Atmospheric concentration of any substance for which a dose or a permissible exposure
limit is published in Subpart G, Occupational Health and Environmental Controls, or in
Subpart Z, Toxic and Hazardous Substances, of 29 CFR 1910, and which could result in
employee exposure in excess of its dose or permissible exposure limit.
Hotline: The outer boundary of the Exclusion Zone. It separates the area of highest
contamination from the Contamination Reduction Zone. It provides an adequate area in which to
conduct site operations taking into account potential contaminant migration.
Hot Work: Work that produces arcs, sparks, flames, heat, or other sources of ignition.
Hot Work Permit: The employer's written authorization to perform operations (for example,
riveting, welding, cutting, burning, and heating) capable of providing a source of ignition.
Immediately Dangerous to Life or Health (IDLH): Any condition or exposure that poses an
immediate or delayed threat to life or that would cause irreversible adverse health effects.
Inerting: The displacement of the atmosphere in a confined space by a non-combustible gas
(such as nitrogen) to such an extent that the resulting atmosphere is non-combustible. This
procedure produces an IDLH oxygen-deficient atmosphere. However, the procedure is used to
isolate the space and control hazards before entry.
Installation: Any DOE property (i.e., "inside the fence.")
Isolation: The process by which a permit space is removed from service and is completely
protected from release of energy and material into the space. Common methods of isolation are
misaligning or removing sections of lines, pipes, or ducts; closing off or venting valves;
providing lockout or tagout of all sources of energy; and disconnecting all mechanical linkages.
Job: The detailed steps required to carry out a task.
Key Personnel: Those personnel/organizations considered to be essential to ensure the safe
operation of the facility, site, project, or task.
LEL/LFL and UEL/UFL: Lower explosive limit/lower flammable limit and upper explosive
limit/upper flammable limit describe the explosion or combustion limits, respectively for
flammable gas or vapor mixtures in air. For example, a concentration below the lower
flammable limit is not sufficient to support combustion, and above the upper flammable limit the
mixture is too "rich" to burn.
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.