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AESC has been successfully providing functional safety assessment and specifically SIL analysis services to its clients. Our staff has extensive experience with the SIL standards and related methodologies, which has been the key to providing our clients with the most up to date and accurate SIL analysis services.

Safety assessment, specifically functional safety assessment has been practiced in various industries and by engineers at AESC for many years utilizing methodologies like FMEA, FMECA, Fault Tree, Event Tree, and Probabilistic Risk Assessment (PRA) in general.

In recent years effort by IEC and ANSI organizations have resulted in coherent guidelines for safety risk assessment targeting "Safety Instrumented Systems" (SIS), and safety systems in general. These guidelines / standards have been published in IEC 61508, and ANSI ISA S84. The main focus of IEC 61508 is Functional Safety of Electrical / Electronic / Programmable Electronic Safety-Related Systems.

These standards provide a systematic approach to safety risk assessment through correlation of probability of safety incidents to a Safety Integrity Level. Safety incidents can be attributed to HW / SW failure on demand or failure during continuous operation. Probability and frequency of these failures are compared using Safety Integrity Levels. The following tables are sample SIL targets:

Safety Integrity Levels, Probability of failure on demand:
Low Demand Mode of Operation
4 10E-5 to 10E-4
3 10E-4 to 10E-3
2 10E-3 to 10E-2
1 10E-2 to 10E-1
Safety Integrity Levels, frequency of dangerous failures per hour:
High demand or Continuous Mode of Operation
SIL Probability of Failure per hour
4 10E-9 to 10E-8
3 10E-8 to 10E-7
2 10E-7 to 10E-6
1 10E-6 to 10E-5

Please contact us for more in depth / additional information on SIL analysis, and how AESC can help with your SIL analysis.

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