Smoke testing is most effective in sewers with diameters equal to or less than 18 inches and is not recommended during or immediately after rainfall events. Smoke testing on sewer systems is generally used for identifying:

(i) Potential sources of I&I;
(ii) Illegal connections to the sanitary sewer system;
(iii) Buried assets such as manholes;
(iv) Defective sewer service laterals and cleanout.

The identification of defects in the sewer system using smoke testing is based on the visual observation of field crews. The location of defects where smoke is observed is translated onto sewer system maps for a desk study by a professional engineer. This information can be used in conjunction with a database of I&I values to generate I&I potential for identified defects.