Best Practices for Arc Exposures and Use of FR Clothing

Jan. 1, 2011
Arc flash burns can be some of the most devastating injuries suffered in the workplace. Engineering controls, administrative controls and appropriate PPE can reduce the risk to employees.

Something that happens in a split second can impact a worker and his or her family for the rest of their lives. While arc flash injuries can be fatal, those that aren’t fatal still require significant recovery time. Studies indicate workers suffering from arc flash and electrical injuries require an average of 22-23 days off work to recover.

An arc flash is the sudden release of electrical energy through the air when a high-voltage gap exists and there is a breakdown between conductors. An arc flash gives off thermal radiation (heat) and bright, intense light that can cause burns, according to the National Institute for Occupational Safety and Health (NIOSH).

Temperatures have been recorded as high as 35,000 degrees F. High-voltage arcs also can produce considerable pressure waves by rapidly heating the air and creating a blast. This pressure burst can hit a worker with great force and send molten metal droplets from melted copper and aluminum electrical components great distances at extremely high velocities.

According to a NIOSH study, “Reducing Non-Contact Electrical Arc Injuries: An Investigation of Behavior and Organizational Issues,” an estimated five to 10 arc flash explosions occur in electric equipment every day in the United States.

Study authors Kathleen Kowalski- Trakofler and Edward Barrett noted, “Personal accounts from electricians also note that many workers have experienced some degree of exposure to an electric arc flash during the conduct of their work. However, because these occurrences did not result in an injury, they were not reported. Explanations for escaping injury have ranged from ‘pure chance’ to practicing proper work procedures, such as using personal protective equipment (PPE).”

Engineering Controls

When trying to eliminate any potential arc-related injuries, the first effort should be to eliminate the exposure through engineering design. If eliminating all arcrelated exposures is not possible, employers should to try to limit the extent of such exposures through administrative controls, including work practices (for example, reducing the available fault current or using work techniques that will put more distance between the worker and the point of the potential arc).

According to OSHA, the four major factors that affect how much heat a worker receives from an arc are:

  • Fault current
  • Arc length
  • Arc duration
  • Distance the worker is from the arc.

If any one of the first three factors – fault current, arc length or arc duration – changes by a certain amount in a certain direction (increases or decreases), a worker’s heat exposure will change by approximately the same ratio or percentage in the same direction (increase or decrease). For example, if the arc duration is reduced by one-half, the amount of heat exposure is also reduced by approximately one-half: arc duration (or fault current or arc length) ÷ 2 = heat exposure ÷ 2

The relationship between the fourth factor – distance from an arc – and heat exposure is different than the first three factors. Heat exposure changes inversely (in the opposite direction) with the approximate square of the distance.

This inverse relationship between heat exposure and distance can be expressed as: Heat exposure = 1 Distance2

For example, doubling a person’s distance from a potential arc by using a longer live-line tool would result in a worker receiving approximately one-quarter of the original heat exposure; tripling the distance would result in approximately a nine-fold decrease in heat exposure.

Selecting Appropriate FR Clothing

OSHA’s Electric Power Generation, Transmission and Distribution Standard, 1910.269(l)(6), requires that workers be trained in the potential hazards of electric arcs and the flames they can produce by igniting other materials in the area. It also prohibits workers from wearing clothing that potentially can increase the extent of injury; for example, if it would ignite and continue to burn, or if it melts on the skin. Thus, workers generally are prohibited from wearing clothing materials made entirely of, or blended with, materials such as acetate, polyester or rayon.

Clothing made from 100 percent natural fibers may be acceptable if its weight is appropriate for the flame and electric arc conditions to which a worker could be exposed. As heat levels increase, these materials will not melt, but they can ignite and continue to burn. The amount of heat required to ignite these materials is dependent upon a number of factors, including the weight, texture, weave and color of the material. This type of clothing does not comply with the “269” standard if it can ignite (and continue to burn) under the electric arc and flame exposure conditions found at the workplace.

When choosing appropriate PPE, look for FR clothing that is rated for particular heat exposures. The FR clothing industry has developed a heat energy rating system for FR fabrics. To identify the appropriate FR clothing to use, the heat energy, measured in calories per square centimeter (cal/cm2), to which workers are exposed needs to be calculated. Guidance for calculating an arc’s heat energy can be found in numerous sources, including NFPA 70E.

FR clothing contaminated with grease, oil, solvents or other flammable substances should not be used because such contamination greatly reduces the effectiveness of the material. As with any PPE that becomes damaged, damaged FR clothing must be replaced or repaired before resuming work.

Contaminated FR clothing must be thoroughly cleaned, if possible, or replaced. (For more information about care and maintenance of FR clothing, see ASTM F1449-01, Standard Guide for the Care and Maintenance of Flame, Thermally and Arc Resistant Clothing). FR clothing must be cared for as instructed by the manufacturer. Clothing that is damaged (for example, torn) often requires special repair techniques. For example, using common nylon thread may reduce the value of the clothing’s FR protection.

The NIOSH study also concluded that “many workers knew of the potential consequences of their actions, yet made a decision to engage in risky behaviors that led to arc flash incidents.

“Using the argument that victims had, on average, significant electrical experience and job experience, it can be conjectured that they recognized the hazards of the task … when the arc flash incident occurred but made a conscious decision to engage in a risky behavior that led to the event. For example, an experienced electrician should know when to turn the power off while performing a specific task or when to use the correct tool.”

Engineering and administrative controls, training and appropriate PPE eliminate the potential for arc flash – or risky behaviors – that contribute to injuries in the workplace.

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