An experimental investigation was performed to determine critical semi-open channel height (h*) and two-sided open channel width (w*) in which hydrogen-air detonation may propagate. Three types of gaseous mixture composition were used: 25%, 29.6% and 40% of hydrogen in air. Experimental setup was based on rectangular (0.11 x 0.11 x 2 m) test channel equipped with acceleration section (0.11 x 0.11 x 1 m). Different channel heights h in range of 15-40 mm and widths w in range of 30-50 mm were used in the test channel. The critical height h* and width w* were defined for each investigated configuration. To determine representative detonation cell sizes lambda and to calculate their relationship to h* and w*, the sooted plate technique was used. The results showed that detonation in stoichiometric H-2-air mixture may propagate in semi-open channel only when the channel height is very close to or higher than approximately 3 lambda. For less reactive mixtures critical relation h*/lambda reaches 3.1 or 3.6 for mixtures with 25% and 40% of hydrogen in air, respectively. For two-sided open channel similar relations w*/lambda were close to 4.9 and 5.5 for 29.6% H-2 and 40%H-2 in air, respectively. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.