I thought it'd be nice to sum them both up at the beginning and break them down later. I tried to tweak the wording a bit too where it seemed awkward. The tense in the hero escape sentences was kinda unclear.
Here's my suggestion anyway:
When a place has more steam present when there shouldn't be, you've got Excessive Steam Syndrome. Two extremely common versions are steam expulsion during a escape sequence after a self-destruct mechanism is triggered and the other is where space faring vessels demonstrate a tendency to belch steam.
In the case of steam produced during a Self-Destruct sequence, after the Self-Destruct Mechanism is active, the Hero will need to escape as quickly as possible while The Supervillain Lair is collapsing around him and he will be hampered by all the steam that seems to be venting into the main escape corridor. Somehow he manages to dash his way out of the crumbling hive of villainy and burst out of the clouds of steam.
It's all very dramatic, but to be completely honest, no one would hire an architect that made vents dump steam into the main exit, especially when people are trying to escape. It just goes against any semblance of sanity or decent design.
The second common example is in speculative fiction spacecraft, where the spacecraft leak steam apparently as part of regular functionality. These vessels have a tendency to vent dense streams of steam-like gas at every occasion, both outside and in.
When an engineer is confined in the bowels of a ship, he's almost guaranteed to run into a cloud of the stuff. Maybe it's hot, like a steam pipe opening up, maybe it's cold, like a liquid oxygen pipe opening to atmosphere. It's usually dangerous, and always cool-looking on film.
Because Space Is An Ocean, this may have started as an homage to classic cinema depicting naval life. On a submarine or steamship, streams of thick steam were ubiquitous. It's an easy and cheap way to make an area look industrial, damaged, dangerous, gritty, or any combination thereof.
On the outside of the ship, ventings usually accompany an atmospheric landing, power-up, lift-off, or other such event. This comes from footage of real spacecraft, which often sever lines and conduits with explosive charges during launch.
See also Self-Destruct Mechanism. Compare to Impressive Pyrotechnics and Made of Explodium. Has nothing to do with fanservice anime that overdo Censor Steam.
"Nullius addictus iurare in verba magistri, quo me cumque rapit tempestas, deferor hospes."