ALARP - as low as reasonably practicable BPCS - Basic process control system FTA - Fault tree analysis HAZOP - Hazard and operability analysis IPL - independent protection layer LOPA - layers of protection analysis MTTR - Mean time between failure PFD - Probability of failure on demand PHA - Process hazard analysis SIF- Safety instrumented function SIS - Safety Instrumented System SRS - Safety requirement specification QRA - Quantitative risk analysis