Smoke test (drain integrity)

A smoke test introduces a controlled flow of harmless dense smoke into a drainage system to reveal leaks, cracks, missing covers, misconnections and the position of soil vents. Engineers seal the section under test, generate smoke from a fan unit and observe where it escapes at ground level, around fittings or through external walls. The technique is particularly useful in London for identifying connections from surface water gullies into foul drains, for confirming vent positions on listed building works and for locating defects that are difficult to see on CCTV. Smoke testing complements pressure and air testing under BS EN 1610 and BS EN 752. The work is carried out by qualified engineers using non-toxic smoke products and providing notice to occupants and neighbours where appropriate.