Zero Energy State
A zero energy state (ZES) is a verified condition where all hazardous energy sources (electrical, mechanical, hydraulic, pneumatic, chemical, thermal, gravitational, stored) have been identified, isolated, locked/secured, relieved or restrained, and tested/verified so the equipment is incapable of spontaneous or unexpected action or hazardous energy release. This is the target condition of lockout/tagout procedures before servicing or maintenance.
On the shop floor, achieving a zero energy state is the end state of a lockout/tagout procedure before any servicing, maintenance, cleaning, or troubleshooting. The process involves: 1) identifying all energy sources (electrical, mechanical, hydraulic, pneumatic, thermal, chemical, gravitational); 2) isolating each source by locking disconnect switches, breakers, or valves; 3) securing against re-energization with personal locks and tags; 4) relieving stored energy by bleeding pressure, discharging capacitors, or blocking raised loads; 5) verifying zero energy by attempting to operate the machine and testing for absence of voltage; and 6) documenting the status. No work is done until the machine is locked out, tagged, and verified by a competent person.
Is 'Zero Energy State' a defined term under OSHA or ANSI?
No, OSHA 29 CFR 1910.147 (LOTO) does not define or use 'zero energy state' in its regulatory text. OSHA states the concept is not used in 1910.147; the hazard is addressed via a complete program for the control of hazardous energy. The term is used in practice (e.g., OSHA interpretation letters, corporate standards, NFPA 70E guidance) but is not a formal OSHA/ANSI defined term.
How does Zero Energy State relate to WorkSafeBC lockout requirements?
WorkSafeBC guidance requires that effective de-energization and lockout places the machine in a zero-energy state, where all energy sources are removed/controlled and residual energy discharged, so no hazardous energy exists. For SafeDesk, ZES should be the explicit target condition of any lockout procedure, with fields reflecting that no hazardous energy remains.
How should Zero Energy State be verified for electrical equipment?
Best practice combines OSHA 1910.333 and NFPA 70E: de-energize and lock out the electrical source; a qualified person uses an adequately rated test instrument to test each phase conductor phase-to-phase and phase-to-ground to verify de-energization; verify the tester is working before and after on a known live source. Only after this verification can the circuit be considered de-energized and at zero energy from an electrical hazard standpoint.