OSHA Construction eTool: Glossary
U.S. Department of Labor,
Occupational Safety & Health Administration,
Constitution Avenue, NW,
Washington, DC 20210, U.S.A.
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American National Standards Institute.
Sanctioned, endorsed, accredited, certified, or accepted
as satisfactory by a duly constituted and nationally
recognized authority or agency.
A person approved or assigned by the employer to perform
a specific type of duty or duties or to be at a specific
location or locations at the jobsite. See Designated
Equipment is "certified" if it (a) has been tested
and found by a nationally recognized testing laboratory
to meet nationally recognized standards or to be safe
for use in a specified manner; or (b) is of a kind
whose production is periodically inspected by a nationally
recognized testing laboratory; and (c) it bears a
label, tag, or other record of certification.
One who is capable of identifying existing and predictable
hazards in the surroundings, or working conditions
which are unsanitary, hazardous, or dangerous to employees,
and who has authorization to take prompt corrective
measures to eliminate them.
Work for construction, alteration, and/or repair,
including painting and decorating.
Any characteristic or condition which tends to weaken
or reduce the strength of the tool, object, or structure
of which it is a part.
Every laborer or mechanic, regardless of the contractual
relationship which may be alleged to exist between
the laborer and mechanic and the contractor or subcontractor
who engaged him. "Laborer" generally means one who
performs manual labor or who labors at an occupation
requiring physical strength; "mechanic" generally
means a worker skilled with tools.
Contractor or subcontractor.
Alternative designs, materials, or methods to protect
against a hazard which the employer can demonstrate
will provide an equal or greater degree of safety
for employees than the methods, materials or designs
specified in the standard.
A substance which, by reason of being explosive, flammable,
poisonous, corrosive, oxidizing, irritating, or otherwise
harmful, is likely to cause death or injury.
One who, by possession of a recognized degree, certificate,
or professional standing, or who by extensive knowledge,
training, and experience, has successfully demonstrated
his ability to solve or resolve problems relating
to the subject matter, the work, or the project.
The ratio of the ultimate breaking strength of a member
or piece of material or equipment to the actual working
stress or safe load when in use.
Society of Automotive Engineers.
That which fits and has the qualities or qualifications
to meet a given purpose, occasion, condition, function,
The unit by which the flow of current through a conductor
A discharge of electricity through a gas, such as
The path along which electric current flows from start
to finish is called a circuit. The circuit includes
the generator or battery which starts the current,
the wires, and any electrical device that the current
operates. If any part of the circuit is removed, the
current cannot flow. The circuit is then broken or
open. Because electric current seeks to complete its
circuit, it will travel along any path that is presented
(path of least resistance), which is why humans are
at risk of electrocution when they handle damaged
tools or cords, or contact un-insulated wires. In
effect, they become part of the circuit.
A protective device which automatically opens, or
trips, a circuit, without damage to itself, when the
current exceeds a predetermined level.
A substance or body that allows a current of electricity
to pass continuously along it. Metals, such as copper
or aluminum, are good conductors. In a circuit, current-carrying
wires are termed "conductors", as in a flexible cord.
The flow of electrons through a conductor, measured
in amperes (amps). If the current flows back and forth
through a conductor, it is called alternating current
(AC). If the current flows in one direction only,
as in a car battery, it is called direct current (DC).
AC is most widely used because it is possible to increase
("step up") or decrease ("step down") the current
through a transformer. For example, when current from
an overhead power line is run through a pole-mounted
transformer, it can be stepped down to normal household
current. Also, alternating current can travel enormous
distances with little loss of voltage, or power.
When alternating current flows back and forth through
a conductor, it is said to cycle. In each cycle, the
electrons flow first in one direction, then the other.
In the United States, the normal rate for power transmission
is 60 cycles per second, or 60 Hertz (Hz).
To free from any electric connection and/or electric
The flow of an atom's electrons through a conductor.
A conductor used to establish electrical contact with
a nonmetallic part of a circuit.
To direct electric current through a conductor. Power
lines and wires can be intentionally energized (or
de-energized) to carry current to an electrical device.
But conductive sur which are unintentionally energized,
like the metal case of a tool, the metal housing of
a circuit box, or a metal object such as an aluminum
ladder, present a danger of electrocution.
An insulation failure that exposes electrified conductors,
causing current to leak and possibly resulting in
A protective device which allows a piece of metal
to become part of a circuit. The metal melts under
heat created by excessive current, thereby interrupting
the circuit and preventing the flow of electricity
from exceeding the circuit's current-carrying capacity.
