In this paper results of large-scale experiments and numerical simulations of premixed lean hydrogen-air spherical flame propagation with and without high heat losses are presented. Experiments were carried out in a cylindrical volume of 4.5 m(3) covered with thin polyethylene film. The heat loss surface is a 50 mm layer of steel wool. Analysis of heat loss effect on combustion products expansion and flame surface density is done. The combination of these parameters governs the manner in which the flame accelerates. It is shown that the loss of heat released at the combustion can significantly reduce the speed of flame propagation and suppress the acceleration of the flame front. Comparison of experimental results and numerical simulations are presented. The subject and results of the study are of critical importance for the industrial explosion safety and may be applied in the areas of internal combustion engines and detonation suppression devices. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.