The investigation of cryogenic pool spreading and vaporization as the initial step in an accident sequence with the spillage of liquefied hydrogen (LH2) is an essential part of a safety assessment to valuate the risks of hydrogen. Experiments have been conducted to examine the transient LH2 pool spreading behavior on a liquid (water) and solid (aluminum) ground. In a parallel effort, a computer model, LAuV, based on the shallow-layer differential equations has been developed to simulate the pool spreading and vaporization of a spilled cryogen under various conditions taking account of concomitant phenomena such as ice formation on the water surface. The objective of this paper is a description of the LH2 pool spreading test results as well as the performance of the LAuV calculation model. Furthermore a prediction of the consequences of the spill of a tanker truck load for different cryogens is given. The results represent pertinent information as source term for the subsequent analysis steps of dispersion and, in the case of ignition, combustion of the evolved gas cloud. (C) 1997 International Association for Hydrogen Energy.