Cross-Reference List
A list showing all the locations in a PES Program at which a selected list of data objects is operated upon.
Cryogenic Liquid
A refrigerated liquid gas having a boiling point below -130 F (-90 C) at atmospheric pressure. (NFPA 30)
CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
A method of controlling multi-access computer networks in which each station on the network senses traffic and waits for it to clear before sending a message, and two devices that try to send concurrent messages must both step back and try again.
CSST
Critical Steady-State Temperature; The highest ambient temperature at which self-heating of a material as handled (package, container, silo, vessel, etc.) still does not result in a runaway but in a stationary condition as identified by classical explosion theory (see also SADT)
CSTR
Continuous-flow Stirred Tank Reactor; A tank reactor characterized by a continuous flow of reactants into and products from the reaction system. Composition and temperature of the reaction system is at all times identical to composition and temperature of the product stream.
Current (I)
The rate of transfer of electricity normally expressed in Amperes (Coulombs per second).
Current Density (J).
The current (Amperes) passing through unit area of a material (square meters).
Current Sinking
The act of receiving current.
Current Sourcing
The act of supplying current.
Damage Limiting Construction
Construction of equipment (building) with weak sections to limit the damage to the equipment (building). The weak sections fail early and prevent damage to the rest of the equipment (building).
Damage/failure mechanism
The mechanical, chemical, physical, or other process that results in equipment degradation. Identifying and inspecting for indications of the damage mechanism can be used to predict future failures.
Data
A representation of facts, concepts or instructions in a formalized manner suitable for communication, interpretation or processing by human or by "automatic" means. Characters or continuous functions representing information due to know or supposed arrangement.
Data Base
1) A repository for equipment reliability information categorized to facilitate data retrieval or 2) tabular lists of multiple data vectors, with little text except that needed to explain the data presentation format.
Data Cell
A unique compartment of the taxonomy in which data is stored, defined by specific equipment, service and failure descriptions.
Data Communication Equipment (DCE)
The equipment that provides the functions required to establish, maintain, and terminate a connection, as well as the signal conversion and coding required for communication between Data Terminal Equipment and data circuits.
Data Elements
The basic items which form a data set or data vector, e.g. component name, size, failure mode, mean, 5% confidence level, are each a data element.
Data Encoding
The assignment of codes and identifiers to data extracted from plant records so that failure rates may be readily calculated.
Data point
A numerical estimate of equipment reliability as a mean or median value of a statistical distribution of the equipment's failure rate or probability.
Data Resource
A data base, report, technical paper, journal article, or conversation which contains reliability data; subdivided into Data Bases, Data Sources, and Risk Analyses in this book.
Data Sets
A formal or informal collection of information with a cohesive element which distinguishes this data grouping from others; e.g., data from a particular facility, data for a particular time, data for a particular component.
Data Source
Descriptive text in a given subject area whose primary purpose is to discuss a reliability or risk topic but which also contains some useful reliability data.
Data Terminal Equipment (DTE)
Equipment consisting of digital and instruments that convert the user information into data signals for transmission or reconvert the received data signals into user information.
Data Vector
Only those data elements and numerical values that are used to specify failure characteristics, e.g. mean, distribution, failure modes, either as the cause or a contributing cause of the incident or as a response to the initiating event.
Data Window
A time frame established for a given data study.
De Minimis Risk
A level of risk that would be perceived by most to be broadly acceptable, and not requiring further reduction.
Dead-heading
A blockage on the discharge side of an operating pump which results in the flow reducing to zero and an increase in the discharge pressure. The energy input from the deadheaded pump increases the temperature and pressure of the fluid in the pump.
Deadheading
A blockage on the discharge side of an operating pump which results in the flow reducing to zero and an increase in the discharge pressure. The energy input from the deadheaded pump increases the temperature and pressure of the fluid in the pump.
Deadtime
The interval of time between initiation of an input change or stimulus and the start of the resulting observable response. Dimension (Time).
Decision tree
A logic tree used in reliability-centered maintenance (RCM) to help determine the correct type of maintenance (e.g., predictive, preventive) to perform to reduce the likelihood of equipment failures.
Decommissioning
Completely de-inventorying all materials from a process unit and permanently removing the unit from service. Decommissioning normally involves permanently disconnecting the unit from other processes and utilities, and is often followed by removal of the process piping, equipment, and support structures.
