H2S:  Hydrogen Sulfide.

H Clip: Small metal clips formed like an “H” that fits at the joints of two plywood (or wafer board) sheets to stiffen the joint. Normally used on the roof sheeting.

Habitable Space:  Building space intended for continual human occupancy. Such space generally includes areas used for living, sleeping, dining and cooking, but does not generally include bathrooms, toilets, hallways, storage areas, closets, or utility rooms.

Habitat:  The place where an organism lives.

Half-Mask:  A type of respirator inlet covering that covers the user’s nose and mouth (to under the chin).

Halide Refrigerants - Refrigerants containing halogen chemicals

Halide Torch:  A propane torch used in the process of leak checking.

Hallos: A family of compounds containing bromine, fluorine, iodine and chlorine used in fighting fires that breakdown in the atmosphere depleting stratospheric ozone.

Halocarbons:  Manmade chemicals that, when released into the atmosphere as greenhouse gases, can disrupt global climate patterns. Their most common use is in refrigeration and air conditioning technologies.

Halogenated Hydrocarbon:  A chemical material that has carbon plus one or more of these elements: chlorine, fluorine, bromine, or iodine.

Halogens:  Substance containing fluorine, chlorine, bromine, and iodine.

HALON 1301:  A gas used for fire suppression in data centers. Halon extinguishes a fire by rapidly absorbing oxygen in the room. Historically halon was much preferred over water systems because halon does not damage electrical equipment like water does. Now however, halon has been linked to ozone depletion and its use is being phased out by the EPA. Replacement products include C02, HFC-227 (Heptafluoropropane – Marketed as FM-200), Inergen, Water.

Halon Dump:  The act of halon being discharged into a room. This generally causes a big mess because of the pressure at which the gas is released. Typically the ceiling tiles blow out and any loose papers are spread all around the room. A halon dump will generally cause a system shutdown.

Halomethanes:  The sum of bromoform, bromomethane (methyl bromide) and chloromethane (methyl chloride).

Handicapped Person: Any individual who is: 1) handicapped as defined in Section 7 (6) of the Rehabilitation Act of 1973; 2) under a disability as defined in Section 1614 (1) (3) (A) or 223 (d) (i) of the Developmental Disabilities Services and Facilities Construction Act; or 3) who is receiving benefits under Chapter 11 or 15 of Title 38, U.S.C. Other conditions may apply state to state, which can deem an individual as handicapped for the purposes of the WAP.

Hanger:  A device attached to walls or other structure for support of pipe lines.

Hantavirus Pulmonary Syndrome (HPS):  Hantavirus Pulmonary Syndrome (HPS) is characterized by a sudden onset of fever, pain, vomiting, and onset of respiratory distress and prostration. Mortality rates are high despite symptomatic treatment.

HAPs (Hazardous Air Pollutants): Any of the 189 chemicals listed under Title III of the CAAA. All HAP sources will have to comply with GACT or MACT standards.

Hard Ducting: Permanently installed ductwork not intended to be disassembled for normal cabinet servicing or testing. 

Hard Water:   Alkaline water containing dissolved salts that interfere with some industrial processes and prevent soap from lathering.

Hardware: Metal accessories such as door knobs, towel bars, toilet paper holders, etc.

Hardwood: Hard tree species with dense wood that contains more energy per piece than softwood. (E.g. Elm, Hickory, Oak, Maple, Beech, Birch, Ash...)

Harried:  A person or animal who/that is harassed or bothered.

Harvested Rainwater:  The rain that falls on a roof and is channeled by gutters to a storage tank or cistern. The uses of this water are dependent on any pollutants that may be picked up from the roof surface.

Hatch: An opening in a deck, floor or roof. The usual purpose is to provide access from inside the building.

Haunch: An extension, knee-like protrusion of the foundation wall that a concrete porch or patio will rest upon for support.

Hawk: A flat wood or metal tool 10 inches to 14 inches square with a handle used by plasterers to carry plaster mortar or mud.

Hay Fever:  A form of atopy characterized by an acute irritative inflammation of the mucous membranes of the eyes and upper respiratory passages accompanied by itching and profuse watery secretion, usually without temperature elevation, followed occasionally by bronchitis and asthma; the episode recurs annually at the same or nearly the same time of the year, in spring, summer, or late summer and autumn, caused by an allergic reaction to the pollen of trees, grasses, weeds, flowers, etc.  Syn: allergic coryza.

Hazard:   Risk, peril, jeopardy to which an individual is subjected.

Hazard Insurance: Insurance for a building while it is under construction.

Hazard Ratio (HR):  The estimated/measured airborne concentration of a substance divided by the occupational exposure limit; this ratio is calculated for each gas, vapour and/or particulate component that poses a respiratory hazard.

Hazard Warning: Any words, pictures, symbols, or combination thereof appearing on a label or other appropriate form of warning that convey the health and physical hazards of the substance(s) present.

Hazardous Atmosphere:  Any atmosphere that is oxygen-deficient, exceeds occupational exposure limits, that presents a fire/explosion hazard, and/or contains an airborne toxic or disease-producing contaminant in concentrations deemed to be hazardous.

Hazardous Air Pollutants (HAPs): Chemicals that cause serious health and environmental effects. Health effects include cancer, birth defects, nervous system problems and death due to massive accidental releases such as occurred at the pesticide plant in Bhopal, India. HAPs are released by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles (cars, trucks, buses, etc.).

