You’re reading an outdated article. Please go to the recent issues to find up-to-date content.
You can never be too careful
Confidence in your skill as an electrician is essential to your safety. However, it can also lead to complacency. Avoiding injuries can cause you to forget the true level of danger you face on a daily basis. This article offers a harsh reminder of the injuries that may result from electricity, common situations in which electrical fatalities have occurred, and recommendations to avoid injury.
Electricity is the fourth-leading cause of death in the construction industry. A study of 244 fatalities conducted by the National Institute of Occupational Safety and Health (NIOSH) found that electrical linemen and electricians accounted for approximately 30 percent of these deaths. The injuries from electrical energy can be grouped into three main categories: electrical shock, burns and trauma.
An electrical shock occurs when current flows through the body. The electricity takes control over muscles. The rhythmic contraction of the heart muscle may become erratic or cease. Skeletal muscles may contract, causing fractures. This control over the skeletal muscle can also indirectly lead to death. Death may result from trauma from a fall caused by lack of muscle control.
The loss of control and level of damage depend on the amount of current allowed to pass, the length of time in the body, and the path through the body. Responses range from a slight tingle to death. The table at right, “Estimated Effects of 60 Hz AC Currents,” shows the body’s various reactions based on the amount of current exposure in Amps and Milliamps (mA).
You can get a practical perspective on this by understanding the body’s resistance to electricity and applying Ohm’s Law (Current = Voltage/Resistance). Typically, the body offers about 100,000 ohms of resistance. Factors affecting resistance include body area contacted, gender, skin thickness, etc. Moisture stands out as a significant factor. Water at the feet can improve grounding. If the skin is cut, there can be direct contact with the body’s moisture. Similarly, if the hands are in salt water, the body’s resistance can get as low as 700 ohms. At this level, 120V can cause 171mA to pass through the body. As seen in the table below, this is enough to cause ventricular fibrillation and death.
There are three types of burns that can be caused by electricity: electric burns, arc (flash) burns and thermal burns. Electric burns are caused by electricity flowing through the body, which can damage bone and tissue. Damage to the skin may not be extensive, particularly at higher voltages. Arc or flash burns are caused by very high temperatures created by an electric arc or explosion. Temperatures as high as 35,000 F have been recorded. Thermal burns occur when clothing catches on fire or a person touches an overheated conductor or device.
Based on the results of the study mentioned earlier, NIOSH has identified five scenarios which account for most of the fatal injuries described. Three of the scenarios involved contact with overhead powerlines. The contact was either made directly by the worker, through equipment (such as a ladder) or through a vehicle extension, like the boom of a crane. The other two scenarios involved direct contact with exposed energized parts or parts energized as a result of damage or a faulty installation.
In all scenarios, there was at least one missing element of safety. These included the failure to have or implement proper work practices, the absence of personal protective equipment, failure to deenergize using an effective lockout/tagout procedure, noncompliance with regulations and/or no training. NIOSH reported that had the employer been in compliance with the Occupational Safety and Health Administration rules, National Electrical Code and National Electrical Safety Code, most of the fatalities could have been prevented.
Electricity is too dangerous to become careless with. Think about the injuries that may result. Become familiar wth the codes and regulations governing safe installation and use.ation and use. EC
O’CONNOR is with Intec, a safety consulting, training and publishing firm that offers on-site assistance and produces manuals, training videos and software for contractors. Based in Waverly, Pa., he can be reached at 607.624.7159 or [email protected].