In order of importance the arc blanket is designed to manage thermal radiation of both the heat and fi re created by the blast event, a pressure wave, and a molten spray.
The blanket must be able to prevent heat from reaching the worker until the overcurrent protective device can clear the fault energy. An important reason as to why an arc blanket is effective is the fact that the heat from the arc is dissipated quite quickly. The temperature drops as the square of the distance from the source. As an example, if at one foot, the temperature is at 1000 degrees, at two feet, the temperature would be (½) 2 x 1000 or ¼ x 1000 which is 250 degrees.
Less has been quantifi ed regarding the pressure wave but it is not unreasonable to estimate it at 1 pound per inch squared. Without the blanket the pressure wave will exert an estimated force on the worker of between 400 to 500 pounds. The worker will undoubtedly be knocked into the opposite direction of the force and into whatever electrical material is found there. If there is a blanket in place and
the blanket is 6 foot x 8 foot, the total area is 6 x 8 x 144= 6912 square inches then per our estimate above the blanket would be managing 6912 pounds of force and thus protecting the worker from the effects of the pressure wave.
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