GFCI (Ground-fault circuit interrupter)
A device that detects an insulation failure by comparing
the amount of current flowing to electrical equipment
with the amount of current returning from the equipment.
Whenever the difference is greater than 5 milliamps,
the GFCI trips and thereby interrupts the flow of
A conducting connection, intentional or unintentional,
between an electrical circuit or equipment and the
earth, or to some conducting body that serves in place
of the earth.
A fault, or insulation failure, in the wire used to
create a path to ground.
To prevent the buildup of hazardous voltages in a
circuit by creating a low-resistance path to earth
or some other ground plane.
Placement of live parts of electrical equipment where
they cannot accidentally be contacted, such as in
a vault, behind a shield, or on a raised platform,
to which only qualified persons have access.
Opposition to the flow of alternating (AC) electric
current. See Resistance.
Non-conductive materials used to cover or surround
a conductor, permitting it to be handled without danger
of electric shock.
Any material, such as glass or rubber, that prevents
the flow of electric current.
One thousand watts.
To lock a switch in the "off" position by means of
a padlock, or to lock electrified equipment behind
a locked door, to which only qualified persons have
Low resistance to A/C current.
A unit of measurement equaling one thousandth (1/1000)
of an ampere.
The unit by which resistance to electrical current
is measured. From Ohm's Law (Current=Voltage/Resistance,
or in other words, Current=Voltage/Ohms), a mathematical
expression of the relationship between these three
Any current in excess of the rated capacity of equipment
or of a conductor.
In AC power systems, load current is drawn from a
voltage source which typically takes the form of a
sine wave. Ideally, the current drawn by the loads
in the system is also a sine wave. With a simple,
resistive load such as a light bulb, the current sine
wave is always aligned with the voltage sine wave.
This is called single-phase. A single-phase power
system normally uses three wires, called hot, neutral,
and ground, and the voltage is typically 120/240.
Most home and office outlets operate in this manner.
With some loads, such as motors, and in high voltage
systems, the current sine wave is purposely delayed
and lags behind the voltage sine wave. The amount
of this lag is expressed in degrees and is called
a phase difference. A common example is three-phase
power, where the system has three "hot" wires, each
120 degrees out of phase with each other.
A device to which the conductors of a cord are attached,
which is used to connect to the conductors permanently
attached to a receptacle.
The relationship between poles of positive and negative
charge, particularly with regard to wiring of conductors
where the ungrounded (hot) conductor and grounded
(neutral) conductor form a circuit.
One familiar with the construction and operation of
the equipment and the hazards involved.
A channel designed expressly for holding wires, cables,
or busbars, including conduit, tubing, wireways, busways,
gutters, or moldings.
The stated operating limit of a piece of equipment,
expressed in a unit of measure such as volts or watts.
A device, such as a jack or an outlet, to which conductors
are attached, and where a plug makes contact with
a source of electric current.
Anything that impedes the flow of electricity, particularly
in direct (DC) current. Resistance is measured in
To identify electric equipment by class, group, and
the temperature range for which it is approved.
The unit by which electrical force or pressure is
The fundamental force or pressure that causes electricity
to flow through a conductor. Measured in volts.
The unit by which electric energy, or the ability
of electricity to do work, is measured. A thousand
watts, or one kilowatt, equals 1.34 horsepower.
Adjustable suspension scaffold
A suspension scaffold equipped with a hoist that can
be operated by an employee on the scaffold.
A secure point of attachment for lifelines, lanyards,
or deceleration devices.
A strap with means both for securing it about the
waist and for attaching it to a lanyard, lifeline,
or deceleration device. (As of January 1, 1998 body
belts are not acceptable as part of a personal
fall arrest system.)
Straps which may be secured about the employee in
a manner that will distribute the fall arrest forces
over at least the thighs, pelvis, waist, chest, and
shoulders, with means for attaching it to other components
of a personal fall arrest system.
A rigid connection that holds one scaffold member
in a fixed position with respect to another member,
or to a building or structure. See Cross
A structural block used at the end of a platform to
prevent the platform from slipping off its supports.
Cleats are also used to provide footing on sloped
surfaces such as crawling boards.
