If, despite primary explosion protection measures, it is possible for a hazardous, potentially explosive atmosphere to form (to a degree that requires measures to protect employees against explosion hazards), the ignition of this hazardous, potentially explosive atmosphere must be effectively prevented. All possible sources of ignition are evaluated, and the appropriate protective measures applied. Effective sources of ignition on equipment and installations can, for example, be prevented using types of protection corresponding to the necessary level of protection.
The classification of potentially explosive areas into zones (The frequency and duration of the occurrence of a hazardous explosive atmosphere and the local environmental conditions) forms the basis for defining the level of protection for equipment. It is furthermore necessary to know the key explosion-related figures for the flammable materials (grouping, temperature classes, dust ignition and smouldering temperatures) as well as the local ambient conditions.
The explosion characteristics help the owner/ managing operator to specify the risk in the area precisely and help the operating equipment manufacturer to select a suitable solution for the operating equipment and finally they help the installation engineer to select and assign the suitable Ex Equipment. Ultimately, this data is found in the Ex Equipment labelling. The procedures for applying secondary explosion protection measures will be described in greater detail in the following chapter.
