Most severe burn injuries and fatalities are caused by non-flame resistant clothing igniting and continuing to burn.
Clothing made from 100% cotton or wool 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. If they do not choose FR clothing, employers need to make a determination of whether or not the clothing worn by the worker is acceptable under the conditions to which he or she could be exposed. FR clothing is acceptable with respect to the OSHA apparel requirements.
NOTE: Clothing made from the following types of fabrics, either alone or in blends, is prohibited by this paragraph, unless the employer can demonstrate that the fabric has been treated to withstand the conditions that may be encountered or that the clothing is worn in such a manner as to eliminate the hazard involved: acetate, nylon, polyester, rayon.
The fit of FR clothing is important to the safety of the worker. When the surface of FR clothing is heated, heat is conducted through the material; and any FR clothing touching the skin can result in a burn.
It is recognized that employees typically provide part or all of their own work clothing. However, no matter who provides the clothing employees wear, the employer is responsible for ensuring that the flame resistance or flame-retardant-treated conditions of apparel worn by an employee who is exposed to the hazards of electric arcs or flames are maintained whether made from natural materials of appropriate weight or made from synthetic materials. The flame resistant or flame-retardant-treated properties of apparel can be compromised if the garment is incorrectly laundered or repaired and, in any case, will diminish to the point of ineffectiveness after many washings. Since the employer is responsible for ensuring that apparel remain flame resistant or flame-retardant-treated, the employer may wish to instruct his or her employees as to appropriate laundering.
Arc Rated Clothing
OSHA generally requires protective clothing and other protective equipment with an arc rating greater than or equal to the employer's estimate of available heat energy. As explained earlier, untreated cotton is usually acceptable for exposures of 2 cal/cm2 or less (Arc Flash Boundary minimum requirement is 1.2 cal/ cm2). If the exposure is greater than that, the employee generally must wear flame-resistant clothing with a suitable arc rating in accordance with § 1910.269(l)(8)(iv) and (l)(8)(v).
Arc-rated FR protected equipment/clothing must contain a label or other mark that describes the maximum incident energy rating.
The arc rating of a fabric is either an ATPV (Arc Thermal Performance Value) or an Ebt (Energy breakopen threshold).
Arc Thermal Performance Value (ATPV) is incident energy on a fabric or material that would result in a 50% chance of the onset of a second degree burn as measured in cals/cm2. Higher rated values provide more protection.
Energy Breakopen Threshold value is determined when the incident energy a fabric is exposed to would result in a 50% chance of breakopen occurs before the onset of a second degree burn. Once the fabric or material breaks open, direct exposure to arc flash may result in additional injuries.
Annex H in NFPA 70E 2015 provides guidelines to the proper clothing, personal protective equipment (PPE), and shock protective equipment when either the arc flash PPE category method or the incident energy method is used to perform an arc flash risk assessment.
Figure 1: Poly/Cotton Shirt and Pants Arc Test
Courtesy of Westex® by Milliken®
Figure 2: ATPV Rating Label
Figure 3: An Electrician in Full Arc Flash Suit
Credit: Dennis Schroeder / NREL