But in bulk, it 'dissipates' strongly upward, not diffusing around evenly. So make d@mn sure there is no roof configured in a way to let it collect or pool, as it did in the containments around some overheated nuclear reactors after the big earthquake a dozen years ago.
Hydrogen has one of the widest combustion ratios of air-to-hydrogen. Many of these ratios are explosive. So proper venting is critical to getting hydrogen away from ignition sources. Bob Wilson
