Is an E‑stop enough for lockout?

What counts as an energy-isolating device

1910.147(b) defines it as a mechanical device that physically prevents the transmission or release of energy, and names examples: a manually operated circuit breaker, a disconnect switch, a manually operated switch that disconnects the conductors from all ungrounded supply conductors with no pole operable on its own, a line valve, a block, and similar devices.

The same definition says it plainly: push buttons, selector switches and other control circuit type devices are not energy-isolating devices.

What does not count

• Emergency stop buttons. They drop a control relay. A fault, a reset or a second person can start the machine.
• Start and stop buttons, selector switches and key switches on the control panel.
• Guard interlocks and light curtains. They protect the operator in production, not the person inside the machine during maintenance.
• A PLC, an HMI screen or a drive's stop command. Software can be wrong, and a drive keeps its DC bus charged.

What does

• The disconnect switch or breaker that feeds the machine, locked OFF.
• The plug of a corded machine, unplugged and under your control (or in a plug lockout).
• A lockable valve on air, hydraulic, steam, gas, chemical or water lines, with the line downstream bled.
• A block or pin that holds a raised part mechanically.

After isolation: stored energy

Locking the disconnect does not empty an air receiver, a hydraulic accumulator, a drive's capacitors or a hot barrel. 1910.147(d)(5) requires that stored and residual energy be relieved, disconnected, restrained or otherwise made safe after the locks go on, and checked again if it can build back up.