suspension, one in the other.
*Energy Recovery Ventilation System*	A device or combination of devices applied to provide the outdoor air for ventilation in which energy is transferred between the intake and exhaust airstreams.
*Environment*	The sum of all external conditions affecting the life of an organism.
*Environmental Factors*	Conditions other than indoor air contaminants that cause stress, comfort, and/or health problems (e.g., humidity extremes, drafts, lack of air circulation, noise, and over-crowding).
*EPA*	U.S. Environmental Protection Agency
*Epidemic*	Widespread outbreak of a disease.
*Ergonomics*	The study of people adjusting to their work environment; the science of adapting working conditions to the worker.
*Etiology*	The science of causes or origins; the cause of a specific disease.
*ETS*	Environmental tobacco smoke.
*EVR*	Effective ventilation rate; the ventilation rate based on the actual quantity of outdoor air delivered to the occupied areas of a building or space.
*Exfiltration*	Air leakage outward through cracks and interstices and through ceilings, floors, and walls of a space or building.
*Exhaust Air*	Air removed from a space and not used therein.
*Exhaust Ventilation*	Mechanical removal of air from a portion of a building (e.g., piece of equipment, room, or general area).
*Exposure*	An event in which an organism comes in contact with a chemical or biological agent.
*Exposure Assessment*	Measurement or estimation of the magnitude, frequency, duration, and route of exposure of humans, animals, materials, or ecological components to substances in the environment. The assessment also describes the size and nature of the exposed population.

· F ·

Term	Definition
*Fabric Filter*	A cloth that catches dust particles.
*Fatigue*	Physical or mental exhaustion; weariness; tiredness.
*Flash Point*	The lowest temperature at which a combustible liquid or gas gives off a flammable vapor that will burn when exposed to an open flame.
*Flow Hood*	Device that easily measures airflow quantity, typically up to 2,500 cfm.
*Flue Gas*	The air coming out of a chimney after combustion in the burner it is venting.
*Fogging*	Applying a liquid chemical by rapidly heating it to form fine droplets that resemble smoke or fog.
*Ft²*	Square feet.
*Fumes*	Airborne particles, usually less than 1 micrometer in size, formed by condensation of vapors, sublimation, distillation, calcination or chemical reaction.
*Fumigant*	A biocide that is vaporized to kill pests. Used indoors or outdoors.
*Fungi*	A group of organisms that lack chlorophyll, including molds, mildews, yeasts, mushrooms. They receive their nutrition from decomposing organic matter. Some cause disease in humans.
*Fungicide*	Biocides used to control, prevent, or kill fungi.

· G ·

Term	Definition
*Gas*	A state of matter in which substances exist in the form of nonaggregated molecules, and which, within acceptable limits of accuracy, satisfies the ideal gas laws; usually a highly superheated vapor.
*Gas Sorption*	Devices used to reduce levels of airborne gaseous compounds by passing the air through materials that extract the gases. The performance of solid sorbents is dependent on the airflow rate, concentration of the pollutants, presence of other gases or vapors, and other factors.

· H ·

Term	Definition
*Habitat*	The place where a population lives, including its living and non living surroundings.
*Hard Water*	Alkaline water containing dissolved salts that interfere with some industrial processes and prevent soap from lathering.
*Hazard*	Risk, peril, jeopardy to which an individual is subjected.
*Hazardous Waste*	By-products of society that can pose a substantial or potential hazard to human health or the environment when improperly managed. They have at least one of four characteristics: they are ignitable, corrosive, reactive, or toxic.
*Heavy Metals*	Metallic elements with high atomic weights such as mercury, chromium, cadmium, arsenic, and lead. They can damage living organisms at low concentrations.
*Hedonic Tone*	The degree to which an odor is perceived as pleasant or unpleasant. Expressed in terms of preference by phrases such as "dislike very much" or "like slightly" or by facial expressions such as smiling or frowning.
*HEPA*	High efficiency particulate arrestance (filters).
*Humidity*	The measure of moisture in the atmosphere.
*HVAC*	Heating, ventilation, and air-conditioning system.
*Hydrocarbons (HC)*	Chemical compounds made up entirely of carbon and hydrogen.
*Hypersensitivity*	The immune system's exaggerated response to an allergen.
*Hypersensitivity Diseases*	Diseases characterized by allergic responses to animal antigens. The hypersensitivity diseases most clearly associated with indoor air quality are asthma, rhinitis, and hypersensitivity pneumonitis. Hypersensitivity pneumonitis is a rare but serious disease that involves progressive lung damage as long as there is exposure to the causative agent.

