Learn the benefits of layering arc rated garments for a cost-effective and practical way to achieve both arc flash protection and increased wearer comfort.
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ARC FLASH TRAINING: NFPA 70E PPE Hazard Risk Categories Now Based on Arc rating cal/cm2
By Hugh Hoagland www.e-hazard.com
Perhaps the most significant change to the 2009 NFPA 70E is a redefinition of PPE hazard risk categories (HRC’s). The principles determining a PPE system for each hazard risk level are now based on developing a clothing system meeting a specific tested cal/cm2 level and comprised completely of arc-rated materials.
The key to this approach is wearing the correct amount of arc-rated protection, not necessarily the exact pieces of clothing listed in the 70E tables. For example, if eight cal/cm2 of protection are required, you can wear an eight cal/cm² arc-rated shirt and pants, or a four cal/cm² arc-rated shirt and pants and a four cal/cm² arc-rated coverall; or an eight cal/cm² arc-rated coverall over cotton shirt and pants. See what we mean? It is the total level of arc-rated protection that matters – that and the absence of synthetic materials. You can wear one level of eight calories or two layers of four calories, or any combination equaling the total cal/cm2 necessary to protect you from severe burns if an arc flash occurs. This method applies to all hazard risk categories. The 25 cal/cm2 required for HRC 3 protection can be achieved by wearing a shirt and pants, coveralls, arc flash suit, or any combination of clothing that meets the required protection level. This change gives employers more leeway in developing a protective clothing system that meets the specific needs of their companies.
If you look at the requirements for HRC 2 in Table 130.7(C) (10), you see the following under clothing requirements:
FR Clothing, Minimum Arc Rating of 8
Arc-rated long-sleeve shirt
Arc-rated face shield or arc flash suit hood
Arc-rated jacket, parka, or rainwear (as needed) *
Previously the standard required HRC 2 to include an eight cal/cm² shirt or an eight cal/cm² coverall or a 4 cal/cm² with a cotton t-shirt. The cotton t-shirt was mandated. Now, you choose any eight cal/cm² system be it one layer or more but the cotton t-shirt is no longer mandatory and unrated layers do not add to the protection levels in the HRC’s. Natural fiber clothing like cotton, wool and silk are still allowed but cannot add to the protection level because of the risk of ignition. If a company wants to use cotton for protection, they must rate the system with the cotton underneath and control the cotton layer to assure no ignition. This can be done using the ASTM F1959 arc test method.
While this new approach offers more options in choosing PPE clothing, a company cannot randomly choose, for example, a four cal/cm² arc-rated shirt and a four cal/cm² arc-rated t-shirt, deem it an eight cal/cm² system and issue the clothing to electrical workers. When layers are used, the total system must be tested to get the total arc rating. Why? Because the sum does not always equal the whole. Most often, testing proves the system provides greater protection than the sum of its individual parts. However, the opposite may hold true. Some systems protect better than others. Some are barely additive (i.e. 4 cal/cm² + 4 cal/cm² = 8 cal/cm² ) but other systems such as using a heavy layer over a light layer might allow second degree burns at little more than the outer layer’s protective level (i.e. 4 cal/cm² + 8 cal/cm² = 8.1 cal/cm²) but most systems multiply the protection (i.e. 4 cal/cm² + 4 cal/cm² = 20 cal/cm²) See NFPA 70E Standard for Electrical Safety in the Workplace, 2009 Edition, M.3-3.1