Sewer Gas Trap CR 4
Type mechanical; Perception DC 22; Disable Device DC 21
Trigger proximity; Reset auto
Effect unprotected flame sources are extinguished (no save); targets gain nauseated condition for 1d4 rounds (DC 15 Fortitude save to be only sickened for 1 round); after 1 round open flames explode (1d6 damage in a 15-ft.-radius, DC 15 Reflex save for half damage); causticity (targets take 1d4 acid damage per round in 100-ft.-radius, no save)
Despite recent renovations, the sewers in the Three Sisters are quite old and still contain many hazards. Some of these dangers are obvious and bear murderous intent, but others are innocuous; due to collapsing tunnels and blockages, dangerous fumes build up in pockets of air trapped behind debris or waste. These sewer gas traps can easily be dislodged by a wandering party (or sometimes even from vibrations from above or below). When it hits, a sewer gas trap can extinguish flame, cause explosions, and in some deadly cases, be caustic or toxic. Creatures with the scent ability automatically notice a sewer gas trap.