The most insidious of the Damp’s, Whitedamp exposure is difficult for the victim to detect until it is too late. Similar to carbon monoxide poisoning the gas is odorless and colorless and not flammable.
When entering an area with Whitedamp, the DM secretly rolls a cons save for each player exposed
Each failed con save adds a level of exhaustion, however the player is unaware this is occurring
For each failed con save the player may make a wisdom save to determine something strange is happening. However the save is initially quite difficult. It becomes progressively easier as the level of exhaustion increases
If the party is in bright light, the player may notice the blue skin tint around the lips that is the hallmark of whitedamp poisoning (Medicine check 14, but only if another victim is visible and within bright light ).
Recovery from Whitedamp
Recovery from whitedamp poisoning will occur naturally after a few minutes of breathing clean area, provided only 1-3 levels of exhaustion were inflicted.
4+ levels require a greater restoration spell, or the exhaustion can be recovered via sleep as normal exhaustion.