Hazardous Material: A material for which there is statistically significant evidence based on at least one study conducted in accordance with established scientific principles that acute or chronic health effects may occur in exposed employees. The term “health hazard” includes materials which are carcinogens, toxic or highly toxic agents, reproductive toxins, irritants, corrosives, sensitizers, hepatoxins, nephrotoxins, neurotoxins, agents that act on the hematopoietic systems, and agents
which damage the lungs, skin, eyes, or mucous membranes. The term “physical hazard” includes materials for which there is scientifically valid evidence that it is a combustible liquid, a compressed gas, cryogenic, explosive, flammable, an organic peroxide, an oxidizer, pyrophoric, unstable (reactive), or water-reactive.

Hazardous Waste:  Pollutants that are harmful to people, fish, wildlife or plants.

Haze: Haze consists of sufficient smoke, dust, moisture, and vapor suspended in air to impair visibility. The term regional haze means haze that impairs visibility in all directions over a large area.

HAZMAT:  Hazardous Material.

HC:  An exhaust and evaporative pollutant of hydrogen and carbon atoms resulting from unburned fuel. HC contributes to the formation of ozone which is responsible for the choking, coughing, and stinging eyes associated with smog. Ozone damages lung tissue, aggravates respiratory disease, and makes people more susceptible to respiratory infections. Children are especially vulnerable to ozone’s harmful effects, as are adults with existing disease.

HCFCs (Hydrochlorofluorocarbons): Refrigerants and solvents which do not have as much potential to destroy atmospheric ozone if released into the environment as
CFCs. Most are less efficient as refrigerants than CFCs and some are quite toxic.

HDD - Heating Degree Day(s):  The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating systme sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average termperature(s).

He:  See high efficiency particulate air filter.

Head:  Another word for pressure.

Head, Static:  The amount of pressure a pump has to work against.

Head, Total Static:  Static head from the surface of the supply source to the free discharge surface.

Head Adiabatic:  The energy in foot pounds required to compress adiabatically and to deliver one pound of a given gas from one pressure level to another.

Head Crash:  The act of a hard disk head physically contacting the surface of the hard disk media. This generally renders the disk surface and the head inoperable. Head crashes are caused when minute dirt particles accumulate on the disk surface. If the head hits the dirt, it will wobble vertically and crash into the disk.

Head Friction:  Head required to overcome friction of the interior sur­face of a conductor and between fluid particles in motion.

Head Polytropic:  The energy in foot pounds required to compress polytropically and to transfer one pound of a given gas from one pressure level to another.

Head Pressure:  A term used to describe the hot gas pressure on the outlet side of the refrigeration compression.

Head Pressure Control:  A pressure actuated safety  control which opens elec­trical circuit if high-side pressure becomes too high.

Head Velocity:  Height of fluid equivalent to its velocity pressure in flow­ing fluid.

Header:  The main distribution pipe.

Health-Based Standard (Primary Standard): A dosage of air pollution scientifically determined to protect against human health effects such as asthma, emphysema, and cancer.

Health Care Professional:  An individual who is licensed by a provincial licensing authority or equivalent to practice medicine or nursing and possesses relevant experience and knowledge in the field of occupational health and safety.

Health Effects of Indoor Pollutants:  Indoor air pollution consists of toxic gases or particles that can harm your health. Indoor sources of toxic gases or particles can lead to indoor levels much higher than those found outdoors. A partial list of indoor air pollutant sources includes pressed wood products, aerosol sprays, solvents, cleaning agents, moth balls, unvented or malfunctioning gas appliances, cigarettes, and wood stoves. Because there are many indoor sources of pollutants, and because people spend most of their time indoors, indoor exposures can be high and pose a significant risk to health. People may react differently to air pollutants, depending on factors such as age, preexisting medical conditions, and individual sensitivity. Immediate effects can include headache, nausea, asthma symptoms, irritation to the respiratory system or skin, fatigue, and dizziness. Long-Term exposure may cause cancer, heart disease, and respiratory disease. Specific indoor pollutants, their sources and their potential health effects are shown in the linked table.

Health Risk Assessment (HRA): A document that identifies the risks and quantities of possible adverse health effects that may result from exposure to emissions of toxic air contaminants. A health risk assessment cannot predict specific health effects; it only describes the increased possibility of adverse health effects based on the best scientific information available.

HealthcarePro Dustbags:  A Lindhaus trade name for high filtration dustbags.

Hearing Protector:  A device that is worn to reduce the effect of noise on the auditory system.

Heart Failure: A condition caused by weakening of the heart muscle. The heart is strained and can not pump enough blood. Fluid can build up in the lungs and other parts of the body. Symptoms can include shortness of breath and swelling of the legs, ankles and feet.

Hearth: The inner or outer floor of a fireplace, usually made of brick, tile, or stone.

Heartwood: The wood extending from the pith to the sapwood, the cells of which no longer participate in the life processes of the tree.

Heat: Form of energy that is transferred by virtue of a temperature difference. see latent heat, radiant heat, sensible heat.

Heat Accumulation: Heat stored in the thermal mass (of a building). See Thermal mass.

Heat Anticipator: A very small electric heater in a thermostat that causes the thermostat to turn off before room temperature reaches the thermostat setting, so that the house does not overheat from heat remaining in the furnace and ducts after the burner shuts off.

