Use In Hazardous Environments; Protective Measures; Classification Meeting Cenelec And Iec; Foreword - WAGO 750 Series Manual

9 Use in Hazardous Environments

9.1 Foreword

Today's development shows that many chemical and petrochemical
companies have production plants, production, and process automation
machines in operation which use gas-air, vapor-air and dust-air mixtures
which can be explosive. For this reason, the electrical components used in
such plants and systems must not pose a risk of explosion resulting in injury to
persons or damage to property. This is backed by law, directives or regulations
on a national and international scale. WAGO-I/O-SYSTEM 750 (electrical
components) is designed for use in zone 2 explosive environments. The
following basic explosion protection related terms have been defined.

9.2 Protective measures

Primarily, explosion protection describes how to prevent the formation of an
explosive atmosphere. For instance by avoiding the use of combustible
liquids, reducing the concentration levels, ventilation measures, to name but a
few. But there are a large number of applications, which do not allow the
implementation of primary protection measures. In such cases, the secondary
explosion protection comes into play. Following is a detailed description of
such secondary measures.

9.3 Classification meeting CENELEC and IEC

The specifications outlined here are valid for use in Europe and are based on
the following standards: EN50... of CENELEC (European Committee for
Electrotechnical Standardization). On an international scale, these are
reflected by the IEC 60079-... standards of the IEC (International
Electrotechnical Commission).
9.3.1 Divisions
Explosive environments are areas in which the atmosphere can potentially
become explosive. The term explosive means a special mixture of ignitable
substances existing in the form of air-borne gases, fumes, mist or dust under
atmospheric conditions which, when heated beyond a tolerable temperature or
subjected to an electric arc or sparks, can produce explosions. Explosive zones
have been created to describe the concentrations level of an explosive
atmosphere. This division, based on the probability of an explosion occurring,
is of great importance both for technical safety and feasibility reasons.
Knowing that the demands placed on electrical components permanently
employed in an explosive environment have to be much more stringent than
those placed on electrical components that are only rarely and, if at all, for
short periods, subject to a dangerous explosive environment.
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Use in Hazardous Environments • 213
Foreword