air ejectors, or jet-air movers: blow air or steam through a tube, creating a low pressure area, thereby causing large quantities of air to be drawn into the tube.

air purifying respirators: remove contaminants by passing the breathing air through a purifying element.

atmospheric supplying respirators: provide a source of clean breathing air from a remote location; the air is supplied to the worker from either a stationary or portable source.

atmospheric hazards: (contaminated air), including atmospheres that are asphyxiating, toxic, or oxygen-enriched.

attendant: an individual stationed outside the confined space to monitor the authorized entrant.

authorized entrant: an employee who is authorized by an employer to enter a permit space.

axial flow fans: draw in air and discharge air along the path of the shaft. That is, the air flows in a straight line through the fan.

belly: the space between the lip and toe of trench.

belly in/wall slough: a collapse caused when a large mass of soil falls from the side of a trench and leaves a large overhang.

benching: relies on the maximum allowable slope principal but employs one or more vertical sided portions.

blanking or blinding: the absolute closure of a pipe, line, or duct by the fastening of a solid plate (such as a spectacle blind or a skillet blind) that completely covers the bore and that is capable of withstanding the maximum pressure of the pipe, line, or duct with no leakage beyond the plate.

block out: a process for isolating objects that can move or fall.

boiling point : the temperature at which a liquid turns into a vapor. (Unit I).

cave-in: the separation of material (rock or soil) from the side of the excavation into the excavation.

centrifugal flow fans: draw in air parallel to the shaft, but turn the air go degrees and discharge it perpendicular to the shaft.

closed-circuit SCBA: exhaled air is recycled by removing the carbon dioxide with an alkaline scrubber and by replenishing the consumed oxygen with oxygen from a solid, liquid, or gaseous source.

combustible gas indicators (Cal): measures the concentration of a flammable vapor or gas in air, indicating the results as a percentage of the lower explosive limit (LEL) of the calibration gas.

combustible liquids: a liquid that has a flash point of 100(F or more.

confined space entry permit: explains the hazards in the space and how these hazards will be controlled.

confined space supervisor: the responsible individual who authorizes entry; makes certain all work conditions are safe, only properly trained workers are doing appropriate tasks, and a confined space entry permit has been issued.

double block and bleed: the closure of a line, duct, or pipe, by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves.

duct work: contains the air stream and directs it where you want it to go. It may consist of rigid material or flexible hoses or tubing.

engulfment: occurs when a worker in a confined space is trapped or enveloped by solid or liquid material.

entrant: the individual who will actually enter the confined space.

entry permit: a written document provided by the employer that specifies the conditions of entry into a hazardous confined space.

entry: the action by which a person passes through an opening into a permit required confined space; occurs as soon as any part of the entrant's body breaks the plane of an opening into the space.

excavation: any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal.

finance: command function responsible for tracking all costs related to an incident.

flammable liquid: a liquid that has a flash point below 100(F (36(C).

flash point: the minimum temperature at which a liquid generates enough vapor to form an ignitable mixture with air.

hazardous atmosphere: an atmosphere that may expose employees to the risk of death, incapacitation, impairment of ability to self-rescue (that is, escape unaided from a permit space), injury, or acute illness.

heat stress: results from a combination of temperature within the space, exertion, and use of personal protective equipment.

ignition temperature: the minimum temperature that a liquid must be raised to initiate or cause self-sustained combustion.

immediately dangerous to life or health (IDLH): any condition that poses an immediate or delayed threat to life or that would cause irreversible adverse heath effects or that would interfere with an individual's ability to escape unaided from a permit space.

inerting: the displacement of the atmosphere in a permit space by a noncombustible gas (such as nitrogen) to such an extent that the resulting atmosphere is noncombustible.

isolation: the process by which a permit required space is removed from service and protected against the release of energy and material into the space.

LC50: lethal concentration of a substance in air that will kill 50% of test animals when inhaled over a period of time, usually one hour.

LD50: the amount of substance that when fed to or applied on test animals, will kill half of the animals in the test. It is the lethal dose for 50% of the animals being tested under specific conditions.

Liaison Officer: responsible for coordinating all responding agencies.

liquid splash-protective suits: are designed to keep liquids off the wearer's skin.

line breaking: the intentional opening of a pipe, line, or duct that is or has been carrying flammable, corrosive, or toxic material, an inert gas, or any fluid at a volume, pressure, or temperature capable of causing injury.

lip: usually refers to the area at the top of both sides of a trench.

lip slide: often caused by piling the excavated spoil too close to the edge, thereby creating a load on the lip of the trench.

local negative pressure ventilation: a method of ventilation that places an exhaust intake close to the contaminant's point of origin.

lockout/tagout: the most common means of isolating an energy source. (unit 4)

logistics: command function responsible for providing facilities and services to support personnel at the incident, such as food, areas for rehabilitation and emergency medical treatment.

lower explosive limit (LEL): the concentration of flammable vapors in the air is below a level which will result in a flame, given an ignition source.

