• Try to eliminate any potential arc-related injuries. When workers can be exposed to electrical arcs, the first effort should be to eliminate the exposure through engineering design. If eliminating all arc-related exposures is not possible, 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). (See Factors Affecting Heat Exposure.)

• Grease, oil, solvents, or other flammable substances. FR clothing that becomes contaminated with grease, oil, solvents, or other flammable substances should not be used because such contamination greatly reduces the effectiveness of the clothing material. As with any PPE that becomes damaged, damaged FR clothing must be replaced before resuming work that requires its use. Contaminated FR clothing must be thoroughly cleaned, if possible, or replaced. See ASTM F1449-01, Standard Guide for the Care and Maintenance of Flame, Thermally and Arc Resistant Clothing.

• Damaged FR 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.

• Use 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 Section 130.7(c) and Appendix D of NFPA 70E. Different methods (for example, software packages, mathematical formula) for calculating heat energy are available. Employers need to make their best estimates based on currently available information. Appendix D of NFPA 70E provides a detailed sample calculation of a flash protection boundary (NFPA 70E, Standard for Electrical Safety in the Workplace, 2004 Edition, National Fire Protection Association). For other methods of estimating incident energy from an electric arc, see OSHA's proposed revision of its electric power generation, transmission, and distribution standards. [See Electric Power Generation, Transmission and Distribution; Personal Protective Equipment. OSHA Federal Register Proposed Rule 70:34821-34980, (2005, June 15). Also available as a 2 MB PDF, 160 pages. See Appendix F to Section 1910.269—Clothing, on page 34940 (page 120 of the PDF version]

Factors Affecting Heat Exposure
Flame-Resistant (FR) Clothing