If you manage a collection system, few diagnostics expose hidden defects as quickly as smoke. This how-to introduction walks you through smoke testing sewer systems with a practical, field-ready approach. You will learn how to plan a test area, select and size equipment, protect workers and the public, and capture results that drive maintenance decisions.
We will cover when to use smoke testing, how to schedule around rainfall and groundwater, and how to coordinate notifications with residents and fire departments. You will see the essentials of setup, manhole isolation, blower placement, and smoke generation, including target airflow and test duration. We will detail observation methods, photo and GIS logging, and symptom recognition for inflow and infiltration, cross-connections, failed traps, and defective laterals.
You will also learn how to interpret findings, rank defects by severity, and link results to corrective actions such as sealing, rehabilitation, or enforcement. The guide includes QA and troubleshooting tips, from avoiding indoor smoke through trap priming to recognizing over pressurization artifacts. By the end, you will be able to execute safe, repeatable smoke tests that reduce infiltration, cut treatment costs, and extend asset life.
Prerequisites and Materials for Smoke Testing
Essential equipment and safety prerequisites
Before smoke testing sewer systems, assemble purpose-built gear and confirm safety controls. A smoke blower is the primary injector; a portable unit like the 5E FLEX Electric Smoke Blower provides consistent output and battery flexibility for field work. Use only non-toxic, non-staining smoke sources, for example a UV-traceable option such as the EZSMOKE Machine, which helps visualize leaks at low flow rates. Equip technicians with gloves, eye protection, and respirators appropriate to site conditions, and stage ventilation fans to clear areas where smoke might accumulate. Add traffic control, cones, and caution signage to inform the public and prevent entry into test zones. Maintain radios or mobile phones for team coordination, and keep a first-aid kit and spill kit on site as standard practice.
Mapping, tools, and expected outcomes
Accurate local sewer system maps are essential to define test segments, locate manholes and service laterals, and anticipate cross-connections that can drive inflow and infiltration. Integrate mapping with tools that support repeatable documentation: smoke blower, non-toxic smoke canisters or a modern fogging alternative like FogTrace, and a handheld GPS to geotag defect locations. Step 1, study GIS or as-built maps, select manhole-to-manhole sections, and note roof vents and cleanouts; outcome, clear test boundaries and fewer missed defects. Step 2, assemble gear and verify consumables, including canister count and battery charge; outcome, uniform smoke density and uninterrupted testing. Step 3, perform a safety briefing, set barricades, and check ventilation and communications; outcome, controlled exposure and fewer public complaints. Step 4, capture baseline weather and ground conditions, then record GPS coordinates and photos for each observed escape point; outcome, precise work orders for repairs and easier retesting.
Steps to Perform a Successful Smoke Test: Preparation
Step 1: Review the sewer system layout and identify testing areas
Compile current GIS as-builts, recent CCTV findings, and manhole inspection logs to map mains, laterals, cleanouts, and structures. Prioritize basins with recurring odor complaints, wet-weather surcharging, elevated inflow and infiltration, or legacy materials such as pre-1970 vitrified clay. Define discrete test segments between manholes, note blower insertion points, and identify properties with roof vents, yard drains, or suspect cross-connections. Mark access constraints, traffic control needs, and easements, then draft a segment-by-segment test matrix with crew roles and expected smoke travel paths. Expected outcome: a targeted plan that focuses resources where smoke testing most effectively reveals defects in mains, laterals, and manholes, consistent with proven results reported in industry case work.
Step 2: Ensure weather conditions are optimal for smoke testing
Select a dry-weather window, ideally 24 to 72 hours without rainfall, to minimize dilution and false inflow signals. Favor calm conditions, with winds under 10 mph, for stable visible plumes around vents, service laterals, and surface defects. Aim for moderate temperatures, roughly 40 to 90 degrees Fahrenheit, and avoid heavy fog or strong gusts that can disperse or mask smoke. Confirm groundwater and river stages are normal to reduce background infiltration, and document barometric trends for consistency. Expected outcome: clear, repeatable smoke observations that leverage smoke testing’s non-invasive, fast, and accurate advantages noted by technical references.
Step 3: Notify residents or stakeholders about the testing schedule
Deliver at least 48 hours’ notice to residents, businesses, and facility managers via door hangers, email, or utility alerts, including the test window and contact number. Explain that non-toxic simulated smoke will be used, and instruct occupants to fill seldom-used traps, adding 1 to 2 cups of water to floor drains and tubs. Coordinate with local fire and police dispatch to prevent false alarm responses, and schedule sensitive facilities, such as schools and healthcare, during low-occupancy hours. Provide guidance for any interior smoke observation, ventilate and contact the field crew, since indoor smoke indicates a plumbing defect. Expected outcome: informed stakeholders, minimized disruptions, and faster field progression with fewer call-backs, setting the stage for efficient smoke injection and observation in the next phase.
Steps to Conduct the Test: Execution
Step 1: Set up and calibrate the smoke blower at the designated location
With traffic control and PPE in place, position a purpose-built smoke blower over the upstream manhole of the target reach, then gasket or sandbag the interface to prevent bypass. Select a unit with at least 1,500 cfm capacity for mains and multiple laterals, and verify seals, clamps, and hoses are tight to avoid dilution at the source. Load manufacturer-approved smoke fluid or candles and perform a 10 to 15 second idle test to confirm a dense, white to gray plume and stable output. If needed, temporarily plug downstream outlets to focus the test segment. Materials include the blower, smoke medium, manhole tools, temporary plugs, radios, and a calibrated gas detector. Expected outcome is a consistent smoke feed that holds throughout the segment without escape at the entry point, aligning with smoke testing equipment guidance.
