Management of Change
A management system to identify, review, and approve all modifications to equipment, procedures, raw materials, and processing conditions, other than replacement in kind, prior to implementation to help ensure that changes to processes are properly analyzed (for example, for potential adverse impacts), documented, and communicated to employees affected.
Management Review
A PSM program element that provides for the routine evaluation of other PSM program management systems/elements with the objective of determining if the element under review is performing as intended and producing the desired results as efficiently as possible. It is an ongoing due diligence review by management that fills the gap between day-to-day work activities and periodic formal audits.
Management System
A formally established set of activities designed to produce specific results in a consistent manner on a sustainable basis.
Master/Slave
Device setting action (in control)/device carrying out action. A mode of operation where one data station (the master) controls the network access of one or more data stations (the slaves).
Master/Slave Mode
The feature ensuring the protection of each program when more than one program resides in memory.
Master/Slave System
A system of interlinked computers under the control of one computer (master computer).
Material Choke
A mass of bulk solids or powders in a rotary valve or screw feeder that prevents a flame from being transmitted.
Material Identification
The name of a chemical. It may be a trade name, chemical name or any other name a chemical is known by. On a MSDS this section also includes the name, address, and emergency telephone number of the distributing chemical company. Importance: Proper identification of a chemical allows an employee to get additional health hazard and safety information.
Maurer Discharge
See "Bulking Brush Discharge".
Maximum Allowable Concentration (MAC)
The maximum concentration in air of a toxic material that the facility and the public authorities having jurisdiction are willing to tolerate at a populated downwind location in the event of a major accident.
Maximum Credible Event (MCE)
A hypothetical explosion, fire or toxic event that has the potential maximum consequence to the occupants of the building under consideration from among the major scenarios evaluated. The major scenarios are realistic and have a reasonable probability of occurrence considering the chemicals, inventories, equipment and piping design, operating conditions, fuel reactivity, process unit geometry, industry incident history, and other factors. Each building may have its own set of MCEs for potential explosion, fire or toxic material release impacts.
Maximum Experimental Safe Gap (MESG):
The maximum gap of the joint between the two parts of the interior chamber of a test apparatus which, when the internal gas mixture is ignited and under specified conditions, prevents ignition of the internal gas mixture through a 25- mm-long joint, for all concentrations of the tested gas or vapor in air. The MESG is a property of the respective gas mixture, but can vary depending on the test apparatus.
Maximum Explosion Pressure, Pmax
The maximum pressure occurring in a closed vessel during the explosion of an explosible dust atmosphere determined under specific test conditions.
Maximum Individual Risk
The individual risk to the person(s) exposed to the highest risk in an exposed population.
Maximum Potential Quantity
The maximum amount of a chemical that can be released from a process containment system. Such a system may be an isolated pressure vessel and associated piping or two or more interconnected and communicating vessels without isolation capability. This quantity is different from and often much greater than both the typical chemical inventory and design maximum inventory for a containment system.
Maximum Pressure After Decomposition
The maximum pressure which is obtained in a closed vessel. This pressure depends on the adiabatic temperature rise and the specific gas production.
Maximum Rate of Explosion Pressure Rise
The maximum value of the pressure rise, dp/dtmax, per unit time during explosions of all explosive atmospheres in the explosible range of a combustible particulate solid in a close vessel under specified test conditions.
Mean
The measure of central tendency of a distribution often referred to as its arithmetic average.
Mean Time Between Failure (MTBF)
For a stated period in the life of a functional unit, the mean value of the length of time between consecutive failures under stated conditions.
Mean Time To Failure (MTTF)
1/?, where ? is the instantaneous failure rate. Dimension (Time).
Mean Time To Repair (MTTR)
The statistical average of time taken to identify and repair a fault. Normally expressed as t. Dimension (Time).
Mechanical Integrity
An management system focused on ensuring that equipment is designed, installed, and maintained to perform the desired function.
Mechanical Integrity Program
A program to ensure that process equipment and systems are and remain mechanically suitable for operation. It involves inspection, testing, upgrading and repairs of equipment, as well as written procedures to maintain on-going integrity of equipment
Mechanical Turbulence
Turbulence caused by the wind speed variations and the surface roughness elements, and can be thought of as simple mechanical mixing or stirring of the air.
Median
Midpoint of the failure data distribution.
Median Lethal Concentration/Dose
Concentration or dose levels, respectively, that kill 50% of exposed laboratory animals in controlled experiments.
Median Lethal Dose , LD50
A statistically derived single dose of a chemical that is expected to cause death in 50% of tested animals.
Medical Treatment
As defined by OSHA, treatment (other than first aid) administered by a physician or by registered professional personnel under the standing orders of a physician.
Melting Point
The temperature at which a solid substance changes to a liquid state. For mixtures, the melting range may be given. Importance: The physical state of a substance is critical in assessing its hazard potential, route of exposure and method of control.
Memory
That portion of the programmable controller used for storage of data and program information.
Memory Utilization
The amount of memory required for a specified part of a program.
Mental Models
An individual's or groupW's simplified representation of a process or system that explains the relationship between its various inputs, internal processes, and outputs.
Mesoscale
The distance scales ranging from about 1 to 100 km.
Mesoscale Puff Models
Used for estimating transport and dispersion at distances ranging from a few kilometers to 100 km, intermediate scale. The pollutant release is modeled as a series of puffs, which are allowed to have curved trajectories to account for space and time variations in meteorology.
Methodology
The use of a combination of two or more incident investigation tools to analyze the evidence and determine the root causes of the incident.
Metrics
Leading and lagging measures of process safety management efficiency or performance. Metrics include predictive indicators, such as the number of improperly performed line-breaking activities during the reporting period, and outcome-oriented indicators, such as the number of incidents during the reporting period.
Microcalorimetry
Isothermal techniques of high sensitivity in which heat fluxes from the converting sample material are measured very accurately. Differential Microcalorimetry is performed if the heat fluxes from the sample are compared with those of a reference material.
Microprocessor
The control and processing portion of a computer or microcomputer that can be built with large scale integration (LSI) circuitry usually on one chip. A large scale integrated circuit that has all the function of a computer, except memory and input/output systems. The IC thus includes the instruction set, ALU, registers and control functions. Usually a monolithic, Large-Scale Integrated (LSI) Central Processing Unit (CPU) on a single chip or semiconductor material; memory, input/output circuits, power supply, etc. are needed to turn a microprocessor into a microcomputer.
Minimal Cut Set
The smallest combination of component and human failures which, if they all occur, will cause the top event to occur. The failures all correspond to Basic or Undeveloped Events.
Minimal Cut Set Approach
A term used in Fault Tree Analysis to describe the smallest combination of component and human failures which, if they all occur, will cause the top event to occur. The failures all correspond to Basic or Undeveloped Events.
Minimum Autoignition Temperature (MAIT) of a Dust Cloud
The minimum temperature at which a given dust cloud will auto ignite when exposed to air heated in a furnace at local atmospheric pressure.
Minimum Explosible Concentration (MEC)
The lowest concentration of a combustible dust in air, expressed in grams per cubic meter that will propagate a flame.
Minimum Flammable Mass
The lowest mass of fuel in the flammable range that will cause a defined level of damage.
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
Minimum Oxygen Concentration (MOC)
See Limiting Oxidant Concentration.
Minor Incidents
Accidents or near misses that have acceptable consequences but for which recurring events of this magnitude may warrant an investigation.