There is a shortage of research in the literature on the evaporation rate of the liquid pool under instantaneous conditions, which is important for the risk assessment of the liquid hazard leakage accidents. Previous perfect thermal contact model and typical pool boiling could not completely represent the boiling process in the spreading liquid pool. In this work, the spreading liquid pool was characterized as a free-surface jet impingement on the plate surface. Liquid nitrogen (LN2) was adopted to simulate liquid hydrogen (LH2) and liquid natural gas (LNG) leakage, and a series of transient jet impingement boiling experiments were conducted on the concrete surface. Liquid jetted upon the stagnation region, and the transient heat flux from the concrete surface was estimated by transfer function method. The boiling curve obtained in the present study appears significantly different from the typical pool boiling, which indicate that large deviation will occur when the typical pool boiling correlations are used for instantaneous leakage, at least for the stagnation region. A point between the onset of nucleate boiling point and fully developed nucleate boiling point was recognized, which represents the turn of forced convection dominated to nucleate boiling dominated. It is confirmed that the heat transfer was enhanced with increased jet height z, and the peak values were found at zid = 8. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.