214 • Use in Hazardous EnvironmentsWAGO-I/O-SYSTEM 750ETHERNET TCP/IP7 Use in Hazardous Environments7.1 ForewordToday’s development shows that many chemical and petrochemicalcompanies have production plants, production, and process automationmachines in operation which use gas-air, vapor-air and dust-air mixtureswhich can be explosive. For this reason, the electrical components used insuch plants and systems must not pose a risk of explosion resulting in injury topersons or damage to property. This is backed by law, directives or regulationson a national and international scale. WAGO-I/O-SYSTEM 750 (electricalcomponents) is designed for use in zone 2 explosive environments. Thefollowing basic explosion protection related terms have been defined.7.2 Protective measuresPrimarily, explosion protection describes how to prevent the formation of anexplosive atmosphere. For instance by avoiding the use of combustibleliquids, reducing the concentration levels, ventilation measures, to name but afew. But there are a large number of applications, which do not allow theimplementation of primary protection measures. In such cases, the secondaryexplosion protection comes into play. Following is a detailed description ofsuch secondary measures.7.3 Classification meeting CENELEC and IECThe specifications outlined here are valid for use in Europe and are based onthe following standards: EN50... of CENELEC (European Committee forElectrotechnical Standardization). On an international scale, these arereflected by the IEC 60079-... standards of the IEC (InternationalElectrotechnical Commission).7.3.1 DivisionsExplosive environments are areas in which the atmosphere can potentiallybecome explosive. The term explosive means a special mixture of ignitablesubstances existing in the form of air-borne gases, fumes, mist or dust underatmospheric conditions which, when heated beyond a tolerable temperature orsubjected to an electric arc or sparks, can produce explosions. Explosive zoneshave been created to describe the concentrations level of an explosiveatmosphere. 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 permanentlyemployed in an explosive environment have to be much more stringent thanthose placed on electrical components that are only rarely and, if at all, forshort periods, subject to a dangerous explosive environment.
