Towards A Holistic Approach for Quantifying Losses RELATED to SAFETY Instrumented Systems by Including Organizational FACTORS

According to IEC standards (IEC, 1998), failures of safety instrumented systems can be categorized either as random or systematic failures. A major distinguishing feature between random hardware failures and systematic failures is that system failure rates arising from random hardware failures can be estimated, while events leading to systematic failures cannot be easily predicted.

Several authors have pointed out the lack of a standard concerning systematic failures. Redmill (1998), for instance, states that it is an unfortunate omission a safety standard based on modern principles that does not have guidance on the importance of human factors. In the same way, Hokstad & Corneliussen (2004) proposed a model for loss of safety by quantification systematic failures. Summers (2008) believes that a quality management system must be used to sustain the rigor necessary to maintain equipment reliability.

Although several initiatives to close this gap may be clearly seen as, for example, Colombo & Demichaela (2008) and Costella et al (2009), one should bear in mind that an explicit consideration of organizational factors is to be made, because safety systems failures continue to happen. This means, for example, that automation-related issues in the context of standards should be considered, Kitamura et al (2005). The consideration of organizational factors brings into play the understanding that the nature of accidents, Hollnagel (2004), is as important as their causes. A discussion on the role of latent failures, Reason (1997), is fundamental in this context. The review of accident modeling approaches is also relevant, as discussed in Qureshi (2007) for example.

It is highly desirable to link human factors to organization and safety management through a holistic model (Bellamy et al, 2008). Holism is the idea that the properties of a system cannot be determined or explained by the sum of its components alone. Compared to technical factors, the human and organizational components of a technological system are characterized by their multi-dimensional aspect and intrinsic complexity due to the nonlinear interactions which influence their behavior (Zio, 2009). A possible model for this purpose is the one proposed by Levenson (2002). In this way we want to discuss and show how a systemic model, which is holistic and has an intrinsic complexity can contribute to establish this important link and in the future to offer elements for quantifying the influence of organizational factors on the quantification of the loss of safety, in the context of safety instrumented systems.

References

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