Arc Flash vs Arc Blast - "Arc flash” is the extremely high-temperature discharge of fire produced by an electrical fault in air, while “Arc blast” refers to the high-pressure pressure wave caused by a sudden arc fault in electrical systems that can cause injury or death unless workers are wearing personal protective equipment ppe.
Arc Flash
Arc Flash is an energy discharge of light and heat that forms when a fault occurs in an electrical circuit. The arcing results in a tremendous amount of energy being released as current flowing through ionized air.
Arc Flash accidents produce some of the highest temperatures known to occur on earth - up to 35,000 degrees Fahrenheit at the arc terminals. The intense heat from an arc flash causes the sudden expansion of air. This can result in a blast with very strong air pressure.
Think of them as the cause (arc flash) and effect (arc blast). When a short circuit (or arc flash) occurs, it can often cause arc blast, a type of highly dangerous electrical explosive event that has very high temperatures: The heat and flames generated by an arc blast is enough to vaporize metal components, as well as cause life-threatening (or even deadly) burns to personnel in the immediate vicinity. Shrapnel from exploded equipment can turn metal objects into high-speed shrapnel, which threaten to seriously injure or kill workers in the general area of the blast. Arc blast often causes damage to eyesight because of high-intensity light that is capable of causing both temporary and long-term vision problems.
Arc Blast Pressure
Another item associated with an electric arc is the blast energy or pressure. This hazard is not presently covered in NFPA 70E or IEEE Std 1584. This force can be significant and can blow workers away from the arc causing falls and injuries that may be more severe than burns. In one case, with approximately 100 kA fault level and arc current of 42 kA, on a 480-V system, an electrician was thrown 25 feet away from the arc. Being forced away from the arc can reduce the electrician’s exposure to the heat radiation and molten copper but can subject the worker to falls or impact injuries. The approximate initial impulse force at 24 inches was calculated to be approximately 260 lb/ft2 as determined from the equation below.
Arc rated PPE is not tested for protection from any type of blast pressure and at this time, there are no accepted calculation methods for determining the hazard of blast pressure for any particular situation.
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