A device that is used to couple (connect) parts of
the personal fall arrest system and positioning device
systems together. It may be an independent component
of the system, such as a carabiner, or it may be an
integral component of part of the system, such as
a buckle or D-ring sewn into a body belt or body harness,
or a snaphook spliced or sewn to a lanyard or self-retracting
Controlled access zone (CAZ)
An area in which certain work (e.g., overhand bricklaying)
may take place without guardrail systems, personal
fall arrest systems, or safety net systems, and access
to the zone is controlled.
Two braces which cross each other in the form of an
Any mechanism, such as a rope grab, rip-stitch lanyard,
specially-woven lanyard, tearing or deforming lanyard,
automatic self-retracting lifeline/lanyard, etc.,
which serves to dissipate a substantial amount of
energy during a fall arrest, or otherwise limit the
energy imposed on an employee during fall arrest.
The additional vertical distance a falling employee
travels, excluding lifeline elongation and free fall
distance, before stopping, from the point at which
the deceleration device begins to operate. It is measured
as the distance between the location of an employee's
body belt or body harness attachment point at the
moment of activation (at the onset of fall arrest
forces) of the deceleration device during a fall,
and the location of that attachment point after the
employee comes to a full stop.
A scaffold consisting of platforms supported on fabricated
end frames with integral posts, horizontal bearers,
and intermediate members.
Load refusal, breakage, or separation of component
parts. Load refusal is the point where the ultimate
strength is exceeded.
The act of falling before a personal fall arrest system
begins to apply force to arrest the fall.
Free fall distance
The vertical displacement between onset of the fall
and just before the fall arrest system begins to apply
force to arrest the fall. This distance excludes deceleration
distance, and lifeline/lanyard elongation, but includes
any deceleration device slide distance or self-retracting
lifeline/lanyard extension before they operate and
fall arrest forces occur.
A barrier erected to prevent employees from falling
to lower levels.
A gap or void 2 inches (5.1 cm) or more in its least
dimension, in a floor, roof, or other walking/working
A manual- or power-operated mechanical device to raise
or lower a suspended scaffold.
Impossible to perform the construction work using
a conventional fall protection system (i.e., guardrail
system, safety net system, or personal fall arrest
system) or technologically impossible to use any one
of these systems to provide fall protection.
A mobile, fixed-size, self-supporting ladder consisting
of a wide flat tread ladder in the form of stairs.
A platform at the end of a flight of stairs.
A flexible line of rope, wire rope, or strap which
generally has a connector at each end for connecting
the body belt or body harness to a deceleration device,
lifeline, or anchorage.
The edge of a floor, roof, or formwork for a floor
or other walking/working surface (such as the deck)
which changes location as additional floor, roof,
decking, or formwork sections are placed, formed,
or constructed. A leading edge is considered to be
an "unprotected side and edge" during periods when
it is not actively and continuously under construction.
A component consisting of a flexible line connected
vertically to an anchorage at one end (vertical lifeline),
or connected horizontally to anchorages at both ends
(horizontal lifeline), and which serves as a means
for connecting other components of a personal fall
arrest system to the anchorage.
A roof having a slope less than or equal to 4 to 12
(vertical to horizontal).
Those areas or surfaces to which an employee can fall.
Such areas or surfaces include, but are not limited
to, ground levels, floors, platforms, ramps, runways,
excavations, pits, tanks, material, water, equipment,
structures, or portions thereof.
Maximum intended load
The total load of all persons, equipment, tools, materials,
transmitted loads, and other loads reasonably anticipated
to be applied to a scaffold or scaffold component
at any one time.
A gap or void 30 inches (76 cm) or more high and 18
inches (48 cm) or more wide, in a wall or partition,
through which employees can fall to a lower level.
Open sides and ends
The edges of a platform that are more than 14 inches
(36 cm) away horizontally from a sturdy, continuous,
vertical surface (such as a building wall) or a sturdy,
continuous horizontal surface (such as a floor), or
a point of access. Exception
For plastering and lathing operations the horizontal
threshold distance is 18 inches (46 cm).
The process of laying bricks and masonry units such
that the surface of the wall to be jointed is on the
opposite side of the wall from the mason, requiring
the mason to lean over the wall to complete the work.
Related work includes mason tending and electrical
installation incorporated into the brick wall during
the overhand bricklaying process.
fall arrest system
A system used to stop an employee in a fall from a
working level. It consists of an anchorage, connectors,
a body harness, and may include a lanyard, deceleration
device, lifeline, or suitable combinations of these.