Heat Balance Model (of thermal comfort): A model of human thermal response based on the assumption that a necessary condition for thermal comfort is a balance between the metabolic heat production and the heat loss from the body (generally an analytical model).

Heat Capacity: The amount of heat necessary to raise the temperature of a body by one degree. Numerically, the mass multiplied by the specific heat.

Heat Demand: The amount of energy needed to keep the temperature of a room or building at a given value.

Heat Exchanger: A device, usually consisting of an arrangement of metal tubing used to transfer heat from one fluid to another, often used to conserve energy by heating incoming air using the heat from outgoing air.

Heat Exchangers (Air-To-Air):  Advanced air-to-air heat exchanger designs for cooling enclosures include two types of heat transfer methods. One design consists of a finned-tube coil which contains liquid refrigerant. The warm air exhausted from the equipment cabinet to the heat exchanger is directed past the coil, causing the refrigerant to boil and absorb heat.  The resultant refrigerant vapor rises to the upper portion of the tubes, where the heat is removed by the cooler ambient air and the refrigerant condenses back to liquid, completing the cooling cycle in a continuous process. The most recent developments in enclosure heat exchanger design employ high-efficiency heat transfer elements fabricated of embossed convoluted metal foil or thin-film polymer material, constructed into two totally separate air paths. The air leaving the hot enclosure is directed through one side of the exchanger, where the heat passes through the element walls into the ambient-side air stream and is dissipated.

Heat Exchangers (Water-To-Air):  If ambient air cannot be utilized directly as a cooling medium, another cost-effective method of cooling is a water-to-air system.  Water is used to remove heat from air circulated within the electrical enclosure.
Cooling water is circulated through a finned-tube coil, which is installed in a compartment isolated from the enclosure to protect the contents from possible leakage of water. As the heat-laden air circulates through the coil, the heat is absorbed by the water and carried away, in a continuous process.  Water-to-air systems are easy to install and usually require minimum maintenance. The water used must be reasonably clean and cold enough to ensure proper operation of the cooling system under the most severe anticipated conditions.  In cases where sufficiently cold water is available, below ambient-temperature cooling can be achieved.

Heat Gain: Sum of internal heat gains (like heat gains from persons, lighting and apparatus) and solar heat gains.

Heat Island Effect:  The increase in ambient temperature that occurs over large paved areas compared to natural landscape. See also “Urban Heat Island.”

Heat Load: The heat flux which has to be removed from a room to maintain (or prevent to exceed) a required air temperature or humidity.

Heat Loss: The amount of heat escaping through the building shell as measured for a specific period of time (month, year, etc.)

Heat Loss (from the body): The loss of heat from the surface of the human body by conduction, convection, radiation and evaporation.

Heat Loss (from a building): Heat flow through building envelope components (walls, windows, roof).

Heat Meter: An electrical municipal inspection of the electric meter breaker panel box.

Heat of Compression:  Mechanical energy of pressure changed into energy of heat.

Heat of Fusion:  Heat released from a substance when a change of state occurs from a liquid to solid state.

+Heat of Respiration:  Process by which oxygen and carbohydrates are assimilated by a substance; also when carbon dioxide and water are given off by a substance.

Heat Pump: Apparatus that transfers heat from a low (unusable) temperature level to a (usable) higher temperature level.

Heat Reactivated Dryers:  Are categorized as internal or external heat reactivated. Internal type – Process air enters the dryer through the inlet piping, is then dried as it passes through the desiccant bed, and discharges through the outlet piping as dry air. Regeneration of the desiccant is accomplished at atmospheric pressure, using steam or electric heaters, embedded in the desiccant bed. External type – Process air enters the dryer through the inlet piping, is then dried as it passes through the desiccant bed, and discharges through the outlet piping as dry air. Reactivation is accomplished using a reactivation blower or a cooler.

Heat Recovery: The process of extracting heat, (usually from a fluid, gas or air) that would otherwise be wasted. For example heat recovery using a heat exchanger between incoming and exhaust air.

Heat Recovery System:  Produces and stores hot water by transfer­ring heat from condenser to cooler water.

Heat Rise: The number of degrees of temperature increase that air is heated as it is blown over the heat exchanger. Heat Rise equals supply temperature minus return temperature.

Heat Sink:  The area or media where heat is absorbed into. 

Heat Strengthened Glass: Flat or bent glass that has been heat-treated to a specific surface and/or edge compression range to meet the requirements of ASTM C 1048, kind HS. Heat-strengthened glass is approximately two times as strong as annealed glass of the same thickness when exposed to uniform static pressure loads. Heat-strengthened glass is not considered safety glass and will not completely dice in the manner fully tempered glass will.

Heat Transmission: Heat transfer through a construction, due to conduction, convection and radiation.

Heat Transfer:  Movement of heat from one body or substance to another.

Heat Transfer Coefficient: See U-value.

Heat Transfer Module:  Primary system of heat transfer in a glycol water solution forced-air furnace. The heat transfer module contains the ignitor, burner, and primary solution-circulating coil.

Heat Transmission Coefficient: Heat transmission per unit temperature difference per area unit (usually used for total constructions).

Heat Trim: Work done by the heating contractor to get the home ready for the municipal final heat Inspection. This includes venting the hot water heater, installing all vent grills, registers, air conditioning services, turning on the furnace, installing thermostats, venting ranges and hoods, and all other heat related work.

