Terminology

ACGIH - American Conference of Governmental Industrial Hygienists.

AIHA - American Industrial Hygiene Association.

ASHRAE - American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

ASTM - American Society for Testing and Materials.

Absorption - The process of one substance entering into the structure of another.

Acceptable Air Quality - Air in which there are no known contaminants at harmful concentrations and with which a substantial majority (usually 80 percent) of the people exposed do not express dissatisfaction (ASHRAE 1989-62).

Active System - A system that uses mechanical means to satisfy load demand as opposed to passive systems.

Acute - Effects which are immediately recognizable after an exposure.

Adsorption - The adhesion of a thin film of liquid or gases to the surface of a solid substance.

Aerosol - An assemblage of small particles, solid or liquid, suspended in air.

Air Changes (AC or AC/HR) - A way to express ventilation rates, which are the number of time the air volume of a given space will be replaced in a one hour periods, assuming the air distribution within the space is uniformly mixed.

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 adsorption.

Air Cleaning System - A device or combination of devices applied to reduce the concentration of airborne contaminates, such as microorganisms, dust, fumes, respirable particulates, other particulate matter, gases, and /or vapors in the air.

Air Conditioning - The process of treating air to meet the requirements of a conditioned space by controlling its temperature, humidity, cleanliness, and distribution (ASHRAE 1989-62).

Air Contaminant - An unwanted airborne constituent that my reduce acceptability of the air (ASHRAE 1989-62).

Air Handler System - A mechanical system that heats and/or cools air.  See "Constant Air Volume System" and "Variable Air Volume System."

Air Pollutant - An airborne constituent that may adversely affect health.

Air Sampling Survey - Collection of chemical or biological contaminants on a specific media which is sent to a laboratory for analysis or using direct reading instruments for instantaneous data.

Air, ambient - The air surrounding an object.

Air, exhaust - Air removed from a space and not reused therein.

Air, makeup - Outdoor air supplies to replace exhaust air and exfiltration.

Air, outdoor - Air taken from the external atmosphere and therefore, not previously circulated through the system.

Air, recirculated - Air removed from the conditioned space and intended for reuse as supply air.

Air, relief - Return air discharged from the building which is replaced by outdoor air.

Air, return - Air removed from a space to be then recirculated or exhausted.

Allergens - Biological or chemical compounds which if inhaled or if skin contact is made can cause respiratory disorders, skin rashes, eye irritations, etc.

Antimicrobial - Agent that kills microbial growth.  See "disinfectant", "sanitizer", and "sterilizer".

- Back To Top -

BRI - See "Building - Related Illness".

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".

Breathing Zone - Area of a room in which occupants breathe as they stand, sir or lie down.

Building Envelope - Elements of the building, including all external building materials, windows and walls, which 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, asbestosis, hypersensitivity pneumonitis).

- Back To Top -

CFM - Cubic feet per minute.

CFU - See "Colony Forming Units".

CIH - Certified Industrial Hygienist.

CO - Carbon monoxide.

CO2 - Carbon dioxide.

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 for returning air to the air handler.

Chemical Contaminants - Compounds released from the use of chemicals within a building.

Chemisorb - To take up and hold, usually irreversibly, by chemicals forces.

Chronic - Effects which take a long period of time to manifest.

Colony Forming Units - The number of viable bacteria, yeasts or molds per a specific volume.

Comfort Factors - Conditions other than indoor air contaminants that cause stress, comfort, and/or health problems (e.g., humidity extremes, drafts, lock of air circulation, noise, and overcrowding).

Commissioning - Start-up of a building that includes testing and adjusting HVAC, electrical, plumbing, and other systems to assure proper functioning and adhere to design criteria.  Commissioning also includes the instruction of building representatives in the use of the building system.

Concentration - The quantity of one constituent dispersed in a defined amount of another. 

Condensate - Water that is removed from air as it is being cooled.

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 - An unwanted airborne constituent that may reduce acceptability of the air.

Cooling Coil - A heat transfer device which absorbs heat.

Cooling Tower - A device which cools water by evaporating a portion of it in the air.  Water is cooled to the wet bulb temperature of the air.

- Back To Top -

Demand - The amount of energy per unit of time required to satisfy the utility loads averaged over any given time.

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.

Direct Reading - Instruments that provide instantaneous concentrations of chemical or physical agents.

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.

Dust - An air suspension of particles (aerosol) of any solid material, usually with particle size less than 100 micrometers (μm).

- Back To Top -

ETS - Environmental tobacco smoke.

Economizer Cycle, air - A method of operating an air conditioning system to reduce conditioning load.  Whenever the outdoor air conditions are more favorable (lower or higher heat content) then return air conditions, outdoor air quality is increased.

Energy Management Control System - Manual and /or automatic control and supervision of the operation of active and passive systems to reduce energy costs.

Energy Recovery Ventilation System - A device or combination of devices applies to provide the outdoor air for ventilation in which energy is transferred between the intake and exhaust air steams. 

Ergonomics - Applies science that investigates the impact of people's physical environment on their health and comfort (e.g., piece of equipment, room or general area).

Exfiltration - Air leakage outward through cracks and interstices and through ceilings, floors, and wall of a space or building.

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

- Back To Top -

Filter - Generally a particulate removal device located within the air handler before the heat exchanger.  Filters range in efficiency from 25 to 99.999%.