As of January 1, 1998, using a body belt for fall
arrest is prohibited.
A work surface elevated above lower levels. Platforms
can be constructed using individual wood planks, fabricated
planks, fabricated decks, and fabricated platforms.
Positioning device system
A body belt or body harness system rigged to allow
an employee to be supported on an elevated vertical
surface, such as a wall, and work with both hands
free while leaning.
The manufacturer's specified maximum load to be lifted
by a hoist or to be applied to a scaffold or scaffold
A deceleration device which travels on a lifeline
and automatically, by friction, engages the lifeline
and locks so as to arrest the fall of an employee.
A rope grab usually employs the principle of inertial
locking, cam/level locking, or both.
The exterior surface on the top of a building. This
does not include floors or formwork which, because
a building has not been completed, temporarily become
the top surface of a building.
The hoisting, storage, application, and removal of
roofing materials and equipment, including related
insulation, sheet metal, and vapor barrier work, but
not including the construction of the roof deck.
A safety system in which a competent person is responsible
for recognizing and warning employees of fall hazards.
Any temporary elevated platform (supported or suspended)
and its supporting structure (including points of
anchorage), used for supporting employees or materials
A deceleration device containing a drum-wound line
which can be slowly extracted from, or retracted onto,
the drum under slight tension during normal employee
movement, and which, after onset of a fall, automatically
locks the drum and arrests the fall.
A connector comprised of a hook-shaped member with
a normally closed keeper, or similar arrangement,
which may be opened to permit the hook to receive
an object and, when released, automatically closes
to retain the object. Snaphooks are generally one
of two types
The locking type with a self-closing, self-locking
keeper which remains closed and locked until unlocked
and pressed open for connection or disconnection;
or the non-locking type with a self-closing keeper
which remains closed until pressed open for connection
or disconnection. As of January 1, 1998, the use of
a non-locking snaphook as part of personal fall arrest
systems and positioning device systems is prohibited.
Stair tower (Scaffold stairway/tower)
A tower comprised of scaffold components and which
contains internal stairway units and rest platforms.
These towers are used to provide access to scaffold
platforms and other elevated points such as floors
A roof having a slope greater than 4 in 12 (vertical
A pair of poles or similar supports with raised footrests,
used to permit walking above the ground or working
A low protective barrier that will prevent the fall
of materials and equipment to lower levels and provide
protection from falls for personnel.
Tubular welded-frame scaffold
Unprotected sides and edges
Any side or edge (except at entrances to points of
access) of a walking/working surface, e.g., floor,
roof, ramp, or runway, where there is no wall or guardrail
system at least 39 inches (1.0 m) high.
Items whose strength, configuration, or lack of stability
may allow them to become dislocated and shift and
therefore may not properly support the loads imposed
on them. Unstable objects do not constitute a safe
base support for scaffolds, platforms, or employees.
Examples include, but are not limited to, barrels,
boxes, loose bricks, and concrete blocks.
Any surface, whether horizontal or vertical, on which
an employee walks or works, including, but not limited
to, floors, roofs, ramps, bridges, runways, formwork,
and concrete reinforcing steel, but not including
ladders, vehicles, or trailers, on which employees
must be located in order to perform their job duties.
A portion of a scaffold platform used only for access
and not as a work level.
Warning line system
A barrier erected on a roof to warn employees that
they are approaching an unprotected roof side or edge,
and which designates an area in which roofing work
may take place without the use of guardrail, body
belt, or safety net systems to protect employees in
A wedge, block, or large stone placed against the
tires of a vehicle to prevent its moving, especially
on an incline.
The total system of support for freshly placed or
partially cured concrete, including the mold or sheeting
(form) that is in contact with the concrete as well
as all supporting members including shores, reshores,
hardware, braces, and related hardware.
The task of lifting a slab (or group of slabs vertically
from one location to another (e.g., from the casting
location to a temporary (parked) location, or to its
final location in the structure), during the construction
of a building/structure where the lift-slab process
is being used.
A method of concrete construction in which floor and
roof slabs are cast on or at ground level and lifted
into position using jacks.
Limited access zone
An area alongside a masonry wall that is under construction
and clearly demarcated to limit access by employees.
Concrete members (such as walls, panels, slabs, columns,
and beams) which have been formed, cast, and cured
before final placement in a structure.
The construction operation in which shoring equipment
(also called reshores or reshoring equipment) is placed,
as the original forms and shores are removed, to support
partially cured concrete and construction loads.
