What Is Arc Flash Testing?
Arc flash testing is the process of determining the arc rating for materials and equipment to be used in electrical hazardous environments or a means of evaluating PPE which is not arc rated for exposure to potential electric arcs (such as shoes, boots, respirators, etc.).
Arc ratings are important in assisting companies and manufactures to comply with consensus standards and regulations (OSHA , OHSA, etc.) and and in keeping the workforce safe in a potential arc flash situation. Arc flash testing allows safer choices of PPE for your hazard and minimizing injury.
Arc flash testing is used to determine the heat transfer response through a material, fabric, or fabric system when exposed to the thermal energy from an electric arc. In some cases arc testing is also used to evaluate ignition and other material responses.
In the standards, a copper fuse wire is placed between two electrodes (open arc testing uses an arc gap of 30 cm) to initiate an arc flash delivering both radiant and convective energy to the samples being evaluated. In ASTM F1959 and IEC 61482-1-1 alternating current is set for 8,000 amperes and exposed from 2-150 cycles from a 50-60 Hz supply. The voltage in the testing is sufficient to sustain the 30 cm arc and is usually in the range of 2500V. The IEC 61482-1-2 Box test method uses uses two current options depending on the desired Arc Protection Class (APC) and exposes samples to a 2.5 mm arc gap for 30 cycles using a small constrained box. The Box method exposes the sample to more convection but only offers two APC levels. The APC levels are used primarily in the EU while the open arc Arc Ratings are used internationally.
In open arc testing, three flat panels housing copper sensors are stationed 30 cm from the electrodes, and the incident energy received by the panels is calculated by measuring the change in temperature over time by copper calorimeters placed on each side of the panels and averaged for each panel. The panel also contains copper calorimeters and the energy which passes through the fabrics is measured and compared to the Stoll curve to determine a level of survivable burn. In any case in which the Stoll criteria has not been met but the fabric begins to crack open or display a formation of holes of a certain size, this point becomes the arc rating. The (Arc Thermal Performance Value (ATPV) or Energy Breakopen Threshold (EBT) are functional equivalents (see our ATPV vs. EBT Article) . Usually knits receive EBT (because they are more insulative than they are strong) and woven fabrics receive at ATPV because they are stronger than they are insulative. The lowest of these two points is designated as the “Arc Rating” of a material. This arc rating may be used for determining PPE using IEEE 1584 or OSHA 1910.269 tables or tables in NESC (IEEE/ANSI C-2 National Electrical Safety Code).
Definition of Arc Flash Testing
An arc flash is an electric arc or an electrical explosion from an arcing fault and is defined as a sustained luminous discharge of electricity across a gap in a circuit or between electrodes which produces both radiant and convective heat with the potential to ignite clothing and burn workers with severe consequences including death. Arc flash testing is related to but not the same as electrical shock hazards, but with the thermal hazards of encountering an arc flash event. An arc flash victim is often not shocked and does not usually come into contact with the electricity directly.
Arc flash testing is performed to determine a product or material’s response to an electrical arc event by establishing an arc rating (a value attributed to materials describing their performance in an arc flash hazard). The arc rating is expressed in cal/cm² as either an ATPV (arc thermal performance value- indicating a 50% probability of crossing the Stoll Curve model; which is not necessarily a second degree burn) or an EBT (breakopen threshold energy). This value is found on the label of arc rated clothing when the fabric was tested to ASTM F1959 or IEC 61482-1-1.
There are several different test methods written around an arc, including those used to evaluate flame-resistant fabrics and materials ( ASTM F1506, ASTM F1959, IEC 61482-2, IEC 61482-1-1 and IEC 61482-1-2), garments (ASTM F2621 and IEC 61482-1-1 Method B), gloves (ASTM F2675, proposed IEC hand protective device standard), face and eye protection (ASTM F2178 and proposed IEC standard), blankets (ASTM F2676), and other products a worker with potential exposure to electrical arc hazards may use. ASTM F2621 can also be used for non-arc rated types of PPE like respirators, boots, shoes, etc. but these materials are not considered arc rated by that testing. Non-arc rated PPE is only evaluated since not all PPE can receive or has received an arc rating.
Why Perform Arc Flash Testing?
Performing arc flash testing or making sure the PPE you use has an arc rating, allows you to choose proper PPE for your hazard and assures the fabric you are wearing will not contribute to injury. OSHA requires all companies performing electrical work have a safety program in place as well as a hazard assessment for the degree of arc flash hazards present. An arc flash hazard calculation predicts the hazard level based on the incident energy exposure specific to the task. Another means is to use a hazard table to determine the exposure level.
From here, you choose clothing with an arc rating equal to or exceeding the anticipated hazard level. The arc rating of the clothing can only be determined by performing arc flash testing. Testing is usually performed on fabrics by the clothing manufacturers, however combined or layered fabrics can be tested to determine the arc rating of the system by a garment company or an end user to assure the system chosen meets the needs of the anticipated hazard.
Both OSHA and NFPA 70E prohibit the use of meltable fibers which can increase the extent of injury (unless they are used in a blend and have been tested at meet the minimum standard requirements). Arc flash testing indicates the material’s response to an arc event and will help to rule out any fibers potentially melting and dripping, or igniting in real-life situations. All arc rated (AR) clothing is flame resistant (FR). Arc rated clothing is normally considered PPE (personal protective equipment) and is not intended to prevent all injuries, but it has been proven to prevent serious injury and even death by mitigating the impact of an arc flash. The most serious injuries typically occur when clothing ignites- arc flash testing is performed to ensure clothing will not ignite when faced with an arc flash. Matching the PPE to the hazard most often results in no injury to the worker since arc hazard assessment is typically very conservative.
Who Needs an Arc Rating?
Arc flash testing is relevant for any worker potentially exposed to an electric arc generating an incident energy of >2 cal/cm² (a typical threshold of second degree skin burn in arc flash exposures, see OSHA 1910.269 and NESC). Anyone with exposure to electrical hazards must have arc rated PPE available, as mandated by consensus standards (like NFPA 70E, CSA Z462, OSHA 1910.269, CAN/UL S801 and others.