ATEXI0 5

How can an explosion be prevented?

Most important is the prevention of the formation of an Ex atmosphere. If this is not possible,potential sources of ignition must be avoided. For electrical equipment for use with gases, vapours and mists special design methods aredescribed in comprehensive works standards and are assigned to “ignition protection categories“ (see Table 2). Several ignition protection categories can be combined in one unit.The methods of protection with Ex dusts concentrate mainly on the sealing of the housing (IPprotection).Principles and requirements for Ignition protection categories non-electrical equipment for use in Ex areas are described in thenew EN 13463-1. Standards for appropriate types of ignition protection are currently in preparation.Measures that can be taken to reliably exclude potential sources of ignition, depend upon theequipment category required. In the foreground is usually the consideration of the permissible light metal alloys, electrostatic charge, possible arcing and heat due to friction.

Table 2

Ignition protection categoriesIdentificationcan be used in zoneSafety principle Increased safetyEEx e1 Non-sparking equipmentEEx nA 2 Pressurised encapsulationEEx d1 Sand encapsulationEEx q1 Enclosed switching deviceEEx nC 2 Intrinsic safety (special requirements)EEx ia0 Intrinsic safetyEEx ib1 Energy-limiting equipmentEEx nL 2 EncapsulationEEx m1 Oil encapsulationEEx o1 Pressurisation EEx p1 Simplified pressurisationEEx nP 2Vapour-proof housingEEx nR2 no arcs, sparks or hot surfacescontrols an internal explosion and extinguishes the flamelimits the energy of the sparks andthe temperature of the surfaceseparates source of ignition frompotentially explosive atmosphere