The most common shock-related, nonfatal injury is a burn. Burns caused by electricity may be of three types:
Electrical 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.
Burns from arc blasts and arcing. 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.
Thermal contact burns. 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, gases, or dusts. OSHA standards, National Fire Protection Association (NFPA) standards, 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.
1. Which of the following is a luminous electrical discharge occurs when high voltages exist across a gap between conductors and current travels through the air?
a. Arc blast
c. Arc-metal blast
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.
Thermal radiation. 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.
High pressure blast. 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.
Molten metal blast. 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.
2. Each of the following is a primary hazard associated with an arc blast EXCEPT _____.
a. bleve forces
b. thermal radiation
c. explosive blast wave
d. molten metal
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.
3. Before initiating electrical work, each of the following should be accomplished EXCEPT _____.
a. de-energize all circuits and equipment
b. perform lock-out/tag-out
c. test for voltage by touching wires together
d. test circuits and equipment
Defective or misused electrical equipment is a major cause of electrical
fires. Different types of fire extinguishers are designed to fight different types of fire. The three most common types of fire extinguishers are: air pressurized water, CO2 (carbon dioxide), and dry chemical. The following table provides information regarding the type of fire and which fire extinguisher should be used.
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:
Water is one of the most commonly used extinguishing agents for type A fires. You can recognize an APW by its large silver container. They are filled about two-thirds of the way with ordinary water, then pressurized with air. In some cases, detergents are added to the water to produce a foam. They stand about two to three feet tall and weigh approximately 25 pounds when full.
This type of extinguisher is filled with Carbon Dioxide (CO2), a non-flammable gas under extreme pressure. These extinguishers put out fires by displacing oxygen, or taking away the oxygen element of the fire triangle. Because of its high pressure, when you use this extinguisher pieces of dry ice shoot from the horn, which also has a cooling effect on the fire.
Dry chemical extinguishers put out fires by coating the fuel with a thin layer of fire retardant powder, separating the fuel from the oxygen. The powder also works to interrupt the chemical reaction, which makes these extinguishers extremely effective.
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.
4. Which class of fire extinguisher would you use to extinguish a small electrical fire?
a. Class A or ABC
b. Class C or ABC
c. Class B or C
d. Class C or D
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.
5. What is recommended to keep electrical equipment in good working order?
a. A corrective maintenance program
b. A "just-in-time" maintenance program
c. A preventive maintenance program
d. An as-needed maintenance program
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