Smoke Testing FAQ

What exactly is a Smoke Test? 

A high capacity blower technique is used to test each sewer line with smoke. Smoke blowers are placed on manholes and smoke is blown through the sewer system. Any location where smoke is identified during the test, except plumbing vent stacks, is a potential break or Inflow/Infiltration source for excess water 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 storm 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 smoke testing, the City of Twin Falls will give notices to the community through its Public Service Announcement PSA system.  

Is the smoke that is used hazardous? 

The smoke that comes out of the vent stacks on houses or holes in the ground is non-toxic, harmless. It does not create a fire hazard. Twin Falls Police and Fire Departments will be made aware of the test areas and schedule. 

Will the smoke enter my home?

The smoke will not enter a home if the plumbing is in good condition and if drain traps contain some water. Outside, it is normal for smoke to be seen coming from roof vents, building foundations, manhole covers and yard cleanouts. Smoke coming from the vents on the roofs of homes indicates to the work crew that smoke has filled all sewers. Smoke will enter your home if the vents connected to your building’s sewer pipe are inadequate, defective or improperly installed, if the traps under sinks, tubs, basins, showers and other drains are dry, defective, improperly installed or missing, or if the pipes, connections and seals of the wastewater drain system in and under your building are damaged, defective, has plugs missing, or are improperly installed.

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 the residence. Field inspectors will be documenting the testing, taking photos, and measuring distances so that the defects may be found later and repaired.


Can the resident stay inside while the testing is performed?

Homeowners may stay inside during the testing. However, since any smoke may create minor irritations for some people with respiratory difficulties, those who have asthma, emphysema or other breathing problems are advised to avoid direct contact with the substance. 

What if the smoke does enter my house?

If you see or smell the smoke inside your home, this could indicate that gases and odors from the sewer system also are entering. Notify the work crew immediately. Although we cannot correct any problems on private property, we can help identify the source so that you know what action to take.

Will the smoke set off my smoke alarm?

The smoke will not set off a smoke alarm nor is it a fire hazard. Twin Falls Fire Department will be notified in advance so they will know the difference between the testing and a true emergency.

How are City crews recognizable in the field? 

Personnel carry identification badges. Crew members operate from vehicles with proper signage for ease of recognition. 

What happens after the smoke testing has been completed?

The City of Twin Falls will notify residents who need to make corrections with a letter explaining the nature of defect found, ways to correct it, and a list of licensed sewer contractors who can make corrections, if need be. Again, most corrections can be easy fixes, such as disconnecting a downspout from the ground and letting the water flow above ground away from the home.

What happens if the testing locates a leak or a bad connection to public lines?

The work crew will document the information, which will be used by the Public Utilities Department to determine repair priorities and programs.


Smoke Testing