Application in Explosive Environments • 139
Foreword
WAGO-I/O-SYSTEM 750
DeviceNet
6 Application in Explosive Environments
6.1 Foreword
Today’s development shows that many chemical and petrochemical com-
panies have production plants, production, and process automation ma-
chines 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 in-
jury 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 explo-
sive environments. The following basic explosion 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
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 sec-
ondary explosion protection comes into play. Following is a detailed de-
scription 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
reflected by the IEC 60079-... standards of the IEC (International Electro-
technical
Commission).
6.3.1 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 un-
der atmospheric conditions which, when heated beyond a tolerable tem-
perature 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 ex-
plosion occurring, is of great importance both for technical safety and fea-
sibility reasons. Knowing that the demands placed on electrical compo-
nents 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 envi-
ronment.
