LOPA - A Method to Analyse Safety Integrity Systems according to IEC 61511

摘要

The Layer Of Protection Analysis, abbrev. LOPA, is a semi quantitative risk analysis method. The different layers, which are already applied or still in the planning phase will be analysed and evaluated via the LOPA in order to reduce the hazards for people, environment or machine to a tolerable residual risk. Herewith, one will consider any imaginable damage initiating events. With the adequate table of values for the occurrence frequency of such initiating events and for the failure probability of each protection layer, the remaining residual risk can be defined and compared to the required tolerable residual risk. Depending on the applications, some weighting factors having a corresponding risk reduction, such as for example the length of stay in a hazardous area, will be taken into account. Should the results show that the tolerable residual risk has not been achieved or has been under estimated, one would, in case no other constructive protection layers are possible, plan and apply a safety integrity system (SIS). The LOPA method allows defining the safety requirements in form of the necessary safety integrity levels SIL for the SIS.