Arc flash clothing is designed to provide a barrier from heat and flame, to minimize total burn injury and to help provide the wearer with extra seconds of protection to help escape possible secondary explosions or fires in the work area. 
Arc Flash clothing can increase the chances of survival and decrease the need for medical treatment (skin grafts) and the chances of subsequent infections. It can help preserve the quality of life of a worker exposed to an electric arc event. PPE is not designed to be firefighting gear; it is worn to help reduce the risk of more serious injury. Wearing ordinary clothes, especially synthetic fabrics like nylon, in an electric arc incident may make injuries worse than if the skin was not covered at all. Denim jeans and jackets, cotton shirts, cotton/synthetic T-shirts, sweatshirts, fleeces or nylon jackets are fuel sources that ignite, burn and frequently melt onto the skin. The heavier the weight of the fabric, the more fuel there is to burn. While the explosion may be over in a fraction of a second, but non-flame retardant clothing may keep burning. Remeber, it takes just three seconds to sustain third degree burns.
In electric arc blasts, even FR clothing can break open due to the extreme energy. Its prudent to wear loose-fitting layers, with an FR outer layer, and underwear that won’t melt. Suitable flame retardant ppe will help insulate the wearer from heat, resist breaking open, and will not ignite or continue to burn when exposed to a high intensity, short duration explosion and fire.
NFPA 70-E
To help workers understand the burn dangers more easily, the NFPA assigns a 0-4 number to hazard/risk categories representing the danger level. The minimum hazard rating for arc blast puts the burn exposure at 4 cal/cm2, which is a NFPA 70-E “Category 1 Hazard” rating. FR apparel must be worn for the “Category 1 Hazard” level. When selecting an FR garment for electric arc hazards, look for labels that show the arc rating as required by to the ASTM F1506 standard below.
| Arc Hazard Risk Category: NFPA 70E (2004) |
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NFPA 70e Hazard/Risk Category | Energy FR Apparel on FR Garment Level | ATPV Rating |
1 | 5 cal/cm2 | ≥4 |
2 | 8 cal/cm2 | ≥8 |
3 | 25 cal/cm2 | ≥25 |
4 | 40 cal/cm2 | ≥40 |
Examples of such arc flash clothing is more than just shirts and pants. It could include flame resistent hat, face shield, flame resistant neck protection, hearing protection, suit, insulated rubber gloves with leather protectors, and insulated leather footwear.
All ppe must meet the requirements as shown in the latest edition of NFPA 70E "Electrical Safety In The Workplace". PPE, sufficient for protection against the potential for explosion, is required for every part of the body.
Definitions Arc Thermal Performance Value (ATPV): This value is presented in calories per square centimeter and represents the maximum capability for arc flash protection of a particular arc flash clothing.
Flame Resistant (FR): “Flame resistant” can describe a fabric naturally resistant to burning but also can represent a material with special treatment applied to the fabric.
Fabric Weight: This is usually represented in one of two ways: ounces per square yard or grams per square meter.
Heat Attenuation Factor (HAF): This is the amount of heat blocked by the fabric. Even though a fabric may be 100 per cent flame resistant, that does not mean it will block all of the heat to which it is exposed. An HAF of 85 per cent means that it will block 85 per cent of the heat the ppe encounters.
Calories per Centimeter Squared: This is a number identifying the amount of energy that can be delivered to a point at a particular distance from an arc flash. Once this value is known, the ATPV rating of the ppe required for work at that distance from the potential flash hazard is also known.
Arc flash clothing: This term is primarily used to describe all safety equipment used by personnel to protect personnel. This includes fall protection, confined space, electrical hazards, and so on.
Hazard Risk Category (HRC): This is a 2004 NFPA 70E rating of exposure levels for particular types of equipment. The values range from zero to four, with a zero HRC not requiring any ATPV-rated PPE. The minimum ATPV rating for Categories One through Four are as follows:
- Category One: five calories per square centimeter
- Category Two: eight calories per square centimeter
- Category Three: 25 calories per square centimeter
- Category Four: 40 calories per square centimeter
Fabrics
100 Percent Cotton: It was not all that long ago that 100% cotton was considered the appropriate ppe when an electrical arc exposure was present. It was considered that 100% cotton provided much better protection than polyester, which is true. However, ppe testing proved that 100% cotton only served to add fuel to explosive energy. It was also proven that the best way to protect a person from being burned was for the person to wear flame restardant clothing.
Flame-Retardant 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 retardant performance throughout the life of the ppe. 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 retardant chemical impregnated into 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 retardant chemical acts in the solid phase to produce this charring. The mechanism of action is not based on a gaseous process of extinguishing or “snuffing out” the flame.
It is very important that ppe be maintained in a clean condition to realize their full protection potential.
Flame-Retardant 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 retardant performance of the ppe 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.
93 Percent DuPont™Nomex® , Five Percent Kevlar, and Two Percent Antistatic Fiber: This long-winded description is most commonly know by its trade name “Nomex IIIA.” manufactured by DuPont™. Nomex IIIA is a lightweight, inherently flame-resistant fiber blend. It does tend to have a higher heat let-through rate. 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.
Care and Cleaning
A variety of flame-resistant fabrics are available in today’s marketplace. Each fabric has unique wear, comfort, appearance, and durability characteristics. Each of these issues should be considered when making an ppe purchase.
Industrial laundering creates more wear on a garment than home laundering. Also, it has been found that heavy facial growth has a negative effect on wear life of a collared shirt. Additionally, repeated abrasion of any type shortens wear life in the area on the ppe where the abrasion occurs.
Note: Indura ppe should not be laundered with hypochlorite (chlorine) bleach because repeated exposure will break down the finish and is destructive to the fabric and the color. Most flame-resistant fabrics, including DuPont™ Nomex® , bear instructions warning against the use of chlorine bleach because it may weaken to the fabric strength and color even if flame resistance is not affected.
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