Fumes - Airborne particles, usually less than 1 micrometer in size, formed by condensation of vapors, sublimation, distillation, calcinations, or chemical reaction.

- Back To Top -

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 Adsorption - Devices used to reduce levels of airborne gaseous compounds by passing the air though 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.

- Back To Top -

HVAC - Heating, ventilation, and air conditioning system.

Heat Exchanger - Part of an air handler that provides a surface for heating or cooling air.

Heat Gain - The amount of heat gained by a space from all sources, internal and external, including persons, lights, machines, sunshine and so forth.

Heat Loss - Heat flow from a building mass to the outside when the outdoor temperature is lower than desired indoor temperature.

Heat Pump - A refrigeration machine possessing the capability of reversing the flow so that its output can be either heating or cooling.  When use for heating extracts heat from a low temperature source and raises it to the point at which it can be used.

Heat, sensible - Heat that results in a temperature change but no change in state.

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.

- Back To Top -

IPM - Integrated pest management.

Indicator Compounds - Chemical compounds, such as carbon dioxide, whose presence at certain concentration may be used to estimate certain building conditions (e.g., airflow, presence of sources).

Infiltration - The uncontrolled inward air leakage though cracks and spaces and around windows and doors in any building.

- Back To Top -

MCS - See "Multiple Chemical Sensitivity".

mg/m³ - See "Milligram per Cubic Meter".

MSDS - Material Safety Data Sheet

Make-up Air - Air brought into a building from the outdoors through the ventilation system and that has not been previously circulated through the system.

Microbiologicals - See "Biological Contaminants".

Microorganism - A microscopic organism especially a bacterium, fungus or a protozoan.  See "Biological Contaminants".

Milligram per Cubic Meter - The concentration of a chemical compound in milligrams per cubic meter of air.

Molds - See "Biological Contaminants".

Multiple Chemical Sensitivity - A team 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 action regarding this phenomenon.

- Back To Top -

NTIS - National Technical Information Service.

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 supplies to a space than is exhausted from the space so the air pressure within the space is less than that in surrounding areas.

- Back To Top -

Occupational Health Physician - Board certified physician trained in regulation, evaluation and treatment of occupational disease/injuries.

Occupies Zone - The region within an occupied space between planes 3 and 72 inches (75 and 1800 mm) above the floor and more than 2 feet (600 mm) from the walls or fixed air-conditioning equipment (see ASHRAE Standard 55-1981-Ref 1).

Odor - A quality of gases, liquids or particles that stimulates the olfactory organ.

Oxidation - A reacting in which oxygen combines with another substance.

- Back To Top -

PELs - Permissible Exposure Limits (standards set by OSHA).

PM - Preventative Maintenance.

PPM - See "Parts Per Million".

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.

Parts Per Million - A concentration which expresses the amount of a chemical contaminant (parts) of air or water.

Passive System - A system that uses nonmechanical means to provide cooling or heating, including energy stored in construction mass.

Plenum - Air compartment connected to a duct or ducts.

Positive Pressure - Condition that exists when more air is supplies to a space than is exhausted, so the air pressure within that space is greater than in surrounding areas.

Pressure Drop - The resistance of a device to the flow of a fluid though it.  The pressure drop of a filter is a measure of its resistance to airflow through it.  Resistance is measured in inches w.g. in the Inch-Pound system of measurement.  It is measure in Pascals in the SI system.

Psychosocial Factors - Psychological, organizational, and person stressors that could produce symptoms similar to poor indoor air quality.

- Back To Top -

RELs - Recommended Exposure Limits (recommendations made by NIOSH).

Reentrainment - 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.

Reheat - The application of sensible heat to supply air that has been previously cooled below the temperature of the conditioned space by wither mechanical refrigeration or the introduction of outdoor air to provide cooling.

Relative Humidity (RH) - The relative difference between the amount of water vapor in the air and temperature.  If water vapor remains the same, RH will decrease as temperature increases because warmer air can hold more water.

Rhinitis - Eye irritation.

- Back To Top -

Sanitizer - One of the three groups antimicrobials registers by EPA for public health issues.  EPA considers an antimicrobial to be a sanitizer when it reduces but does no necessarily eliminate all the microorganisms on a related 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.

Saprophyic Bioaerosols - See "Microorganism".

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 ozone, or may be spread throughout the building.

Soil Gases - Gases that enter a building from the surrounding ground (e.g., radon, volatile organics, pesticides).

Stack Effects - 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 end exhausted from a space.  At static pressure equilibrium has been reached. 

Sterilizer - One of the three groups of antimicrobials registered by EPA for public health issues.  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."

- Back To Top -

TVOCs - Total Volatile Organic Compounds.

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.

- Back To Top -

Unitary Air Conditioning Equipment - A unitary air conditioner consists of one or more factory-made assemblies which normally include an evaporator or cooling coil, an air moving device, and a compressor and condenser combination, and which may include a heating function as well.

- Back To Top -

VOCs - See "Volatile Organic Compounds".

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 - 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 (ASHRAE 62).

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. 

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 air in storage.  In sufficient quantities, VOCs can cause eye, nose and throat irritation, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals; some are suspected of causing 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.

- Back To Top -

- Back To Top -

- Back To Top -