Advantages of Layered Clothing San Francisco CA

Arc flash protective clothing has been around for many years now. Early (pre-1997) arc flash personal protective equipment (PPE) was typically made of one or two fabric layers. If you needed more protection the clothing was heavier, but still one or two layers. Today's arc flash clothing is often made with a multi-layered construction, which makes the clothing lighter and easier to wear. This aspect of arc flash PPE really gets to the heart of protecting people. It has been recognized for some time that wearing layers of clothing would increase the ability of the PPE system to dissipate the heat from an arc flash. The word "system" is emphasized because we must view arc-rated clothing and PPE as a system of individual articles of clothing and equipment that, when used together properly, greatly improve their performance over that when used individually.

PPE systems could also include such items as rubber or silicone hearing inserts, UV-rated safety glasses or goggles, arc-rated face shield or hood, heavy leather safety shoes and underlayers. Underlayers, as the name implies, is the clothing worn under the arc flash protective clothing. Wearing underlayers made of meltable fabrics greatly increases the chances of a residual burn from an arc flash. As an example, Spandex is a synthetic fiber that can melt at temperatures as low as 180 degrees F. I bring this up because when an arc flash hits the outer layer of clothing, even arc-rated clothing, it heats up tremendously. Some of this heat is transferred through the fabric (think of pulling your jeans out of a hot dryer and putting them on). Enough heat can be transferred through the arc-rated clothing to melt the underlayers. This would be a very painful burn. Electrical workers must be trained in this type of hazard, as most people would not think of it. Cotton underlayers are recommended in most circumstances, although increased protection can be provided by FR (fire resistant) underlayers.

The rule-of-thumb is that for every layer of clothing worn under arc-rated clothing, the heat drops by 50 percent. By wearing FR daily wear and cotton underlayers, the heat would drop by 50 percent for each layer, at least on those areas that are covered. The air between the layers of clothing increases the ability of the arc-rated clothing to dissipate heat, much like a down jacket is warmer due to the air pockets around the feathers. One protest I often hear is that wearing a tee-shirt as required by the NFPA (National Fire Protection Association) 70E Table 130.7(C)(10) is too hot and uncomfortable in the summer. Actually, a person wearing a tee-shirt will stay cooler, since the tee-shirt wicks moisture from the body, allowing it to evaporate more effectively. I live in Texas and I'll guarantee it is cooler with the tee-shirt than without. The tee-shirt also provides that air layer so important to dissipating heat, at least on the areas covered by it.

Wearing just the arc-rated FR clothing provides a 50 percent probability of a second-degree burn at 15 cal/cm². Wearing FR daily wear clothing underneath increases that rating to 24 cal/cm². Adding underlayers, such as the longjohns would further increase that rating to 46 cal/cm₂. The preceding numbers would all be for a 50 percent probability of a second-degree burn. I am not advocating wearing longjohns in Texas during the summer, or almost any other time, but wherever underlayers would cover, those areas would have the benefit of increased heat dissipation.

Table 1 shows how much lighter multi-layered clothing is, while providing increased arc flash ratings. This is one of the reasons the NFPA 70E Committee voted to eliminate the weights of fabrics from Table 130.7(C)(11). Note that an older generation 65 calorie arc flash suit would weigh 34oz/yd². This would be very uncomfortable and restrict movement to a degree that most tasks would not be practical, at least for many people. Multi-layer arc-rated clothing and PPE in the newer systems weigh in at 15.5 oz/yd²; a reduction of more than half! This is the type of weight reduction that can improve wearability and reduce heat stress.

Another issue to consider though, is the maximum arc rating for the clothing. At Shermco we issue 65 cal/cm² (HRC4) arc flash protective clothing to our technicians. We don't expect them to exceed the 40 cal/cm² exposure recommended by the NFPA 70E Committee. But because we work on power systems that can be in unknown condition, we want our technicians to have a cushion when it comes to arc ratings. The newer 65 cal/cm² clothing weighs less than older generation 25 to 31 cal/cm² clothing, so our technicians receive more protection at about the same weight as clothing that may have been inadequate. As a member of the 70E Committee representing NETA—the InterNational Electrical Testing Association—at what point the blast hazard becomes more of a threat than the arc flash hazard is not known. We believe the 40 cal/cm² limitation is conservative, but videos I've seen (and use in the training classes I conduct) indicate that the limit may not be much higher.

The 40 cal/cm² recommendation is important, because many manufacturers market a 100 cal/cm² rated flash suit and at the August 70E Report on Proposals (ROP) meeting there were indications that proposals would again be submitted asking for a Hazard/Risk Category 5 (minimum 100 cal/cm² rating). This was considered during the last cycle and rejected because, as one Committee member put it, "bigger is not always better." At that arc energy the probable pressure wave could cause internal injuries, including crushing the rib cage and collapsing body cavities. You'd look good in your casket, but you would still be in your casket. Use arc flash PPE and clothing that is appropriate for the work and the hazard, which is what OSHA (Occupational Safety and Heath Administration) requires us to do. Don't get hooked into using the highest arc rating that can be purchased, as heat stress probability rises and working ability goes down.

As a member of the IEEE/NFPA Collaboration on the Arc Flash Phenomena, I would also like to encourage corporations and individuals to consider funding a series of 2,500 arc flash tests that are planned. This testing would refine and enhance what we know about the incident energy from an arc flash and also provide a basis for determining the extent of the arc blast hazard, as well as other hazards from an electrical arc, such as electromagnetic pulse, shrapnel and toxic gases. This is testing that will provide safety benefits to our workers and those yet to enter the field for many years to come. To learn more about this testing program, contact either Sue Vogel (s.vogel@ieee.org) at the IEEE (Institute of Electrical and Electronics Engineers, Inc.) or Mark Early (mwearly@nfpa.org) at the NFPA.

Electrical safety, especially around arc flash hazards, is a critical aspect of employee safety. Understanding the importance of a layered system of protective clothing and additional PPE is part of being a qualified electrical worker as well as providing protection in the case of an electrical incident. Layering clothing provides extended performance of arc-rated clothing and offers a method to minimize burns to heat transfer during an arc flash.

Jim White is the Training Director for Shermco Industries, a NETA Full Member company and an independent full-service provider of electrical maintenance and design services to light, medium and heavy industries nationwide. For more information, visit www.shermco.com