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Smoke Testing in Sewer System

If you live on the East side of the ward, you may have recently received a mail notification from the city regarding smoke testing in the sewer system. Last year, the West side of the ward had completed such testing. This test is part of a city program that aims to assess its sewage infrastructure to identify defects in its infrastructure, locating areas in need of repair.

How is testing conducted?

Smoke is blown into the sewers by City contractors and observed closely. Contractors will take note of nearby areas such as catch basins, driveway drains, or connected downspout where smoke could exit. Rest assured, this method of assessment is of industry standard, and smoke used in testing is odourless, harmless, and dissipates quickly.

How to prepare for smoke testing?

Upon receipt of smoke testing notification, ensure all plumbing traps under sink, floor drains, and washroom facilities have water in the traps to act as barrier to smoke from entering the home. Please note: City's contractor does not require access indoors, nor will they need to request personal information from residents.

For more details information about the program: Smoke Testing Sanitary Sewer Systems – City of Toronto

Is it safe? Is there any harm to health? Will I be able to smell the smoke?

In short, the smoke used is harmless to human health. Should one be able to smell the smoke, it is an indicator that the home has been exposed to continuous small concentrations of methane hydrogen gases (chemical by-products developed in the sewer headspace).

Attached are links to researched data of the materials used for this project:

Liquid Smoke by Hurco -

LiquiSmoke Test Results -

Yellow-Green Tracer Dye -



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