Firedamp is a clear gas with not detectable smell that often accumulates deep in mines. The gas is heavier then air and typically pools in the bottom of large chambers
For each round spent breathing the firedamp the player must make a con 18 save. Each failed save will result in one level of temporarily exhaustion. However since the first effect of the firedamp is to impair reasoning, an Wis (18) save is required to notice the effect
An affected target can’t take reactions and must roll a d10 at the start of each of its turns to determine its behavior for that turn. d10 Behavior
1 The creature uses all its movement to move in a random direction. To determine the direction, roll a d8 and assign a direction to each die face. The creature doesn’t take an action this turn.
2–6 The creature doesn’t move or take actions this turn.
7–8 The creature lies down and goes to sleep
9–10 The creature can act and move normally.
At the end of each of its turns, an affected target can make a Wisdom saving throw. If it succeeds, the target is aware of the effects of the gas
Anyone observing or interacting with someone being effected by firedamp may notice the person acting strangely when they reach the second level of exhaustion (Per 18- level of exhaustion).
Finally the firedamp is extremely explosive. Any open flame will ignite it in a massive explosion, damage and radius depending on the size of the cloud