Heating: The process of active heat supply for the benefit of climate control.

Heating Capacity (Also Specific Heat):  The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree.

Heating Coil:  Any coil that serves as a heat source.

Heating Control:  A device that controls the temperature of a substance by operating a unit which releases heat.

Heating Degree-days (DD): The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating systme sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average termperature(s).

Heating Load: The maximum rate of heat conversion needed by a building during the very coldest weather.

Heating Season: The period of the year during which heating the building is required to maintain comfort conditions

Heating Seasonal Performance Factor (HSPF): Rating for heat pumps describing how many Btus they transfer per kilowatt-hour of electricity consumed.

Heating Value:  Amount of heat which may be obtained by burning a fuel. The heating value is usually expressed in Btu per lb.

Heatless Dryer:  Heatless reactivated dryer. By means of expanding cold dry air to near atmospheric pressure inside the regeneration tower, the dryer air picks up moisture from the saturated desiccant bed and is then purged to atmosphere.

Heavy Fuel Oil (HFO): Industrial fuels suitable for use in boiler plant (includes Type 4, 5, 6). Heavy fuel oils are the last to be distilled during the refining process. Except for start-up and flame stabilization, virtually all petroleum used in steam plants is heavy oil.

Heavy Metals:  Toxic, high-density, metallic elements such as lead, silver, mercury and arsenic.

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.

Heel Bead: Sealant applied at the base of a channel, after setting the light or panel and before the removable stop is installed, one of its purposes being
to prevent leakage past the stop.

Heel Cut: A notch cut in the end of a rafter to permit it to fit flat on a wall and on the top, doubled, exterior wall plate.

HEGA Filtration:  This is an Austin Air trade name and is an acronym that stands for High Efficiency Gas Adsorption filtration. This is a four-stage system of filtration that provides HEPA filtration combined with an Activated Military Carbon Cloth filter to remove a wide variety of odors and gasses.

Helmet:  The portion of a respirator that completely covers the head and neck, may cover portions of the shoulders and may offer head or eye protection; also known as a hood; see inlet covering; refer to CSA Z94.4 for the definition.

Hemoglobin: Responsible for carrying oxygen in the blood.

HEPA:   High efficiency particulate arrestance (filters).

HEPA Filter: HEPA stands for High Efficiency Particulate Arrestance. HEPA filters were developed during World War II as a safety device for the Manhattan Project, the American effort to develop nuclear weapons. HEPA filters use glass fiber as a filter and can clean 99.7 per cent of particles above 0.3 microns in diameter. Though brittle, these filters are now widely used in a variety of filtration devices, and are widely considered to be the best air filter available to the public.

HEPA Filter Unit: Self-contained device consisting mainly of a HEPA filter, a prefilter, and a fan. These units can be used to provide clean air to supplement a building ventilation system.

HEPA Silent Technology:  This is a Blueair trade name for a combination of mechanical and electrostatic filtration that captures 99.97% of particles at 0.1 micron on level one. At this speed the air purifier not only filters at very high levels but also functions very quietly.

HEPA Type:  This is a term that may indicate that a particular bag or filter is manufactured much like a true HEPA filter or that higher than normal levels of filtration are being provided by the vacuum cleaner or air purifier. However, it should be noted that “HEPA Type” or “HEPA Like” is not true HEPA filtration. While HEPA type filters may provide superior filtration than regular filters, check carefully to understand what the actual filtration efficiency (See “Filtration Efficiency” and particle sizes retained actually are. Also, the system may not be completely sealed which means that while the filter may provide the claimed levels of filtration in a laboratory, if air bypasses the filter when the appliance is in use, these levels of filtration will not be obtained.

HEPA Type Bags:  This is a term that indicates a higher level of bag filtration than normal dust bags. Be aware that while these bags may offer significant improvement over normal bags it is unlikely that they meet the stringent specifications for true HEPA filtration. Some companies are even using the HEPA acronym but changing the words that it stands for! “HEPA Type” is not true HEPA. Check carefully to understand what the actual filtration efficiency (See “Filtration Efficiency”) and particle sizes retained by “HEPA Type” dust bags actually are.

HEPA-Vacuum Equipment:  Vacuuming equipment designed for abatement, with a high efficiency particulate air filtration system. 

Hepatic:  Associated with the liver.

Hepatitis:  Inflammation of the liver.

Herbicide:  Chemical used to kill plants.

Hermetic Compressor:  A sealed compressor that the internal motor is not serviceable.  Housing.

Hermetic Motor:  Compressor drive motor sealed within same casing which contains compressor.

Hermetic Seal: Vacuum seal between panes of a double-paned window, i.e. insulated glass unit or IGU. Failure of a hermetic seal causes permanent fogging between the panels of the IGU.

Hermetic system:  Refrigeration system which has a compressor driven by a motor contained in compressor dome or housing.   

HERS: Home Energy Rating Systems: A nationally recognized energy rating program that give builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise evaluation of energy losing deficiencies in homes. Builders can use this system to gauge the energy quality in their home and also to have a star rating on their home to compare to other similarly built homes.
Hertz:  In alternating current (AC electricity), the number of cycles per second.

Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX):  High-explosive compound.

HFC (Hydrofluorocarbon):  A class of refrigerants. Generally refers to Hydrofluorocarbon family of refrigerants.

