Technical Glossary - H

Habitat: The place where a population (e.g. human, animal, plant, microorganism) lives and its surroundings, both living and non-living.

Habitat Indicator: A physical attribute of the environment measured to characterize conditions necessary to support an organism, population, or community in the absence of pollutants; e.g. salinity of estuarine waters or substrate type in streams or lakes.

Half-Life: 1. The time required for a pollutant to lose one-half of its original concentration, example, the biochemical half-life of DDT in the environment is 15 years. 2. The time required for half of the atoms of a radioactive element to undergo self-transmutation or decay (half-life of radium is 1620 years). 3. The time required for the elimination of half a total dose from the body.

Halogen: A type of incandescent lamp with higher energy-efficiency than standard ones.

Bromine-containing compounds with long atmospheric lifetimes whose breakdown in the stratosphere causes depletion of ozone. Halons are used in firefighting.

Hammer Mill: A high-speed machine that uses hammers and cutters to crush, grind, chip, or shred solid waste.

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

Hauler: Garbage Collection Company that offers complete refuse removal service; many will also collect recyclables.

Hauling Fee:
A fee charged to roll-off customers calculated from the amount of time it takes to pick up their roll-off container or compactor, dispose of the waste and return it to the customer.

1. The potential for radiation, a chemical or other pollutant to cause human illness or injury. 2. In the pesticide program, the inherent toxicity of a compound. Hazard identification of a given substances is an informed judgment based on verifiable toxicity data from animal models or human studies.

Hazard Assessment:
Evaluating the effects of a stressor or determining a margin of safety for an organism by comparing the concentration which causes toxic effects with an estimate of exposure to the organism.

Hazard Evaluation:
A component of risk evaluation that involves gathering and evaluating data on the types of health injuries or diseases that may be produced by a chemical and on the conditions of exposure under which such health effects are produced.

Hazard Identification: Determining if a chemical or a microbe can cause adverse health effects in humans and what those effects might be.

Hazard Quotient:
The ratio of estimated site-specific exposure to a single chemical from a site over a specified period to the estimated daily exposure level, at which no adverse health effects are likely to occur.

Hazard Ratio: A term used to compare an animal's daily dietary intake of a pesticide to its LD 50 value. A ratio greater than 1.0 indicates that the animal is likely to consume a dose amount which would kill 50 percent of animals of the same species.

Hazardous Air Pollutants:
Air pollutants which are not covered by ambient air quality standards but which, as defined in the Clean Air Act, may present a threat of adverse human health effects or adverse environmental effects. Such pollutants include asbestos, beryllium, mercury, benzene, coke oven emissions, radio-nuclides, and vinyl chloride.

Hazardous Chemical:
An EPA designation for any hazardous material requiring an MSDS under OSHA's Hazard Communication Standard. Such substances are capable of producing fires and explosions or adverse health effects like cancer and dermatitis. Hazardous chemicals are distinct from hazardous waste.

Hazardous Substance:
1. Any material that poses a threat to human health and/or the environment. Typical hazardous substances are toxic, corrosive, ignitable, explosive, or chemically reactive. 2. Any substance designated by EPA to be reported if a designated quantity of the substance is spilled in the waters of the United States or is otherwise released into the environment.

Hazardous Waste:
By-products of society that can pose a substantial or potential hazard to human health or the environment when improperly managed. Possesses at least one of four characteristics (ignitability, corrosivity, reactivity, or toxicity).

Hazardous Waste: Waste that is designated such by regulatory agencies either because it has elevated levels of hazardous chemicals or materials, because it exhibits a potentially dangerous characteristic (e.g., ignitable, corrosive, etc.) or because the material belongs to a general family of materials which have been deemed hazardous by regulatory agencies. Waste, as defined by the Resource Conservation and Recovery Act that is reactive, toxic, corrosive, or otherwise dangerous to living things and/or the environment.

Hazardous Waste Landfill:
An excavated or engineered site where hazardous waste is deposited and covered.

Hazardous Waste Minimization:
Reducing the amount of toxicity or waste produced by a facility via source reduction or environmentally sound recycling.

Hazards Analysis: Procedures used to (1) identify potential sources of release of hazardous materials from fixed facilities or transportation accidents; (2) determine the vulnerability of a geographical area to a release of hazardous materials; and (3) compare hazards to determine which present greater or lesser risks to a community.

Hazards Identification:
Providing information on which facilities have extremely hazardous substances, what those chemicals are, how much there is at each facility, how the chemicals are stored, and whether they are used at high temperatures.

H-Coal Process:
A means of making coal cleaner so it will produce less ash and few sulfur emissions.

The vapor mixture trapped above a solid or liquid in a sealed vessel.

Heat Balance: The outdoor temperature at which a building's internal heat gain (from people, lights, and machines) is equal to the heat loss through windows, roof, and walls.

Heat Capacity:
The amount of heat necessary to raise the temperature of a given mass one degree. Heat capacity may be calculated by multiplying the mass by the specific heat.

Heat Engine: An engine that converts heat to mechanical energy.

