Glossary · Hazards and harm
Stored energy
Also known as: residual energy
In machine safety, stored energy is energy retained in mechanical, electrical, hydraulic, pneumatic, thermal, chemical or gravitational form after normal operation stops, for example in springs, capacitors, accumulators or raised loads.
- Machine safety
- Maintenance
In one sentence
Stored energy stays in springs, capacitors, accumulators and raised loads after a machine stops, and must be released or blocked before work.
Example
After the main switch of a press brake is turned off, the upper beam can still descend under gravity and the hydraulic accumulator is still pressurized; the lockout procedure includes blocking the beam and bleeding the accumulator.
How it applies
- Maintenance: Switching off is not isolation, and isolation is not a zero-energy state. 29 CFR 1910.147 requires that, after lockout or tagout devices are applied, all potentially hazardous stored or residual energy be relieved, disconnected, restrained or otherwise rendered safe.
- Machine safety: Designers should provide means to release or restrain stored energy, such as discharge circuits, bleed valves and mechanical blocks, and make the energy state visible where possible.
- Technical documentation: For each energy source, the procedure must say where energy is stored, how to release or block it and how to verify that it is gone. Link these steps to the lockout/tagout procedure.
- Evidence: Keep an energy source list for each machine and update it when components change.
Stored energy vs. energy isolation
Energy isolation separates the machine from its supplies. Stored energy remains inside the machine and needs its own release step.