In the Functional Safety Lifecycle, the next step after hazard and risk assessment is “allocation of safety functions to protection layers”. This is a process whereby suitable control measures are specified for each of the potential hazardous events found during the H&RA. This includes mechanical safeguards such as pressure relief valves, and also Safety Instrumented Systems (SIS).
The process of “allocation” is deciding which protective measures will be put in place, and how reliable they need to be. If a safety instrumented function (SIF) is to be used, the reliability required from it will be expressed as a safety integrity level, or SIL. There are four SILs – 1, 2, 3 and 4, which give increasing levels of reliability. The next task during “allocation” is to carry out “SIL determination”; in other words to decide what SIL is required from each SIF.
The most common technique used for SIL determination is layer of protection analysis (LOPA). See “what is a LOPA?” for more information.
LOPA of oil storage site (based on typicals approach)Industry: Water + Waste
LOPA of continuous annealing process in steel industryIndustry: Mining / Metal / Cement
Review of earlier LOPA and PHR studiesIndustry: Mining / Metal / Cement
Review of earlier LOPA in preparation for HSE intervention visitIndustry: Oil and Gas Onshore
HazOp of foam manufacturing processIndustry: Chemical
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