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Absorbtance: The proportion of incident heat radiation that enters a body and raises its temperature, expressed as a decimal fraction of one.
Absorption cycle: A heat pump process in which the hygroscopic property of a concentrated salt solution is used to evaporate liquid from a vessel and thereby to cool the liquid.
Abutment joint: A joint that allows for relative movement between dissimilar materials that meet at the joint.
AC: See Alternating current.
Acoustical privacy: A state in which intelligible sound is not transmitted between users of a building.
Acoustic tiles: Small units of ceiling finish material that absorb a major %age of incident sound.
Activated charcoal filtration: The cleansing of air or water by passing it through a volume of charcoal that is specially produced to have a large ratio of surface area to volume.
Active: Adjective for any system that requires the application of energy from an external source for its function, as contrasted with a passive system, which uses only ambient flows of energy.
Adiabatic: Changing volume without the loss or gain of heat.
Aerobic: Taking place in the presence of oxygen.
Air barrier: A sheet material or coating that is designed to pre vent the passage of air through the enclosure of a building.
Air chamber: A short, capped extension of a plumbing supply line that contains air that acts as a cushion to absorb the shocks that would otherwise cause water hammer.
Air, combustion: Air whose oxygen content is used to sustain a flame.
Air-inflated structure: A structure made up of one or more tubes of thin, airtight material which are stiffened against buckling by being inflated with air.
Air-supported structure: A structure made up of a thin, airtight material that is supported by a slight air pressure in the inhabited space that it shelters.
Allowable stress: See Stress, allowable.
Alternating current (AC): Electricity delivered in the form of current that reverses polarity at rapid, regular intervals, usually 50 or 6o times per second.
Ambient: Occurring naturally in the environment.
Anaerobic: Taking place without the presence of oxygen.
Anticlastic: Saddle-shaped, curved positively along one principle axis and negatively along the other.
Aqueduct: A large pipe or channel that transports water from a distant source to a city.
Arc fault circuit interrupter: A device that shuts off electricity to any circuit on which a spark or arc is being generated.
Arch: A structural device, usually concave on its underside, that translates applied loads, usually vertical, into inclined forces that flow along the axis of the device.
Area of refuge: An area within a building that is securely protected against heat, smoke, and flames in case of fire.
Artesian well: A vertical hole in the ground, dug or drilled, that fills with water because of subterranean pressure.
Artificial lighting: Lighting other than day lighting, usually electric lighting.
Atmospheric inversion: A stagnant layer of cold air near the ground.
Atrium: An interior courtyard in a building, often covered with a skylight.
Automatic sprinkler system: See Sprinkler system, automatic.
Autumnal equinox: The day in late September when the north-south axis of the earth lies perpendicular to the sun’s rays. Day and night have the same length on the autumnal and vernal equinoxes.
Awning: A sloping, roof-like cover projecting outward over a window or door.
Awning window: An operating window whose sash is hinged along a horizontal axis on or near its top edge.
Backer rod: A ropelike cylinder of soft plastic foam that is pressed into a joint to limit the depth to which a mastic sealant material will penetrate.
Ballast, fluorescent: An electrical assembly in a fluorescent light fixture that serves both to provide the high voltage necessary to start the lamp and to limit the current to the lamp once it's started.
Base plate: A steel slab that serves to spread the heavy load from a steel column over an area of concrete large enough that the allowable stress of the concrete is not exceeded.
Beam: A solid structural member that resists transverse bending forces by means of a latticelike pattern of internal forces of tension and compression.
Bearing wall: A vertical, planar building element that supports superimposed gravity loads.
Bioremediation: Using life processes in plants to purify sewage and other toxic wastes.
Brittle: Having little tensile strength and a tendency to break without warning.
Builder, custom: A person or company that builds buildings to order.
Builder, speculative: A person or company that builds buildings before their buyers are known.
Bus bar: A rectangular strip of highly conductive metal, usually copper or aluminum, used to carry large quantities of electricity to points of distribution in a building.
Buttress: A structural device made of concrete, brickwork, or stonework in which the dead weight of the material com bines with the angular thrusts of vaults or arches to produce a resultant force whose line of action falls safely within the foundations of a building.
Buttress, engaged: A buttress that is integral with the walls of the building.
Buttress, Hying: A buttress that uses inclined arches to reach across an intervening space such as a church aisle to brace the central portion of the building.
Building separation joint: A planar discontinuity through a building to divide the building into smaller buildings that are able to move without distress.
Caisson: A vertical, columnar foundation element made of concrete cast into a hole drilled in the ground so that it rests on a firm layer of soil or rock at some distance below the surface. Also the cylindrical steel shell used to prevent the drilled hole from collapsing.
Camber: An upward curvature built into a beam so that the beam will be flat when it's fully loaded.