Heat Gain: - an increase in the amount of heat contained in a space, resulting from direct solar radiation, heat flow through walls, windows, and other building surfaces, and the heat given off by people, lights, equipment, and other sources.

Heat Island Effect:
A "dome" of elevated temperatures over an urban area caused by structural and pavement heat fluxes, and pollutant emissions.

Heat Loss: A decrease in the amount of heat contained in a space, resulting from heat flow through walls, windows, roof and other building surfaces and from ex-filtration of warm air.

Heat Pump: An air-conditioning unit which is capable of heating by refrigeration, transferring heat from one (often cooler) medium to another (often warmer) medium, and which may or may not include a capability for cooling. This reverse-cycle air conditioner usually provides cooling in summer and heating in winter.

Heat Pump:
An electric device with both heating and cooling capabilities. It extracts heat from one medium at a lower (the heat source) temperature and transfers it to another at a higher temperature (the heat sink), thereby cooling the first and warming the second.

Heat Rate:
A number that tells how efficient a fuel-burning power plant is. The heat rate equals the Btu content of the fuel input divided by the kilowatt-hours of power output. Energy input per unit of time usually expressed in kWh\h or BTU\h

Heat Storm:
Heat storms occur when temperatures exceed 100 degrees Fahrenheit over a large area for three days in a row. Normal hot temperatures cause electricity demand to increase during the peak summertime hours of 4 to 7 p.m. when air conditioners are straining to overcome the heat. If a hot spell extends to three days or more, however, nighttime temperatures do not cool down, and the thermal mass in homes and buildings retains the heat from previous days. This heat build-up causes air conditioners to turn on earlier and to stay on later in the day. As a result, available electricity supplies are challenged during a higher, wider peak electricity consumption period.

Heat Transfer: Flow of heat energy induced by a temperature difference. Heat flow through a building envelope typically flows from a heated or hot area to a cooled or cold area.

Heating Degree Day:
A unit that measures the space heating needs during a given period of time.

Heating Load: The rate at which heat must be added to space in order to maintain the desired temperature within the space.

Heating Seasonal Performance Factor: A representation of the total heating output of a central air-conditioning heat pump in Btu’s during its normal usage period for heating, divided by the total electrical energy input in watt-hours during the same period.

Heating Value: The amount of heat produced by the complete combustion of a given amount of fuel.

Heavy Metals: Metallic elements with high atomic weights; (e.g. mercury, chromium, cadmium, arsenic, and lead); can damage living things at low concentrations and tend to accumulate in the food chain.

Heavy Water: A type of hydrogen atom that may be used as fuel for fusion power plants. Also called DEUTERIUM, it is found in abundance in the seas.

Hedging Contracts: Contracts which establish future prices and quantities of electricity independent of the short-term market. Derivatives may be used for this purpose. HELIOCHEMICAL - Using solar radiation to cause chemical reactions.

A process that uses the sun's rays to produce heat.

Heptachlor: An insecticide that was banned in some food products in 1975 and in all of them 1978. It was allowed for use in seed treatment until 1983. More recently it was found in milk and other dairy products in Arkansas and Missouri where dairy cattle were illegally fed treated seed.

Herbicide: A chemical pesticide designed to control or destroy plants, weeds, or grasses.

Herbivore: An animal that feeds on plants.

Hertz: A unit of electromagnetic wave frequency that is equal to one cycle per second. - It is named after Henrich R. Hertz.

Heterotrophic Organisms: Species that are dependent on organic matter for food.

High End Exposure (dose) Estimate:
An estimate of exposure or dose level received anyone in a defined population that is greater than the 90th percentile of all individuals in that population, but less than the exposure at the highest percentile in that population. A high-end risk descriptor is an estimate of the risk level for such individuals. Note that risk is based on a combination of exposure and susceptibility to the stressor.

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

High-Density Polyethylene:
A material used to make plastic bottles and other products that produce toxic fumes when burned.

High-Level Nuclear Waste Facility: Plant designed to handle disposal of used nuclear fuel, high-level radioactive waste, and plutonium waste.

High-Level Radioactive Waste (HLRW):
Waste generated in core fuel of a nuclear reactor, found at nuclear reactors or by nuclear fuel reprocessing; is a serious threat to anyone who comes near the waste without shielding.

High-Line Jumpers: Pipes or hoses connected to fire hydrants and laid on top of the ground to provide emergency water service for an isolated portion of a distribution system.

High-Risk Community:
A community located within the vicinity of numerous sites of facilities or other potential sources of environmental exposure/health hazards which may result in high levels of exposure to contaminants or pollutants.

High-Sulfur Coal: Coal whose weight is more than one percent sulfur.

High-to-Low-Dose Extrapolation:
The process of prediction of low exposure risk to humans and animals from the measured high-exposure-high-risk data involving laboratory animals.

Holding Pond:
A pond or reservoir, usually made of earth, built to store polluted runoff.

Holding Time: The maximum amount of time a sample may be stored before analysis.

