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Common Indoor Air Quality Terms
Below are listed a few common terms that you will see used in conjuction with discussions about Indoor Air Quality. Many of these are used in our project protocols as well. Click on the letter below that corresponds to the first letter in the word you are trying to identify.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

ACGIH American Conference of Governmental Industrial Hygienists.
ASHRAE American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

American Society for Testing and Materials.

ACTION LEVEL A term used to identify the level of indoor radon at which remedial action is recommended.

AFD Air filtration device(negative air machine). In relation to mold remediation, all AFD's shall be HEPA rated.
ACTION LEVEL A term used to identify the level of indoor radon at which remedial action is recommended.

AHU This is the abbreviated form used for the term "Air Handling Unit" which is described below.
AIR CLEANING An indoor air quality 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.

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 in 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).


This refers to equipment used to provide conditioned air to a space. The air handler unit generally 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 duct work, registers or grilles, or boilers and chillers.


Biological material, including bacteria, viruses, fungi, mold spores, pollens, skin flakes and insect parts are ubiquitous in indoor environments. These particulates range from less than one to several microns in size. When airborne, they are usually attached to dust particulates of various sizes so that all sizes of airborne particulates may include them.


Agent that kills microbial growth.

APR Air Purifying Respirator
BIOCIDE Substance or chemicals that kills organisms such as molds.

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."


That area of a room in which occupants breathe as they stand, sit, or lie down.

BUILDING ENVELOPE Elements of the building, including all external building materials, windows, and walls, that enclose the internal 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").


CADR Clean air delivery rate. The CADR refers to the efficiency of filtering equipment. Although HEPA filters are installed in certain equipment the CADR may reduce the efficiency of the equipment due to air bypass. Ensure all equipment is HEPA rated prior to use. Particulate monitors may be used on-site to verify the efficiency of the equipment.

Space located 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 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.


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 Carbon monoxide is an odorless, colorless, and tasteless gas. It results from incomplete oxidation of carbon in combustion.
CO2 Carbon dioxide Carbon dioxide is a colorless, odorless, and tasteless product of completed combustion. Sources of this include all combustion processes and the human metabolic process. CO2 is also found in ambient atmosphere.

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.


Air that has been heated, cooled, humidified, or dehumidified to maintain an interior space within a carefully defined "comfort zone."

CONTAINMENT BARRIER Fire-retardant polyethylene sheeting (6 mil minimum) used to construct the walls and ceiling of the containment area that separate the remediation work area from adjacent areas of the building.
CONSTANT AIR VOLUME SYSTEMS Air handling system that provides a constant air flow while varying the temperature to meet heating and cooling needs.
DAILY/PROJECT LOG On site record keeping of the projects progress. Typically maintained by the shift supervisor. The project log shall assist in determining remediation progress, identifying significant events (loss of pressure, injuries, loss of power, etc.), and a timetable of project segments (air sampling performed, containment establishment, material & equipment usage, etc.)

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.

DECONTAMINATION STATION A constructed 1-3 level area designed for the safe entrance and exit of remediation workers and equipment and to control the distribution of contaminants.

Components of the ventilation system that distribute and return air to promote air circulation in the occupied space. Generally speaking, supply air enters a space through a diffuser or vent and return air leaves a space through a grille.


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.


Dust is comprised of particles in the air that settle on surfaces. Large particles settle quickly and can be trapped by the body's defense mechanisms. Small particles are more likely to be airborne and are capable of passing through the body's defenses and entering the lungs.


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).


Mixture of smoke from the burning end of a cigarette, pipe, or cigar and smoke exhaled by the smoker.

EPA Environmental Protection Agency

The science that investigates the impact of people's physical environment on their health and comfort (e.g., chair design, monitor location, desk configuration or height, etc.)

ENVIRONMENTAL CONSULTANT Occupational Health and Safety / Indoor Environmental Consultant who will independently monitor work activities of the mold remediation contractor. The EC will provide guidance on the type of removal (e.g. full, local, source) to use in remediation, the construction of containments and decontamination stations and the use of personal protective equipment.

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

FINE DUST REMOVAL Fine dust removal is required for successful remediation. Fine dust must be removed by HEPA vacuum and wiping surfaces with a damp cloth (typical "shop" vacuums area insufficient and may increase the levels of fine dust in the work area. Fine dust removal and distribution may be monitored utilizing real time laser particle counters.
FLOW HOOD Device that easily measures airflow quantity, typically up to 2,500 cfm.

Formaldehyde is a colorless water-soluble gas. Due to its wide use, it is frequently considered separately from other volatile organic compounds (VOCs)

FULL CONTAINMENT Utilized when large scale contamination exist within a structure and the possibility of cross contamination exits. Double layered fire resistant poly barriers are constructed to isolate the work area from adjacent areas AFD's must be utilized to negatively pressurize the work area with respect to adjacent areas. Monitoring of full containment must be performed to continuously record and verify pressurization. Unaffected materials within the work area (drywall, ceilings, hard furniture items, etc.) should be covered with fire resistant polyethylene (protective barriers). Access areas (electrical outlets, light switches, handing chandeliers, etc.) should be covered with a two-ply polyethylene barrier (double critical) to ensure that spores are not distributed into unaffected wall cavities.

