Confused About Arc Flash Compliance?
Written by Pam Tompkins, CSP, CUSP on . Posted in Safety Management.
If you’re in a quandary over arc flash compliance, you’re not alone, according to Incident Prevention’s recent survey.
Are you confused concerning arc flash compliance? Join the crowd of electric utility professionals who are struggling to understand arc flash implementation issues.
A recent survey conducted by Incident Prevention indicated there is no standard method for developing and implementing electric utility arc flash implementation plans. In particular, survey participants identified four areas of uncertainty:
• Selecting and utilizing appropriate engineering software to calculate arc flash data.
• Selecting standard working distances for various types of work performed.
• Developing engineering controls and work rules to reduce energy levels.
• Identifying and developing processes to manage secondary arc flash conditions.
Selecting Appropriate Software
Survey participants were asked to list engineering software and/or methodology used to calculate transmission and distribution arc flash data. The question yielded a wide range of answers including using NESC tables 410-1 and 410-2, ArcPro, Power On, IEEE 1584, Table 4 NFPA 70E, Milsoft WindMil, ASPEN, CYME and SKM. Several respondents cited using only one method for all operating voltages, but many used a combination of several methods to calculate arc energy levels.
Last year I received a call from an electric utility with distribution operating voltages over 15 kV struggling to implement an arc flash implementation plan. Their engineering software yielded incident energy values at 23 cal/cm2 and greater. Their question was “What do we do? Our employees work in extreme temperatures reaching 110 degrees.”
My first questions to the utility were, “What is the operating voltage?” and “What engineering software was used to calculate incident energy levels?” After review, it was determined the software was typically used for low voltage systems and had a history of yielding extremely high numbers when used on voltages over 15 kV.
Selecting appropriate software for each operating voltage is extremely important to ensure valid incident energy levels are identified. The proposed 2012 edition of NESC, Clause 9 contains a number of low-voltage evaluations for typical transformer installations which will help identify the appropriate low voltage software.
Identifying Work Distances
The question yielding the largest variation of answers in the Incident Prevention survey involved identifying working distances during overhead, underground and substation operations. Selecting the appropriate working distance is important since engineering software requires working distances to be inputted into the calculator. Working distances should be identified by each utility since the arc flash software will default to a value that may not be appropriate for the work environment.
When working distances are used, they should represent real-world working conditions. NESC-2012 is proposing adding a note requiring assessments to be performed to “determine potential exposure to an electric arc considering the worker’s assigned task and/or work activities.” If workers do not perform gloving operations, the working distance calculators should include hot stick applications, etc. Arc energy levels reduce greatly as the worker moves away from the energy source.
Multiple working distances should always be used in the calculators. Once engineering criteria is loaded it is an easy adjustment to add multiple working distance calculators for gloving, hot stick operations, gang-operated switch operation, etc. Employees should receive specific information concerning working distances used in the evaluations and why incident energy levels could be substantially higher if energized work is performed closer than the selected distance.
Arc Flash Protection Boundary
The arc flash protection boundary, measured at 1.2 cal/cm2, is the distance at which a worker will likely receive a second-degree burn. Many utilities identify the arc flash protection boundary to determine requirements for arc flash protection when workers are in the vicinity of energized work. The arc flash protection boundary is normally calculated to determine worksite exposures.
Engineering Controls
The survey indicated utilities are using engineering controls and changing work rules to minimize arc flash exposures. Answers included use of remote racking tools, changing fuses and circuit breakers, changing setting on relay and adding instantaneous relays as needed, modifying relay settings, requiring electronic “hot line tag,” updating hot line work rules, reconductoring, looking at design specifications and new equipment to reduce energy levels, transferring load to other circuits, changing recloser settings to faster curves, etc.
NESC-2012 is proposing changes to indicate “engineering controls can be utilized to reduce arc energy levels and work practices can be utilized to reduce exposure levels.” This validates the theory that arc flash implementation is not just a PPE program. Remember, PPE is the last line of defense!
Secondary Arc Flash Conditions
The last area of concern managing secondary arc flash conditions was identified as a serious arc flash issue requiring engineering controls and the development of work rules to minimize exposure. Many respondents stated energized work on various voltages and sizes of three-phase, pad-mounted equipment has been minimized, if not stopped completely.
Arc flash implementation is not easy to develop and manage. Approaching the issue as a team, including engineers, safety professionals and line workers, will ensure all issues have been addressed appropriately.
Reference: NESC-2007, Change Proposals- NESC-2012, NFPA 70E
About the Author: Pam Tompkins, a Certified Safety Professional and Certified Utility Safety Administrator, is President of SET Solutions in Lexington, South Carolina. The company specializes in helping small- to medium-sized electric utilities comply with safety and training requirements. Prior to forming SET in 2000, Tompkins worked in the electric utility industry for more than 20 years.
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