September 2024 | AIChE

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September 2024

Distributed Control System (DCS)

A system which divides process control functions into specific areas interconnected by communications (normally data highways), to form a single entity. It is characterized by digital controllers and typically by central operation interfaces. Distributed control systems consist of subsystems that...

Disproportionation

A chemical reaction in which a single compound serves as both oxidizing and reducing agent and is thereby converted into a more oxidized and a more reduced derivative; e.g., a hypochlorite upon appropriate heating yields a chlorate and a chloride.

Dispersion Models

Mathematical models that characterize the transport of toxic/flammable materials released to the air and/or the water.

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.

Directional Probability

Probability in a given wind direction.

Directional Incident Outcome

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

Dilution

Reduction in concentration due to effect of wind.

Dike

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

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)

Deviation

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

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