Don't know what EDO-04 accident you refer to, but in at least one of them the one way valves to the smaller bellows were defect and not working. On both units of the dual Rebreather setup. That the diver wasn't properly trained and diving shallow water probably didn't help much, either, but those components of his RBs were not in working order. The state police of the area posted an anlysis and warning including pictures on their website, the damaged/faulty valves were clearly visible.