What happens when the water seal is lost from a plumbing trap?
When the water seal is lost from a plumbing trap sewer gases can back up out of that fixture and not just smell bad. Sewer gases contain methane which is an explosive gas – possibly quite dangerous. In addition to occasional methane gas explosions inside buildings, I’ve had a report of an outdoor septic tank explosion too when an owner built a brush fire atop the tank. In sum, dry plumbing traps are caused by evaporation at an unused fixture, leaks at the trap, or siphonage due to improper plumbing vent line installation. Dry traps can leak smelly or dangerous sewer gases into a building. Check for dry plumbing traps, particularly at un-used basement or lower floor fixtures and at floor drains which might be connected to the sewer line. “Dry trap” means that there is no water in the trap bend or weir. See Plumbing Vent Defects for diagnostic details of venting problems and see PLUMBING FIXTURE TRAPS for fixture trap inspection and defect diagnosis. .
