ALARP model

The following examples explain the overall method of SIL determination. These examples provide an idea of the method the actual analysis is a more involved procedure. 

The production consists mainly of 50,000 barrels of oil per day (for cost purpose). 

Gas and liquid production lines from the separator are not shown. 

Process engineering and design using Visual Basic 

Vessel V-001 is protected by a PRV. To reduce the flare load, the PRV has been designed only for a fire contingency, and it is expected that block discharge will not be a design contingency for the inlet separator. 

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Realistically, it has to be concluded that the term ALARP really does not provide much help to risk management professionals and facility managers in defining what levels of risk are acceptable. It may be for this reason that the U.K. HSE chose in the year 2006 to minimize its emphasis to do with ALARP requirements from the Safety Case Regime for offshore facilities. Other major companies have also elected to move away from ALARP toward a continuous risk reduction model (Broadribb, 2008). 

The results of the PRA show that the AP1000 has significantly less dependence on operator action to reduce plant risk to acceptable levels than current plants. This was shown through the sensitivity analyses and the operator action contributions from both the risk decrease and risk increase measures. Almost all operator actions credited in this PRA are performed in the control room there are very few local actions outside the control room. Further, the human actions modelled in the AP 1000 PRA are generally simple. Thus, the tasks for AP 1000 operators are easier and less likely to fail. If it were assumed that the operators never perform any actions credited in the PRA, the plant events CDF would still be lower than the result obtained for many eurrent pressurised water reactors including operator actions.This low dependence on operator aetion is therefore ALARP. 

Axle counter application risk models were developed to support the derivation of Safety Cases for individual axle counter installation projects. In accordance with the UK safety case regime, each project will have to prove that the technological and procedural solution accepted for the project is the As Low As Reasonably Practicable (ALARP) solution. 

For specific highly critical hazards (ones that have major contributions to safety risk) the QRA approach is recommended, but only if it is possible to develop QRA models representing the system before changes or a similar already existing system so that data and the model predictions can be validated and verified. The QRA should then be used in support of the options identification and analysis and the ALARP argumentation. 

The conclusion of the Safety justification was that a set of restrictions, dependencies and other safety measures had been identified which enabled the train operations, associated with V2.01 testing, to be performed at a level of risk which is tolerable and ALARP. This Safety justification can thus be seen a subset of the reasoning model that is the System Safety Case for VLUP. 

Figure 7-9 ALARP Review Process Figure 7-10 Restrictions identification and analysis process Figure 7-11 Development of QRA models in support of staged project implementation...

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