Functional hazard analysis safety targets

Prove the accomplishment of Functional Hazard Analysis (FHA) safety targets ... 

A strategy that makes easier for the team to handle with large nodes was proposed and the main initiating events identified during the Petrobras coke drums HAZOP analysis were presented. Some LOPA results were commented in order to provide the reader the type of answers this approach allows. These results include the identification of the logics that need to be defined as safety instrumented functions and the required target SIL to achieve a tolerable frequency of occurrence for a specific hazard scenario. 

In order to determine the required SIL level, a detailed hazard analysis is performed for the equipment under control (EUC). From the hazard analysis, all safety functions are identified (example—Detect failure of braking). A target safety integrity level is assigned to each of the safety functions (example—detect failure of braking—SIL 3) in order to ensure the residual risk is lower than the acceptable risk (in other words, the risk is sufficiently reduced). The outcome will be an EUC safety function specification detailing the function and target SIL level (between 1 to %) required for each safety function identified in the hazard analysis. 

Which general targets could be formulated for a safety concept. ISO 26262 clearly defined that the functional and technical safety concept should be defined derived from the ITEM Definition, a system on vehicle level and the resulting safety goals from the Hazard and Risk Analysis. 

The extent to which structured methods/tools/techniques are applied is a function of the system s complexity and the system failure consequence, and will be more rigorous with increasing system complexity and severity of consequence (ACJ 25.1309 para 7.e). An analysis may range from a simple report that interprets test results or compares two similar systems to a detailed analysis that may (or may not) include estimated numerical probabilities. The depth and scope of an analysis depends on the types of functions performed by the system, the severities of failure conditions, and whether or not the system is complex. In considering the likely failure sequences, Lloyd and Tye (1995, p. 75) remind us to take account of the fact that, following a series of failures, the pilot himself will be under increased stress and may be more likely to make mistakes. Regardless of its type, an analysis should show that the system and its installation could tolerate hazards and failures to the extent that the applicable safety targets are accomplished in an auditable fashion. 

The design of most process plants relies on redundant safety features or layers of protection, such that multiple layers must fail before a serious incident occurs. Barrier analysis ) (also called Hazard-Barrier-Target Analysis, HBTA) can assist the identification of causal factors by identifying which safety feature(s) failed to function as desired and allowed the sequence of events to occur. These safety features or barriers are anything that is used to protect a system or person from a hazard including both physical and administrative layers of protection. The concepts of the hazard-barrier-target theory of incident causation are encompassed in this tool. (See Chapter 3.)... 

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