· I ·

Term	Definition
*IAP*	Indoor air pollution
*IAQ*	IAQ Indoor air quality.
*IAQ Coordinator*	An individual at the school and/or school district level who provides leadership and coordination of IAQ activities.
*IAQ Management Plan*	A set of flexible and specific steps for preventing and resolving IAQ problems.
*Ignitable*	Capable of burning or causing a fire.
*Immune System*	All internal structures and processes providing defense against disease-causing organisms such as viruses, bacteria, fungi, and parasites.
*Indicator Compounds*	Chemical compounds, such as carbon dioxide, whose presence at certain concentrations may be used to estimate certain building conditions (e.g., airflow, presence of sources).
*Individual Risk*	The increased risk for a person exposed to a specific concentration of a toxicant.
*Indoor Air*	The air that people breathe inside a built environment.
*Indoor Air Pollutant*	Particles of dust, fibers, mists, bioaerosols, and gases or vapors.
*Indoor Climate*	Temperature, humidity, noise, and lighting inside a structure.
*Infiltration*	Air leakage inward through cracks and interstices and through ceilings, floors, and walls of a space or building.
*Inflammation*	A protective tissue response to injury that destroys, dilutes, or walls off both the injurious agent and the injured tissue, characterized by symptoms such as pain, heat, redness, swelling, and loss of function.
*Inhalable*	Particles small enough to be inhaled, but large enough so that they are not quickly exhaled.
*IPM*	Integrated pest management.

· J ·

There are no entries for this letter

· K ·

There are no entries for this letter

· L ·

Term	Definition
*Lethal Concentration (LC50)*	The concentration of a substance needed to kill half of a population at a specific time of observation.
*Lethargy*	A condition of abnormal drowsiness or torpor; a great lack of energy; apathy.
*Lipid Solubility*	The maximum concentration of a chemical that will dissolve in fatty substances. Lipid-soluble substances do not dissolve in water.
*Liquefaction*	Changing a solid into a liquid.

· M ·

Term	Definition
*Maintenance*	Care and upkeep of the surrounding environment.
*Make-Up Air*	Air brought into a building from outdoors through the ventilation system and that has not been previously circulated through the system.
*Makeup Air*	Outdoor air supplied to replace exhaust air and exfiltration.
*Malaise*	A vague feeling of discomfort or uneasiness.
*Masking*	The phenomenon where a quality in a mixture obscures one or more other qualities in it.
*MCLs*	Maximum Contaminant Levels.
*MCS*	See "Multiple Chemical Sensitivity."
*Mg/M³*	Milligrams per cubic meter.
*Microbes*	Microscopic organisms such as algae, insects, viruses, bacteria, fungi, and protozoa, some of which cause diseases.
*Microbiologicals*	See "Biological Contaminants."
*Microenvironment*	A particular part of the large environment that is in some way whole by itself. Used to describe a subset of the global environment such as the indoor environment.
*Micron*	A unit of linear measure equal to one millionth of a meter, or one thousandth of a millimeter.
*Microorganism*	A microscopic organism, especially a bacterium, fungus, or protozoan.
*Mist*	Liquid particles measuring between 40 and 500 microns. By contrast, particles making up fog are less than 40 microns.
*Mitigation*	Measures taken to reduce adverse effects on the environment.
*Morbidity*	The number of sick individuals or cases of disease in a population.
*Mortality*	The number of individual deaths in a population.
*MSDS*	Material Safety Data Sheet.
*Multiple Chemical Sensitivity*	A term used by some people to refer to a condition in which a person is considered to be sensitive to a number of chemicals at very low concentrations. There are a number of views about the existence, potential causes, and possible remedial actions regarding this phenomenon.
*Mutagen*	Any substance e that can cause a change in genetic material.
*Mutagenic*	Able to cause a permanent change in the structure of DNA.

