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NESC revisions and the utilities industry

August 1, 2008
How will the recent revisions of the National Electric Safety Code affect my employees?

Answered by Scott M. Margolin, international technical director, Westex Inc., Chicago.

The National Electric Safety Code was revised last year. The new code contains significant changes regarding arc flash hazards and flame-resistant protective apparel, which will have a notable impact on the way electric utilities protect their employees. The new version takes effect Jan. 1, 2009.

The changes are similar in direction and general philosophy to NFPA 70E (which does not apply to transmission and distribution utilities): perform a hazard assessment, require FR clothing to cover the upper and lower body, and require the arc rating of the FR clothing to go up as the hazard rises.

NESC rule 410A3 states: "Effective January 1, 2009, the employer shall ensure that an assessment is performed to determine potential exposure to an electric arc for employees who work on or near energized parts or equipment. If the assessment determines a potential employee exposure greater than 2 cal/cm2 exists, the employer shall require the employee to wear clothing or a clothing system that has an effective rating at least equal to the anticipated level of arc energy."

Two of the major directional changes are the requirement for full-body coverage, meaning a flame-resistant shirt and pants or coverall, and the intent to match the protection of the FR clothing to the potential hazard.

Full-body protection means "upper and outer" programs (which require FR shirts and jackets but allow non-flame-resistant, 100 percent cotton pants) will no longer be permissible. Luckily, a number of pant fabric choices are available from a few brands that make cotton or cotton-rich denim blends, ducks and other popular work-pant styles. These are essentially indistinguishable from typical non-FR pants in style, appearance and weight.

The second new direction is the need to have the protection increase with the hazard. Under old guidelines, any flame resistance was sufficient because by not igniting in an arc and continuing to burn, it minimized injuries to a survivable level. However, FR clothing should ideally be rated to insulate from the known hazard in addition to not igniting, allowing the worker to avoid all second- or third-degree burn injuries. This is measured by arc thermal performance value, or arc rating.

The rules that apply here use 1,000 volts as a dividing line. They state that at less than 1,000 volts, on secondary, non-network systems, FR clothing with an arc rating of at least 4 calories is required, but that at greater than 1,000 volts, tables 410-1 and 410-2 should be used. These tables contain various fault currents and clearing times; as either or both rise, so does the potential incident energy, and therefore the protection required.

Depending upon where one falls in these charts, basic FR clothing arc ratings are 4 calories, 8 calories and 12 calories, with the higher ratings providing more insulation from burn injury.

The new rules have been public for a year, and compliance is expected in four months. If you operate in an NESC state, these rules apply, and it is probably time to get help and get compliant.

Originally published in the August 2008 issue of Safety+Health.