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Minimum Igniting Current (MIC) Ratio
The ratio of the minimum current required from an inductive spark discharge to ignite the most easily ignitable mixture of a gas or vapor, divided by the minimum current required from an inductive spark discharge to ignite methane under the same test conditions.
Minimum Ignition Energy (MIE)
The minimum amount of energy released at a point in a combustible mixture that caused flame propagation away from the point, under specified test conditions. The lowest value of the minimum ignition energy is found at a certain optimum mixture. The lowest value is usually quoted as the minimum ignition energy.
Minimum Ignition Temperature (MIT) of a Dust Cloud
The lowest temperature of a hot surface on which the most ignitable mixture of dust with air is ignited under specified test conditions.
Minimum Ignition Temperature (MIT) of a Dust Layer
The lowest temperature of a hot surface at which ignition occurs in a dust layer under specified test conditions.
Minimum Ignition Voltage
Voltage across capacitor of specified capacitance which upon discharge is just sufficient to effect ignition of the most easily ignitable composition of a given fuel-oxidant mixture
Minor Incidents
Accidents or near misses that have acceptable consequences but for which recurring events of this magnitude may warrant an investigation.
Mist
A dispersion of fine liquid droplets in a gaseous medium.
Mitigate
Reduce the impact of a loss event.
Mitigation
Lessening the risk of an accident event sequence by acting on the source in a preventive way by reducing the likelihood of occurrence of the event, or in a protective way by reducing the magnitude of the event and/or the exposure of local persons or property.
Mitigation Event
Equipment and/or procedures designed to respond to an accident event sequence by hindering accident propagation and/or reducing the accident consequences.
Mitigation Factors
Systems or procedures, such as water sprays, foam systems, and sheltering and evacuation, which tend to reduce the magnitude of potential effects due to a release.
Mitigative Barrier
A barrier designed to interrupt the chain of events after a loss event, given that there has been a loss of containment of a hazardous material or energy.
Note: Specific to a hazards evaluation of an incident sequence, a mitigative barrier is in between the loss of event (the loss of containment) and the scenario's impact, helping reduce the consequences of the incident scenario, and thus, helping reduce the scenario's risk.
Morphological Approach
A structured analysis of an incident directed by insights from historic case studies but not as rigorous as a formal hazard analysis.
Mortality Index
An index based on the observed average ratio of casualties to the mass of material or energy released, as derived from the historical record. It is used to characterize the potential hazard of toxic material storage.
Mutagen
A substance or agent capable of altering the genetic material in a living cell. Importance: If a substance is known to be a mutagen, a potential health hazard exists, and special protection and precaution sections should be checked on the MSDS.
Mutagenic Toxin
A chemical that produces chromosomal damage.
Near Miss
An event in which an accident (that is, property damage, environmental impact, or human loss) or an operational interruption could have plausibly resulted if circumstances had been slightly different.
Near-Field
The area within a few hundred meters downwind of the source where there is possible influence of local structures, source geometry, and initial plume momentum and buoyancy effects.
Near-Miss
An unplanned sequence of events that could have caused harm or loss if conditions were different or were allowed to progress, but actually did not.
Near-Miss Incident
The description of less severe incidents (i.e., below the threshold for inclusion in a lagging metric), or unsafe conditions that activated one or more layers of protection. Although these events are actual events (i.e., a lagging metric), they are generally considered to be a good indicator of conditions that could ultimately lead to a severe incident.
Net Positive Suction Head (NPSH)
The net static liquid head that must be provided on the suction side of the pump to prevent cavitation.
Neutral Buoyant Gas
A gas with density approximately equal to that of air at ambient temperature.
Neutral Cloud
The in-cloud density is equal to the ambient density. Neutral cloud and passive cloud are synonymous.
Neutral Stability
The ambient boundary layer is well-mixed, with Pasquill stability class D, Ri = 0, and 1/L = 0. Usually occurs with high winds and/or small surface heat fluxes.
Noncombustible Material
A material that, in the form in which it is used and under the conditions anticipated, will not ignite, support combustion, burn, or release flammable vapors when subjected to fire or heat
Nonconductive
Possessing a conductivity of less than 102 pS/m or a resistivity greater than 1010 W-m.
Nondestructive testing/examination (NDT/NDE)
Evaluation of an equipment item with the intention of measuring an equipment parameter without damaging or destroying the equipment item.
Nonflammable Gas (NFPA 55)
A gas that does not meet the definition of a flammable gas.
Normal Operation
The phase of process operation between the startup phase and shutdown phase. Any process operations that can be performed during this period to support continued operation within safe upper and lower operating limits is a normal operations task.
Normal Operations
Any process operations intended to be performed between startup and shutdown to support continued operation within safe upper and lower operating limits.
Normalization of Deviance
A gradual erosion of standards of performance as a result of increased tolerance of nonconformance. Also normalization of deviation.
Nose of Vapor Cloud
The front surface of vapor cloud, that is, the surface farthest along in the along-wind direction. All surfaces of a vapor cloud are usually defined by a certain concentration such as the LFL.
Occupant Vulnerability
Proportion of building occupants that could potentially suffer an injury or fatality if a postulated event were to occur. The level of injury is defined according to the technical basis of the occupant vulnerability model being used.
Occupational Incident
An incident involving injury to workers.
Off-Site exposure
People, property, or the environment located outside of the site property line that may be impacted by an on-site incident.
Off-Site population
Persons located outside of the site property line that may be impacted by an on-site incident.
On-Site Personnel
Employees, contractors, visitors, service providers, and others present at the facility.
On-Stream Factor
The fraction of the time that a process unit is operating
Onset Temperature
Defined to be the temperature at which the heat that is released by a reaction can no longer be completely removed from the reaction vessel, and consequently, results in a detectable temperature increase. The onset temperature depends on detection sensitivity, reaction kinetics, on vessel size and on cooling, flow and agitation characteristics. Scaling of onset temperatures and application of "rules of thumb" concerning onset temperatures must be regarded as highly unreliable.
Operating Instructions
A series of sequential written details describing how to operate equipment.
Operating Limits
The values or ranges of values within which the process parameters normally should be maintained when operating. These values are usually associated with preserving product quality or operating the process efficiently; however, they may also incorporate the safe upper and lower limits of the process, or other important limits.
Operating Mode
A phase of operation during the operation and maintenance stages of the life cycle of a facility. Operating modes include start-up, normal operation, shutdown, product transitions, equipment cleaning and decontamination, maintenance, and similar activities.
Operating Pressure
The maximum pressure at which a flame arrester can be used according to its certification.
Operating Procedures
CCPS RBPS Element 08: This Element ensures proper development, upkeep, and consistent use of the procedures required to operate the processes safely.
Operating Procedures
Written, step by step instructions and information necessary to operate equipment, compiled in one document including operating instructions, process descriptions, operating limits, chemical hazards, and safety equipment requirements.
Operating Window
The parameters (i.e., safe upper and lower limits, run time) under which equipment can function without failure.
Operational Discipline (OD)
The performance of all tasks correctly every time.
Individuals demonstrate their commitment to process safety through OD, executing the organization's Conduct of Operation (COO) RBPS Element each and every day.
Operational Interruption
An event in which production rates or product quality is seriously impacted.
Operational Readiness
CCPS RBPS Element 14: This Element verifies during commissioning that new, changed, or maintained equipment and processes are in a safe condition and are ready to start-up and use.
Operational Readiness
A PSM program element associated with efforts to ensure that a process is ready for start-up/restart. This element applies to a variety of restart situations, ranging from restart after a brief maintenance outage to restart of a process that has been mothballed for several years.