· N ·

Term	Definition
*Natural Ventilation*	The movement of outdoor air into a space through intentionally provided openings, such as windows and doors, or through nonpowered ventilators or by infiltration.
*Negative Pressure*	Condition that exists when less air is supplied to a space than is exhausted from the space, so that the air pressure within that space is less than in surrounding areas.
*NIOSH*	National Institute for Occupational Safety and Health. .
*Nitrogen Oxides (NOX)*	Nitrogen compounds such as NO and NO₂ produced by combustion. They help to from ozone and photochemical smog.
*NO₂*	Nitrogen Dioxide

· O ·

Term	Definition
OA	Outdoor air.
*Occupied Zone*	The region within an occupied space between planes 3 and 72 in. (75 and 1800 mm) above the floor and more than 2 ft (600mm) from the walls or fixed air-conditioning equipment.
*Odor*	A quality of gases, liquids, or particles that stimulates the olfactory organ or sense of smell.
*Odor Character or Quality*	The property of the odor sensation that permits a person to distinguish odors of different substances based on prior exposure.
*Odor Descriptor*	Adjective given to an odor such as "floral," "caramel," "putrid."
*Odorant*	A substance that stimulates the olfactory receptors.
*Odor Pervasiveness*	The rate of decrease of odor perception associated with the decrease in odorant concentration.
*Odor Threshold*	Concentration of odorous air at which half of the judges in a panel detect the odor.
*Odorimetry*	Measurement of olfactory sensations.
*Opacity*	The amount of light obscured by particulate matter in the air.
*Organic*	1. Any compound containing carbon. 2. Substances derived from living organisms.
*OSHA*	Occupational Safety and Health Administration.
*Outdoor Air*	Air taken from the external atmosphere and, therefore, not previously circulated through the system.
*Oxidation*	A substance containing oxygen that reacts chemically to produce a new substance.
*Oxidation*	A reaction in which oxygen combines with another substance.
*Ozone (O₃)*	A very reactive oxidant containing three atoms of oxygen.

· P ·

Term	Definition
PA	Pascal; unit of pressure measurement.
*PAHs*	Polycyclic Aromatic Hydrocarbons.
*Particulate Matter*	A state of matter in which solid or liquid substances exist in the form of aggregated molecules or particles. Airborne particulate matter is typically in the size range of 0.01 to 100 micrometers.
*Particulates*	Fine liquid or solid particles such as dust, smoke, mist, fumes, and fog found in air and emissions.
*Pathogenic*	Capable of causing disease.
*Pathogens*	Microorganisms that can cause disease in other organisms, humans, animals, or plants.
*PCBs*	Polychlorinated biphenyls.
*pCi/l*	Picocuries per liter; a measure of radon concentration.
*PELs*	Permissible Exposure Limits (standards set by OSHA).
*Perception*	Awareness of the effects of stimuli.
*Persistence*	Length of time a compound remains in the environment once introduced.
*Pest*	Any form of animal, plant, or terrestrial life that is injurious to health or the environment.
*Pesticide*	Substance intended to control, prevent, or kill a pest.
pH	A measure of acidity or alkalinity on a scale of 0 to 14 where 7 is neutral. A pH less than 7 is acid and a pH greater than 7 is alkaline or base.
*Phosphates*	Alkaline builders used in detergents to soften water.
*Phytotoxic*	Something that harms plants.
*PICs*	Products of incomplete combustion. All particles and gases that are emitted from an object at the time it is burning.
*PIU*	Perimeter induction unit.
*Plenum*	Air compartment connected to a duct or ducts.
*Plug Flow*	A flow regime where the flow is predominately in one direction and contaminants are swept along with the flow.
*Plume*	A visible or measurable discharge of a contaminant body from a given point of origin. Can be a visible body of pollution such as smoke coming from a stack or a measured amount such as heat in water coming from a power plant boiler.
PM	Preventive Maintenance.
*Pollutant Pathways*	Avenues for distribution of pollutants in a building. HVAC systems are the primary pathways in most building, however all building components interact to affect how air movement distributes pollutants.
*Pollution*	Unwanted by-product of human activity. the presence of matter or energy whose nature, location, or quantity produces undesired environmental effects.
*Positive Pressure*	Condition that exists when more air is supplied to a space than is exhausted, so the air pressure within that space is greater than that in surrounding areas.
*PPB*	Parts per billion.
*PPM*	Parts per million.
*Pressure, Total*	In flowing air, the sum of the static pressure and the velocity pressure.
*Pressure, Velocity*	In flowing air, the pressure due to the velocity and density of the air.
*Preventive Maintenance*	Regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventive maintenance helps to prevent parts, material, and systems failure by ensuring that parts, materials and systems are in good working order.
*Productivity*	The efficiency with which a person performing a specific function does a job, or the output of a worker under specific environments and conditions.
*Psychological Factors*	Psychological, organizational, and personal stressors that could produce symptoms similar to poor indoor air quality.

