According to NFPA 70E section 130.7 (C) (12) (a), layering of non-melting flammable garments is permitted to be worn under FR garments for added protection. However, the system arc rating of the innermost FR layer must be sufficient to prevent breakopen and ignition of the flammable under layer.

If Table 130.7 (C) (9) is used to determine the HRC category; only FR layers within the layered system are used to determine system arc rating. Arc ratings of individual layers cannot simply be added together. Any garment worn as the outer layer, including rainwear, must be FR.

Meltable fibers such as acetate, nylon, polyester, polypropylene, and spandex cannot be used in under layers next to the skin the only exception being an incidental amount of elastic is permitted in socks and underwear.

Because of changes to the 2009 Edition of NFPA 70E, we can no longer advise our customers to simply add individual single layer arc ratings together to arrive at a system arc rating for layered garments. Annex M.3.1 of the 2009 Edition of NFPA 70E states that the total system arc rating cannot be determined by adding the arc ratings of the individual layers. The only way to determine the total system arc rating is to conduct a multilayer arc test on the combination of all the layers assembled, as they would be worn.

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