An arc flash is the light and heat produced from an electric arc supplied with sufficient electrical energy to cause substantial damage, fire, or injury, but the greatest risk is burn injuries due to exposure to the heat generated by the arc (Wikipedia, arc flash). Potential threats from arc flashes are serious enough that the possibility of occurrences should always be risk assessed prior to the start of projects by using tools for lock out tag out (LOTO) such as those found at www.LOTOBuilder.com and for project risk analyses, or job safety analyses (JSA) such as found at www.JSABuilder.com, to help workers understand and avoid risks to facilitate working smart. Many more tools and information about arc flash are widely available on the internet. For professionals, safety precautions are usually taken in addition to simply wearing PPE when working around arc flash, helping to prevent injury.[1]
Electrical arcs involve a negative incremental resistance, which cause their electrical resistance to decrease in response to arc temperature increases. Therefore it sort of self amplifies itself, as the arc develops and gets hotter, the resistance drops accordingly until some part of the system is eliminated (i.e. breaker trips, conductor melts or vaporizes) providing sufficient distance to break the circuit and extinguish the arc.[2] Workers who may errantly eliminate that distance by straying into an open power line/source may become the path to ground that completes a circuit (i.e. part of) and thus be impacted by having an arc pass through them; often a fatal mistake. Electrical arcs, when well controlled and fed by limited energy, produce very bright light, and are used in arc lamps (enclosed, or with open electrodes), for welding, plasma cutting, and other industrial applications. Arc flash temperatures can be far greater than the Sun's surface and can reach or exceed 35,000 °F (19,400 °C) at the arc terminals.[3] During an arc flash, electrical energy can potentially vaporize metal, which changes from solid state to gas vapor, expanding it with explosive force. For example, when copper vaporizes it suddenly expands by a factor of 67,000 by volume.[4]
Obviously, arc flash is a serious health hazard where it may be essential for individuals who may potentially encounter such events to access more authoritative resources to become better educated regarding the potential threats and appropriate precautionary responses before undertaking work activities. For work situations, it is also highly recommended that where appropriate, arc flash be addressed in Health Risk Assessments (HRA) along with potential mitigations proactively developed using tools such as are available at www.JSABuilder.com. JSABuilder is an inexpensive database powered tool that can be used to develop job hazard analyses (JHA) or activity hazard analyses (AHA). Also, a similar great tool available for developing electrical tagout plans, can be found at www.LOTOBuilder.com. In most instances the first consideration for workers will be to recognize potential situations that may present electrical threats. For unplanned encounters that might involve downed power lines, once identified, individuals should carefully seek a safe egress route (if available) and/or call the local fire department and power company to mobilize experts who can assess and eliminate any threats.
Be alert and always remember that arc flash threats often do not look very distinctive or threatening until a path to ground is provided. Individuals need to be very careful to not accidently be who/what provides a potentially fatal path to ground. An example of a threat could be where power lines have been knocked down and are laying on the ground or on a car. If someone happened to be trapped in the car injured the initial tendency might be to try to immediately get to that individual to provide assistance, however, if a downed electrical line was laying on the vehicle, the rescuer touching (or getting too close to) the vehicle could provide a path to ground. A potentially fatal mistake for the rescuer.
In the course of most work activities, arc flash events are relatively uncommon, however identifying the potential risks that are present is important especially when workers will be using power tools. So, it makes sense for workers to discuss where the potential risk areas are during a project kickoff or each morning tailgate safety meeting so everybody is familiar with the hazards. A few example type activities that could inadvertently place a worker where they might potentially have an encounter with an arc flash hazard might be as follows:
- Working around overhead power lines if accidently contacted by heavy equipment; working below creates issues for individuals on/operating equipment and for workers adjacent to the equipment who could inadvertently become a path to ground.
- Electrical power lines knocked down- Could be encountered for some reason not necessarily related to work activities directly, perhaps encountered during mobilization to a site or maybe at the site due to a weather-related event.
- Active power panels- The boxes may offer some level of protection but should be treated with respect as they cannot be assumed to provide complete protection.
- Energized in-wall wiring at construction sites- Lines should be de-energized prior to commencement of work, preferably using appropriate LOTO procedures.
- Subsurface power lines- Lines must be cleared prior to digging. Contact with active power sources will place workers and equipment at risk. Local lines should be de-energized and some sort of LOTO used.
- Solar power installations- May not be straight forward with respect to LOTO in some instances. Check for status and presence of inverters and batteries. Shutting off the breaker from the power grid may not be sufficient to de-energize the worksite system.
All potential sources of electrical energy should be discussed prior to the start of work at least daily. As the kickoff safety discussion progresses, if it is discovered that site conditions are different than presented in the JSA worksheet or LOTO procedure, that documentation should be annotated with appropriate Management of Change (MOC) notes. Those notes update the documentation to be accurate so the work can proceed in a safe manner. Always be thorough when safety is involved, especially with respect to arc flash as mistakes can be fatal and final. Use care and make sure everybody goes home safe each and every night.
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It's also FREE to try out our online JHA software at www.JSAbuilder.com. Discover this outstanding JHA/AHA software that will help your team work safely and go home at the end of each work day without harm. Follow JSABuilder on Twitter @JSABuilder, where we tweet about Health and Safety, post Safety tips, and provide updates on current Health and Safety topics.
References:
- Safe Work Practices for the Electrician by Ray A. Jones, Jane G. Jones -- Jones and Bartlett Publishing 2009 Page 40
- http://donklipstein.com/bulb1.html#wbs: The Great Internet Light Bulb Book, Part I
- KM Kowalski-Trakofler, EA Barrett, CW Urban, GT Homce in: "Arc Flash Awareness: Information and Discussion Topics for Electrical Workers". DHHS (NIOSH) Publication No. 2007-116D. Accessed January 10, 2013.
- Electrical Safety in the Workplace by Ray A. Jones, Jane G. Jones -- National Fire Protection Agency 2000 Page 32