There's technically more than 10.
Fill entire level with water (Good, WONDERFUL on N!)
Fill entire level with acid (Bad)
Fill entire level with lava (Bad)
Fill room with lava (Bad, Unannounced)
Fill room with acid (Bad, Unannounced)
Destroy all walls (Bad, Announced in BETA 2)
Destroy nearby walls (Bad, Unannounced)
Blow up all barrels (Good for veterans, Neutral for newbies that don't push barrels away, Unannounced)
Spawn enemies (Usually Good, Unannounced)
Meditech (Good, Unannounced)
Armour Depot (Good, Unannounced)
Kill lever (Useless, Unannounced)
"You smell blood" (Useless, Unannounced)
Of all 13: 6 bad, 5 good, 2 useless
Of the unannounced ones: 3 bad, 4 good, 2 useless
Therefore the current chance of something bad happening (in 0.9.9.1 BETA 2) is 1 in 3, assuming you know what all the level announcements mean. This is dropped to 1 in 9 if you carry an envirosuit.
Currently levers are already benefiting players more than they're hurting players (Although the "Destroy walls" lever is totally fucking brutal), which must be taken in to consideration should lever flavours be added.
Should this be added:
We would need more lever types. Even though levers can't really be compared to potions or scrolls (as they're immobile), most potion/scroll systems have 20+ effects.
We would need more unannounced unavoidable dangerous levers. Only 1 lever can currently hurt you if you pay attention to level messages and carry an envirosuit, so all that would be required is to identify the destroy walls lever and all other levers become dangerless.