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

FUNGICIDE Substance or chemical that kills fungi.
GAS SORPTION Devices used to reduce levels of airborne gaseous compounds by passing the air through materials that extract the gases.


High efficiency participate air (HEPA) filtering equipment that has a 99.97% efficiency at .3 micrometers.


Heating, ventilation, and air-conditioning system.


Diseases characterized by allergic responses to pollutants. The hypersensitivity diseases most clearly associated with indoor air quality are asthma, rhinitis, and hypersensitivity pneumonitis.


A group of respiratory diseases that cause inflammation of the lung. Most forms of hypersensitivity pneumonitis are caused by the inhalation of organic dusts, including molds.


Indoor air quality.

IAQ BACKGROUNDER A component of the IAQ Tools for Schools Action Packet that provides a general introduction to IAQ issues in educational facilities.

An individual (usually with facility management) who provides leadership and coordination of all IAQ activities.


A set of flexible and specific steps for preventing and resolving IAQ problems in any kind of commercial facility.


Integrated pest management.


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).


Particles and dust, fibers, mists, bioaerosols, and gases or vapors.

LOCAL REMOVAL Used when surface or expected contamination is less than 30 square feet. Double layered fire resistant poly barriers are constructed to isolate the work area from adjacent areas AFD's must be utilized to negatively pressurize the work area with respect to adjacent areas. Double or single stage decontamination stations are appropriate. Negative pressurization is still required. Monitoring of full containment must be performed to continuously record and verify pressurization.

See "Outdoor Air Supply."


See "Biological Contaminants."

MOLD Molds are a group of organisms that belong to the kingdom Fungi. In this document, the terms fungi and mold are used interchangeably. There are over 20,000 species of mold.

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.

mVOC Microbial volatile organic compound, a chemical made by a mold which may have a moldy or musty odor.
NEGATIVE AIR MACHINE Typically a HEPA rated air mover used to create pressure differential between the work area and adjacent areas.

Condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas. Under this condition, if an opening exists, air will flow from surrounding areas into the negatively pressurized space.


The two most prevalent oxides of nitrogen are nitrogen dioxide (NO2) and nitric oxide (NO). Both are toxic gases with NO2 being a highly reactive oxidant, and corrosive. NO gradually reacts with the oxygen in the air to form NO2.

Non-porous HVAC system surface Galvanized steel surfaces.
ORGANIC COMPOUNDS Chemicals that contain carbon. Volatile organic compounds vaporize at room temperature and pressure. They are found in many indoor sources, including many common household products and building materials.
OSHA Occupational Safety and Health Administration

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."

PAPR Powered air purifying respirator.

Permissible Exposure Limits (standards set by the Occupational, Safety and Health Administration).


Air compartment connected to a duct or ducts.


See "Preventive Maintenance."

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.

PESTICIDES Pesticides are chemicals that are used to kill or control pests which include bacteria, fungi, weeds, and other organisms, in addition to insects and rodents. Most pesticides are inherently toxic. Most contain volatile organic compounds.

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. Under this condition, if an opening exists, air will flow from the positively pressurized space, outward to surrounding areas.

PPE Personal Protective Equipment

Parts per million.


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.


Primarily done on a building's mechanical systems, this involves a 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.

PROTECTIVE BARRIER Fire-retardant polyethylene sheeting (6 mil minimum) used to construct containment areas and decontamination stations.

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


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.


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.


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

REMEDIATION The formal process that occurs in the removal of microbial contamination from the project site. Components consist of of five phases: Initial Testing, Project Design, Actual Tear-out, Post-Remediation Acceptance Testing, Build Back
SENSITIZATION Repeated or single exposure to an allergen that results in the exposed individual becoming hypersensitive to the allergen.

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.


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 altogether during periods when they leave the building. (Contrast with Building Related Illness.)


Sources of indoor air pollutants. Indoor air pollutants can originate within the building or be drawn in from outdoors. Common sources include people, fixtures and furnishings, photocopiers, plants, food, etc.

SPORE Molds reproduce by means of spores. Spores are microscopic; they vary in shape and size (2-100 micrometers). Spores may travel in several ways--they may be passively moved (by a breeze or waterdrop), mechanically disturbed (by a person or animal passing by), or actively discharged by the mold (usually under moist conditions or high humidity).

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


Condition that exists when an equal amount of air is supplied to and exhausted from a space. At static pressure, equilibrium has been reached.


Compounds, such as sulfur hexaflouride, which are used to identify suspected pollutant pathways and to quantify ventilation rates. Trace gases may be detected qualitatively by their odor or quantitatively by air monitoring equipment.


Threshold Limit Values (guidelines recommended by the American Conference of Governmental Industrial Hygienists).

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

Defined as the total air, which is a combination of the air brought inside from outdoors and the air that is being recirculated within the building.


The rate at which indoor air enters and leaves a building. Expressed in one of two ways: the number of changes of outdoor air 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").


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.






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