In terms of safety, which device cannot serve as an isolating device for LOTO?

The selection of portable generators as a device that cannot serve as an isolating device for Lockout/Tagout (LOTO) is correct because portable generators are designed to be mobile and provide temporary power. They are not fixed installations and may not effectively isolate energy sources in a controlled manner. While they can supply energy, they lack the necessary features for isolation, such as means to securely lock out and tag the device, ensuring it cannot be re-energized while maintenance or servicing is performed.

In contrast, push-buttons, selector switches, and locking mechanisms are typically integrated into systems designed for energy control and can be used to isolate machinery safely. These devices often include features that allow them to be locked in the off position or tagged, ensuring that equipment cannot be unintentionally started. This makes them appropriate for use in LOTO procedures, contributing to worker safety by preventing accidental energization during maintenance.