Smoke Testing FAQs

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What exactly is a smoke test?

Wastewater crews from the City of San Luis Obispo will use a high capacity blower technique to test each sewer line. High-capacity smoke blowers are placed on sanitary sewer manholes and smoke is blown through the sewer system. Any location where smoke is visible during the test, except plumbing vent stacks, is a potential I/I source for stormwater to enter the sewer system. These locations will be documented via pictures and sketches.


What is the benefit to the City for performing a Smoke Test?

Smoke testing is one technique utilized to identify sections of sewers that may exhibit inflow during heavy rainfall.  Smoke testing is best used to detect inflow sources such as roof downspouts, driveway, yard and area drains, foundation drains, faulty connections, and water drainage system cross connections. It can also detect structural damages and leaking joints in sewer pipes.


How will residents know when Smoke Testing will be performed in their neighborhoods?

Prior to beginning, the City of San Luis Obispo will notify all homes/buildings on the streets to be smoke tested at least 24 to 48 hours in advance. These notices will be in the form of door hangers. 

How are City crews recognizable in the field?

City of San Luis Obispo personnel are uniformed. Crew members also operate from official City vehicles with recognizable signage.


Is the smoke that is used hazardous?

The smoke that is used is 100% nontoxic and nonhazardous. It is specifically formulated for this kind of testing and is not harmful to plants, animals or humans. It will not leave a residue, and it does not create a fire hazard. The San Luis Obispo Police and Fire Departments will be made aware of the test areas and schedule.


Do residents have to do anything to prepare their homes for Smoke Testing?

Plumbing drain traps should be filled with water to prevent the smoke from entering your building.  To do this, run the faucet for 30-60 seconds or pour about 3 cups of water in floor and sink drains, filling the traps.  Make sure to check seldom-used floor drains and plumbing fixtures in your home (such as basement floors, garage sinks, etc.) If smoke does enter, please consult a licensed plumber promptly, as this is an indication of possible defects and could allow for potentially dangerous sewer gases to also enter the building.


Does the resident need to be home when the Smoke Testing is performed?

Homeowners do not need to be home and at no time will field crews need to enter a residence or business without permission. Field inspectors will document the testing, take photos and measure distances so that the defects may be found later and repaired.


What happens after the smoke testing has been completed?

The City will notify residents who need to make corrections on their property with a letter explaining the nature of defect found, ways to correct it, and a list of licensed sewer contractors, if needed. Most of the corrections necessary for residents can be easily fixed, such as simply disconnecting a downspout and letting the water flow above ground away from the home.