"I'm fairly sure at least one of the buildings exploded due to hydrogen build up" There were four explosions. The no. 1 and 3 buildings exploded quite visibly

"I'm fairly sure at least one of the buildings exploded due to hydrogen build up" There were four explosions. The no. 1 and 3 buildings exploded quite visibly and video of both events is readily available. The no. 2 reactor suppression pool exploded and damaged the suppression pool. The no. 4 reactor also experienced an explosion; this event was initially believed to be related to the no. 4 spent fuel pool, but was later attributed to accumulated hydrogen from the no. 3 reactor.