ILME: APX Gehäuse aus Aluminiumdruckguss - APV ATEX

7 To determine if these conditions may occur, it is necessary to follow the procedure described below. Analysis of emissions - Assessment of the substances used and identification of combustive dusts - Acquisition of all data on the chemical-physical properties of the combustive dusts involved and as required for assessment purposes - Identification of the emission sources, intended as points or parts of a processing plant from which combustive dust may leak causing the formation of a potentially explosive atmosphere Note: a layer of dust may represent a source of emission because it could cause the dispersion of a cloud in the presence of air flows. The dust may also act as ignition source in existing explosive atmospheres. - Assessment of the emission degree for each emission source As for gases, the emission degrees of dust can be classified as follows: - Continuous: if the emission is continuous or can occur for long periods of time during the ordinary use of processing equipment (inside storage equipment, silos, hoppers) - First: if the emission can occur periodically or occasionally during the ordinary use of the processing equipment (samplings, areas where loading and discharge operations are carried out) - Second: if the emission is unlikely to occur during the ordinary use of processing equipment, but can occur occasionally and only for short periods of time, for example due to a fault (flanges, bag discharge units) Classification of areas The current reference standard for the classification of areas where dangers may occur in presence of flammable gases, vapours or mists is EN 60079-10-1. The probability of the formation of an explosive atmosphere due to the presence of gases, that is the classification of the type of zone, is essentially related to the emission degree and ventilation. Zones are classified as Zone 0, Zone 1, Zone 2 and safe areas. Zones can be defined as follows: - Zone 0 Area around a continuous degree emission - Zone 1 Area around a first degree emission - Zone 2 Area around a second degree emission For combustive dust there is a rather direct transition between the degree of the emission source and the type of dangerous zone that forms: - Zone 20 Area around continuous degree emissions - Zone 21 Area around first degree emissions - Zone 22 Area around second degree emissions The presence of a suction system is extremely important to maintain the areas clean. If the suction system is adequate and guaranteed, it is possible to reduce the classification of zones because this type of equipment prevents the formation of layers, thus reducing the emission sources and the extent of the dangerous area. After determining the type of dangerous zone, it is necessary to determine its extension in accordance with the requirements of the standard. At present the reference standard is EN 60079-10-2 . Table 1 – Categories of ATEX products and application zone Category Protection level Presence and duration of the explosive atmosphere ZONE (gases) ZONE (dust) 1 - Very high - Two protection barriers - Safety guaranteed even with two faults - Permanent, frequent or for long periods of time during the ordinary use of equipment Zone 0 Zone 20 2 - High - One protection barrier - Safety guaranteed even with one fault - Occasionally, probable during the ordinary use of equipment Zone 1 Zone 21 3 - Normal - Safety guaranteed during the use of the equipment normal - Unlikely during the ordinary use of the equipment - For short periods only Zone 2 Zone 22