The batteries themselves are DC. You could drop an entire array in a pool full of people and you wouldn't do much damage as they'd all discharge at their individual cell voltage levels as they short. It's not that dangerous unless the individual cells are going past 24VDC in that particular type of environment and someone's within a couple of feet of that pack and acting as a ground path to somewhere else. The inverter equipment hooked up to the batteries, on the other hand, and the charging equipment, should be kept well off the floor. AC-charged water is much more dangerous.
Charging batteries generate hydrogen and oxygen, Hydrogen rises to the top, Oxygen can mix pretty well with a primarily-nitrogen atmosphere. Not a problem for a battery bank, single-level, on the floor. Cooling is about as simple as a large fan blowing across the array/pack, as that's where a majority of the cooling-capable metal (terminals) is located, anyways.