IDK if this is bug or feature, so... if aquanauts inhale smoke on land mission, they can become uncounscious. The problem is, the same happens underwater too, which frankly doesn't make much sense, because they're wearing helmets. Wearing armor helps however, both Ion Armor and Mag. Ion Armor seem to prevent the stunning effect. You can see it in the attached save, it's from the 2016/08/20 nightly.