Machine Safety, Codes and Standards, and Inspection
Domain scope
This domain tests risk assessment, guarding, interlocks, emergency stops, lockout/tagout, functional safety, standards adoption, and inspection methods. The exam expects you to distinguish legal requirements from voluntary standards and to select appropriate inspection techniques.
Core rules
- Risk assessment follows a hierarchy: eliminate, substitute, engineer controls, administrative controls, then PPE.
- Guards must prevent access to hazards and be difficult to defeat; interlocks must stop hazardous motion before access.
- ISO 12100 provides risk-assessment principles; ISO 13849 addresses safety-related control system performance levels.
- A standard becomes enforceable when adopted by law or contract.
- Lockout/tagout isolates energy, including stored hydraulic, pneumatic, and electrical energy.
- Common NDT methods: visual, dye penetrant, magnetic particle, ultrasonic, and radiography.
- Inspection sampling does not prove every item is defect-free.
Worked example
A light curtain uses approach speed K = 2000 mm/s, stopping time T = 0.20 s, and a constant C = 100 mm. The minimum safety distance is S = K×T + C = 2000×0.20 + 100 = 500 mm. Mounting the curtain closer would allow a hand to reach the hazard before the machine stops.
Traps
- Treating a voluntary standard as law without adoption.
- Using an emergency stop as a substitute for guarding or interlocks.
- Forgetting stored energy in lockout procedures.
- Selecting NDT by convenience rather than defect type and orientation.
- Assuming a functional safety rating covers mechanical guard strength.