The materials and technology for manufacturing personal protective equipment (PPE) that can protect workers from exposure to the hazards of electric arcs is rapidly improving through the research efforts of the National Fire Protection Association (NFPA) and other groups. Clothing, face shields, gloves, and other gear must provide the level of protection needed for a given hazardous situation.
To achieve this goal, it’s important to know which PPE standards to follow. Just because a garment is labeled “flame-resistant (FR)” does not mean it is safe to wear in an electric arc incident, and in fact, it may be even more dangerous because, even though it has been treated to prevent bursting into flames, it will melt in the high heat, increasing worker injury. This is the reason that natural fibers, such as cotton, which will not melt, are specified, rather than acrylics, for underwear worn under PPE. The most important characteristic of your clothing is the Arc Thermal Performance Value (ATPV), which shows how much arc flash incident energy the clothing can withstand, measured in calories per square centimeter.
Two types of boundaries
PPE is designed to protect workers from the electrical arc and resultant flash, or flame. However, PPE cannot protect from the high-pressure sound wave, or arc blast, caused by the sudden arc fault, which can collapse a lung, vaporize metal, or propel objects at high velocities for long distances.
To protect workers from electrical shock, equipment must be labeled with a “limited approach boundary” based on the voltage, or electrical pressure, of equipment when it is energized. The higher the voltage, the further a blast can reach and injure a worker.
The limited approach boundary is different from—and can be closer or farther than—the flash protection boundary. The flash protection boundary is based on the fault current level and the time of exposure to the flash for each piece of electrical equipment.
Anyone working within this boundary must wear PPE rated at the level calculated by an arc flash incident energy study of the equipment. The objective is to limit the chance of an unprotected person receiving second degree level burns caused by an arc flash.
Determine PPE level
The newest version (2015) of NFPA 70E, the standard for electrical safety in the workplace, classifies PPE levels for arc ratings based on the amount of incident energy that it can withstand measured in units of cal/cm2. For example, an arc rating within the range of 25 to 39 cal/cm2 is classified PPE level 4.
This arc rating for a piece of equipment is calculated based on the working distance, available fault current, and length of exposure, as well as other factors. There are two basic methods of determining the arc rating: tables or incident energy calculations.
NFPA 70E contains hazard category classification tables listing job tasks and voltage parameters, and shows the appropriate PPE rating and flash protection boundary for each. If the specific job task does not appear in the table, the incident energy must be calculated, either by formula or using commercially available software programs.
Arc rated PPE
NFPA 70E lists four levels of PPE and the required protective garments and gear required based on the incident energy possible due to an arc flash. For example, PPE level 3 requires an arc rated (AR) long sleeved shirt, long pants (AR), coverall (AR), flash suit jacket (AR), flash suit pants (AR), flash suit hood, gloves, hard hat, safety goggles, ear protection, and leather shoes.
Manufacturers supply PPE designed for each of the four levels, tested according to ASTM F1506, a performance specification for the materials to be used in clothing worn by electrical workers exposed to arc flash. In addition to ASTM F1506, other arc flash standards exist, including ASTM F1891 (rainwear), ASTM F2178 (eye and face protection), and ASTM F2675 (gloves).
It’s important when ordering PPE to perform specific site risk assessment to determine the correct arc rating. This prevents over-spending on PPE rated higher than required for the site, as well as discomfort and lack of dexterity in performing tasks wearing higher level arc flash suits. Ordering higher-rated PPE than necessary may also result in electrical workers cutting corners on safety.
PPE should be ordered for individual fit, to maximize comfort and ease of use, which will also ensure safety. For example, female workers may require much smaller face shield hoods and gloves.