IAQ Glossary

ACTION LEVEL: A term used to identify the level of indoor radon at which remedial action is recommended. (EPA's current action level is 4 pCi/L.)

AHU: See "Air Handling Unit."

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 EXCHANGE RATE: The rate at which outside air replaces indoor air in a space. Expressed in one of two ways: the number of changes of outside air per unit of time air changes per hour (ACH); or the rate at which a volume of outside air enters per unit of time - cubic feet per minute (cfm).

AIR HANDLING UNIT (AHU): For purposes of this document 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 PASSAGES: Openings through or within walls, through floors and ceilings, and around chimney flues and plumbing chases, that permit air to move out of the conditioned spaces of the building.

ANIMAL DANDER: Tiny scales of animal skin.

ALLERGEN: A substance capable of causing an allergic reaction because of an individual's sensitivity to that substance.

ALLERGIC RHINITIS: Inflammation of the mucous membranes in the nose that is caused by an allergic reaction.

ANTIMICROBIAL: Agent that kills microbial growth. See "disinfectant," "sanitizer," and "sterilizer."

BREATHING ZONE: Area of a room in which occupants breathe as they stand, sit, or lie down.

BUILDING ENVELOPE: All external building elements (materials, windows, and walls) that enclose the internally occupied space.

BUILDING-RELATED ILLNESS (BRI): 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). Also: A discrete, identifiable disease or illness that can be traced to a specific pollutant or source within a building. (Contrast with "Sick building syndrome").

CENTRAL AIR HANDLING UNIT (Central AHU): This is the same as an Air Handling Unit, 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. 1 CFM equals approximately 0.472 liters per second (l/s).

CHEMICAL SENSITIZATION: Evidence suggests that some people may develop health problems characterized by effects such as dizziness, eye and throat irritation, chest tightness, and nasal congestion that appear whenever they are exposed to certain chemicals. People may react to even trace amounts of chemicals to which they have become "sensitized."

CO: Carbon monoxide.

CO₂: Carbon dioxide.

COMBINATION FOUNDATIONS: Buildings constructed with more than one foundation type; e.g., basement/crawlspace or basement/slab-on-grade.

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.

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 (CAV) SYSTEMS: Air handling system that provides a constant volume of air flow while varying the air temperature to meet heating and cooling needs for comfort.

DIFFUSERS AND GRILLES: Components of the ventilation system that supply, distribute and return air to promote air circulation in an occupied space. As used in this document, supply air enters a space through a diffuser or vent and return air leaves a space through a grille.

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.

DRAIN TILE LOOP: A continuous length of drain tile or perforated pipe extending around all or part of the internal or external perimeter of a basement or crawlspace footing.

DRAIN TRAP: A dip in the drain pipe of sinks, toilets, floor drains, etc., which is designed to stay filled with water, thereby preventing sewer gases from escaping into the room.

ENVIRONMENTAL TOBACCO SMOKE (ETS): Mixture of smoke from the burning end of a cigarette, pipe, or cigar and smoke exhaled by the smoker (also secondhand smoke (SHS) or passive smoking).

ERGONOMICS: Applied science that investigates the impact of people's physical environment on their health and comfort (e.g., determining the proper chair height for computer operators).

EXHAUST: Mechanical removal of air from a portion of a building (e.g., piece of equipment, room, or general area).

FUNGI: Any of a group of parasitic lower plants that lack chlorophyll, including molds and mildews.

HUMIDIFIER FEVER: A respiratory illness caused by exposure to toxins from microorganisms found in wet or moist areas in humidifiers and air conditioners. Also called air conditioner or ventilation fever.

HVAC: Heating, ventilation, and air-conditioning system.

HYPERSENSITIVITY DISEASES: Diseases characterized by allergic responses to pollutants. 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.

HYPERSENSITIVITY PNEUMONITIS: A group of respiratory diseases that cause inflammation of the lung (specifically granulomatous cells). Most forms of hypersensitivity pneumonitis are caused by the inhalation of organic dusts, including molds.

IPM: Integrated pest management.

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).

INDOOR AIR POLLUTANT: Particles and dust, fibers, mists, bioaerosols, and gases or vapors.

MCS: See "Multiple Chemical Sensitivity."

MECHANICALLY VENTILATED CRAWLSPACE SYSTEM: A system designed to increase ventilation within a crawlspace, achieve higher air pressure in the crawlspace relative to air pressure in the soil beneath the crawlspace, or achieve lower air pressure in the crawlspace relative to air pressure in the living spaces, by use of a fan.

MICROBIOLOGICALS: See "Biological Contaminants."

MODEL BUILDING CODES: The "standardized" building codes published by the Model Code Organizations (below) and commonly adopted by states or other legal jurisdictions to control local construction activity for occupant health and safety.

MODEL CODE ORGANIZATIONS: Organizations of building inspection and code enforcement officials, and related participants that establish a "model" code. The "model" is available to government agencies or bodies having jurisdiction for enforcement of building regulations. They may be adopted by the jurisdiction in total or in part. This helps reduce the burden on smaller jurisdictions to develop and maintain their own codes, plus it allows for more commonality in the building codes between jurisdictions.

