Smoke testing is used to locate the cause of sewer gas odors in or around buildings.
Smoke testing utilizes a smoke generator, that forces thick, white smoke into a drain and vent line system. This white smoke will normally come out of roof vent openings, clean out access points, and manhole covers.
In the event that there is an opening in a vent or drain line, this white smoke will come out at that point. It is common to see this white smoke come out of disconnected vent pipes, cracked vent pipes, failed wax rings under toilets, drains that lack p-traps, dry drains with no water in their p-traps, and broken drain fixtures.
A small opening in a drain or vent pipe, no larger than a nickel, can cause sewer gas to leak out, creating a sewer gas odor issue, that often will exist for months, and many times, years, causing unpleasantness and annoyance for many.
One factor that has increased the amount of odor issues in recent years, is the effect low water consumption toilets and faucets have had on the municipal sewer systems around the country. Toilets have gone from 7 ½ gallons per flush in the 50s to 5 ½ gallons per flush in the 60s, to 3 ½ gallons per flush in 80s, to 1.6 gallons per flush in 1994, and now to 1.28 gallons per flush in 2011. Less water in sewers causes less dilution of sewage, which means more sewer gases, especially hydrogen sulfide, and methane. Besides causing odor issues, these gases are highly destructive to cast iron pipes and concrete sewers.