Hollow Stem Auger Drilling:
Conventional drilling method that uses augurs to penetrate the soil. As the augers are rotated, soil cuttings are conveyed to the ground surface via augur spirals. DP tools can be used inside the hollow augers.

Homogeneous Area: In accordance with Asbestos Hazard and Emergency Response Act (AHERA) definitions, an area of surfacing materials, thermal surface insulation, or miscellaneous material that is uniform in color and texture.

Hood Capture Efficiency:
Ratio of the emissions captured by a hood and directed into a control or disposal device, expressed as a percent of all emissions.

Hopper: The hopper is the part of a garbage truck or compactor where trash is emptied before compaction into the container.

Horsepower (HP): A unit for measuring the rate of doing work. One horsepower equals about three-fourths of a kilowatt (745.7 watts).

Host: 1. In genetics, the organism, typically a bacterium, into which a gene from another organism is transplanted. 2. In medicine, an animal infected or parasitized by another organism.

Household Hazardous Waste:
Hazardous products used and disposed of by residential as opposed to industrial consumers. Includes paints, stains, varnishes, solvents, pesticides, and other materials or products containing volatile chemicals that can catch fire, react or explode, or that are corrosive or toxic.

Household Waste (Domestic Waste):
Solid waste, composed of garbage and rubbish, which normally originates in a private home or apartment house. Domestic waste may contain a significant amount of toxic or hazardous waste.

Hot (Colloquial):
The word is sometimes used to describe electric utility lines that are carrying electric currently. It also is used to refer to anything that is highly radioactive.

Hot Dry Rock: A geothermal resource created when impermeable, subsurface rock structures, typically granite rock 15,000 feet or more below the earth's surface, are heated by geothermal energy. The resource is being investigated as a source of energy production.

HSPF (Heating Seasonal Performance Factor): A measure of heating efficiency for the total heating output of a central air-conditioning heat pump. Efficiency is derived according to federal test methods by using the total Btu’s during its normal usage period for heating divided by the total electrical energy input in watt-hours during the same period.

Human Equivalent Dose:
A dose which, when administered to humans, produces an effect equal to that produced by a dose in animals.

Human Exposure Evaluation:
Describing the nature and size of the population exposed to a substance and the magnitude and duration of their exposure.

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

Humus: The end product of composting, also called compost.

HVAC (Heating Ventilation and Air Conditioning):
A system that provides heating, ventilation and/or cooling within or associated with a building.

Hybrid Vehicle: Usually a hybrid EV, a vehicle that employs a combustion engine system together with an electric propulsion system. Hybrid technologies expand the usable range of EVs beyond what an all-electric-vehicle can achieve with batteries only.

Hydraulic Conductivity:
The rate at which water can move through a permeable medium. (i.e. the coefficient of permeability.)

Hydraulic Gradient:
In general, the direction of groundwater flows due to changes in the depth of the water table.

Hydrocarbons (HC): Chemical compounds that consist entirely of carbon and hydrogen. Oil and natural gas are hydrocarbons.

Hydroelectric Power: Electricity produced by falling water that turns a turbine generator. It is also referred to as HYDRO.

Hydroelectric Spill Generation: Hydroelectric generation in existence prior to January 1, 1998, that has no storage capacity and that, if backed down, would spill. This term also refers to a hydro resource that has exceeded or has inadequate storage capacity and is spilling, even though generators are operating at full capacity.

Hydrochloroflurocarbon (HCFC):
A compound that consists of hydrogen, chlorine, fluorine and carbon.

Hydrofluorocarbon (HFC): A compound that consists of hydrogen, fluorine, and carbon.

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

Hydrogeological Cycle: The natural process recycling water from the atmosphere down to (and through) the earth and back to the atmosphere again.

The geology of ground water, with particular emphasis on the chemistry and movement of water.

Hydrologic Cycle:
Movement or exchange of water between the atmosphere and earth.

The science dealing with the properties, distribution, and circulation of water.

Hydrolysis: The decomposition of organic compounds by interaction with water.

Hydronic: A ventilation system using heated or cooled water pumped through a building.

Hydronic Heating: A system that heats a space using hot water which may be circulated through a convection or fan coil system or through a radiant baseboard or floor system.

Having a strong affinity for water.

Hydrophobic: Having a strong aversion to water.

A water system, usually small, in which a water pump is automatically controlled by the pressure in a compressed air tank.

Hydrothermal Systems:
Underground reservoirs that produce either dry steam or a mixture of steam and water.

: A process that uses water to help produce pipeline-quality gas from coal.

Hypersensitivity Diseases:
Diseases characterized by allergic responses to pollutants; diseases most clearly associated with indoor air quality are asthma, rhinitis, and pneumonic hypersensitivity.

Bottom waters of a thermally stratified lake. The hypolimnion of a eutrophic lake is usually low or lacking in oxygen.

Hypoxia/Hypoxic Waters:
Waters with dissolved oxygen concentrations of less than 2 ppm, the level generally accepted as the minimum required for most marine life to survive and reproduce.