Building Arc Flash Awareness
There is no room for error when dealing with this type of exposure.
- By Mary Beth Villalobos
- Apr 01, 2006
IMAGINE being an employee in a workplace and going about your duties as you would on a daily basis . . . and an arc flash occurs. There is an explosive pressure wave and fire breaks out. Radiant heat is projected. Dangerous chemicals can be produced. And the damage is serious to fatal.
An electrical arc can occur at any time as a result of a current breaking through insulation or because of a short circuit developing from poor electrical contact. In an instant, arc temperature can reach 20,000 degrees Celsius. The extremely high temperature of these arcs, about four times as high as that of the sun's surface, can cause fatal burns to anyone within 5 feet and serious burns within 10 feet. Clothing can ignite and cause fatal burns because the clothing cannot be removed or extinguished quickly enough to prevent serious burns. More than 2,000 workers are sent to burn centers each year with electrical burns (facts taken from Contractor Tools & Supplies, December 2005).
Enter the NFPA 70E electrical safety standard, which has been the premier standard since 2000 to protect individuals from the burn hazards of an electric arc. The standard is designed to give the industry a more complete picture of how to protect employees from electric arc and is being considered for adoption by regulatory agencies in Canada. It requires employees in an area where there is burn potential from an electric arc to wear flame-resistant protective clothing with a minimum arc rating, or Arc Thermal Performance Value (ATPV), of 8 cal/cm2. Calorie (cal) ratings are determined by the ASTM F1959 Standard Test Method. This test determines how much heat from an electric arc a certain fabric (or system of fabrics) will block before the onset of second-degree burns to the wearer. That amount of energy is reported as the ATPV.
The higher the ATPV, the more protection the fabric will provide. The Hazard/Risk Category (HRC) is determined by the range of expected incident energy exposure. Workers can use the ATPV and HRC information to select personal protective equipment that will best protect them from the expected arc exposure in their work environment.
Arc Thermal Performance Value (ATPV)
Hazard/Risk Category (HRC) 0: For use up to 2 cal/cm2 incident energy exposure, but materials have no arc rating
1: 4 cal/cm2 exposure
2: 8 cal/cm2 exposure
3: 25 cal/cm2 exposure
4: 40 cal/cm2 exposure
Getting Acquainted with 70E
NFPA 70E was the first standard that specifically required arc flash PPE while working on or near live power greater than 110 volts. There has been much confusion about compliance with this standard. Most PPE that complies with the standard does not protect against electrocution, but rather, against the burn potential associated with arc flash.
Much of the confusion comes from misinterpretations of the language of the standard, as well as misleading sales literature. Safety professionals' best bet is to rely upon the manufacturer's expertise and knowledge in this area. Each manufacturer should be able to produce ASTM test data to support its products and its claims. There is no room for error when dealing with this type of exposure.
Industries affected by this standard include petrochemicals, automotive, manufacturing, electric utilities, foundries, and the military, but the list continues to grow. Nearly any type of maintenance or technical service worker needs to be educated in the risks of a possible arc flash.
70E-Compliant Hand Protection
Since the standard was published, many types of PPE have become compliant, including clothing, faceshields, eye protection, and shoes. Arm and hand protection have been somewhat ignored until recently.
In many cases, workers are required to wear three pairs of gloves to be compliant: a knitted cotton glove, covered by a liquid-resistant glove, covered by a leather glove. You can imagine how ergonomically incorrect this combination would be, not to mention the logistics of locating all of your gloves every time you are in a danger area. How often might you skip one or two of your layers just to replace one wire or check one circuit? One accident is all it takes.
New materials are entering the industry to address these concerns. One such product is a lightweight, breathable, soft, and hypoallergenic material that is comfortable to wear for extended periods of time. Gloves and sleeves made with it significantly increase wearers' protection against heat from electric arc, flame, and thermal hazards, and they comply with the NFPA 70E standard. What makes this material different from other materials commonly used in PPE is that its thermo-radiant behavior resists heat transfer from both convective and radiant heat sources. Its properties provide resistance to radiant energy shone on it, whether from flames of combustion, electric arc discharges, or from other heat sources.
Different glove styles are available and range in levels of protection from Hazard Risk Category 2 through 4 in accordance with the standard's requirements. In arc and other tests, these gloves consistently handle radiant heat better than para-aramid fibers alone. They will not support a flame and, in addition, are cooler and more comfortable in hot environments and warmer in cold temperatures than other products.
Look for the APTV/cal rating on the glove to instantly identify the glove/sleeve that is appropriate for the exposure risk. Available products include knitted gloves, loop-in and loop-out terrycloth gloves, sleeves, and leather palm gloves. Some gloves are recommended for use as liners, while others carry an ATPV rating of 4 (can take up to 40 cal/cm2 exposure) and can be worn by themselves.
One accident is too many. Safety professionals today need to educate themselves and their employees about the NFPA 70E standard and to be sure they are in compliance. They should be able to rely upon the hand protection specialist representing the manufacturer to help educate and supply substantive documentation for ASTM standards.
Gloves and sleeves should be clearly marked with their ATPV/cal rating so there is no question when they should be used--just like other PPE. Our goal is a safer workplace and a better-informed workforce.
This article appeared in the April 2006 issue of Occupational Health & Safety.
This article originally appeared in the April 2006 issue of Occupational Health & Safety.