A simple approximate method for evaluation of blast effects and safety distances for unconfinedhydrogen explosions is presented. The method includes models for flame speeds, hydrogendistribution, blast parameters, and blast damage criteria. An example of the application of thismethodology for hydrogen releases in three hypothetical obstructed areas with different levels ofcongestion is presented. The severity of the blast effect of unconfined hydrogen explosions is shown todepend strongly on the level of congestion for relatively small releases. Extremely large releases ofhydrogen are predicted to be less sensitive to the congestion level.