Modeling of hydrogen-air deflagrations on the base of advanced lumped parameter theory and comparison with experiments in closed and vented large scale vessels have been carried out. Burning velocity and overall thermokinetic index for hydrogen-air mixtures with hydrogen concentrations of 20.0-41.7% by volume and at elevated temperature 373.15 K were determined. The slight decrease of overall thermokinetic index with equivalence ratio in enriched by hydrogen mixtures has been revealed, that is inverse to observed for hydrocarbon-air systems. It has been determined that flame stretch during vented deflagration constitutes about 1.5-2.2 for investigated conditions. The Le Chatelier-Brown principle analog, revealed previously for vented hydrocarbon-air deflagrations, has been verified for hydrogen-air systems. It has been shown that suggested correlation for the deflagration-outflow-interaction number, chi/mu, in dependence on Vessel scale and Bradley number is right for both hydrocarbon- and hydrogen-air mixtures. It has been concluded that gained data on vented hydrogen-air deflagrations obey the same general physical regularities that were revealed previously for hydrocarbon-air systems. (C) 1999 Elsevier Science Ltd. All rights reserved.