Includes the following agencies and the model building codes they promulgate:

• Building Officials and Code Administrators International, Inc. (BOCA National Building Code and BOCA National Mechanical Code);
• International Conference of Building Officials (Uniform Building Code and Uniform Mechanical Code);
• Southern Building Code Congress, International, Inc. (Standard Building Code and Standard Mechanical Code);
• International Code Council (ICC International Building Code and International Mechanical Code), is intended to replace the BOCA, ICBO and SBCCI).
• NFPA 5000 Building Code (National Fire Protection Association began its comprehensive model code construction in response to actions by the ICC, which are said not to provide a "consensus standard" required by many jurisdictions.
• Council of American Building Officials (CABO One- and Two-Family Dwelling Code and CABO Model Energy Code).

MULTIPLE CHEMICAL SENSITIVITY (MCS): A condition in which a person reports sensitivity or intolerance (as distinct from "allergic") to a number of chemicals and other irritants at very low concentrations. There are different views among medical professionals about the existence, causes, diagnosis, and treatment of this condition.

OUTDOOR AIR SUPPLY: Air brought into a building from the outdoors (often through the ventilation system) that has not been previously circulated through the system. Also known as "Make-Up Air."

PICOCURIE (pCi): A unit for measuring radioactivity, often expressed as picocuries per liter (pCi/L) of air.

PLENUM: Air compartment connected to a duct or ducts.

PM: Preventive Maintenance.

POLLUTANT PATHWAYS: Avenues for distribution of pollutants in a building. HVAC systems are the primary pathways in most buildings; however all building components interact to affect how air movement distributes pollutants.

POSITIVE PRESSURE: Condition that exists when more air is supplied to a space than is exhausted (or returned to the air handler), so the air pressure within that space is greater than that in surrounding areas. Under this condition, if an opening exists, air will flow from the positively pressurized space into surrounding areas of lower or negative pressure.

PPM: Parts per million.

PRESSED WOOD PRODUCTS: A group of materials used in building and furniture construction that are made from wood veneers, particles, or fibers bonded together with an adhesive under heat and pressure.

PRESSURE, STATIC: The total pressure minus velocity pressure. The portion of the pressure that pushes equally in all directions.

PRESSURE, TOTAL: The sum of the static pressure and the velocity pressure.

PRESSURE, VELOCITY: 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.

PSYCHOGENIC ILLNESS: This syndrome has been defined as a group of symptoms that develop in an individual (or a group of individuals in the same indoor environment) who are under some type of physical or emotional stress. This does not mean that individuals have a psychiatric disorder or that they are imagining symptoms.

PSYCHOSOCIAL FACTORS: Psychological, organizational, and personal stressors that could produce symptoms similar to those caused by poor indoor air quality.

RADON (Rn) AND RADON DECAY PRODUCTS: Radon is a radioactive gas formed in the decay of uranium. The radon decay products (also called radon daughters or progeny) can be breathed into the lung where they continue to release radiation as they further decay.

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.

RELs: Recommended Exposure Limits (recommendations made by the National Institute for Occupational Safety and Health (NIOSH)).

SHORT-CIRCUITING: Situation that occurs when the supply air flows to return or exhaust grilles before entering the breathing zone (area of a room where people are). 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 (SBS): Term that refers to a set of symptoms that affect some number of building occupants during the time they spend in the building and diminish or go away during periods when they leave the building. Cannot be traced to specific pollutants or sources within the building. (Contrast with "Building related illness").

SOIL GAS: The gas present in soil which may contain radon.

SOIL-GAS-RETARDER: A continuous membrane or other comparable material used to retard the flow of soil gases into a building.

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: The overall upward movement of air inside a building that results from heated air rising and escaping through openings in the building envelope, thus causing an indoor pressure level lower than that in the soil gas beneath or surrounding the building foundation.

STATIC PRESSURE: See "Pressure, Static" or the difference between Total Pressure and Velocity Pressure.

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."

SUB-SLAB DEPRESSURIZATION SYSTEM (ACTIVE): A system designed to achieve lower sub-slab air pressure relative to indoor air pressure by use of a fan-powered vent drawing air from beneath the slab.

SUB-SLAB DEPRESSURIZATION SYSTEM (PASSIVE): A system designed to achieve lower sub-slab air pressure relative to indoor air pressure by use of a vent pipe routed through the conditioned space of a building and connecting the sub-slab area with outdoor air, thereby relying solely on the convective flow of air upward in the vent to draw air from beneath the slab.

SUB-MEMBRANE DEPRESSURIZATION SYSTEM: A system designed to achieve lower sub-membrane air pressure relative to crawlspace air pressure by use of a fan-powered vent drawing air from under the soil-gas-retarder membrane.

TLVs - Threshold Limit Values (guidelines recommended by the American Conference of Governmental Industrial Hygenists).

TVOCs. Total volatile organic compounds. See "Volatile Organic Compounds (VOCs)"

VENTILATION AIR: Defined as the total air, which is a combination of the air brought inside from outdoors and the air that is being re-circulated within the building. Sometimes, however, used in reference only to the air brought into the system from the outdoors; this document defines this air as "outdoor air ventilation."

VENTILATION RATE: The rate at which OUTDOOR air enters and leaves a building. Expressed in one of two ways: the number of changes TOTAL AIR VOLUME per unit of time (air changes per hour, or "ach") or the rate at which a volume of outdoor air enters per unit of time (cubic feet per minute, or "cfm").

VOLATILE ORGANIC COMPOUNDS (VOCs): Compounds that vaporize (become a gas) at room temperature. Common sources which may emit VOCs into indoor air include housekeeping and maintenance products, and building and furnishing materials. 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.