Inertial heat dumps utilize the mass of the dump to absorb transient surface deposition of heat by neutral beams of plasmas. A dimensional analysis is performed to rate metallic and ceramic materials for inertial heat dumps. Detailed analysis is made of the calorimeter of the neutral beams of the Doublet III Big Dee fusion device for long pulse operation. Comparison is also made with the Doublet III neutral beam calorimeter plates which were removed after three years of operation.