Functional Safety for Safety Instrumented Systems

Explain functional safety and how a safety instrumented system prevents malfunctions from random, systematic, and common cause failures, while acknowledging perfect safety is unattainable and we strive for safety.

Explore IEC 61508 and IEC 61511 as the core standards for functional safety in safety instrumented systems, guiding manufacturers and designers, integrators, and users.

Identify three major accident drivers in functional safety for safety instrumented systems. They are human failures from training gaps, random failures (such as power loss), and equipment failures.

Emphasizes functional safety management through precise documentation across the safety life cycle, including hazard and risk analysis, FMEA, FTA, LOPA, commissioning and validation reports, and audit records.

Follow a formal modification procedure with qualified personnel to conduct impact analysis, hazard and functional safety risk assessment, verification, and validation before implementing changes across design, commissioning, operations, and maintenance.

Differentiate verification and validation for safety instrumented systems. Verify after each development phase with factory tests; validate on site with client hardware, then conduct independent functional safety assessments and audits.

Explore hazard analysis and hazard and operability analysis, distinguishing hazard, hazardous events, and hazard likelihood. Learn how probability governs whether a hazard leads to harm.

Identify hazards to understand risk, analyze consequences and probabilities, and reduce risk with safeguards; connect safety functions to hazards using techniques like checklist analysis, what-if analysis, and fault tree analysis.

Define risk as the combination of consequences' severity and frequency. Assess whether a hazardous event’s risk stays within tolerable government limits, noting that absent a hazard there is no risk.

We reduce risk from hazardous events to tolerable levels using layers of protection, including a safety instrumented system, and define achieved risk reduction as the move to residual risk.

Explore how a hazards and operability study (hazop) identifies hazards, evaluates risks, and guides collaborative decision making through six steps, from risk identification to action.

Explore layers of protection analysis (LOPA) to quantify risk, guide rational, resource-balanced decisions, and meet tolerable frequency targets with independent safeguards and safety instrumented functions.

Identify possible failure modes, causes, and effects with FMEA, a tool that bridges hazard analysis gaps by analyzing components one at a time and guiding remedial actions.

Analyze undesired system states with fault tree analysis using Boolean logic to identify failure causes, visualize weaknesses with gates and symbols, and support risk reduction decisions.

Learn event tree analysis (ETA) as a hazard and risk reduction technique, tracing initiating events, safety barriers, and outcomes to judge system acceptability and guide improvements.

Explore safety instrumented system terms, from fail-safe design and valve types to redundancy, diversity, voting schemes, and hardware fault tolerance across low, high, and continuous demand modes.

Explore how safety instrumented functions integrate sensor, logic, and actuator subsystems, classify type a and type b failures, and evaluate safe failure fraction and hardware fault tolerance for safety designs.

Use reliability block diagrams to compute the probability of failure on demand (PFG) for interlocks, modeling sensors, logic solvers, and final control elements in series and parallel structures.

Apply Markov analysis to forecast a variable based only on its current state within a four-state safety model, and derive mean time to failure and related reliability metrics.

Transforms user requirements into design and code guided by the SRS, producing safe software that preserves safety functions under faults and follows functional safety standards and testing.