What are the common methods for determining SIL requirements?

Common SIL determination methods: Risk Graph (qualitative, based on consequence severity, exposure time, avoidance probability, and demand rate - provides SIL directly), LOPA (Layer of Protection Analysis - quantitative, calculates risk reduction needed after crediting existing protection layers), Safety Matrix (calibrated table relating consequence and likelihood to SIL), and QRA (Quantitative Risk Assessment - detailed numerical analysis for complex scenarios). Most common in process industry is LOPA, which uses initiating event frequency, consequence severity, and independent protection layer credits. All methods require hazard identification (HAZOP) as input.