Bad Air (CR 1 or 4)

Bad Air CR 1 or 4

XP 400 or 1,200

An invisible hazard, pockets of low-oxygen gas present a danger to miners and spelunkers as well as cavern-delving adventurers.

Nonflammable gases such as carbon dioxide or nitrogen are CR 1 and require a DC 25 Survival check to notice. Creatures breathing the air must make a Fortitude save (DC 15 + 1 per previous check) each hour or become fatigued. After a creature becomes fatigued, slow suffocation sets in. Creatures holding their breath can avoid these effects. Flammable vapors such as coal gas are much more dangerous (CR 4). The gases displace breathable air in the lungs, causing fatigue as described above. In addition, any open flame or spark causes an explosion for 6d6 points of damage (Reflex save DC 15 for half ) to all in the cavern or within 5 feet of an entrance. The fire burns away the oxygen in the air, leaving it unbreathable for 2d4 minutes. After an explosion, flammable gas usually takes several days to build up to dangerous levels again.