The Monte Carlo radiation solver computes the standard deviation error based on Poisson statistics. The user-specified number of histories is divided into several groups. Histories are selected from each group and their physical interactions (emission, absorption, reflection, and so on) are tracked through the domain. At the end of the calculation, each group provides values for the quantities of interest, such as irradiation heat flux or absorbed radiation. The mean value, and standard deviation, of each quantity of interest are computed from the groups. A normalized standard deviation is computed by dividing the standard deviation by the mean value.