CCPS Process Safety Glossary | AIChE

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CCPS Process Safety Glossary

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Demand Rate

The number of demands divided by the total elapsed operating time during which the demands occur.

Demand Spectrum

The total number of demands for the data window experienced by the component population, considering test, interface, failure-related maintenance, and automatic and manual initiation demands.

Demand-Related Failure

A failure that is primarily related to the number of times that a device or system is challenged (cycled) rather than the length of time the device or system is in service. The failure of a piece of wire after repeated bending would be considered to be a demand-related failure. Demand-related failures are sometimes called cyclic failures.

Demographic Data

The description of the population along the transportation route, which can include the development and use of representative urban and rural population densities along the route or more precise estimates (e.g., census data).

Denier

Fiber weight per unit length (gram/9000-m length)

Dense cloud

Cloud density is greater than ambient air density, due to the high molecular weight, the cold temperature, and/or the presence of aerosols in the emissions. Dense cloud and heavy cloud are synonymous.

Dense Gas

A gas with density exceeding that of air at ambient temperature. Sometimes the expression is used loosely to apply to aerosols such as flashing liquid ammonia. See also heavy gas and negatively buoyant vapors.

Dependent Failure

Failure whose probability cannot be expressed as the simple product of the unconditional probability of the individual events, which causes it.

Deposition

The rate at which material accumulates on a surface

Depth Of Study

A measure of level of review, degree of complexity, and extent of detail involved in a CPQRA.

Dermal

Used on or applied to the skin. Importance: Dermal exposure, as well as inhalation exposure, must be considered to prevent adverse health effects.

Dermal Toxicity

Adverse effects resulting from skin exposure to a substance. Also referred to as "Cutaneous toxicity". Importance: Ordinarily used to denote effects in experimental animals.

Design Basis Incident (DBI) (or maximum credible incident)

A serious incident that has some small likelihood of occurring during the lifetime of a facility but consequences of which (resulting hazard zones) are used in siting, plant layout, and/or emergency planning decisions.

Design Case

Conditions to be used for the design of a vent system to ensure it will meet safety, health, environmental, and commercial objectives. For emergency vent headers, this will normally be based on the worst credible case scenario. For normal process vents, the design should take into consideration all non-emergency situations unless they will be addressed by some other means, such as by providing a temporary vent system for maintenance operations.

Design Institute for Emergency Relief Systems (DIERS)

Institute under the auspices of the American Institute of Chemical Engineers founded to study relief requirements for reactive chemical systems and two-phase flow systems.

Detection

A countermeasure strategy intended to identify an adversary attempting to plan or commit a chemical security event or other criminal activity via either real-time observations or pre-incident analysis of the activities/intelligence.

Detection Systems

A mechanical, electrical, or chemical device that automatically identifies the presence of a material or a change in environmental conditions such as pressure, temperature, or composition. (Bartleby.com)

Determine

To conclude; to reach an opinion consequent to the observation of the fit of sample data within the limit, range, or area associated with substantial conformance, accuracy, or other predetermined standard; to obtain firsthand knowledge of.

Deterrence

A countermeasure strategy intended to prevent or discourage the occurrence of a breach of security by means of fear or doubt.

Detonable Limits

The minimum and maximum concentrations of a combustible material, in a homogeneous mixture with a gaseous oxidizer, that will propagate a detonation

Detonation

A release of energy caused by the propagation of a chemical reaction in which the reaction front advances into the unreacted substance at greater than sonic velocity in the unreacted material.

Detonation Flame Arrester

A flame arrester used to prevent the transmission of a detonation.

Detonation Momentum Attenuator

A mechanical device inside of a detonation flame arrester whose purpose is to reduce both the high pressure and the dynamic energy of a detonation and to split the flame front before it reaches the actual flame arrester element, thus avoiding structural damage to the element. (This device is also called a shock absorber device by some manufacturers.)

Deviation

A process condition outside of established design limits, safe operating limits, or standard operating procedures.

Device

Part of a Programmable Electronic System.

Diagnostic Alarm

See Pretrip Alarm.

Diagnostic Program (Active - On Line)

A troubleshooting aid for identifying hardware malfunctions in a system or a program before they result in failure of the system to perform its desired function.

Diagnostic Program (Active)

A troubleshooting aid for correcting hardware malfunctions in a system or a program before they become a safety hazard.

Diagnostic Program (Passive - Off Line)

A troubleshooting side for locating hardware malfunctions in a system or a program to aid in locating coding errors in newly developed programs.

Diagnostic Program (Passive - On Line)

A troubleshooting aid for identifying hardware malfunctions in a system or a program when they occur.

Diagnostic Program (Passive)

A troubleshooting aid for locating hardware malfunctions in a system or a program to aid in locating coding errors in newly developed programs.

Diagnostic Programs

Computer programs that isolate equipment malfunctions or programming errors.

Diagnostic Routine

An electronic-computer routine designed to locate a malfunction in the computer, a mistake in coding, or both. A routine used to locate a malfunction in a computer, or to aid in locating mistakes in a computer program. Thus, in general, any routine specifically designed to aid in debugging or troubleshooting.

Diagnostics

A frequent (in relation to the process safety time) automatic test to reveal faults.

Dielectric Constant (?r).

A dimensionless parameter expressing the ratio of the permittivity of a material to that of vacuum. Metals have an infinite dielectric constant while gases and vapors have a dielectric constant close to unity.

Differential Scanning Calorimetry (DSC)

A technique in which the difference in energy inputs into a substance and a reference material is measured as a function of temperature, while the substance and the reference material are subjected to a controlled temperature program. (ASTM E 1445)

Differential Thermal Analysis (DTA)

A technique in which the temperature difference between a substance and reference material is measured as a function of temperature while the substance and the reference material are subjected to a controlled temperature program. (ASTM E 1445)

Digital System

Any programmable electronic system such as a PLC, DCS, or microcomputer.

Dike

An embankment or wall built to act as a barrier blocking passage of liquids to surrounding areas. (Dictionary.com)

Dilution

Reduction in concentration due to effect of wind.

Direct Address

An address that designates the storage location of an item of data to be treated as an operand.

Direct Addressing

A method of addressing in which the address part of an instruction contains a direct address.

Direct Digital Control (DDC)

A mode of control wherein digital computer outputs are used to directly control a process. A computer control technique that sets the final control-elements position directly by the computer output. Used to distinguish from analog control.

Directional Incident Outcome

An incident outcome whose consequences produce an effect zone determined by a given wind direction.

Directional Probability

Probability in a given wind direction.

Discipline

Within the context of Operational Discipline (OD), discipline refers to; 1) an orderly or prescribed conduct or pattern of behavior, and 2) a rule or system of rules governing conduct or activity. The word discipline, as used in OD, does NOT refer to punishment.

Disconnect

See Connect.

Discrete

Refers to individual, distinct things such as bits, characters, or circuit components. This also refers to On-Off type input/output modules. Pertaining to distinct elements or to representation by means of distinct elements, such as characters.

Discrete I/O

Inputs that accept on/off signals form limit switches, push buttons, and other types of switches or contact closures. On/off outputs that can operate medium power loads (e.g., solenoids, power relays, starters, lights).

Dispersion Coefficient

The standard deviation s in a specified direction of the Gaussian distribution model used in atmospheric dispersion. The dispersion coefficient is normally expressed as a function of distance for a given weather stability.