Daily peak

The maximum volume of gas delivered in anyone day during a given period, usually a calendar year.

Dangerous area

Definition of an area so far as danger may arise from electrical causes.

Dangerous atmosphere

An atmosphere containing any flammable gases or vapour in a concentration capable of ignition by any cause. or containing a toxic gas or vapour in such a concentration which will be dangerous to human life.

Darcy

A unit of permeability. A porous medium has a permeability of I darcy when a pressure gradient of I atm/cm on a rock sample of 1 cm2 cross section will force a liquid of 1-cp viscosity through the sample at the rate of I cc per sec.

Data

General term used to denote facts. numbers. letters, and symbols. The basic elements of information; usually but not always expressed in numerical form.

Data bank

A system for describing. storing, and retrieving high volumes of complex structured data. A data bank is comprised of the data base and a set of data bank software (data base management system. DBMS) which store and retrieve information according to predefined data descriptions. and for carrying out additional operations. Also called data base system.

Data base

Physical storage of data belonging to a data bank.

Data processing

Any operation carried out with data.

Data set

A logical entity of data consisting of several elements (fields) grouped under one criterion.

Datum

Any numerical or geometrical quantity or set of such quantities which may serve as a reference or base for other quantities. In geodesy two types of datums must be considered: a horizontal datum which forms the basis for computations of horizontal control surveys in which the curvature of the earth is considered, and a vertical datum to which elevations are referred. World Geodetic System 1972 (WGS72). Represents pre 1972 data evaluation of the best global fit datum. Used for Transit and early GPS. World Geodetic System 1984 (WGS84). Represents pre 1984 data evaluation of the best global fit datum. Used for transit and LPS. Mean Sea Level (MSL). The average height of the surface of the sea at a tide station for all stages of the tide over a given period,usually determined from hourly height readings measured from a fixed predetermined reference level (ChartDatum). Lowest Astronomical Tide (LAT). The lowest tide level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions.

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