Toxic

Toxic atmospheres are composed of poisonous compounds and vary radically in their consistencies. Some toxic atmospheres are capable of sustaining oxygen-breathing life-forms, while others immediately suffocate those within them. Regardless of whether or not they allow creatures to breathe, toxic atmospheres are threats to most living creatures, as they act as an inhaled poison (see page 417). Though the specific type of poison varies, many toxic atmospheres act as existing poisons but with radically different onset times and save DCs. Low-level toxic atmospheres can have onset times measured in hours or days, while heavily toxic atmospheres have onset times measured in rounds.