The most common shock-related, nonfatal injury is a burn. Burns caused
by electricity may be of three types: electrical burns, arc burns,
and thermal contact burns. Electrical burns can result when a
person touches electrical wiring or equipment that is used or maintained
improperly. Typically, such burns occur on the hands. Electrical burns
are one of the most serious injuries you can receive. They need to
be given immediate attention. Additionally, clothing may catch fire
and a thermal burn may result from the heat of the fire.
Arc-blasts occur when powerful, high-amperage currents arc through
the air. Arcing is the luminous electrical discharge that occurs when
high voltage exists across a gap between conductors and current travels
through the air. This situation is often caused by equipment failure
due to abuse or fatigue. Temperatures as high as 35,000°F have
been reached in arc-blasts.
- arc-blast - explosive release of molten material from equipment caused by high-amperage arcs
- arcing - the luminous electrical discharge (bright, electrical sparking) through the air that occurs when high voltages exist across a gap between conductors
Current exited this man at his knees, catching his clothing on fire and burning his upper leg.
Arc Blast Hazards
There are three primary hazards associated with an arc-blast.
- Arcing during an arc blast gives off thermal radiation (heat) and intense light, which can cause burns. Several factors affect the degree of injury, including skin color, area of skin exposed, and type of clothing worn. Proper clothing, work distances, and overcurrent protection can reduce the risk of such a burn.
- A high-voltage arc can produce a considerable pressure wave blast. A person 2 feet away from a 25,000-amp arc feels a force of about 480 pounds on the front of the body. In addition, such an explosion can cause serious ear damage and memory loss due to concussion. Sometimes the pressure wave throws the victim away from the arc-blast. While this may reduce further exposure to the thermal energy, serious physical injury may result. The pressure wave can propel large objects over great distances. In some cases, the pressure wave has enough force to snap off the heads of steel bolts and knock over walls.
- A high-voltage arc can also cause many of the copper and aluminum components in electrical equipment to melt. These droplets of molten metal can be blasted great distances by the pressure wave. Although these droplets harden rapidly, they can still be hot enough to cause serious burns or cause ordinary clothing to catch fire, even if you are 10 feet or more away.
Five technicians were performing preventative maintenance on the electrical system of a railroad maintenance facility. One of the technicians was assigned to clean the lower compartment of an electrical cabinet using cleaning fluid in an aerosol can. But, he began to clean the upper compartment as well. The upper compartment was filled with live circuitry.
When the cleaning spray contacted the live circuitry, a conductive path for the current was created. The current passed through the stream of fluid into the technicians arm, and across his chest. The current created a loud explosion.
Co-workers found the victim with his clothes on fire. One worker put the fire out with an extinguisher, and another pulled the victim away from the compartment with a plastic vacuum cleaner hose. The paramedics responded in 5 minutes. Although the victim survived the shock, he died 24 hours later of burns.
This death could have been prevented if the following precautions had been taken:
- Before doing any electrical work, de-energize all circuits and equipment, perform lock-out/tag-out, and test circuits and equipment to make sure they are de-energized.
- The company should have trained the workers to perform their jobs safely.
- Proper personal protective equipment (PPE) should always be used.
- Never use aerosol spray cans around high-voltage equipment.
Extinguishing the Fire
Electricity is one of the most common causes
of fires and thermal burns in homes and workplaces.
Defective or misused electrical equipment is a major cause of electrical
fires. If there is a small electrical fire, be sure to use only a
Class C or multipurpose (ABC) fire extinguisher, or you might make
the problem worse. All fire extinguishers are marked with letter(s)
that tell you the kinds of fires they can put out. Some extinguishers
contain symbols, too.
The letters and symbols are explained below (including suggestions
on how to remember them):
||A (think: Ashes) = paper, wood, etc.
||B (think: Barrel) = flammable liquids
||C (think: Circuits) = electrical fires
Do not try to put out fires unless you have received
proper training. If you are not trained, the best thing you can do
is evacuate the area and call for help.
Thermal burns may result if an explosion occurs when electricity ignites
an explosive mixture of material in the air. This ignition can result
from the buildup of combustible vapors, gasses, or dusts. Occupational
Safety and Health Administration (OSHA) standards, the NEC, and other
safety standards give precise safety requirements for the operation
of electrical systems and equipment in such dangerous areas. Ignition
can also be caused by overheated conductors or equipment, or by normal
arcing at switch contacts or in circuit breakers.
A 29-year-old male maintenance worker was found at 3:45 a.m. lying on his back and convulsing. Beside him were an overturned cart and an electrical welding machine, both lying in a pool of water on the concrete floor. Arcing was visible between the welding machine and the floor. The worker was transported to the closest hospital, where he was pronounced dead.
An examination of the welding machine showed that there were exposed conductors in the machine’s cables. There were numerous cuts and scrapes in the cables' insulation. On other parts of the machine, insulation was damaged or missing. Also, the machine did not have a ground connection.
Investigators concluded that the maintenance worker was electrocuted when he tried to turn off the welding machine, which was sitting on the cart. The metal frame of the machine had become energized due to the damaged insulation. When he touched the energized frame, he completed the conducting path to the ground. The current traveled through his body to the ground. Since he was probably standing in water, the risk of ground fault was even greater.
You must take steps to decrease such hazards in your workplace:
- Ground circuits and equipment.
- Keep all equipment in good operating condition with a preventative maintenance program.
- Never use electrical equipment or work on circuits in wet areas. If you find water or dampness, notify your supervisor immediately.
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