IE‐614 Midterm Exam Safety Engineering Spring 2012 1. Electric safety involves controlling 2 main hazards through one hazard is only evident under high voltage and current conditions. List them and describe some ways you can control the hazards. There are two main hazards of electricity are: electrical shock and electrical arcflash/blast. OSHA statistics show that several hundred deaths occur annually as a result of electrical shock. Over one-half of these deaths are the result of contact with low voltage, primarily 120-volts. Residential, commercial, industrial, farm, and utility accidents are included in these statistics. NIOSH statistics show that electrical contact results in 4,000 non-disabling and 3,600 disabling injuries annually in the United States. Many of the electrical shock accidents that occur in commercial and industrial facilities are the result of contact with 277-volts. This is due to the extensive use of 277-volt fluorescent lighting. Employees generally perform maintenance on these light fixtures without performing a proper lockout/tagout of the circuit. Studies also show that 10-15 employees are hospitalized every day with arc-flash burns, which are often catastrophic to the victims physically, psychologically, and financially. In reality, the hazards associated with the use of electricity are real and can affect anyone. Electrical shock - Electrical shock occurs when a person’s body completes the current path between two energized conductors of an electrical circuit or between an energized conductor and a grounded surface or object. Essentially, when there is a difference in potential from one part of the body to another current will flow. The effects of an electrical shock can vary from a slight tingle to immediate cardiac arrest. The severity depends on several factors: body resistance wet or dry skin are major factors of resistance, circuit voltage, amount of current flowing through the body, current path through the body, area of contact, duration of contact. Although the majority of electrocutions are the result of hart-failure, burns are the most common shock related injury. An electrical accident can result in an electrical burn, arc burn, thermal contact burn, or a combination of burns. Electrical burns are among the most serious burns and require immediate medical attention. They occur when an electric current flows through tissue or bone, generating heat that causes tissue damage. The body cannot dissipate the heat generated by current flowing through the resistance of the tissue therefore, burns occur. To further illustrate how easily a person can receive a fatal shock, when considering a voltage that is common to every location in the United States, 120-volts. Under average working conditions where the person is perspiring and has a resistance of only 1000-ohms from hand-to-hand, using the simple Ohm’s Law formula (current
Page 1 of 20
equals the voltage divided by the resistance) the current flow will be 0.12 amperes or 120 mA which is in most cases fatal.
Electrical Arc-Flash/Blast- is a type of electrical explosion that results from a low impedance connection to ground or another voltage phase in an electrical system. Arc flash temperatures can reach or exceed 35,000 F at the arc terminals. The massive energy released in the fault rapidly vaporizes the metal conductors involved, blasting molten metal and expanding plasma outward with extreme force. The result of the violent event can cause destruction of equipment involved, fire, and injury not only to the worker but also to nearby people. In addition to the explosive blast of such a fault, destruction also arises from the intent radiant heat produced by the arc. The metal plasma arc produces tremendous amounts of light energy from far infrared to ultra violet. Surfaces of nearby people and objects absorb this energy and are instantly heated to vaporizing temperatures. The effects of this can be seen on adjacent...