This paper suggests a method for calculating the incident energy and the arc flash boundary (AFB) distance for dc systems when an arc-in-a-box situation is involved. The method uses the dc maximum power method and a multiplying factor instead of using distance exponents. The method may also be used for an arc-in-open-air by using a multiplying factor of 1. It is based on the basic assumption that the spherical energy density can be increased to a new value to account for the additional reflected heat radiation from a box situation and that the ratio of the new value to the spherical energy density equals a multiplying factor for correcting -from the energy density for an arc-in-open-air situation to an arc-in-a-box situation, based on a simplified equation or methodology. When calculating the AFB, the method requires the use of an iterative process , since the multiplying factor is a nonlinear variable and is based on the distance from the arc. This paper should provide a good starting point for further discussion and development regarding dc arc-in-a-box situations.Index Terms -arc-in-a-box, dc maximum power method, multiplying factor.