Hg. (MERCURY):  Heavy silver-white metallic element; only metal that is liquid at ordinary room temperature.

HHR:  See Highest Hazard Ratio.

Hi-Volume Sampler: Also called a Hi-Vol. A device used in the measurement and analysis of suspended particulate pollution.

High Blood Pressure: A condition (that usually has no symptoms) involving higher than normal pressure of the blood against the blood vessels. High blood pressure increases the risk of developing heart disease, a heart attack and a stroke.

High Density Absorbing Agent:  This is Zeolite which has the power to absorb odorous components. This then allows the titanium oxide to react with the Flash Streamer using the photo catalytic layer as a catalyst. This kills germs and bacteria and neutralizes noxious gases and unpleasant odors.

High Efficiency Filter: A filter that provides 90% efficiency against 1 micrometer diameter particles in accordance with the current edition of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Specification 52. 

High Efficiency Filtration:  The unofficial filtration industry description for filters designed to trap small size contaminants.

High Efficiency Gas Furnace:  A furnace with efficiencies from 85 to 95 percent.

High Efficiency Particulate Air Filter (He, Hepa, HEPA):  A filter that has been tested to ensure an efficiency equal to or exceeding 99.97% for removal of particles having a mean aerodynamic diameter of 0.3 µm from the air.

 High Explosives (HE):  Materials that release large amounts of chemical energy when detonated.

High Intensity Discharge:  A generic term for mercury, vapor, metal halide, and high pressure sodium lamps and fixtures.

High Limit: A bimetal thermostat that turns the heating element of a furnace off if it senses a dangerously high temperature.

High Performance Building:  A green or sustainable building often with an emphasis on the use of advanced technology, or “smart infrastructure,” and its impact on tenant ability to control key building comfort measures such as temperature and light levels to increase performance.

High Pressure Cleaning Air: Air at 80-100 PSIG used for cleaning air in baghouses and cartridge filters.

High Pressure Cut Out:  See head Pressure Control.

High Risk (biosafety level 4): Risk level of agents and/or operations requiring additional control measures beyond those for moderate risk. These are agents or operations with various dangerous combinations of the following characteristics: (1) low infective doses for personnel, animals or plants; (2) high concentrations: (3) release of microbial aerosols: and (4) genetic alteration or recombination that significantly increases potential pathogenicity or virulence.

High Side:  The side of the refrigeration system that the condensing takes place.

High Side Float:  A metering device that controls the level of the liquid refrigerant in the high-pressure side of the device.

High Velocity Airflow Tools:  These are tools used with Dyson vacuum cleaners and direct high velocity airflow down into the carpet pile. This directional airflow agitates and dislodges dust and dirt for easy removal. Also, because there is constant airflow curtains or upholstery fabrics will not become stuck to the tool during vacuuming.

High Velocity Return Air Slots: Unique Baker Company devices which help to prevent escape or entry of particulates at the front access opening, or behind the viewscreen.

High Volume Low Pressure:  In spray painting applications, Spray equipment which delivers material at a low pressure of no more than 10 PSI (at the air cap), however, with greater volume of air.

High-Early Cement: A portland cement sold as Type III which sets up to its full strength faster than other types.

High-End Health Risk:  Use of the term ‘high-end health risk’ usually relates to the maximally exposed individuals in a population.

High-efficiency Particulate Air (HEPA) Filter:  Throwaway, extended-media, dry type filter used to capture particulates in an air stream; HEPA collection efficiencies are at least 99.97% for 0.3 micrometer diameter particles.

High-Vacuum Pump:  A pump that can create a vacuum in the 1000 to 1 micron range.

Highest Hazard Ratio (HHR):  The highest calculated Hazard Ratio (HR) for any gas, vapour and/or particulate component that poses a respiratory hazard.
Highlights: A light spot, area, or streak on a painted surface.

Highly Toxic: A substance is considered to be highly toxic if: (a) A substance that has a median lethal dose (LD50) of 50 milligrams or less per kilogram of body weight when administered orally to albino rats weighing between 200 and 300 grams each.
(b) A substance that has a median lethal dose (LD50) of 200 milligrams or less per
kilogram of body weight when administered by continuous contact for 24 hours (or less
if death occurs within 24 hours) with the bare skin of albino rabbits weighing between 2
and 3 kilograms each.  (c) A substance that has a median lethal dose (LD50) in air of 200 parts per million by volume or less of gas or vapor, or 2 milligrams per liter or less of mist, fume, or dust, when administered by continuous inhalation for 1 hour (or less if death occurs within 1 hour) to albino rats weighing between 200 and 300 grams each.

HIMA:  Health Industry Manufacturer’s Association. A trade association, whose membership includes both pharmaceutical manufacturers and filter manufacturers, that defines and sets standards governing the validation of filters for sterilizing liquids.

Highway Engine:  Any engine which is designed to transport people or property on a street or highway.

Hinge: A jointed or flexible device that allows the turning or pivoting of a part, such as a door or lid, on a stationary frame.

Hip: The external angle formed by the meeting of two sloping sides of a roof.

Hip Rafter: A rafter that forms the intersection of an external roof angle.

Hip Roof: A roof that rises by inclined planes from all four sides of a building.

Hip Shingles: Shingles used to cover the inclined external angle formed by the intersection of two sloping roof planes.

