Core Concepts
Hazard Identification
The systematic process of recognizing things that could cause harm.
Risk Assessment
Evaluating the likelihood and severity of harm from identified hazards.
Safety Instrumented Systems (SIS)
Automated systems designed to take a process to a safe state when dangerous conditions occur.
Fail-Safe Design
Designing systems so that failure results in a safe condition.
Layers of Protection Analysis (LOPA)
A method to determine the required safety integrity level for each protective layer.
Worked Examples & Applications
Safety Integrity Level (SIL): SIL 1: Risk reduction factor 10-100. SIL 2: 100-1000. SIL 3: 1000-10000. SIL 4: 10000-100000. Example: A chemical reactor overpressure protection might require SIL 2 (reduce risk by factor of 100-1000).
Fault Tree Analysis (FTA): Top event: Reactor explosion. Intermediate events: Pressure sensor fails AND relief valve stuck AND operator ignores alarm. Boolean logic: P(top) = P(A) × P(B) × P(C) if AND gate.
Practice Questions
Q: What is a fail-safe design? A: Designing a system so that any failure automatically brings it to the safest possible state (e.g., emergency brakes apply when power is lost).
Q: What is SIL? A: Safety Integrity Level — a measure of the reliability required for a Safety Instrumented System, from SIL 1 (lowest) to SIL 4 (highest).