Exothermic Chemical Reaction
A reaction involving one or more chemicals resulting in one or more new chemical species and the evolution of heat.
Expansion Ratio , rv
The ratio of the volume after combustion to that prior to combustion.
Expected Number of Failures (ENF)
The average number of occurrences of the fault event during a specified time interval.
Experience-based criteria
Risk criteria that are calibrated or validated against established consensus as reflected in historical precedents/decisions about tolerance of major hazard risks, particularly those subjected to broad public discussion or scrutiny.
Explosibility
The ability of a dust to take part in a closed explosion when dispersed in air at a suitable concentration and in the presence of an effective ignition source.
Explosibility Index
A numerical measure of the explosion hazard potential of a dust as determined by multiplying the dust Ignition Sensitivity Index by its Explosion Severity Index.
Explosion (CCPS)
A release of energy that causes a pressure discontinuity or blast wave.
Explosion (NFPA)
The bursting or rupture of an enclosure or container due to the development of internal pressure from a deflagration.
Explosion Efficiency, e
The ratio of the mechanical energy released in an explosion to the heat of combustion times the flammable mass in a vapor cloud (net efficiency). Alternately, the ratio of the mechanical energy released in an explosion to the heat of combustion times the total mass of fuel in a vapor cloud (gross efficiency).
Explosion Overpressure
Any pressure above atmospheric caused by a blast.
Explosion Prevention
Where the gas composition is maintained outside the flammable region.
Explosion Protection
Where devices are provided to minimize pressure development if ignition occurs.
Explosion Severity Index
An overall measure of the potential hazard associated with a closed vessel explosion of a combustible dust as given by Equation [4.2] (page 156).
Explosion Vent
An intentionally weakly supported panel in the wall of an enclosure designed to give way in the event of an explosion in order to reduce the explosion overpressures and thereby protect the rest of the structure.
Explosion-Pressure-Resistant
Property of vessels and equipment designed to withstand the expected explosion pressure without becoming permanently deformed.
Explosion-Pressure-Shock-Resistant
Property of vessels and equipment designed to withstand the expected explosion pressure without rupturing, but allowing permanent deformation.
Explosions
A release of energy that causes a pressure discontinuity or blast wave.
Explosive
A chemical that causes a sudden, almost instantaneous release of pressure, gas, and heat when subjected to sudden shock, pressure, or high temperature. OSHA 1994
Exponential wind profile
Formula proposed for vegetative canopies that is also valid for other types of surface obstacles (Cionco, 1965).
Exposure hours
An equipment item's operating time in hours.
Exposure Period
Expressed in terms of a continuous variable, such as the time equipment is operating, or as a function of a discrete variable, such as the number of demands (also called cycles in some tests) imposed on a piece of equipment.
Exposure, Demand-related
The historical number of demands experienced by the equipment population.
Exposure, Time-related
The historical operating time of the equipment population.
Expression system
in genetic engineering, the cells (host organism) into which a gene is inserted to manufacture desired proteins; the gene is combined with a genetic vector (such as a virus or circular DNA molecule called a plasmid) to provide the genetic context in which it will function in the cell; that is, the gene will be expressed as the protein of interest.
External
A WDT that is independent of the PES. An electronic internal timer which will generate priority interrupt unless periodically recycled by a computer. It is used to detect program stall or hardware failure conditions.
External Event
Event caused by (1) a natural hazard-earthquake, flood, tornado, extreme temperature, lighting, etc.; or (2) man-induced events-aircraft crash, missile, nearby industrial activity, sabotage, etc., or (3) an interruption of facilities such as electric power or process air.
External Safety
A term used in the Netherlands to refer to "risks to the surrounding area in handling hazardous materials, in the use, storage, and transport of those materials." [VROM 2005]
Extrinsic Factor
As used in this publication, a factor that is not an intrinsic property of a material being handled (see intrinsic property).
F-N Curve
A plot of cumulative frequency versus consequences (often expressed as number of fatalities).
Facility
The physical location where a management system activity is performed. In early life-cycle stages, a facility may be the company's central research laboratory, pilot plant, or the engineering offices of a technology vendor. In later stages, the facility may be a typical chemical plant, storage terminal, distribution center, or corporate office. In the context of this document, a facility is a portion of or a complete plant, unit, site, complex or offshore platform or any combination thereof.
Facility Manager
On-site Engineering section or group providing service to the local facility.
Fail To Danger
Describes an equipment fault which would inhibit or delay automatic shut-down should a demand occur. The fail-to-danger fault has a direct and detrimental effect on safety.
Fail-Safe
A feature incorporated for automatically counteracting the effect of an anticipated possible source of failure. A system is fail-safe if failure of a component, signal, or utility, initiates action that return the system to a safe condition.
Fail-Safe Circuit
A circuit that has an output state which indicates that either a circuit input or the circuit itself has failed. Finds circuit application in complex systems where self-healing subsystems exist. When a subsystem failure is detected, a backup subsystem is automatically inserted.
Fail-Safe Control
A system of remote control for preventing improper operation of the controlled function in event of circuit failure.
Fail-Safe Operation
An electrical system so designed that the failure of any component in the system will prevent unsafe operation of the controlled equipment.
Fail-Safe Shutdown
The ability of a Process Control System to have its outputs assume a predefined state within a specified delay after detecting the occurrence of a power supply voltage drop or an Internal Failure.
Failure
An unacceptable difference between expected and observed performance.
Failure Frequency
The number of failure events that occur divided by the total elapsed calendar time during which those events occur or by the total number of demands, as applicable.
Failure Mode
Manner in which failure occurs. A failure mode might be identified as loss of function; spurious operation (function without demand); an out-of-tolerance condition; or a simple physical characteristic such as a leak observed during inspection.
Failure Mode and Effects Analysis
A hazard identification technique in which all known failure modes of components or features of a system are considered in turn and undesired outcomes are noted.
Failure Modes, Effects, and Criticality Analysis (FMECA)
A variation of FMEA that includes an estimate of the potential severity of consequences of a failure mode.
Failure Probability
The probability - a value from 0 to 1 - that a piece of equipment will fail on demand (not to be confused with fractional dead time) or will fail in a given time interval.
Failure Rate
The number of failure events that occur divided by the total elapsed operating time during which these event occur or by the total number of demands, as applicable.
Failure Severity
The degree of function degradation of equipment usually noted through deficient performance ; categorized by the terms "catastrophic," "degraded," and "incipient."
Falsifiability
A concept where a specific effort is made to disprove a speculated hypothesis, in addition to the efforts made to prove the hypothesis.
Far-Field
The area beyond the influence of local structures and plume buoyancy effects. Typically the far-field begins at about 1000 m from the source.
Farad
A unit of capacitance equal to Coulombs per volt. See Capacitance.
Faraday Pail (Cage).
Grounded metal sheet or mesh enclosure that prevents external electric fields from exerting an influence inside it.
Fast-Acting Valve
A valve that closes a path of deflagration propagation in a pipe or duct in response to upstream detection of a deflagration.