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.
Mitigation System
Equipment and/or procedures designed to respond to an accident event sequence by interfering with accident propagation and/or reducing the accident consequences.
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.
Mixing depth, zi
Maximum elevation of mixing in a typical daytime boundary layer.
Mode of Transportation
The specific type of transportation of concern (for example, truck, rail, barge, pipeline).
Momentum Flux
Mathematically, ru2 (in Newtons/m2), the product of the cloud density and speed squared.
Momentum Force
Mathematically, ru2A (in Newtons), the product of the cloud density, speed squared, and cross-sectional area.
Monin-Obukhov length, L
Accounts for the effects of stability and is proportional to u*3 divided by the surface turbulent heat flux, Hs, to or from the ground surface: L= -(u*3/k)/(gHs /cp ρ T), where g = 9.8 m/s2 is the acceleration of gravity, cp = 1005 J kg-1K-1 is the specific heat of air at constant pressure, and T is the air temperature (in K). The friction velocity, u*, in this formula is based on the surface stress, to. Hs (in Watts/m2 is positive during the day and negative at night.
Monin-Obukhov similarity theory
Used in many boundary layer and transport and dispersion models to estimate winds, temperatures, and turbulence in the atmospheric boundary layer. This theory states that the mean wind and temperature profiles and turbulent velocities in the boundary layer are completely determined by three scaling lengths (zo, d, and L) and a scaling velocity (u*).
Monoclonal antibody (MAb)
a highly specific, purified antibody that recognizes only a single epitope.
Monomer
A simple molecule that is capable of combining with a number of other molecules to form a polymer. (NFPA 49)
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.
Multiplexer
A device for accomplishing simultaneous transmission of two or more signals over a common transmission medium. A device or circuit that samples many data lines in a time-ordered sequence, one at a time, and puts all sampled data onto a single bus. A device which combines two or more separate signals for transmission through a single fiber. Optical multiplexers combine signals at different wavelengths. Electronic multiplexers combine signals electronically before they are converted into optical form. A device that allows selection of one of many input channels of analog data under computer control.
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.
National Emphasis Program (NEP)
An inspection/enforcement program designed by OSHA to more thoroughly examine the implementation of PSM programs in the refining and chemical industries. There are NEPs for the refinery sector (OSHA Directive CPL 03-00-004) and the chemical sector (OSHA Directive 09-06 (CPL 02)).
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.
Negatively Buoyant Vapors
Vapors or aerosol with a specific gravity greater than ambient air so the vapors tend to sink to low spots and to spread along the ground by gravity spreading.
Net Positive Suction Head (NPSH)
The net static liquid head that must be provided on the suction side of the pump to prevent cavitation.
Network
A maximal interconnected group of graphical Elements of a Ladder Diagram Program, excluding the left and right Power Rails.
Neurotoxin
A chemical which produce their primary toxic effects on the nervous system
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.
No-Observed-Adverse-Effect-Level (NOAEL)
An exposure concentration at which there are no statistically and biologically significant increases in the frequency or severity of adverse effects between the exposed population and its appropriate control group; i.e. there are no adverse physiological effects.
Node
Sections of equipment with definite boundaries (e.g., a line between two vessels) within which process parameters are investigated for deviations. The locations on P&IDs at which the process parameters are investigated for deviations (e.g., a reactor). The concept of dividing a process into nodes for analysis is commonly, but not exclusively, used in HAZOPs.
Non-Accident-Initiated Event
An event due to causes unassociated with the movement-related aspects of transportation such as improperly closed valves or pressure build-up due to contamination.
Non-Process
Industries which do not comprise the CPI as their primary function but which use comparable or equivalent complex equipment systems to perform their function.
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.
NOx
Oxides of Nitrogen; undesirable air pollutants. Importance: Often listed on a MSDS as a hazardous decomposition product.
Nutraceutical
Extracts of foods claimed to have a medicinal effect on human health.
Objectivity
Freedom from bias.
Observation
The noting and recording of information to support findings. Also field observation.
Obsolete
Refers to PES equipment status. A PES becomes obsolete if the plant determines it shall be replaced or if the producer ceases support of the PES.
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.