Which action is the primary control measure to prevent energy release during a safe shutdown?

• A. Depressurize lines
• B. Purge residual air
• C. Verify that no energy remains
• D. Lockout/tagout energy sources

Answer: (D)

Lockout/tagout energy sources is the primary control measure because it creates a physical and visible barrier that prevents any energy from being released or equipment from being energized while work is being done. By isolating electrical, pneumatic, hydraulic, and other energy sources and securing them with locks and warning tags, you ensure that the machine cannot start or discharge stored energy until authorized personnel verify it’s safe to remove the devices. This approach protects workers from sudden starts, unexpected releases, and stored-energy hazards throughout the shutdown process.

Depressurizing lines and purging residual air reduce some types of stored energy, but they don’t guarantee that all energy sources are secured or that energy cannot be released if a valve is reopened or a source is energized. Verifying that no energy remains is a crucial follow-up step, but it relies on prior isolation to be effective; without locking out, there’s still a risk of re-energization or energy release.