Quantitative risk analysis initiating event

Potential emergency situations may initially be identified by a properly performed Process Hazards Analysis (PHA). Other sources of potential events include incident reports as well as user or plant experience with similar processes or equipment at your plant or other plants. Various CCPS Guidelines contain additional information on process hazards analysis and quantitative risk analysis. ... 

The next task is an analysis showing that no control system failure can cause an initiating event that can result in a hazard. If control system failure can initiate a hazardous sequence, then safety instrumented functions MUST NOT be designed into common equipment without detailed quantitative risk analysis. That language in the standard is strong and clear. Most of the time, initiating event analysis shows a problem with combined control and safety. 

Risk Analysis—The development of a quantitative estimate of risk based on engineering evaluation and mathematical techniques for combining estimates of initiating event frequency and independent protection layers and consequences. 

If control system equipment failure can cause an initiating event, then quantitative analysis must be done for all components where failure might initiate a hazard. For those failures with no other protection layer, the frequency of failure will result directly in an incident. The detailed quantitative analysis must show that these failures will not increase risk beyond tolerable levels. 

In the quantification of the analysis, the importance of initiating event groups, component failures, safety system failure and operator errors should be derived to identify where the contributions to the risk are coming from and where there may be weaknesses in the design or operation of the safety systems. This could use quantitative measures of importance (such as Bimbaum and Fussell-Vesely — see Ref [10]) where applicable. This should be supported by sensitivity studies where there are uncertainties in the models and data. 

SESSION II Risk Theory and Risk Analysis for Landslides. [1] Landslide Risk Management concepts and framework and examples (2.5 h) [2] Deterministic and Probabilistic models for slope stability evaluation (2 h) [3] Introduction to modelling of catastrophic landslide events (2 h) [4] Empirical models for travel distance (1.5 h) [5] Application examples of probabilistic methods and semi quantitative methods for landslide hazard zonation (2h) [6] Landslide Frequency Assessment (1.5 h) [7] Different components of vulnerability to landslides. Prevention and long term management of landslides (3.5 h) [8] Case Studies coal waste dump risk assessment, example from motorway in La Reunion Island, Aknes Rock slope in Norway (2 h) [9] Application of QRA to other geotechnical problems Internal erosion of dams, crater lake hazard (1.5 h) [10] Advanced numerical models initiation of landslides, propagation of sediments/climate change effects (3.5 h). 

In most cases a three tier approach is adopted, as shown in Fig. II/4.2.3-1. Initially, a qualitative or semiquantitative approach is taken to assess the risk and screen it. When risks are in a high risk zone or there is the possibility of a major accident event, then quantitative risk assessments are carried out to prescribe necessary control measures. It is quite common that in many cases a combined approach is necessary to justify consequence analysis. Mostly, when a quantitative approach is undertaken, prior preliminary analysis is done. From the diagram it is seen that whenever all replies to the queries shown in the diagram after qualitative analysis are NO, then the action stops. If any reply is YES, then the next level of analysis is carried out. A similar approach is applicable for semiquantitative and quantitative analyses (Fig. II/4.2.3-1). 

Layer of protection analysis (LOPA) LOPA is a systematic and structured way of quantification of risk reduction and safety integrity level (SIL) determination. Usually, it starts its work on the data developed in HAZOP analysis. For each documented undesired event with an initiating cause, it provides an independent protection layer (IPL), which will mitigate or prevent the hazard. Then, the total amount of risk can be determined. If safety instrumented function is necessary, LOPA methodology can be used to determine SIL also. From ISA 84 transaction it is found that LOPA is a simplified risk assignment tool used to evaluate the effectiveness of IPLs that are designed to reduce the likelihood or severity of an undesirable event. Quantitative PHA LOPA deals with single cause consequence pairs. Detailed documentation is possible and can be applied for continuous process. 

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