Histamine: Histamine is a substance your body injects into your bloodstream to help you stay alert. However, it is often triggered by allergens. It causes fluid to be released into the skin (which causes swelling and hives), and when released into the sinuses can cause a runny nose and watery eyes.

Histoplasmosis:  A disease caused by the fungus Histoplasma capsulatum; may infect lungs, skin, mucous membranes, bones, skin, and eyes.

Historic Image Restoration:  The renovation of a building or community that saves and restores the historic image of that place.

Histotoxic Hypoxia:  Hypoxia caused by an inability of the cells in tissue to utilize available oxygen in the blood; for example, arsenic poisoning.

HIV: Human Immunodeficiency Virus. This is the virus that causes AIDS.

HIV/HBV Research Facility: A laboratory producing or using research laboratory scale amounts of HIV or HBV. Research laboratories may produce high concentrations of HIV or HBV but not in the volume found in production facilities

Hives:  Pronunciation (hīvz).  Syn: urticaria Syn: wheal.

Hoistway: A shaftway for the travel of one or more elevators.

Hold-up Volume:  Also called Retention Volume. Volume of fluid retained in a filter and/or housing after purging the assemble with air or suitable gas.

Holding Chamber: (Also: extender, spacer, reservoir) Intended to help medicine from an inhaler to get into the lungs. It holds the spray, making it easier to inhale the medication.

Holdover:  The ability to stay cold after heat removal from the evaporator stops.

Holistic:  A wide-reaching approach to a theory, a task, or a problem that encompasses all the elements of the system because of the interdependency of those elements.

Hollow-Tube Gasket:  A sealing device made of rubber or plastic with tubular cross section.

Home Care Company: Organization that provides many aspects of COPD care in the home, including the use and care of respiratory equipment, teaching, monitoring and review of environment and treatment.

Home Energy Rating Ssystems (HERS):  A nationally recognized energy rating program that gives builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise evaluation of energy losing deficiencies in homes. Builders can use this system to gauge the energy quality in their home and also to have a star rating on their home to compare to other similarly built homes.

Home Heating Index: The number of Btus of energy used by a home divided by its area in square feet, then divided by the number of heating degree days during the time period.

HOME Program: A program created under Title II (the Home Investment Partnership Act) of the National Affordable Housing Act of 1990. Provides funds for states to expand the supply of decent and affordable housing for low-income people. This program can be easily coordinated with a state's WAP efforts.

Home Run (Electrical): The electrical cable that carries power from the main circuit breaker panel to the first electrical box, plug, or switch in the circuit.

HON: Hazardous Organic NESHAPS.

Honeycomb: Areas in a foundation wall where the aggregate (gravel) is visible. Honeycombs can be usually be remedied by applying a thin layer of grout or other cement product over the affected area. Also, a method by which concrete is poured and not puddled or vibrated, allowing the edges to have voids or holes after the forms are removed.

Hoop-wrapped Cylinder:  A composite cylinder that has composite material only onthe cylindrical portion of the aluminum liner, while the crown and base of the liner are left unwrapped.

Horizontal: Parallel to or in the plane of the horizon.

Horizontal Cartridge Unit: A cartridge-type dust collector where the filters are in a horizontal configuration and the contaminated air typically enters the top of the unit and moves in a downward direction.
Horizontal Flow:  Often used in attics/crawl spaces, this furnace takes air from its side, heats it and sends warm air out the other side.

Horizontal Laminar Airflow: An essentially unidirectional airflow with minimum turbulence, leaving a vertically-mounted filter and flowing parallel to the work surface.

Horizontal Laminar Flow Bench: A ventilated cubicle with solid sides having a table-height work surface and unidirectional, minimum turbulence air entering from a vertically mounted high efficiency filter at one side and leaving the cubicle at the opposite (open) side.

Horizontal Recycling:  A recycling system that turns a majority of the original product back into a similar product as the original.

Horizontal Wells:  A well constructed in a horizontally drilled borehole.  A horizontal well can provide a means for greater access to a laterally extensive plume, thus improving contaminant recovery rates. 

Horsepower (HP):  A unit of work equal to 33,000 foot pounds per minute, 550 foot pounds per second, or 746 Watts.

Horsepower Brake (BHP):  The horsepower input to the compressor shaft, or more generally to any driven machine shaft.

Horsepower Gas:  The actual work required to compress and deliver a given gas quantity, including all thermodynamic, leakage and fluid friction losses. It does not include mechanical losses.

Horsepower Ideal:  The horsepower required to isothermally compress the air or gas delivered by the compressor at specified conditions.

Horsepower Indicated:  The horsepower calculated from compressor-indicator diagrams. Applied only to displacement type compressors.

Horsepower Peak:  The maximum power required by a given compressor when operating at a (1.) constant discharge pressure with variable intake pressure, or (2.) constant intake pressure with variable discharge pressure.

Horsepower Theoretical:  The horsepower required to compress adiabatically the air or gas delivered by the compressor through the specified range of pressures.

Hose Bib: An outdoor faucet with hose threads on the spout. Also commonly used to supply washing machines and wash basins.

Host:  An individual who is parasitized or infected by a parasite or pathogen.

Hot Air Furnace:  A heating unit where heat is distributed by means of convection or fans.

Hot cell:  A heavily shielded and environmentally controlled enclosure in which radioactive materials can be handled remotely with manipulators and viewed through shielding windows to limit danger to operating personnel.

