Fabrics for Electric Arc-Flash Protection

100 Percent Cotton: It was not all that long ago that plain old cotton was considered the appropriate protective clothing when an electrical arc exposure was present. The thinking was that cotton provided much better protection than polyester, nylon, acetate, and the like. This is true. However, along came products that soon made untreated cotton an undesirable fabric for these situations.

Flame-Resistant Treated 100 Percent Cotton: One such fabric available today is marketed under the trade name "Indura." This fabric is made by Westex and is guaranteed to maintain flame resistant performance throughout the life of the garment. This fabric has an expected wear life of 50 to 75 home launderings. This means that five sets of shirts and pants, each worn once per week, will last 12 to16 months in the range of light- to severe-use conditions.

In Indura-engineered fabrics, the flame resistant chemical impregnated on the cotton fiber core acts as a catalyst promoting the charring of the fabric. This accelerated charring prohibits the support of combustion by reducing the fuel source. The flame resistant chemical acts in the solid phase to produce this char. The mechanism of action is not based on a gaseous process of extinguishing or "snuffing out" the flame.

It is very important that flame resistant fabrics be maintained in a clean condition to realize their full protection potential.

Flame-Resistant Treated 88 Percent Cotton, 12 Percent Nylon: Previously, it was stated that nylon was an undesirable fabric for electric arc-blast protection. With this blend there is a mechanical type reaction when it is exposed to excessive heat. The nylon melts and essentially fills up the gaps between the cotton fibers creating a more solid defense against the heat source. This fabric is sold under the trade names of "Banwear" (made by Itex) and "Indura UltraSoft" (made by Westex). Both of these products guarantee that the flame resistant performance of the fabric is maintained throughout the life of the garment. One can expect Banwear and Indura UltraSoft to last 18 to 30 months when worn daily and home laundered once per week.

45 Percent Combed Cotton Fiber, 55 Percent Modacrylic: Modacrylic is a shortened name for "fibrous flame-resistant fiber." By combining these two fibers the fabric "Firewear" is produced. Firewear is manufactured by Springfield LLC. These woven fabrics range in weight from 5.5 to 9.5 ounces per square yard and are available in both twill and plain weaves. Firewear also is available in knits from 6.0 to 14.0 ounces per square yard. Before the fibrous flame-resistant fibers are exposed to heat and flames, they look and feel just like any other textile fiber. Upon exposure to flames, a reaction begins: certain molecular components of the fiber emit non-combustible gas that is released through tiny pores in the fiber. This smothers the fire in much the same way that a fire extinguisher does. These gases shut off the oxygen feeding the flames, thereby preventing further burning. Firewear has an expected wear life of 18 to 30 months when worn daily and home laundered once per week.

93 Percent Nomex, Five Percent Kevlar, and Two Percent Antistatic Fiber: This long-winded description is most commonly know by its trade name "Nomex IIIA." This is the latest and greatest of the Nomex line that has been manufactured by Dupont. Nomex IIIA is a lightweight, inherently flame-resistant fiber blend. It does tend to have a higher heat let-through rate and is not recommended for use around molten metals. This fabric is available in weaves from 3.3 to 7.5 ounces per square yard. Some weights are available in ripstop and twill weaves. Nomex IIIA has an expected wear life of 30 to 48 months.

60 Percent Kevlar, 40 Percent Polybenzimidizole: This blended fabric is marketed under the trade name of "PBI/Kevlar." The polybenzimidizole fiber is manufactured by Celanese Acetate; the Kevlar fiber is made by Dupont.

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