Functional safety, safety PLCs, emergency stop circuits, Safety Integrity Level (SIL), safety relays, lockout/tagout, and machine guarding — the safety-instrumented layer sitting on top of every process this program has automated.
Functional safety is a genuinely separate engineering discipline from the process control this program has built through Modules 3-11, not a stricter version of the same thing — and this module treats it that way. It starts with why a safety instrumented system stays architecturally independent from the process PLC, works through what a safety PLC and a safety relay each actually certify, and covers exactly what an e-stop circuit does and does not guarantee.
It closes on the two disciplines every automation engineer eventually has to apply directly: lockout/tagout for stored and residual energy, and machine guarding's hierarchy of controls — the physical and procedural layer no logic solver, however well certified, can substitute for.