· Q ·

There are no entries for this letter

· R ·

Term	Definition
RA	Return air.
*Radiant Heat Transfer*	Radiant heat transfer occurs when there is a large difference between the temperatures of two surfaces that are exposed to each other, but are not touching.
*Radon*	A colorless, odorless gas that occurs naturally in almost all soil and rock. Radon migrates through the soil and groundwater and can enter buildings through cracks or other openings in the foundation. Radon can also enter well water. Exposure to radon can cause lung cancer.
*Re-entrainment*	Situation that occurs when the air being exhausted from a building is immediately brought back into the system through the air intake and other openings in the building envelope.
*Re-entry*	Situation that occurs when the air being exhausted from a building is immediately brought back into the system through the air intake and other openings in the building envelope.
*Recirculated Air*	Air removed from the conditioned space and used for ventilation, heating, cooling, humidification, or dehumidification.
*RELs*	Recommended Exposure Limits (recommendations made by NIOSH).
*Respirable Particles*	Respirable particles are those that penetrate into and are deposited in the nonciliated portion of the lung. Particles greater than 10 micrometers aerodynamic diameter are not respirable.
*Return Air*	Air removed from a space to be then recirculated or exhausted.
RH	Relative humidity.
*RSP*	Respirable suspended particles.
*Residual*	Amount of a pollutant remaining in the environment after a natural or technological process has taken place.
RF	Radio frequency; portion of electromagnetic spectrum.
*Risk*	The probability of injury, disease, or death under specific circumstances. In quantitative terms, risk is expressed in values ranging from zero, which represents the certainty that harm will not occur, to one, which represents the certainty that harm will occur.
*Risk Assessment*	1. The use of factual information to define the nature and impact of an adverse effect on individuals or populations who have been exposed to hazardous materials and situations. 2. A quantitative or qualitative evaluation to determine the probability of an adverse effect to human health or the environment by exposure to specific pollutants.
*Risk Communication*	Exchange of information about health or environmental risks between risk assessors, risk managers, the general public, and other interest groups such as the news media.
*Risk Management*	The process of evaluating alternative responses to risks and selecting among them. Includes consideration of technical, scientific, social, economic, and political information.
*Route of Exposure*	The means by which toxic agents gain access to an organism such as ingestion, inhalation, dermal exposures; and intravenous, subcutaneous, intermuscular administrations.
*RTU*	Roof top unit; a packaged AHU unit on the roof.

· S ·

Term	Definition
SA	Supply air.
*Sanitation*	1. Control of physical factors in the human environment that could harm development, health, or survival. 2. Process of putting an environment into a state that will not harm human health.
*Sanitizer*	One of three groups of antimicrobials registered by EPA for public health uses. EPA considers an antimicrobial to be a sanitizer when it reduces but does not necessarily eliminate all the microorganisms on a treated surface. To be a registered sanitizer, the test results for a product must show a reduction of at least 99.9% in the number of each test microorganism over the parallel control.
*SBS*	See "Sick Building Syndrome.
*Sensitization*	An allergic condition that usually affects the skin or lungs. Once exposure to a substance has caused a reaction, the individual may be sensitized to it, and further exposure may elicit an adverse reaction even at low levels.
*Sewage*	The waste and waste water produced by residential and commercial establishments and discharged into sewers.
*Sewer*	A channel or conduit that carries waste water and storm water runoff from the source to a treatment plant or receiving stream.
*SF₆*	Sulfur hexafluoride; a physiologically inert gas used as a tracer in building investigations.
*Short-Circuiting*	Situation that occurs when the supply air flows to exhaust registers before entering the breathing zone. To avoid short-circuiting, the supply air must be delivered at a temperature and velocity that results in mixing throughout the space.
*Sick-Building Syndrome*	Term sometimes used to describe situations in which building occupants experience acute health and/or comfort effects that appear to be linked to time spent in a particular building, but where no specific illness or cause can be identified. The complaints may be localized in a particular room or zone, or may be spread throughout the building.
*Sludge*	A solid residue from air or water treatment processes. Can be a hazardous waste.
*Smoke*	The airborne solid and liquid particles and gases that evolve when material undergoes pyrolysis or combustion.
*Soil Gases*	Gases that enter a building from the surrounding ground (e.g., radon, volatile organics, pesticides).
*Solvent*	1. A substance capable of dissolving or dispersing one or more other substances. 2. The liquid component of a solution in which a substance is dissolved.
*Sources*	Sources of indoor air pollutants. Indoor air pollutants can originate within the building or be drawn in from outdoors. Common sources include people, room furnishings such as carpeting, photocopiers, art supplies, etc.
*Stack Effect*	Pressure-driven airflow produced by convection as heated air rises, creating a positive pressure area at the top of a building and a negative pressure area at the bottom of a building. The stack effect can overpower the mechanical system and disrupt ventilation and circulation in a building.
*Static Pressure*	Condition that exists when an equal amount of air is supplied to and exhausted from a space. At static pressure, equilibrium has been reached.
*Sterilization*	The destruction of all living organisms in water or on the surface of various materials. In contrast, disinfection is the destruction of most living organisms.
*Sterilizer*	One of three groups of antimicrobials registered by EPA for public health uses. EPA considers an antimicrobial to be a sterilizer when it destroys or eliminates all forms of bacteria, fungi, viruses, and their spores. Because spores are considered the most difficult form of a microorganism to destroy, EPA considers the term sporicide to be synonymous with "sterilizer."
*Supply Air*	That air delivered to the conditioned space and used for ventilation, heating, cooling, humidification, or dehumidification.
*Surfactant*	1. Surface active agent used in detergents to cause lathering. 2. Surface active agent that cleans.
*Synergism*	Cooperative interaction of two or more chemicals or other phenomena producing a greater total effect than the sum of their individual effects.

