LOTO and Electrical system


Lockout-tagout (LOTO) or lock and tag is a safety procedure which is used in industry and research settings to ensure that dangerous machines are properly shut off and not able to be started up again prior to the completion of maintenance or servicing work. It requires that hazardous energy sources be "isolated and rendered inoperative" before work is started on the equipment in question. The isolated power sources are then locked and a tag is placed on the lock identifying the worker who has placed it. The worker then holds the key for the lock ensuring that only he or she can start the machine. This prevents accidental startup of a machine while it is in a hazardous state or while a worker is in direct contact with it.

Lockout-tagout is used across industries as a safe method of working on hazardous equipment and is mandated by law in some countries

 


Procedure


Machinery can contain many hazards to workers, some of the common hazards are:

  • Electricity
  • Hydraulic pressure accumulated in a pump or line
  • Pneumatic compressed air
  • Radiation including intense visible or Thermal as well as ionising or particle beams
  • Extremely hot or cold surfaces
  • Gases, including poisonous, suffocating, explosive...
  • A combination of heat and gas in the form of Steam
  • Gravity (falls from height, falling parts, or mechanisms that work with or against it)
  • Kinetic spring tension
  • Other moving parts - fans, belts, gears, sawblades, presses, etc.
  • Many types of liquids (chemical, water, etc.)



In electrical engineering, live-line working, also known as hotline maintenance, is the maintenance of electrical equipment, often operating at high voltage, while the equipment is energised. The first techniques for live-line working were developed in the early years of the 20th century, and both equipment and work methods were later refined to deal with increasingly higher voltages. In the 1960s, methods were developed in the laboratory to enable field workers to come into direct contact with high voltage lines. Such methods can be applied to enable safe work at the highest transmission voltages.


Electrical hazards


Electricity is hazardous: an electric shock from a current as low as 35 milliamps is sufficient to cause fibrillation of the heart in vulnerable individuals. Even a healthy individual is at risk of falling from a high structure due to loss of muscle control. Higher currents can cause respiratory failure and result in extensive and life-threatening burns. The first recorded human fatality occurred in 1879 when a stage carpenter in Lyon, France touched a 250 volt wire. The lack of any visible sign that a conductor is energised, even at high voltages, makes electricity a particular hazard.

At high voltages, it is unnecessary to come into direct contact with charged equipment to be shocked. An electric field surrounds all charged devices. Bringing a conducting object such as a human body into that field can intensify the field enough for electrical breakdown of the air and an arc to jump from the equipment to earth via that person. In the U.S., the Occupational Safety and Health Administration establishes clearance guidelines. Solid materials such as rubber, while excellent insulators at low voltages, are also subject to electrical failure if subjected to a high enough field

General precautions


Calculation of minimum approach distances take account of switching surges and other transients. Transmission systems are often fitted with coordinated protection devices called autoreclosers, which are circuit breakers that automatically attempt to remake a circuit after a fault. In the event that a fault did occur it would be most undesirable for the autorecloser to re-energise the circuit because the limits of approach would be greatly reduced and the workers' position could be compromised. Hence, auto-reclosing equipment is rendered inoperative while live working takes place. Additional protection against unplanned overvoltage events (such as switching surges) can be provided by means of a surge diverter known as portable protective air gap.

An electric arc is extremely bright, including in the ultraviolet, and can cause arc eye, a painful and potentially blinding condition. Workers may be provided with appropriately tinted goggles that protect their vision in the event of a flash, and provide defence against debris ejected by an arc.

Government regulations may regulate conditions for live working conditions. For example, in United States, the Occupational Safety and Health Administration may require that more than one worker be present on site when working on live equipment above a specified voltage. The work may be postponed if adverse weather conditions such as lightning or rainfall are anticipated.






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