Description of the Hazard
Unintentional restarting is a broad category of hazard that describes when a machine becomes energized or begins to operate without explicit and intentional user action. The most common case of unintentional restart is when a machine restarts after a loss of power. Loss of power may occur as a result of a tripped circuit breaker, local power outage, brown-out, or even just a machine being unplugged. If a standard power switch is left in the ‘on’ position when the machinery loses power – then the machine will start as soon as power returns, creating an ‘unintentional restart’ and exposing anybody nearby to an unexpected hazard.
It should be noted that this hazardous behavior is the standard behavior of many industrial machines, even new machinery.
Unintentional restarting is often referred to as: anti-restart, accidental restart prevention, and low-voltage dropout. The terms ‘magnetic switch’ or ‘magnetic starter’ may refer to a device that has built-in protection to prevent an unintentional restart. Unintentional restarts are considered by some as a sub-category of lockout/tagout, also known as the control of hazardous energies.
All injury types can result from an unintentional restart but the most severe injuries result from restarts during machine maintenance. In these cases, a technician may have their hands or body in or near the machine during the restart and the resulting injuries can include amputations, severe lacerations, and death.
While all maintenance activities should employ strict lockout/tagout procedures, these procedures are not always employed on plug-in machinery and accidental restarts during machine maintenance can be severe. Furthermore, even the best lockout/tagout procedures do not prevent unintentional restarting at the conclusion of the maintenance activity.
Impermanent or Portable Machinery
If machinery is commonly moved, disconnected, or otherwise unplugged then the risk of an unintentional restart is increased. The power switch on an unplugged piece of machinery may be inadvertently turned on which would lead to an unintentional restart when the machine was plugged in.
Learn more about how to protect machine operators from this hazard in our machine safety articles on Bench Grinder Safety and Band Saw Safety.
Example – OSHA Fatality Report
At approximately 2:30 a.m. on August 27, 1992, Employee #1 was attempting to unplug the beater of an almond hulling machine … The circuit breaker had tripped, so the machine was not operating when Employee #1 opened the door of the beater to reach the plug … A coworker entered the control room and saw that the breaker was off. He hit the reset button, which caused the beater to cycle enough to catch Employee #1’s arm. Employee #1 sustained a broken left arm and severe lacerations; he was hospitalized…OSHA Accident Report, Accident: 170724041