Risk Graph development

To determine if a SIF is required to reduce risk to a 'Tolerable' level and the amount of risk reduction that any identified SIF is to achieve requires a method that is 'calibrated' to the risk risks associated with the application.

The standard BS IEC 61511 for the process sector identifies several methods - risk matrix, risk graph, Layers of Protection Analysis, (LOPA). In order for a risk matrix and a risk graph to be applicable to the application it needs to be 'calibrated' for that application. This is a team based procedure where the parameters of the method are identified and given a 'value'. Where a company or plant have already a method of risk identification in use, such as that required for any COMAH report, then this must be the basis of the calibration of the SIF/SIL determination method.

Following calibration then any personnel who may be involved in SIF classification need to be trained in the methodology. The method should then be applied to several examples and then these same examples be classified again by a numerical method, such as LOPA /Fault Tree Analysis to verify the method is ' calibrated' for its intended application.

A calibrated risk graph will give a good SIL assessment and a good SIL assessment both minimizes the number of expensive high reliabity safety trips required and focuses them clearly on your safety needs. It is a win-win situation. A lot of emphasis may be put on designing a SIL rated loop but avoiding the need for one in the first place gives a much greater financial return. A good, robust SIL assessment is an excellent investment and is a much lower cost than that of the safety instrumented system itself later in the project. Rowan House are able to give you robust, well-designed SIL assessments and risk graphs. Our CASS certification is UKAS accreditted and we are fully able to give you the service you need.