would the described PLC system meet the definition of an alternative measure which provides effective protection?
Reply: Circuit control systems, such as the PLC system you describe, are not energy isolating devices as defined at ยง1910.147(b). As a result, reliance on a PLC system that controls machine or equipment safety functions, such as stopping or preventing hazardous energy (motion), is prohibited by the LOTO standard and, as a result, is presumed to be ineffective employee protection from injuries resulting from hazards such as component failure, program errors, magnetic field interference, electrical surges, and improper use or maintenance. However, if an employer can demonstrate that a PLC system is an alternative measure which provides effective protection, the PLC system may be used only to protect employees who are performing minor tool changes and adjustments, and other minor servicing activities that take place during normal production operations and are routine, repetitive, and integral to the use of the equipment for production pursuant to the minor servicing exception contained in
