3 If an employee is working within lightning protection limits, section 130.7 of NFPA 70E-2004 requires the employee to wear protective clothing if an arc flash is greater than the second degree burn threshold, 5 J/cm2 (1.2) cal/cm2. In other words, the protective clothing system is designed to protect the employee from second- or third-degree burns on the body. The typical characteristics, degree of protection and minimum arcing required for typical protective clothing systems are given in table 130.7(c)(11). The NFPA standard requires that protective clothing selected for the appropriate hazard or hazard category number have an arc rating of at least the minimum value indicated. [ back to text ] Section (l)(8)(v) of section 1910.269 requires employers to select, in certain situations, protective clothing and other protective equipment with an arc greater than or equal to the incident thermal energy estimated under section 1910.269(l)(8)(ii). Based on laboratory testing required by ASTM F1506-10a, it is expected that protective clothing with an arc value equal to the estimated incident thermal energy can prevent second-degree burns to an employee exposed to this incident heat energy from an electric arc. Note that the actual arc exposure may be more or less severe than the estimated value due to factors such as arc motion, arc length, electric arc due to system reclosure, secondary fires or explosions, and weather conditions. In addition, a worker exposed to incident energy in the arc flash assessment based on the thermal arc power value (ATPV) of the fabric has a 50% chance of sustaining a second-degree burn. Therefore, it is possible (but unlikely) for an employee to suffer a second-degree burn (or worse) in certain circumstances if he or she is wearing clothing that complies with section 1910.269(l)(8)(v). However, reasonable employer estimates and maintaining reasonable minimum distances for workers should limit burns to relatively small burns that extend just beyond the epidermis (i.e., second-degree burns). Therefore, protective clothing and other protective equipment that comply with section 1910.269(l)(8)(v) provide an adequate level of protection for an employee exposed to arc hazards. Some of the most common OSHA standards cited for arcing include: The most effective and foolproof way to eliminate the risk of electric shock or arc flash is to simply turn off the device.
However, in some cases it is not possible to turn off the power. When it comes to avoiding arcing, it`s important to make sure you regularly test your equipment and train your employees, even if it`s not required by law. To get started, we recommend consulting an expert who will perform arc analysis in your workplace. MTAEE is a NETA accredited company that prides itself on serving customers throughout Southern California. We also perform additional services such as electrical tests, coordination studies and evaluations of power supply systems. Paragraph (l)(8)(v) of § 1910.269 does not require arc flash protection for exposures of 2 cal/cm2 or less. Untreated cotton clothing reduces an exposure of 2 kcal/cm2 below the 1.2 to 1.5 cal/cm2 level required to cause burns, and this material should not ignite at such low thermal energy levels. Although paragraph 1910.269(l)(8)(v) does not require clothing to be subject to an electric arc assessment if the exposure is 2 cal/cm2 or less, paragraph 1910.269(l)(8)(iv) requires that the outer layer of clothing be flame retardant under certain conditions, even if the estimated incident heat energy is less than 2 cal/cm2, as discussed later in this Annex. Arc flash can occur for a number of reasons, such as inadequate equipment, lack of training, or human error when working on actual equipment.
Even something as simple as dust buildup can trigger an electric arc. 14 November 2006 Ms. Joanne B. Linhard ORC Worldwide 1910 Sunderland Place, NW Washington, DC 20036 Dear Ms. Linhard, Thank you for sending an email to the Enforcement Programs Directorate (EPD) of the Occupational Safety and Health Administration (OSHA) to interpret OSHA and National Fire Protection Association (NFPA) Standard 70E-2004 for electrical safety in the workplace.