In recognition of May as the Electrical Safety Month, the U.S. Department of
Labor Occupational Safety & Health Administration (OSHA) is reminding employers
and workers about the importance of staying safe when working with electricity
on the job. OSHA's Safety and Health Topics page on electricity features
information about standards, hazards and possible solutions to those hazards.
The page on the Control of Hazardous Energy (Lockout/Tagout) describes why this
practice is important to protect workers from the unexpected startup of
machinery, or the release of hazardous energy during service or maintenance
activities.

"Lockout/Tagout (LOTO)" refers to specific practices and procedures to
safeguard employees from the unexpected energization or startup of machinery
and equipment, or the release of hazardous energy during service or maintenance
activities. This requires that a designated individual turns off and
disconnects the machinery or equipment from its energy source(s) before
performing service or maintenance and that the authorized employee(s) either
lock or tag the energy-isolating device(s) to prevent the release of hazardous
energy and take steps to verify that the energy has been isolated effectively.

There is a difference between turning off a machine and actually disengaging a
piece of equipment. When turning off a control switch, you are opening a
circuit; however, there is still electrical energy at the switch, and a short
in the switch or someone turning on the machine may start it running again.
Failure to lock out and block out machinery before working on it is a major
cause of injury and death. Workers can be electrocuted or lose fingers, hands,
arms, or suffer severe crushing injuries because machinery is inadvertently
turned on while being serviced or maintained. These injuries can be prevented
by establishing an effective lockout program.

An effective lockout/tagout program should include the following:

• An inspection of equipment by a trained individual who is thoroughly familiar
  with the equipment operation and associated hazards
  
• Identification and labeling of lockout devices
  
• Purchase of locks, tags, and blocks
  
• A standard written operating procedure that is followed by all employees.

More info

AplusA-online.de - Source: U.S. Department of Labor Occupational Safety & Health Administration