Hot Gas:  A term applied to the gas found on the high pressure side of the refrigeration system.

Hot Gas Bypass:  A piping system that by passes hot refrigerant gas from condenser into low-pressure side.

Hot Gas Bypass Valve:  A valve which connects the high pressure side of a compressed air system to the suction side and is adjusted so as to maintain a specific pressure on the suction side by controlled bleeding of hot gas to the suction side.

Hot Gas  Defrost:  Defrosting system in which hot refrigerant gas from the high side is directed through evaporator for short period of time and at predetermined intervals, in order to remove frost from evaporator.

Hot Junction:  That part of thermoelectric circuit which releases heat.

Hot Site:  A computer facility intended to provide emergency processing for damaged systems. Computers and power are already installed and simply waiting for the current data sets to be loaded.
 
“Hot Spot”: (See toxic hot spot.)

Hot Start:  The compressor is started automatically, depending on demand. Control panel is energized with no “pre-start” cycle required, as pre-lubrication pump and buffer (seal) air are always “on.” A state of pre-start exists. Steam turbine compressors are “slow-rolling” to maintain “pre-start” turbine temperatures at an adequate, recommended level. “Heavy” instrumentation and monitoring accessories are recommended.

Hot water Heating System:  A system in which water is circulated through heating coils 

Hot Wire: The wire that carries electrical energy to a receptacle or other device - in contrast to a neutral, which carries electricity away again. Normally the black wire. Also see Ground.

House Dust Mites: In fact it’s not dust that causes the problem, but a tiny creature called the house dust mite, also known as Dermatophagoides pteronyssinus. House dust mites are almost always present in house dust, even in the most clean and tidy homes. In a way, they serve a useful purpose in disposing of skin debris in house dust. Its first name ‘Dermatophagoides’ is simply Latin for ‘skin eating.’  Despite its rather fierce appearance under a microscope, the house dust mite does not bite: it eats the skin flakes that make up a large percentage of house dust. The mite is so small that it is impossible to see with the naked eye.  The house dust mite is 80% water and needs a humid environment in which to thrive. They mostly like damp and dusty spots and these can be found somewhere in virtually every home. The house dust mite or, in fact, its waste products or droppings, are the most common trigger of airborne allergy within the home.

House Pressure: The difference in pressure between the indoors and outdoors measured by a manometer.

Household: Any individual or group of individuals who are living together as one economic unit for whom residential energy is customarily purchased in common or who make undesignated payments for energy in the form of rent.

Housewrap:  Any of the numerous spun-fiber polyolefin rolled sheet goods, or perforated plastic films designed to function as drainage planes.

Housing (Filter):  A device used to hold a filter.

HPL:  High Pressure Laminate. The most common and preferred flooring surface for use in data centers. HPL can be manufactured with conductive carbon molecules embedded in the surface to provide electrical conductivity to dissipate static electricity.

HPLC:  High Pressure Liquid Chromatography allows separation and analysis of very small quantities of complex mixtures with high resolution and great sensitivity. Purpose: identify nature of a compound or measure amount or concentration of a compound.

HR:  See Hazard Ratio.

HRDC:  Human Resources Development Canada.

HSPF:  Heating Seasonal Performance Factor. This rating is used in measuring the heating efficiency of a heat pump. The higher the number the more efficient the heat pump system.

Hub: In plumbing, the enlarged end of a pipe which is made to provide a connection into which the end of the joining pipe will fit.

HUD: U.S. Department of Urban Housing and Development

Human Health Risk:  The likelihood (or probability) that a given exposure or series of exposures may have or will damage the health of individuals experiencing the exposures.

Humidification: The act of moisturizing the air with molecules of water.
Humidifier:  A machine that adds water vapor to the air to increase humidity.

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.

Humidifying/Dehumidifying Effect: Latent heat of water vaporization at the average evaporating temperature times the number of pounds of water evaporated or condensed in watts.
Humidistat:  A humidity-sensing control that cycles the humidifier on and off.

Humidity: The "dampness" of the air expressed either as a subjective sensation or as a physical measure of the water vapour in the air (see relative humidity, water vapour pressure).

Humidity, Absolute:  Weight of water vapor per cubic foot of dry air, expressed as grains of moisture per cubic foot.

Humidity, Relative:  The amount of moisture in the air expressed as a percentage of the maximum amount that the air is capable of holding at a specific temperature.

Humidity Ratio: Same as "absolute humidity." The absolute amount of air's humidity measured in pounds of water vapor per pound of dry air.

Humidity Relative:  The relative humidity of a gas (or air) vapor mixture is the ratio of the partial pressure of the vapor to the vapor saturation pressure at the dry bulb temperature of the mixture.

Humidity Specific:  The weight of water vapor in the air vapor mixture per pound of dry air.

Hurricane Clip: Metal straps that are nailed and secure the roof rafters and trusses to the top horizontal wall plate. Sometimes called a Teco Clip.

Hurricane Ties: Metal fasteners used to secure rafters in structures subject to hurricane winds.

HVAC (heating ventilating and air conditioning): A term generally applied to the hardware or the industry concerned with the supply of environmental control in buildings.

HVAC&R (Heating Ventilating Air Conditioning and Refrigeration):  See “Heating, Ventilating and Air Conditioning.”

