Use a ranged attack to destroy the gas source or vent
Cast Gust of Wind to disperse the fumes
Cast Create Water or throw water to clear the area
Use Fire to ignite and remove flammable gas clouds when appropriate
Move characters out of the affected area
Use Jump, Misty Step, or other movement abilities to bypass the fumes
Use poison resistance or immunity gear
Cast Protection from Poison
Drink an Elixir of Poison Resistance
Use a gas mask or similar protective item if available
Disarm nearby traps or vents causing the fumes
Wait for the cloud to dissipate if it is temporary