Decomposition
Breakdown of a material or substance (by heat, chemical reaction, electrolysis, decay, or other processes) into parts or element or simpler compounds. Importance: Decomposition products often present different hazards than the original material.
Decomposition Energy
The maximum amount of energy which can be released upon decomposition. The product of decomposition energy and total mass is an important parameter for determining the effects of a sudden energy release, for example, in an explosion. The decomposition energy can occasionally be obtained from the literature or calculated theoretically. (Barton and Rogers 1997)
Decomposition Flames
Flames that are produced by exothermic decomposition of certain gases in the absence of any oxidant provided that they are above minimum conditions of pressure, temperature, and pipe diameter. Common examples include acetylene, ethylene oxide, and ethylene.
Decomposition Temperature
Temperature at which spontaneous decomposition occurs. In practice it is impossible to indicate the exact value of this temperature, because according to the Arrhenius law the reaction rate will only be zero at absolute zero temperature (0 K). Therefore, in measuring the decomposition temperature the sample quantity and the sensitivity of the measuring device is very important.
Deductive Approach
Reasoning from the general to the specific. By postulating that a system/process has failed in a certain way, an attempt is made to determine what modes of system/component/operator/organization behavior contributed to the failure.
Defensive Measures
Measures directed to reduce the consequences of a runaway to an acceptable level. The chemical reaction of a substance in which the reaction front advances into the unreacted substance at less than sonic velocity. Where a blast wave is produced that has the potential to cause damage, the term explosive deflagration may be used.
Deflagration
A combustion that propagates by heat and mass transfer through the un-reacted medium at a velocity less than the speed of sound.
Deflagration Flame Arrester
A flame arrester used to prevent the transmission of a deflagration.
Deflagration Index, (KSt Value)
The measure of the explosibility of a dust cloud, in units of bar-m/s.
Deflagration Isolation
A method employing equipment and procedures that interrupts the propagation of a deflagration flame front past a point (usually in a pipe).
Deflagration Pressure Containment:
The technique of specifying the design pressure of a vessel and its appurtenances so that they are capable of withstanding the maximum pressures resulting from an internal deflagration.
Deflagration Suppression
The technique of detecting and arresting combustion in a confined space while the combustion is still in its incipient stage, thus preventing the development of pressures that could result in an explosion.
Deflagration to Detonation Transition (DDT)
The transition phenomenon resulting from the acceleration of a deflagration flame to detonation via flame-generated turbulent flow and compressive heating effects. At the instant of transition a volume of pre-compressed, turbulent gas ahead of the flame front detonates at unusually high velocity and overpressure.
Deflagration Venting
The reduction of pressure generated in a vessel by a deflagration by allowing the emergency flow of the vessel contents from the vessel by means of an opening in the vessel, thus avoiding the failure of the vessel by overpressure. The vent opening is usually closed by a pressure-relieving cover (e.g., rupture disk, explosion disk or hatch).
Degraded Failure
A failure which is gradual or partial; it does not cease all function but compromises that function. It may lower output below a designated point, raise output above a designated point or result in erratic output. A degraded mode might allow only one mode of operation. If left unattended, the degraded mode may result in a catastrophic failure.
Delay
A countermeasure strategy that is intended to provide various barriers to slow the progress of an adversary so as to prevent an attack or theft, increase the time necessary to cause an event, or assist in apprehension of an adversary and prevention of theft.
Delay Gates
A specialized logic form of an "AND" gate where all inputs to the gate must be true for a specified time period before the output from the gate can occur. Delay Gates are common when modeling the runaway reaction kinetics of a chemical reactor.
Delphi Method
A polling of experts utilizing the following procedure: Select a group of experts (usually three or more). Solicit, in isolation, their independent estimates on the value of a particular parameter and reasons for the choice. Provide initial results to all experts and all revisions to initial estimates. Use the average of the final estimates as the best estimate of the parameter. Use the standard deviation of the estimates as a measure of uncertainty.The procedure is interactive, with feedback between interactions.
Delphi Technique
A polling of experts. The Classical Delphi is a single estimate (for each questionnaire) of a single parameter by a single group. The Hybrid Delphi uses a single estimate of multiple parameters submitted by multiple groups. It allows the incorporation of published or recorded data during the polling process.
Demand
A plant condition or event which requires a protective system or device to take appropriate action in order to prevent a hazard. (1) A signal or action that should change the state of a device, or (2) an opportunity to act, and thus, to fail.