HVLP:  In spray painting applications, spray equipment which delivers material at a low pressure of no more than 10 PSI (at the air cap), however, with greater volume of air.

Hybrid Electric Vehicle (HEV): Hybrid electric motor vehicles may operate using both electric and gasoline-powered motors. Emissions from hybrid electric motor vehicles are also substantially lower than conventionally powered motor vehicles. (See also Electric Motor Vehicle.)

Hybrid Heat (also Hybrid System):  Provides energy efficient comfort for moderate heating conditions. Can use either gas or electricity.

Hybrid Solar Heating System: Solar heating system that combines active and passive techniques.

Hybrid System (also Hybrid Heat):  Provides energy efficient comfort for moderate heating conditions. Can use either gas or electricity.

Hydraulic Conductivity:  A coefficient of proportionality describing the rate at which water can move through a permeable medium.

Hydraulic Gradient:  The change in total head [pressure] with a change in distance in a given direction.  The [down gradient] direction is that which yields a maximum rate of decrease in head.  [In an unconfined aquifer, the hydraulic gradient describes the slope of the water table.]

Hydrocarbons: In order to understand how crude oil and natural gas can be made up of all of these parts at the same, it helps to know that fossil fuels are composed of hydrocarbons. Hydrocarbons (CnH2n+2) are molecules which contain many carbon (C) and hydrogen (H) atoms linked together. Not all hydrocarbons are the same in shape, size and weight - some are short chains such as methane (CH4) as is the case for natural gas, and some form rings such as benzene (C6H6). Gasoline is really a collection of a specific range of hydrocarbon sizes (around C9H20) which are smaller than the hydrocarbons that make up diesel (around C14H30). (also see boiling points of hydrocarbons)

Hydroelectric Plant: A plant in which the turbine generators are driven by falling water.

Hydroelectric Power:  The use of artificial or natural waterfalls to generate electricity.

Hydrogen Chlorofluorocarbons (HCFC):  Chemical species slated to replace CFCs in the near future.

Hydrogen Sulfide (H2S): Gas emitted during organic decomposition. Also a by-product of oil refining and burning. Smells like rotten eggs and, in heavy concentration, can kill or cause illness.

Hydrogeology:  The geology of ground water, with particular emphasis on the chemical composition and movement of the water.

Hydrological Cycle:  The natural cycle of water from evaporation, transportation in the atmosphere, condensation (rain), and the flow back to the ocean.

Hydrology:  Science dealing with the properties, distribution, and circulation of natural water systems.

Hydronic: A heating system that uses hot water or steam as the heat-transfer fluid.

Hydronic Heating:  A radiant heat system that distributes hot water through pipes, either to radiators or through a thermal mass floor. The floor absorbs heat and evenly radiates it to the living space.

Hydrophilic: Having an affinity for water and aqueous solutions.

 Hydropower (hydroelectricity):  Clean energy technology that uses moving water to produce electricity. Water flows through a hydraulic turbine, which spins and then rotates generators and converts rotational energy into electricity.

Hydrostatic Test:  A calibrated expansion pressure test of the structural integrity of cylinders using accepted test procedures; refer to CSA Z94.4 for the definition.

Hydro-Electric Elevator: An elevator where liquid is pumped under pressure directly into the cylinder by a pump driven by an electric motor without an accumulator between the pump and cylinder.

Hygroscopic Cells:  Are any material with an affinity for moisture. These analyzers use sensing elements that contain moisture adsorbing material. A change in the moisture content of the element is detected by an electric network and is used as a measurement of dew point

Hygroscopic Dust: Dry particles which attract and retain moisture, such as cement, plaster, cocoa, etc.

Hygrostat:  See “Humidistat.”

HyperHEPA Technology:  This is an IQAir trade name for a patented filtration system used in certain models that filters down to 0.003 microns with a guaranteed minimum efficiency of 99%. This system is individually tested and certified using EN 1822 standards.

Hyperresponsiveness: The “twitchiness” of the airways in asthmatics, resulting in excessive reaction to substances, smells, and activity.

Hypersensitivity:   The immune system’s exaggerated response to an allergen.

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 pneumoni are caused by the inhalation of organic dusts.

Hyperventilation: Excessive rate and depth of breathing.

Hypha:  (pl. hyphae) A branching tubular structure that forms the vegetative body of a growing filamentous fungus.

Hyphae:  The principal element of the growing or vegetative form of a mold (filamentous fungi), characterized by branching tube-like growth.

Hypoallergenic:  Hypoallergenic means that a substance has little likelihood of causing an allergic response. Note that it doesn’t mean that the substance is allergy free. However, it does mean that your chances of reacting to the substance are usually less.

Hypophysectomy:  Surgical removal of the pituitary (also know as the hypophysis) gland at the base of the brain.

Hypotension:  Low blood pressure.

Hypothalamic-Pituitary-Adrenal (HPA) Axis:  The HPA axis refers to the hypothalamic-pituitary-adrenocortical axis. It is the internal neuroendocrine system that responds to stress and results in production of corticosteroid hormones that affect the brain, the cardiovascular system, and other systems in getting the body ready for what is known as the “fight or flight” mechanism.

Hypoxia:  Any condition in which there is an inadequate supply of oxygen in tissues of the human body; see also anaemic hypoxia, arterial hypoxia, histotoxic hypoxia.

Hypoxia, Hypoxemia:  A state of reduced oxygen in the blood or organs or tissues.