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Arc flash

Layering flame-resistant clothing

April 1, 2011

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Question: When it comes to electric arc flash protection, can “layering” flame-resistant garments be a cost-effective, practical way to clothe workers as they move between tasks with different hazard ratings?

Responding is Mark Saner, technical manager, Workrite Uniform Co. Inc., Oxnard, CA.

Answer: Yes, layering is a possible solution to address varying arc flash protection needs when balancing protection with worker efficiency, comfort and economics.

During the workday, workers may move between various jobs with varying arc exposures. Having easy access to and the time to don the Hazard Risk Category 3 flash suit is not always the case. The tendency might be to skip the change and simply do the work with HRC 2 daily wear. Not having the correct level of protection when an incident occurs can be costly to both the employee and the employer. One way to get to the higher level of protection needed can be by layering. By having access to an HRC 2-rated coverall to pull on over an HRC 2 uniform, you often can provide a layered HRC 3 level of protection. This layering of protective clothing (along with the other appropriate personal protective equipment) satisfies the NFPA 70E standard for electrical safety requirements for arc protection.

For example, the combination of a daily-wear shirt with an arc rating of  8.7 cal/cm² (HRC 2) and an 8.7 cal/cm² arc-rated coverall over it achieves a 27.2 cal/cm² (HRC 3) level when tested. This layered combination achieves the HRC 3 level and is much easier to carry around and slip into than an HRC 3 flash suit.

Test results show the air layer between garments typically increases the arc rating more than simply adding the ratings of the two FR garments together. As shown in the above example, the actual layered rating of 27.2 cal/cm² is higher than the 17.4 cal/cm² sum of the two 8.7 cal/cm² ratings. However, note that there is no measurable standard for the extra protection afforded by air trapped between garments due to the many variables involved with individual situations – such as the amount of air trapped, tightness of garments, size of wearer, etc. Although adding the actual combined rating of the garments worn is a commonly used maximum rating number, the actual rating of the combination is not really known unless the specific combination of fabrics has been arc tested.

The key to the above example is analysis that shows 67 percent of all tasks at a typical industrial company rank at or below HRC 2, with many tasks at HRC 1 or 0. The example shows how the worker is adequately protected with a primary layer during duties that occupy most of his or her time. When moving to the higher arc exposure task, the additional coverall boosts the protective clothing to HRC 3, providing increased protection with acceptable comfort and mobility. It is then easy to shed the coverall when returning to more common duties.

It is likely that workers may require multiple garments to maintain safety while performing multiple tasks. There may be many pieces of clothing, but only one philosophy: proper protection at all times for changing risk. Layering is a sensible answer that combines comfort, convenience and safety.

Editor's Note: This article represents the independent views of the author and should not be construed as National Safety Council endorsements.

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