Combining technical and organisational elements in layer of protection analysis

Traditionally, in process industry, risks are reduced with technical solutions and organisational measures. The performance of both types of "solutions" depends on many factors and can not easily be compared. Especially the effectiveness of organisational measures such as the use of procedures, education, training and improving the safety culture are hard to quantify. Nevertheless, in an integral approach towards safety, there is a strong need to compare both types of measures to choose the best solution for a given situation. This paper describes the method used by TNO to combine organisational and technical aspects in one semi-quantitative safety analysis. This analysis is based on Layer of Protection Analysis (LOPA) and is used to calculate the probability of accident scenarios based on the technical safety. In most cases the event or failure frequencies in the LOPA are affected by organisational aspects. The results of a survey of the safety culture, Occupational Health and Safety (OHS) structure and the latent failures within the organisation provide the information to incorporate the organisational aspects in the LOPA. The LOPA results in scenario frequencies which can be compared to predefined risk tolerance criteria. If the criteria are not met, several additional (intended) measures can be added in the LOPA to find the most effective way to reach these criteria. By calculating the costs and amount of risk reduction per measure, the costs and benefits of technical and organisational measures can easily be compared.