'De-Energizing' Electrical Hazards at Mine Sites
Proven strategies and technologies will protect workers and speed the recovery from arc flash incidents in mining operations.
Electricity is a vital element in just about every mining process, from drilling to hauling to processing and more. Despite all of the advances in electrical distribution and control, moving electrons through strands of copper and banks of equipment still poses very real safety dangers at mine sites. Arc flash is one of the most serious.
What Is an Arc Flash?
Created by the release of energy from an electric arc, arc flash is an immensely powerful burst of heat energy. How powerful? An arc flash incident can:
- Severely injure or kill a person from as far away as 10 feet or more in certain situations.
- Cause serious burns. At 35,000 degrees F, arc flash temperatures are hotter than the surface of the sun.
- Produce pressure and sound waves strong enough to throw workers across a room and turn tools and equipment into life-threatening shrapnel.
- Cause vision and hearing loss from extreme light and sound outbursts.
- Cost up to $15 million per incident in health care, worker's compensation, equipment replacement and repair, increased insurance premiums, and lost production time, according to an Electric Power Research Institute study.
Arc flash danger is present throughout a mine site. Most frequently, arc flash incidents occur when an engineer is servicing energized electrical equipment. An action as minor as dropping a wrench can cause an arc flash event if it falls across conductors.
In the mining industry, electrical arc flash incidents are the most common cause of non-fatal electrical injuries, according to a report from the Centers for Disease Control and Prevention. The same report revealed that during a 12-year period in the mining industry, more than 36,000 work days were lost due to sustained electrical injuries.
It's plain to see that arc flash demands the industry's attention and requires plans for reducing the risk and danger.
Assessing the Risk
Mining companies should reach out to electrical distribution experts for help in creating complete programs that limit the possibility of an arc flash and minimize the effects of an incident. For example, GE trains and certifies their power system engineers to perform comprehensive arc flash hazard studies in accordance with NFPA Standard 70E, the National Electrical Code directive for electrical safety in the workplace. Armed with this information, power system engineers can visit mine sites to assess arc flash danger and minimize risk. It's recommended that companies adopt end-to-end safety improvements with initiatives such as:
- Creating and deploying a complete arc flash strategy
- Conducting ongoing employee training
- Matching arc flash protection equipment and clothing with the level of risk
- Identifying and evaluating arc flash potential throughout a location
- Calculating incident energy exposure and arc flash boundaries
- Placing warning labels to indicate arc flash hazard levels
While education and precautions can reduce arc flash occurrences, they can never be totally eliminated. Mining companies can deploy arc flash mitigation strategies to reduce the incident energy of those events, minimizing worker injuries and equipment damage.
Deploying Arc Flash Mitigation Solutions
In the past decade, several technology breakthroughs have improved the management of an arc flash's potential danger. GE engineers have been at the forefront of finding ways to apply these breakthroughs to installed equipment, regardless of the manufacturer. As a result, mining companies can reduce the arc flash risk in their installed infrastructure, increasing the useable life of capital equipment and improving safety.
The following are strategies for companies to deploy in order to reduce their risk of an arc flash incident:
- Mitigate with Instantaneous Zone Selective Interlocking: Instantaneous Zone Selective Interlocking (I-ZSI) protection delivers safety and selectivity against arc flash energy 24/7. This GE-exclusive innovation is a total system rethinking that places the main circuit breaker on an alternate setting if a fault occurs below the feeder, so you always stay up and running. This concept, previously regarded as unobtainable, provides simultaneous selectivity and arc flash protection in a game-changing technology. I-ZSI case studies report arc flash energy can be reduced to just 18-25 percent of the energy released during events with traditional ZSI or staggered protection.
- Mitigate with Reduced Energy Let-thru: Reduced Energy Let-thru (RELT) is a safety window. New digital trip units offer two separate instantaneous set points, so workers can lower the trip threshold with the flip of a switch before servicing energized equipment. This can dramatically lower incident energy potential.
- Mitigate by Retrofitting Fuse-Technology load Interrupter Switches with Fast Circuit Breakers: Older equipment in many mines uses fuses to cut power in load interrupter switches on distribution transformer primaries. Fuses can take up to half a second to respond – an eternity for an arc flash event. Retrofitting fused interrupter switches with modern circuit breakers can cut off power in 3 cycles (3/60 of a second), dramatically limiting the arc flash time and significantly reducing its energy.
- Mitigate with Energy Transfer and Containment: A new arc containment technology that uses arc-to-arc transfer to keep energy low and allow fast mitigation is now available. This hybrid solution can stop an electrical fault in 7 milliseconds or less, mitigating the fault while also transferring the energy into a hardened containment dome. Because the hardened system shuts down the flash and its energy so quickly, it sustains little damage during an event, so workers can quickly install a spare containment dome and have the complete system available for service in hours versus weeks. This solution delivers a greater return on investment through reduced downtime, enhanced productivity, and lessened risk of injury.
- Mitigate proactively with proper design for new mines: The aforementioned arc flash mitigation technologies and strategies should be part of the design for new electrical systems as well as retrofits. Beginning with a proper power-system study and technology selection can significantly improve coordinated performance and safety. Using a proven power-system design software package to design and simulate performance can help to minimize the effects of arc flash.
Is Your Mine Site Prepared for Electrical Safety?
The danger of arc flash can never be completely eliminated. But a focused strategy and ongoing vigilance can reduce risk and maximize the safety and productivity at mine sites around the globe. For more information on arc flash and electrical hazards or how GE's Industrial Solutions business is working with customers in the mining industry to reduce the risk of arc flash, visit http://www.geindustrial.com/arcflash.
Jay Franklin (firstname.lastname@example.org) is Industrial Verticals Sales Leader, GE's Industrial Solution business in Atlanta, Ga. Marty Trivette (email@example.com) is Power Equipment Product Marketing Leader - North America for GE's Industrial Solution business in Raleigh, N.C.