Which statement best differentiates Performance Level (PL) from Safety Integrity Level (SIL)?

Which statement best differentiates Performance Level (PL) from Safety Integrity Level (SIL)?

• A. PL measures environmental impact; SIL measures cost.
• B. PL relates to SRP/CS reliability in machinery safety; SIL relates to electrical/electronics/software safety.
• C. PL is used for humans; SIL is used for animals.
• D. PL and SIL are interchangeable terms.

Answer: (B)

PL and SIL describe safety performance in different domains and with different measurement approaches. Performance Level is used for machinery safety and assesses the reliability of safety-related parts of a machine’s control system (SRP/CS), usually with a qualitative scale (categories a to e) that reflects how well the safety function reduces risk. Safety Integrity Level, on the other hand, applies to electrical/electronic/programmable electronic safety systems and uses a probabilistic measure (levels 1 to 4) linked to the probability of a dangerous failure per hour (PFHD). That combination—PL for machinery safety SRP/CS reliability and SIL for E/E/PE safety integrity—best captures the distinct focus and how each is quantified. The other statements mix up domains or imply interchangeability, which isn’t how these standards define PL and SIL.

PL and SIL describe safety performance in different domains and with different measurement approaches. Performance Level is used for machinery safety and assesses the reliability of safety-related parts of a machine’s control system (SRP/CS), usually with a qualitative scale (categories a to e) that reflects how well the safety function reduces risk. Safety Integrity Level, on the other hand, applies to electrical/electronic/programmable electronic safety systems and uses a probabilistic measure (levels 1 to 4) linked to the probability of a dangerous failure per hour (PFHD). That combination—PL for machinery safety SRP/CS reliability and SIL for E/E/PE safety integrity—best captures the distinct focus and how each is quantified. The other statements mix up domains or imply interchangeability, which isn’t how these standards define PL and SIL.