Consulting-Specifying Engineer - February 2008 - (Page 33)

BY H. LANDIS FLOYD II, PE, Principal Consultant, Dupont, Wilmington, Del. ames Cawley and Gerald Homce of the National Institute for Occupational Safety and Health (NIOSH) published key findings in a comprehensive analyses of workplace electrical injuries. Their report, “Trends in Electrical Injury 1992-2002,” published by the Institute of Electrical and Electronics Engineers in 2006, claims: • Electrical hazards were the sixth leading cause of workplace fatalities • 3,378 workers died from on-the-job electrical injuries • The construction industry accounted for 47% of all electrical deaths, and had a electrical fatality frequency rate six times that of the overall workforce • 46,598 workers were nonfatally injured by electricity • 99% of the electrical fatalities were due to electric shock, but 18,360 of nonfatal electrical injuries involved hospitalization due to electrical burns. These facts underscore the seriousness of electrical safety in the workplace. There is immeasurable pain, suffering, and trauma to the injured, their families, friends, and co-workers. There are significant financial losses, including medical costs, loss of productive workers, and disruption of operations due to damage of critical electrical systems. Two case histories illustrate the potential impact the electrical design engineer has in helping reduce these injuries and fatalities. The case of the exploding motor starter. The electrician’s life will never be the same. The motor control center was less than 10 years old, and installed in a clean, dry, air conditioned room. The task was simple. The overload units in one motor starter needed to be replaced. The electrician turned off the motor starter switch, and locked it in the off position. After successfully replacing one unit, an arc flash occurred as he began to replace the second unit. The electrician received second and third degree burns over 40% of his body. He spent eight weeks in a burn center, and required ongoing reconstructive and J Electrical deaths by industry Electrical fatalities from 1992 to 2002 are shown by industry sector. Transportation, communications, and utilities Wholesale trade Agriculture, forestry, and fishing Service industries Retail trade Public administration Mining Manufacturing Finance, insurance, and real estate Construction Source: Cawley and Homce rehabilitation treatment. An investigation determined that one pole of the disconnect switch had failed to open, and the electrician’s screwdriver had shorted the energized phase to ground. The electrician had failed to test for absence of voltage. The facility owner had not implemented an arc flash hazard assessment and mitigation program that would have included flame resistant clothing to reduce the extent and severity of the burn injuries. The case of the rolling scaffold. This was a fatal mistake for two construction workers. They had been using a rolling scaffold to insulate an overhead pipeline. They had completed the job and needed to move the scaffold back to the construction storage yard. Rather than dismantle the rolling scaffold, they decided to roll it several hundred yards. This seemed like an acceptable solution, because they would need to use the fully assembled rolling scaffold again the next day. Unfortunately, there was an overhead electric power line adjacent to the constriction storage yard. When the workers approached the storage yard, the scaffold contacted the overhead line and both workers were electrocuted. The investigation determined that the construction workers deviated from the job plan when they decided to roll the assembled scaffold rather than disassemble it. In addition, they had failed to notice the close proximity of the scaffold to the overhead line. Lessons learned In both cases, the work was routine, the people involved were experienced in their craft, and equipment or facilities designs were not identified as contributing causes to these tragic events. Deficiencies in design were not identified as contributing causes. But could the facilities design engineers helped prevent these events? This presents a number of questions regarding the role, professional responsibility, and legal liability of the design process. In the case of the exploding motor starter, what if the design engineer recognized that a high-impedance grounded neutral system for a 480 V industrial power distribution system (in accordance with NFPA NEC 2005, article 250.36) would have limited ground fault current to a low value—and therefore provide the client with a safer and more reliable power system? If the system had been high-impedance grounded rather than solidly grounded, the screwdriver contact may have resulted in little more than a ground-indicating alarm instead of the life-changing and permanently disabling injuries from a high-energy arc flash. Although this choice would not reduce the shock hazard exposure that was Consulting-Specifying Engineer • FEBRUARY 2008 33

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Consulting-Specifying Engineer - February 2008 Contents Viewpoint News M/E Roundtable How To Write Control Sequences Mentoring Engineers: Myths, Motivations, and Models Keep Young Electrical Engineers Grounded Protecting a Vulnerable Population Codes & Standards Case Study New Products Equipment Lifecycles Advertisers Index Green Space

Consulting-Specifying Engineer - February 2008

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