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Programmable Logic Controller (PLC)
A PLC is a PE programmable controller (e.g, a PES device, a PE logic solver) that has its embedded software designed in such a way as to provide plant floor user oriented application programming languages, and industrial ESD and response capability similar to electro-mechanical technology. The PLC was originally designed to replace relays in the automotive manufacturing process and has been continuously updated to presently achieve many DCS capability characteristics.
Proof Test
Periodic test performed to detect dangerous hidden failures in a system so that, if necessary, a repair can restore the system to an “as good as new” condition, or as close as practical to this condition.
Proof Test Interval
The time interval between checking a protection system.
Proof Test Time Interval (T)
The interval of time between two successive proof tests. Dimension (Time).
Proof Testing
A run through the process substituting nonhazardous materials (e.g., water) to check for the adequacy of the equipment e.g., heating/cooling load, and to verify procedural steps.
Propagating Factors
Human, process, and environmental actions and influences that contribute to guiding, sustaining, continuing, transmitting, spreading, and extending the sequence of events following the initiating event.
Property Boundary
The boundary that is or can be built upon including the opposite side of a public way. (NFPA 30)
Protection Layer
A concept whereby a device, system, or human action is provided to reduce the likelihood and/or severity of a specific loss event.
Protective System
Systems such as pressure vessel relief valves, which function to prevent or mitigate the occurrence of an incident.
Protocol (Regulated Product Development)
Documentation that ties together all SOPs (standard operating procedures) to direct the work performed in a regulated facility; who approves what, who is allowed to sign off on materials and products, where certain files and documents are kept, and so on; also a detailed plan for a clinical trial, stating (among other things) the trial's rationale, purpose, scope, dosages, routes of administration, length of study, and eligibility criteria.
Proximate Cause
The cause factor which directly produces the effect without the intervention of any other cause. The cause nearest to the effect in time and space.
PSM Audit
An activity to determine and status and quality of a PSM program. This term is not used to describe an audit performed exclusively in response to OSHA's PSM Standard, but to an audit of any PSM program.
Public Emergency Exposure Limit (PEEL)
The maximum concentration in air of a toxic material to which the public might be exposed without significant adverse impacts in the event of an accident.
Puff
A cloud of pollutants resulting from a nearly instantaneous or short duration release.
Puff Release
See Instantaneous Release.
Purge Gas
A gas that is continuously or intermittently added to a system to render the atmosphere noncombustible. The purge gas can be inert or combustible.
Purging
The removal of oxygen from a closed system (equipment and piping) to below the LOC of the particulate solid by means of applying pressure, vacuum, and/or a purge gas.
Qualitative
Based primarily on description and comparison using historical experience and engineering judgment, with little quantification of the hazards, consequences, likelihood, or level of risk.
Qualitative Methods
Refers to the method of evaluation gained through experience (e.g., application, operation, support) or essential, required and desirable features.
Qualitative Risk Analysis
Based primarily on description and comparison using historical experience and engineering judgment, with little quantification of the hazards, consequences, likelihood, or level of risk.
Quality Assurance
A planned, systematic pattern of actions necessary to provide suitable confidence that a system or component will perform satisfactory in actual operation. A systematic pattern of actions throughout design and production, to ensure confidence in a product's conformance with specifications. A set of systematic actions intended to provide confidence that a product or service will continually fulfill a defined need.
Quality Assurance (QA)
Activities performed to ensure that equipment is designed appropriately and to ensure that the design intent is not compromised, providing confidence throughout that a product or service will continually fulfill a defined need the equipment's entire life cycle.
Quality Assurance (QA)
Activities performed to ensure that equipment is designed appropriately and to ensure that the design intent is not compromised, providing confidence throughout that a product or service will continually fulfill a defined need through the equipment's entire life cycle.
Quantitative Methods
Refers to the method of evaluation obtained through measurement or mathematical analysis of essential, required and desirable features. Refers to the method of evaluation gained through measurement or mathematical analysis of essential, required and desirable features.
Quantitative Risk Analysis (QRA)
The systematic development of numerical estimates of the expected frequency and severity of potential incidents associated with a facility or operation based on engineering evaluation and mathematical techniques.
Quantitative Risk Assessment (QRA)
The use of Quantitative Risk Analysis results to make decisions, either through relative ranking of risk reduction strategies or through comparison with risk targets.
Quantitative Risk Assessment (QRA)
A quantitative evaluation of the overall risk, determined by combining the frequencies and consequences of potential incident scenarios.
