Protection is different from starting
With maintained two-hand control, releasing either actuator during the protected phase initiates the specified interruption. A two-hand trip can leave the hands free after starting: it performs a different function and must not be selected merely because it looks similar.
Simultaneous actuation and release before the next cycle help prevent one actuator being held down. Physical positioning must resist operation using one hand, an arm or another body part.
Distance and machine behaviour
Positioning must allow the machine to reach its safe state before a released hand can reach the hazard. Both control response and actual stopping performance matter. A movable station needs measures that preserve the approved separation.
Actuators, logic and final switching elements form part of Machinery safety functions and performance level. A relay’s declared performance does not establish the safety of the installed system on its own.
Other people and tasks
The control does not automatically protect a helper holding material or someone approaching from the side. Those exposures require appropriate work design, Machine guards or other safeguards.
If production requires a hand to hold a workpiece in the danger zone, the design problem cannot be solved by defeating one button. Clamping, feeding and removal must remain compatible with the selected protection.
A process-change example
A hypothetical workstation changes from small parts to assemblies needing two people. The control still requires the operator’s hands but does not control the helper’s hands. Feeding, access and protection for both people must be reviewed before the new process is used.
Verification addresses the complete function and is repeated after relevant workstation or component changes. INSST NTP 70 dates from 1983; its diagrams and inspection frequencies must not be presented as current requirements. Maintenance requires appropriate energy control, not simply keeping hands on the station.
Workstation assessment should observe a complete cycle, including how the component is loaded and removed. If the operator moves the control station to reach material or avoids releasing one actuator, review the work design. The solution must preserve both the required separation and the intended control behaviour.
