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6 Use in Hazardous Environments
6.1 Foreword
Today's development shows that many chemical and petrochemical compa-
nies have production plants, production, and process automation machines in
operation which use gas-air, vapor-air and dust-air mixtures which can be ex-
plosive. For this reason, the electrical components used in such plants and sys-
tems 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 de-
signed for use in zone 2 explosive environments. The following basic explo-
sion protection related terms have been defined.
6.2 Protective measures
Primarily, explosion protection describes how to prevent the formation of an
explosive atmosphere. For instance by avoiding the use of combustible liq-
uids, reducing the concentration levels, ventilation measures, to name but a
few. But there are a large number of applications, which do not allow the im-
plementation of primary protection measures. In such cases, the secondary ex-
plosion protection comes into play. Following is a detailed description of such
secondary measures.
6.3 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 re-
flected by the IEC 60079-... standards of the IEC (International Electrotechni-
cal Commission).
6.3.1 Divisions
Explosive environments are areas in which the atmosphere can potentially be-
come explosive. The term explosive means a special mixture of ignitable sub-
stances existing in the form of air-borne gases, fumes, mist or dust under at-
mospheric 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 atmos-
phere. 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, sub-
ject to a dangerous explosive environment.
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