Quench Drum
A vessel with internal liquid sprays supplied by an external recirculation pump loop with a quenching liquid sprayed directly into the vapor space to contact, cool, and condense at least part of the hot vented gas or vapor stream before these gases enter the main vent header system.
Quench Pool
A closed vessel containing a relatively large volume of liquid. The emergency vent stream is sparged subsurface through the liquid volume at high velocity, resulting in vigorous agitation and circulation of the pool contents in order to maximize cooling and condensation or reaction with the pool liquid. Most or all of the vented stream can be captured; residual vapor and non-condensable gas may be released to the vent header system for further treatment or disposal.
Quenching
Rapid cooling from an elevated temperature, e.g., severe cooling of the reaction system in a short time (almost instantaneously), "freezes" the status of a reaction and prevents further decomposition or reaction.
Rain Out
When a superheated liquid is released to the atmosphere, a fraction of it will flash into vapor. Another fraction may remain suspended as an aerosol. The remaining liquid, as well as portions of aerosol, may "rain out" on the ground.
Random Demands
Where the time or approximate time of the demand occurrence is predictable, the primary concern is whether the ESD system is operational at that time. In other words, the criteria is related to the cumulative probability of failure of the ESD system over the appropriate time interval which ends with the occurrence of the demand.
Rare event
An event or incident whose expected frequency is very small. The event is not statistically expected to occur during the normal life of a facility or operation.
Rate of Reaction
The rate at which the conversion of reactants takes place. The rate of reaction (r) is a function of concentrations (F(c)) and the reaction rate constant (k): r = koF(cA,cB,...,cX). The heat (q) produced by a reaction is a linear function of the rate of reaction which makes the rate of reaction a basic parameter in determining the required cooling capacity during all stages of the reaction process.
Raw Data
The original records from which reliability data is extracted; the facility records of equipment failure, repair, outage, and exposure hours or demands which require analysis and encoding in order to be placed into data elements.
Reactants
Chemicals that are converted into the required products during the reaction process.
Reaction
Any transformation of material accompanied by a change of enthalpy which may be endothermic or exothermic. (ASTM E 1445)
Reaction Induction Time (RIT)
The time a chemical compound or mixture may be held under isothermal conditions until it exhibits a specific exothermic reaction. (ASTM E 1445)
Reaction Kinetics
The complex of data (thermodynamic and kinetic), that determine a reaction.
Reactive Chemical
A substance that can pose a chemical reactivity hazard by readily oxidizing in air without an ignition source (spontaneously combustible or peroxide forming), initiating or promoting combustion in other materials (oxidizer), reacting with water, or self-reacting (polymerizing, decomposing or rearranging). Initiation of the reaction can be spontaneous, by energy input such as thermal or mechanical energy, or by catalytic action increasing the reaction rate.
Reactive Groups
Categories of chemicals that react in similar ways, often because they are similar in their chemical structure. (NOAA 2002)
Reactive Substance/Material
Substance or material which enters into a chemical reaction with other stable or unstable material.
Reactivity
The relative tendency of a substance to undergo chemical reaction (low, medium, or high).
Reactivity, Chemical
See chemical reactivity.
Readiness Review
A work activity that occurs prior to initial start-up or restarting a process unit to verify that the condition of process equipment and safety systems, the status of limiting conditions for operations, and in some cases, the training and qualification status of personnel conform to predefined conditions. Also Operational readiness review and pre-start-up readiness review.
Receptor
An instrument, person, or hypothetical location where the pollutant concentration is observed or calculated.
Recognized and Generally Accepted Good Engineering Practice (RAGAGEP)
"Recognized and generally accepted good engineering practice", a term originally used by OSHA, stems from the selection and application of appropriate engineering, operating, and maintenance knowledge when designing, operating and maintaining chemical facilities with the purpose of ensuring safety and preventing process safety incidents.
It involves the application of engineering, operating or maintenance activities derived from engineering knowledge and industry experience based upon the evaluation and analyses of appropriate internal and external standards, applicable codes, technical reports, guidance, or recommended practices or documents of a similar nature. RAGAGEP can be derived from singular or multiple sources and will vary based upon individual facility processes, materials, service, and other engineering considerations.
Recovery Factors
Feedback factors that limit or prevent the undesirable consequences of a human error.
Reduced Explosion Pressure, Pred
The maximum pressure developed in a vented enclosure during a vented deflagration, or during deflagration suppression.
Reduced Pressure (Pred)
The maximum pressure developed in a vented enclosure during a vented deflagration.