Safety Integrity Level (SIL) is a measure used to evaluate the reliability and effectiveness of safety systems in industrial processes. It indicates the level of risk reduction provided by a safety function, with higher levels representing greater reliability. SIL is part of the IEC 61508 standard, which outlines requirements for electrical, electronic, and programmable electronic safety-related systems. SIL is categorized into four levels, from SIL 1 to SIL 4, with SIL 4 offering the highest level of safety assurance. Each level corresponds to specific performance requirements, including the probability of failure on demand (PFD) and the frequency of dangerous failures. This classification helps organizations ensure that their safety systems meet necessary safety standards and reduce risks effectively.