35
As you lift the loose tile the smell becomes much worse and coughing you notice a green fizzing pool beneath floor. The stone you have just moved was the keystone holding the whole floor in place and without it the floor is now beginning to fall away. Choking you make a dash for the door on the north wall.
Make a L2SR on SPD. If you miss the roll you have fallen foul of the fumes and your last thoughts are of anguish as the acid eats through your flesh. If you make the roll, go to 18.