Smoke testing refers to physical tests made to closed systems of pipes to detect cracks, breaks and sewer odors.
It’s done by forcing forcing non-toxic, artificially created smoke through waste and drain pipes and spotting where plumes of smoke form above ground just over where defects are located.
The area around the section being tested is searched for smoke plumes. Plumes are marked, usually with flags, and defects are noted using measurements from stationary landmarks like the corners of houses. The plumes or markers may also be photographed.
Plumbing smoke tests are also used to find places where pipes will spill fluid, and to check sanitary sewer systems for places where ground water and storm runoff can enter.
This test can be performed when the plumbing is brand new. Though more often it is used to find sewer gas that may plague a building or area. Any sign of smoke escaping can be considered a possible location for sewer gas to escape. Sewer gas typically has a rotten egg smell and can contain methane gas, which is explosive, or hydrogen sulfide gas, which is deadly.
Smoke testing is particularly useful in places such as ventilated sanitary sewer systems, where completely sealing the system is not practical.
Smoke testing may not be done after rain or when ground water is unusually high as this may also prevent detection of defects.