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Incident Prevention Magazine

5 minutes reading time (1055 words)

The Burning Question

Is 100 percent cotton protective in an electric arc flash? While lab tests say so, real life experiences say no!

It is widely understood that clothing made from non-flame resistant synthetic fabrics, such as polyester, nylon and polyester/cotton blends, are not appropriate when working on or near electrically energized parts and equipment. If these garments are exposed to an electric arc flash, they can ignite, melt and drip, which can lead to severe contact burns to the skin. In fact, the OSHA 1910.269 and NFPA 70E standards prohibit this type of clothing.

Many people, however, still consider 100 percent non-flame resistant cotton fabrics to be safe in an electric arc flash. The only thing safer about 100 percent cotton is that it does not contain a meltable component; it will ignite just as readily in an arc flash. In fact, cotton fabrics present major hazards in arcs; they burn hotter than poly-cotton, and are generally worn in slightly heavier weights. This means more fuel for the fire. Once ignition occurs, more fuel and a hotter fire combine to cause severe burn injury.
Heavier fabrics generally require higher incident energies to ignite, and published ignition thresholds often are quite close to the oz/yd2 weight of the test fabric. This has led to policies that allow the use of 100 percent non-FR cotton (of >11 oz/yd2—typically denim jeans), where hazard analysis has determined arc energies are well below eight calories. While at first glance this may seem reasonable, the logic is predicated on two conditions that rarely, if ever, exist outside the lab. One involves the fabric, and the second involves molten metal created by the arc.

The lab test that generates ignition thresholds uses new fabric (the ASTM 1958 ignition standard), not used garments. In the real world, garments age in use and three things typically happen, each of which reduce the energy necessary to ignite:
• 100 percent cotton garments lose mass through abrasion (and remember, weight is closely related to ignition threshold).
• Cotton garments typically develop thin spots, often at the knees, elbows, collar and above pockets. These areas can ignite at much lower energies than the same fabric when new and support flame-spread to the rest of the garment.
• Flammable contaminants, whether they be hydrocarbons from work or fabric softener, bug spray, etc. from home, will all reduce the amount of energy necessary to ignite the fabric.
It is strongly recommended to thoroughly clean an FR garment that becomes soiled with a flammable contaminant and retire garments that are worn out. The primary difference between non-FR 100 percent cotton clothing versus FR clothing is that if ignition occurs, FR garments will self-extinguish after the source of ignition is removed, while non-FR 100 percent cotton will continue to burn long after the fuel that initially helped cause ignition has been consumed. This continued burning can be the difference between life and death.

The lab arc uses a thin wire to initiate the arc and electrodes with a 12-inch gap—this creates a very "clean" arc with much less molten metal than most utility or industrial equipment. Actual equipment arcs usually involve a large volume of molten metal and the arc can "wander." Molten copper spraying out at 1900 degrees Fahrenheit can easily cause ignition of non-FR cotton regardless of weight. Many mannequins exposed to arc flash using actual equipment at the KEMA lab in Chalfont, Pa. (while dressed in FRC) were covered with molten copper to well below the knees, even though the faulted disconnect or splice was at chest level.
Another rationalization used to support the wearing of non-FR cotton pants is that arcs are expected to occur at torso height. The lab uses a Faraday cage to contain the arc, but of course there's no such restrictor in real gear. While the equipment that arcs may be at chest level, the arc can travel out in any direction, including down. There's plenty of high-speed video analysis of arcs in both low- and high-voltage equipment that shows this phenomenon. Some hot stick video even shows that several cycles "stay home," while the last cycle rockets out eight to 10 feet, directly at the mannequin.
Another rationalization is that working in a bucket obviates the need for FR pants because, the theory goes, the bucket will protect the legs. Again, video analysis of arcs and lab tests paint a very different picture. Most people would agree that when an electrical worker is in a bucket, the work is almost always above the top lip, usually by several feet. We've just discussed how arcs in real life wander (KEMA has frightening video of an arc shooting directly into a bucket). The bucket then becomes a confined space, and in effect intensifies the arc. The non-FR pants instantly ignite and burn so fiercely that the instrumented mannequin required extensive repairs. Test witness Ed Smith, shop steward for the UWUA 1-2, says, "There's a dangerous but common misperception that heavy cotton won't burn. In fact, it ignited easily, burned vigorously, and consumed the clothing quickly. If you work around electricity, you need to be in FR clothing."
With all of the potential problems associated with non-FR 100 percent cotton, you're probably asking, "Why are electrical workers allowed to wear non-FR cotton?" In the past, utility companies had valid concerns about the options available in FR clothing. The fabrics were stiff and very uncomfortable, and the garment styles were nowhere near the styles linemen were used to wearing. In addition, the requirements of the primary standard for the electric utility industry, OSHA 1910.269, were unclear when it came to clothing.
Today, you can find market-proven, engineered FR fabrics made from blends of natural and synthetic fibers, such as INDURA(r) Ultra Soft(r), that offer the soft, breathable comfort of cotton with enhanced durability, as well as many styles including denim, high ATPVs and flame resistance that is guaranteed for the life of the garment. The impending revision to the 1910.269 standard will clarify the clothing issue and close the loophole that led some utility companies to justify policies that allow the use of non-FR 100 percent cotton. ip

Scott M. Margolin is field technical manager for Westex Inc. He can be contacted at

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Tuesday, 19 January 2021

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