Machine Guarding, Lockout/Tagout and Electrical Safety
Machine Guarding, Lockout/Tagout, and Electrical Safety
This domain tests control of hazardous energy and prevention of access to moving parts. It is high-severity content, so procedure quality and verification matter more than slogans.
Core rules
- 1910.212 requires guarding at the point of operation, power transmission, and other moving parts where operation could injure. Guards must prevent contact, be secure, and not create new hazards.
- Interlocks must stop hazardous motion before access is possible; a defeatable interlock is a common citation.
- 1910.147 lockout/tagout applies to servicing and maintenance where unexpected energization or release of stored energy could injure. The sequence: notify affected employees, shut down, isolate all energy sources, apply locks and tags, release stored energy, and verify isolation by attempting startup or testing.
- Only the person who applied a lock removes it; group lockout uses a group lockbox or equivalent.
- 1910.333 covers electrical safe work practices; 1910.335 covers PPE. NFPA 70E provides arc flash risk assessment and PPE guidance.
- Stored energy includes springs, gravity, hydraulic pressure, capacitors, and residual heat.
Worked example
A jam occurs inside a conveyor. The operator stops the belt with the local control, but the disconnect is 20 m away and the belt can coast. Correct reasoning: stopping is not isolation. Apply LOTO at the disconnect, lock and tag, release tension and block the gravity-loaded section, then verify by trying the start control and checking for zero energy. The local stop button is not a lockout device, and the coasting belt is stored kinetic energy. The task only proceeds after verification.
Traps
- Using tagout alone where a lock can be applied.
- Locking the control switch but not the upstream disconnect.
- Skipping verification because the procedure always works.
- Treating minor servicing as exempt without checking the 1910.147 exception criteria.