There is something which seems unclear to me in the rulebook. When a fire or a flood event occurs, we have to roll the dice to know which room the event occurs in. When it happens in a room where there are inactive players, what should we be doing? Should these players be allowed to retreat immediately, consuming the necessary time, or should they wait until their turn to retreat? Or even worse, are they dead already (i doubt so)?

Furthermore, if this situation occurs and the inactive players have already reached the Rescued spot, what happens to them? Are they allowed to retreat even though time is up or do they die?

This one must be sorted one by one. Fire first: Gnome has to move out of a room on fire at the end of Action phase (No. 2), if he failed to extinguish the fire. The move is free (it takes no time, at least if I can remember well enough). So if his room is put on fire as result of another players event cards, this does not affect the Gnome in question... he must wait his turn and then either leave the room, or try to put out the flames (the only action he can do in the room).

Water comes next: as written in the rules, the Gnome who happens to be in a room with high water at the end of his turn, is dead. Whats more, if he happens to be in such a room at the beginning of his turn, the only action possible is No action (in other words, wait to die). But again, as the water got to the room during another player, he doesn´t have to be stressed at the time (I am not sure about the timing, if the high water occurs during his very own Updates phase). During the Gnomes own turn, he can do nothing in the room, but he can try to leave her, if there is at least one completely empty (or maybe on-fire) room across one hatch leading from the flooded room - he simply opens the hatch and water level equalizes on low level and the Gnome is safe (he can move away of pump the water or do anything else).

Yes, just to be clear, if a gnome is in a room and on another player's turn, that room is flooded, the gnome is not in immediate danger. However, on his turn, he can take no actions. Movement, however, comes before actions, so he can open a hatch as part of his movement phase, thereby reflowing the water, and thereby saving himself from drowning. As he is now in a room with low water, he can perform an action as normal.

Same with fire. If a gnome finds himself in a room that is on fire at the start of his turn, he can open a hatch and leave as part of his movement phase, or he can stay and perform an Extinguish Fire action, which is the only action he can take as mentioned above. If unsuccessful, he then gets one free move out of the room to save himself.

If a gnome has fainted from too much grog, and the room he is in either floods or catches on fire, he's out of luck...and dead, unless he comes to on that turn, of course.

So if an inactive gnome isn't in immediate danger even if a fire pops in his room, that means that he survives if this happens when the inactive gnome has already reached the rescued space?

Because the Gnomes die at the end of their turn, then someone who has reached the rescue space (and as a consequence will not have an another turn) is pretty safe. At least I would say so.

The only problem would be time events, but it is another story.