· T ·

Term	Definition
*Teratogen*	Substance that causes malformation or serious deviation from normal development of embryos and fetuses.
*Threshold Limit Value*	Air concentration of chemical substances to which healthy workers can be exposed for 8-hour work days during a 40-hour work week without suffering an adverse effect.
*TLVs*	Threshold Limit Values (guidelines recommended by ACGIH).
*Total Suspended Particulate Matter*	The mass of particles suspended in a unit volume of air when collected by a high-volume air sampler.
*Toxic*	Of, affected by, or caused by a toxin; to cause a poisonous reaction.
*Tracer Gases*	Compounds, such as sulfur hexafluoride, which are used to identify suspected pollutant pathways and to quantify ventilation rates. Tracer gases may be detected qualitatively by their odor or quantitatively by air monitoring equipment.
*Transfer Air*	The movement of indoor air from one space to another.
*TSP*	Total suspended particulate concentration.
*Turbidity*	Haziness in air caused by particles, or cloudy condition in water caused by suspended silt or organic matter.
*TVOCs*	Total volatile organic compounds.

· U ·

Term	Definition
*UG/M³*	Micrograms per cubic meter.
UL	Underwriters' Laboratory.
*Ulocladium*	A rapidly growing, dark brown or black fungus that is a potential allergen. Its spores are unusually large (1015 um). It is typically found in soil and is frequently encountered at low levels indoors.
UM	Micrometer.
*Upper Respiratory Tract*	Structures that conduct air into the lungs, including the nasal cavity, mouth, pharynx, and larynx.

· V ·

Term	Definition
*Variable Air Volume System*	Air handling system that conditions the air to a constant temperature and varies the outside airflow to ensure thermal comfort. Ventilation Air-Defined as the total air, which is a combination of the air brought into the system from the outdoors and the air that is being recirculated within the building. Sometimes, however, used in reference only to the air brought into the system from the outdoors.
*VAV*	Variable air volume system.
*Vector*	An organism that carries disease such as an insect or rodent.
*Ventilation*	The process of supplying and removing air by natural or mechanical means to and from any space. Such air may or may not be conditioned.
*Viscosity*	Friction or resistance to the flow of a liquid.
*VOCs*	See "Volatile Organic Compounds."
*Volatile*	1. Able to evaporate readily. 2. Able to go to gas phase from a liquid or solid phase.
*Volatile Organic Compounds (VOCs)*	Compounds that evaporate from the many housekeeping, maintenance, and building products made with organic chemicals. These compounds are released from products that are being used and that are in storage. In sufficient quantities, VOCs can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans. At present, not much is known about what health effects occur at the levels of VOCs typically found in public and commercial buildings. VAPOR a substance in gas form, particularly one near equilibrium with its condensed phase, which does not obey the ideal gas laws; in general, any gas below its critical temperature.

· W ·

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· X · Y · Z ·

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