Abstract
In the European Union, assessing the hazard of the explosion in a plant of a dust or gas atmosphere is mandatory for its manager (European directive 1999/92/EC). This assessment relies on three different steps:the identification of the position of explosive areas and their frequency (appear during normal process, appear rarely during normal process, do not appear during normal process, do not appear at all) based on the standards IEC 60079-10-1 for gas atmospheres and IEC 60079-10-2 for dust atmospheresthe identification and the assessment of the frequency occurrence of ignition sources based on the standard EN 1127-1 the assessment of the plausible consequences of an explosion based on the standard ISO 14121-1. When the assessment highlights that the hazard of explosion is too high, some corrective measures must be implemented to decrease this hazard to a reasonably value. It is common that for a large plant, several dozens of actions need to be implemented.
To the authors’ knowledge, there is a lack of method in the literature to help HSE engineers to rank the actions to be taken. What should be corrected first? A very rare deviation that could severely injure or even kill an operator or a less dangerous but more frequent one?This paper proposes a method derived from the determination of a SIL level (standard IEC 61511-3). A similar decision tree is build which is based on the consequences of the explosion defined in ISO 14121-1. It takes into account the probability of attendance of an operator in the hazardous area and the frequency of occurrence of an ignition source and of an explosive atmosphere.
This method gives an index for each couple of [consequence of an explosion/ frequency of occurrence of an explosion]. It thus permits to compare each situation and correct the one with the highest index first. This method is very flexible and can be adapted to every situation. It allows emphasizing one or two of the used parameters according the safety policy of the firm who uses it. It is thus possible to justify to the authorities the choice of the prioritized actions. This method will be illustrated with two case studies.