Rollover protective structure (ROPS)
Vehicle structures such as roll-bars, frames, roll-protective
cabs etc., designed to prevent the vehicle operator
from being crushed as a result of a rollover.
A device, usually worn around the waist, consisting
of a strap or straps anchored to a vehicle so as to
hold a person in his seat.
A supporting member that resists a compressive force
imposed by a load; or the operation by which a supporting
member is placed.
Vertical slip forms
Forms that are jacked vertically during the placement
AND EXCAVATION [top]
Bell-bottom pier hole
A type of shaft or footing excavation, the bottom
of which is made larger than the cross section above
to form a belled shape.
Benching (Benching system)
A method of protecting employees from cave-ins by
excavating the sides of an excavation to form one
or a series of horizontal levels or steps, usually
with vertical or near-vertical surfaces between levels.
The separation of a mass of soil or rock material
from the side of an excavation, or the loss of soil
from under a trench shield or support system, and
its sudden movement into the excavation, either by
falling or sliding, in sufficient quantity so that
it could entrap, bury, or otherwise injure and immobilize
The horizontal members of a shoring system installed
perpendicular to the sides of the excavation, the
ends of which bear against either uprights or wales.
Any man-made cut, cavity, trench, or depression in
an earth surface formed by earth removal.
The vertical or inclined earth surfaces formed as
a result of excavation work.
The breakage, displacement, or permanent deformation
of a structural member or connection so as to reduce
its structural integrity and its supportive capabilities.
An atmosphere which by reason of being explosive,
flammable, poisonous, corrosive, oxidizing, irritating,
oxygen deficient, toxic, or otherwise harmful, may
cause death, illness, or injury.
A method of protecting employees from cave-ins, from
material that could fall or roll from an excavation
face or into an excavation, or from the collapse of
adjacent structures. Protective systems include support
systems, sloping and benching systems, shield systems,
and other systems that provide the necessary protection.
An inclined walking or working surface that is used
to gain access to one point from another, and is constructed
from earth or from structural materials such as steel
Registered Professional Engineer
A person who is registered as a professional engineer
in the state where the work is to be performed. However,
a professional engineer registered in any state is
deemed to be a "registered professional engineer"
within the meaning of this standard when approving
designs for "manufactured protective systems" or "tabulated
data" to be used in interstate commerce.
The members of a shoring system that retain the earth
in position and in turn are supported by other members
of the shoring system.
A structure that is able to withstand the forces imposed
on it by a cave-in and thereby protect employees within
the structure. Shields can be permanent structures
or can be designed to be portable and moved along
as work progresses. Additionally, shields can be either
pre-manufactured or job-built in accordance with 29
CFR 1926.652(c)(3) or 29
CFR 1926.652(c)(4). Shields used in trenches are
usually referred to as "trench boxes" or "trench shields."
Shoring (Shoring system)
A structure such as a metal hydraulic, mechanical,
or timber shoring system that supports the sides of
an excavation and which is designed to prevent cave-ins.
Sloping (Sloping system)
A method of protecting employees from cave-ins by
excavating to form sides of an excavation that are
inclined away from the excavation so as to prevent
cave-ins. The angle of incline required to prevent
a cave-in varies with differences in such factors
as the soil type, environmental conditions of exposure,
and application of surcharge loads.
The dirt, rocks, and other materials removed from
an excavation and either temporarily or permanently
Natural solid mineral material that can be excavated
with vertical sides and will remain intact while exposed.
Unstable rock is considered to be stable when the
rock material on the side or sides of the excavation
is secured against caving-in or movement by rock bolts
or by another protective system that has been designed
by a registered professional engineer.
A ramp built of steel or wood, usually used for vehicle
access. Ramps made of soil or rock are not considered
A structure such as underpinning, bracing, or shoring,
that provides support to an adjacent structure, underground
installation, or the sides of an excavation.
Tables and charts approved by a registered professional
engineer and used to design and construct a protective
Trench (Trench excavation)
A narrow excavation (in relation to its length) made
below the surface of the ground. In general, the depth
is greater than the width, but the width of a trench
(measured at the bottom) is not greater than 15 feet
The vertical members of a trench shoring system placed
in contact with the earth and usually positioned so
that individual members do not contact each other.
Horizontal members of a shoring system placed parallel
to the excavation face whose sides bear against the
vertical members of the shoring system or earth.
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