How to Determine the Safety Integrity Level (SIL) of a Safety System

The Challenge of Safety Systems Electronic systems that carry out safety functions, such as gas detection systems, are becoming more complex, making it impossible in practice to determine every failure mode or improbable to test all possible behaviours. It is difficult to predict the safety performance, although testing is still essential because some dangerous failures can be only detected through periodic maintenance. The challenge for system engineers is to design a system in such a way as to prevent dangerous failures or to control them when they arise. For a Gas Detection System, dangerous failures may arise from any of the following: * Incorrect specifications of the system, including omissions in the safety requirement specifications (e.g. operation in unexpected poisoning gases, release of gases that cannot be detected, or lack of sensitivity to trigger the alarms) * Random failures of hardware (reliability of electronic components) and systematic failures of hardware and software (e.g. wrong design, software bugs, etc.) * Common root cause failures (power outage) * Environmental influences (e.g. temperature, humidity, presence of interference gases, etc.) * Human error