Analysis of Ignition Risk on Mechanical Equipment in ATEX

Until the implementation of the ATEX directive 94/9/CE, the certification of equipment intended to explosive atmospheres was only dedicated to electrical equipment. Since the 1st July 2003, the non-electrical sources of inflammation are also to be looked at before putting an ATEX equipment on the market (pumps, couplers, reducing gears,...). Among these sources, mechanical friction and impacts are a main cause of ignition of explosive atmosphere. The risk analysis of the equipment consists in considering the failures, which can lead to ignition. If the failure involves a friction between two parts or an impact, we shall estimate if this friction or impact dissipates a sufficient amount of energy to ignite the surrounding explosive atmosphere. As part of the European program MECHEX, we have studied the process of degradation of the mechanical energy into heat during friction and impacts and we have examined the mechanisms of ignition at the contact zone. An extensive experimental program is presented and some "simple" modelling is proposed on purpose of practical applications. For frictional situations, a critical rubbing power is calculated without any limitations as for a potential lower boundary concerning the rubbing velocity. For "impacts", the relevant parameter for ignition is not the kinetic energy of the projectile but its velocity and the nature of the materials.