mechanical hazards: could include uncontrolled electricity, unintentional activation of equipment, falling objects, inadequate footing, or releases of steam or compressed air.

mechanical ventilation: supplies air to the space (using positive pressure) or exhausts it from the space (using negative pressure).

miscibility: the ability of a gas or liquid to dissolve in another gas or liquid.

molecular weight: the atomic weight of all atoms in a specific molecule.

negative pressure/exhaust ventilation: pulls contaminated air out of a space.

negative-pressure respirators: also known as demand respirators, draw air into the face-piece via the negative pressure created by user inhalation.

operations section: responsible for most of the tactical planning and direct action.

open-circuit SCBA: air is exhaled directly into the ambient atmosphere.

oxygen deficient atmosphere: an atmosphere with an oxygen level below 1g.5%.

oxygen enriched atmosphere: an atmosphere with an oxygen level greater than 21%.

oxygen meter: an instrument that detects the concentration of oxygen in air.

permissible exposure level (PEL): average concentration that must not be exceeded during 8-hour work shift of a 40-hour work week.

permit system: an employer's written procedure for preparing and issuing permits for entry.

permit-required confined space: a confined space with one or more of the following characteristics:
* Contains or may contain a hazardous atmosphere.
* Contains a material that may engulf a person inside.
* Has an internal shape that could allow a person to be trapped or asphyxiated, such as inwardly converging walls or a floor that slopes downward and tapers to a smaller cross-section.
* Contains any other recognized serious safety or health hazard.

permit-required confined space program (permit space program): an employer's overall program for controlling, and, where appropriate, for protecting employees from, permit space hazards and for regulating employee entry into permit spaces.

pH: a logarithmic scale which can measure the acidity or alkalinity of materials. The scale ranges from 0 to 14, with 7 considered neutral.

planning: command function responsible for collecting, evaluating, and disseminating information about the incident and available resources.

positive-negative/push-pull ventilation: flushes the atmosphere by supplying and exhausting large volumes of air. It doesn't reduce the total amount of contaminants released, but moves them out of the confined space into the atmosphere.

positive-pressure respirators: maintain a positive pressure in the face-piece during both inhalation and exhalation.

positive pressure/supply ventilation: pushes air into a space, causing contaminated air to exit through any available openings.

Public Information Officer: responsible for verifying, coordinating, and disseminating all media releases.

recommended exposure level (REL): average concentration limit recommended for up to a 1 0-hour workday during a 40-hour workweek.

rescue service: the personnel designated to rescue employees from a hazardous confined space.

Safety Officer: assesses hazardous and unsafe situations in an emergency incident.

self-contained breathing apparatus (SCBAs): a device which supplies grade d breathing air from a pressurized source carried by the user.

shield system: a structure or system that normally does not prevent a cave-in but is able to withstand the soil forces caused by a cave-in and thereby protect employees within the structure. Shields may be permanent structures or may be designed to be portable and moved along the trench. Shields used in trenches are usually referred to as "trench boxes" or "trench shields".

shoring: a system of uprights (vertical members of a trench shoring system) which bear against the soil, walers (horizontal members of a trench shoring system) which- hold the uprights against the soil, and braces (cross members of a trench shoring system) which force the walers tightly against the uprights. Walers are also called stringers or rangers.

short-term exposure level (STEL): 15-minute exposure limit that must not be exceeded during the workday.

side wall shear: a collapse caused when an entire wall of earth shears-away from the side.

sloping: a method of protecting employees against cave-ins by cutting back the sides of an excavation to a safe slope.

solubility: the ability of one substance to mix with another.

specific gravity: refers to the weight of a liquid or solid in comparison to an equal volume of water.

spoil: the soil, rocks, or other materials removed from a trench.

supplied-air respirators (SARs): respirators connected to a remote source of grade d breathing air by an airline hose.

testing: the process by which the hazards that may confront entrants of a permit space are identified and evaluated.

trench: a narrow excavation (in relation to its length) made below the surface of the ground.

threshold limit value-ceiling (TLV-C): concentration that should never be exceeded.

threshold limit value-short-term exposure limit TLV-STEL): 15-minute exposure limit that should not occur more than 4 times during the workday.

threshold limit value-time weighted average (TLV/TWA): average concentration limit for a normal 8-hour workday and a 40-hour workweek that should not cause adverse effects.

toe: the area on both sides of the floor of a trench.

upper explosive limit (UEL): the concentration of flammable vapors is above a level which will result in a flame given an ignition source. There is not enough oxygen to support combustion (the mixture is too rich to ignite).

vapor density: the tendency of a gas or vapor to rise or fall in air. Air has a vapor density of 1.0; gases and vapors with vapor densities less than 1.0 will rise in air; those with vapor densities greater than 1.0 will sink in air.

vapor protective suits: should be used when the chemical(s) encountered are volatile, particularly hazardous, and have known skin toxicity.

vapor pressure: the ability of a liquid to move from the liquid state to the gas state (a vapor). Vapor pressure is often measured in millimeters (mm) of mercury (Hg).

ventilator: a high powered fan which forces large amounts of air into a work area.