Cant strip: A beveled piece of material that prevents a sharp, 90-degree crease in a roofing membrane where it goes from a horizontal roof deck to a vertical parapet wall or perimeter curb.
Cantilever: The portion of a beam or truss that projects beyond its nearest point of support.
Capillary action: The drawing of water through a fine crack or small hole by the combined forces of cohesion in water and adhesion between water and the material through which it's drawn.
Capillary break: An intentional widening of a crack or hole so that a drop of water can't bridge across it and pass through by capillary action.
Casement window: An opening window that is hinged on a vertical axis at or near a side jamb.
Catchment area: An area of ground or roof used to collect rainwater.
Catenary: The curve of a cable or chain that hangs freely under its own weight.
CAV: See Constant air volume system.
Cavity wall: A masonry wall that contains a vertical, planar airspace that is intended to eliminate water leakage through the wall and , incidentally, to reduce heat flow through the wall.
Cement, portland: A dry, gray powder that is mixed with water to form a binder for concrete. Not to be confused with concrete—there is no such thing as a cement sidewalk or a cement slab.
Centering: A structure used temporarily to support an arch, dome, or vault during its construction.
Cesspool: A pit in the ground used to disperse sewage into the ground without first digesting it; generally illegal.
Chair: A device used to support steel reinforcing bars until concrete has been poured around them and cured.
Chase: A hollow space provided in a building to house a run of pipes, wires, and /or ducts.
Chiller: A machine that produces cold water for cooling a building.
Chimney: A vertical tube to conduct smoke out of a building.
Chord: The top or bottom elements in a truss.
Circuit: A single run of electrical wiring that serves a limited number of fixtures and /or receptacles.
Circuit breaker: A device that shuts off electrical flow automatically if the capacity of an electrical circuit is exceeded, thus preventing damage to the circuit and building.
Cistern: A vessel for the storage of water.
Clerestory: A vertical window placed at the junction of two roof planes that meet at different levels.
Cloud gel: An extremely low-density, transparent solid that can be used as an insulating material between panes of glass in a multiple glazing assembly.
Column: A vertical, linear element of structure that supports primarily vertical loads.
Combustion air: See Air, combustion.
Compartmentation: The partitioning of a building into smaller units by means of fire-resistant walls and floors to restrict the spread of fire.
Compensated foundation: See Foundation, floating.
Composite: Made of two or more materials that work together.
Compost: The product of fermentation of organic waste materials, used to modify soil to increase its agricultural productivity.
Compression: A squeezing together.
Compression cycle: A heat pump process in which a working fluid is compressed and cooled, then allowed to expand and absorb heat.
Compressive stress: The intensity of a squeezing action, expressed in units of force per unit area.
Concrete: A rocklike material made by mixing together gravel or crushed stone, sand, and a binder of portland cement and water.
Concrete, air-entrained: Concrete that contains microscopic air bubbles. Air-entrained concrete flows more freely when freshly mixed and is much more resistant to freeze-thaw damage than ordinary concrete.
Condensate: A liquid created by condensing a gas, such as the liquid water produced when moist air contacts a cold surface.
Condensation: The changing of a material from a gaseous state to a liquid state.
Condenser: A component of a steam-driven power plant in which spent steam is cooled to return it to a liquid state.
Conduction: The passage of heat or electricity through a solid material.
Conduit: A plastic or metal tube through which electric wires pass.
Constant air volume system (CAV): A heating and /or cooling system in which the rate of air circulation is constant, but the temperature of the air varies.
Continuity: In a structure, the property of having structural elements joined rigidly together so that they act as a single unit.
Control joint: An intentional, usually straight-line crack in a surface of material that tends to shrink, used to avoid random cracking in the material.
Convection: Circulation that is powered by the difference in density between warm and cool air or water.
Convective: Using convection as a mode of heat transfer. Convector: A device for heating air by means of steam or hot water that circulates through metal tubing that is exposed to the air. A convector usually has many metallic fins attached to the tubing to increase its surface area. The fin-tube assembly is usually housed in a sheet-metal enclosure with openings for the circulation of air.
Cooling, radiational: The cooling of the earth at night by direct radiation of terrestrial heat into the blackness of space.
Corbel: A masonry structural device in which each brick or stone projects slightly over the one below it.
Crawl space: A continuous access area, not tall enough to stand in, beneath the ground floor of a building.
Creep: The long-term shortening of concrete under compressive stress.
Cross connection: A faulty plumbing installation that allows sewage or contaminated water to be drawn into water supply pipes if water pressure in the pipes should fail.
Crown: A slight upward curvature in the paving of a road; a curvature in a piece of lumber.
Curtain board: A noncombustible sheet material that hangs from the ceiling of an industrial building to help restrict the spread of fire through the building.