A Dangerous restart occurs when power or energy is applied to a device whose "on / off" switch was in the "on" position when power was applied. In the United States the National Institute for Occupational Safety and Health (NIOSH) refers to this hazard as "The Uncontrolled Release of Mechanical, Electrical and Other Types of Hazardous Energy"
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The dangerous restart hazard is currently addressed by the Occupational Safety and Health Administration (OSHA), the National Fire Protection Association (NFPA) and the Canadian Standards Association (CSA) with mandatory requirements for hazard reduction through the use of industrial grade safety devices.
The mandatory safety devices require installation by licensed electricians. The cost for implementing this safety device including installation averages between US$300 and US$1,000 depending on electrical requirements of the machinery and local electrician rates.
Due to the cost and size restriction, there are currently no requirements for restart hazard reduction on appliances, small tools and handheld power equipment.
There are currently an average of 25 power tools and appliances in the average wood, metal and home economics shops in public middle and high schools across the U.S. that possess dangerous restart hazards.
Example #1
Mother and child are working in kitchen with countertop mixer. The mixer is on with cake frosting in the bowl. Power is cut as a result of a local power outage. The mother turns away to evaluate why the power is out. The mixer power switch is still in the "on" position. The young child reaches into the bowl of the now powerless mixer to sample the frosting. Power is restored. The mixer comes on, causing injury to the child's hand.
Example #2
Man is using electric trimmer to cut hedges around exterior of home. Trimmer is plugged into outlet on exterior of home 75 feet from where man is working. The trimmer switch is locked in the "on" position and in normal use. Extending beyond the reach of the trimmer's power cord, the plug is accidentally pulled from the outlet on the house 75 feet away. The man puts down the trimmer, switch still locked in the "on" position, and walks with his back away from the trimmer towards the outlet. A 4-year-old boy playing nearby sees the trimmer on the ground and approaches it. He picks it up with both hands. Back still turned, the man re-inserts the trimmer's power cord plug into the outlet. The trimmer starts immediately, severely injuring the boy's fingers on both hands.
Example #3
A 25-year-old male worker at a concrete pipe manufacturing facility died from injuries he received while cleaning a ribbon-type concrete mixer. The victim’s daily tasks included cleaning out the concrete mixer at the end of the shift. The clean-out procedure was to shut off the power at the breaker panel (approximately 35 feet from the mixer), push the toggle switch by the mixer to make sure that the power was off, and then enter the mixer to clean it. No one witnessed the event, but investigators concluded that the mixer operator had shut off the main breaker and then made a telephone call instead of following the normal procedure for checking the mixer before any one entered it. The victim did not know that the operator had de-energized the mixer at the breaker. Thinking he was turning the mixer off, he activated the breaker switch and energized the mixer. The victim then entered the mixer and began cleaning without first pushing the toggle switch to make sure that the equipment was de-energized. The mixer operator returned from making his telephone call and pushed the toggle switch to check that the mixer was de-energized. The mixer started, and the operator heard the victim scream. He went immediately to the main breaker panel and shut off the mixer.
Example #4
A couple in New Jersey was closing up their pool cabana for the winter prior to leaving the residence for their winter home in Florida. It was common practice to shut off the circuit breaker for the cabana during the winter. The couple then loaded the pool furniture, including several seat cushions into the cabana. Inside the cabana was an electric cook top used for entertaining during the summer months. At some point the burner switch for the cook top was accidentally switched to the "on" position. As a result of the cabana breaker being off, the cook top did not heat up. The couple left for their Florida home.
In early January a water leak was reported in the main house by the couple's alarm company and a plumber was summoned to repair the problem. The plumber repaired the leak and prior to leaving, made sure that he turned on all of the circuit breakers in the panel. This included the circuit breaker for the cabana cook top.
Later that evening the fire department was called to extinguish a blaze caused by the cushions located on top of the cook top in the cabana. By the time the fire department had arrived the fire had destroyed both the cabana and the residence.
No-volt release
The motor controllers for large electric motors normally incorporate a type of circuit breaker known as a no-volt release. If the power fails, the circuit breaker opens and the motor will not restart when the power is restored. The circuit breaker must be reset before the motor can be started again.