Zero mechanical state is the condition in which a machine's moving parts cannot move unexpectedly because all power is isolated and residual energy is controlled.
A machine-safeguarding term describing the condition in which every power source that could cause unexpected motion has been locked out, and residual energy — such as gravity, spring tension, or trapped air or fluid pressure — has been released or blocked so that no part of the machine can move. It is closely related to zero energy state but focuses specifically on preventing hazardous mechanical motion.
Before changing a die on a mechanical power press, operators lock out the motor, exhaust air from the clutch and brake system, and insert safety blocks under the slide so it cannot drift down, placing the press in a zero mechanical state.
Zero energy state addresses every form of hazardous energy, while zero mechanical state specifically targets the conditions that could cause machine motion; both concepts aim to protect workers during servicing and maintenance.
Heavy components like press slides or raised platforms can move under their own weight even when all power is isolated, so mechanical blocks physically prevent gravity-driven movement.
Power presses, robotic cells, conveyors, and other machines with heavy moving parts or stored pneumatic and hydraulic energy commonly require documented procedures for reaching ZMS before servicing.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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