Experiments simulating mixing of liquid oxygen (LO2) and liquid hydrogen (LH2) have been performed to investigate the potential threat to the RTGs (Radioisotope Thermoelectric Generators) from an explosion of these cryogens as a result of a launch vehicle accident. The influence of the bottom wall of a dewar (spilled mode) has been evaluated in this investigation by using a shallow dewar (38.7 cm I.D. and 30.5 cm tall). The jet size was 1.27 cm O.D. and the jet velocity was varied from 3.97 to 8.75 m s-1. The jet dump duration times were 0.45 and 1.15 s. Gas temperatures and the boil-off of the hydrogen were measured using thermocouples and hot films. The general mixing behavior was observed with high speed measured using thermocouples and hot films. The general mixing behavior was observed with high speed video imaging.