Step 2: Introduce smoke into the sewer line, monitor discharge points
Ramp the blower from low to operating speed while watching for confirmation at nearby roof vents, which indicates system connectivity. Deploy a two-person walking team on both sides of the corridor, progressing in 50 to 100 foot grids to observe manhole lids, curb inlets, yard drains, cleanouts, foundations, and landscaped areas. Smoke at roof vents is expected; smoke at storm drains, surface cracks, or building perimeters signals cross-connections or leaks. Record time-to-first-smoke, estimated plume intensity, wind conditions, and any odors. Use non-toxic, non-staining smoke, as specified in the NASSCO smoke testing specification, and photograph each anomaly. Expected outcome is a mapped set of verified discharge points that pinpoint illicit connections and I/I pathways.
Step 3: Utilize GPS data to record findings and capture anomalies
Log each observation with mapping-grade GPS, one meter accuracy or better, including coordinates, timestamp, structure type, plume intensity scale 0 to 3, time-to-first-smoke in seconds, and upstream and downstream manhole IDs. Attach photos and technician notes, then sync to your GIS. Create layers for defect category and severity to prioritize CCTV, dye testing, or immediate repairs. Example: smoke at storm inlet SI-17 within 45 seconds, intensity 3, 25 feet north of MH-12, suggests a direct sanitary-to-storm tie. Expected outcome is a defensible, GIS-driven work order list that targets the highest I/I contributors first, reducing investigation time and cost.
Post-Testing Analysis and Documentation
Prerequisites and materials: completed smoke test logs with segment IDs, GIS basemap, timestamp-enabled camera, handheld GPS with sub-meter accuracy, tablet or field notebook, and a standard defect code list.
Step 1. Analyze smoke patterns and locate defects
Begin analysis in the field while residual smoke is still visible so you can corroborate observations with crew notes. Surface plumes that track along a property line usually indicate a broken or offset lateral or failed joint; log alignment and approximate stationing, for example 12+50 left, to speed excavation or CIPP later. Smoke entering building interiors often points to defective plumbing or dry traps; advise occupants to refill floor drains, which is consistent with municipal smoke testing guidance. Smoke emerging from storm inlets, curb lines, or roof gutters indicates an illicit cross-connection between sanitary and storm systems; record inlet IDs and upstream connectivity. Differentiate expected from abnormal emissions: smoke from roof vents is normal, while smoke from a cleanout cap suggests a missing cap or cracked riser, typically a quick fix.
Step 2. Document findings with photographic and GPS evidence
Photograph each emission point twice, a wide shot with a fixed landmark and a close-up with a scale or ruler; include manhole IDs, reach, and address in the frame when feasible. Use a camera with timestamp or embed EXIF metadata and cross reference with the test log for blower rate and duration. Capture GPS coordinates for each defect and map them to a GIS point layer, following proven GPS-based defect mapping practices. Record conditions that affect dispersion, wind speed, recent rainfall, and blower CFM, to contextualize anomalies and minimize false positives. Example entry: MH A-12 to MH A-13, defect P-3, 41.2571, -95.9382, severity High, smoke in storm inlet S-44.
Step 3. Review results and develop maintenance or repair plans
Aggregate photos, GPS points, and notes into your GIS, then classify defects by severity, inflow and infiltration risk, proximity to structures, and safety. Fast-track low-cost corrections, replace missing cleanout caps, reseal cleanouts, notify owners to refill traps, and schedule dye tests for suspected cross-connections. Plan medium-scope repairs, chemical grouting of joints, lateral spot liners or CIPP, and manhole chimney seals. Reserve capital projects for high-impact issues, mainline CIPP or open cut replacement, and rerouting illicit storm ties. Estimate I and I reduction by defect type, create work orders with unit costs, and define timelines. Expected outcomes include a prioritized rehab plan, updated GIS layers to guide CCTV, fewer odor complaints, and measurable cost savings from this non-invasive, fast, and accurate method.
Tips and Troubleshooting for Effective Smoke Testing
Troubleshooting common field issues
Before smoke testing sewer systems, confirm prerequisites and materials: charged smoke canisters or liquid smoke, a calibrated blower, test section maps, caps for roof vents and cleanouts as required, and a defect log with GPS and photo capture. Step 1, prevent building intrusions by filling every floor drain, sink, and fixture trap with 1 to 2 liters of water, guidance consistent with the City of Toronto’s program Smoke Testing Sanitary Sewer Systems. Step 2, if smoke enters a structure, ventilate immediately, document the room and fixture, and suspect dry traps, cracked laterals, or improper connections, escalate for plumbing inspection if entry persists. Step 3, smoke emerging from yards, utility easements, or cleanouts indicates leaks or cross connections, record coordinates, photos, and surface conditions for repair planning, see context in Smoke Testing of Sanitary Sewer Lines. Step 4, if smoke output is weak, verify blower flow, reseal manhole pick holes and inflow points, and recheck segment isolation, the expected outcome is visible, consistent plumes only where defects or planned vents exist.
Alternative approaches for complex networks
When networks are large or braided, combine smoke with targeted diagnostics. Step 1, run CCTV to localize structural defects and confirm connectivity, a best practice for inflow and infiltration confirmation. Step 2, deploy dye testing to verify suspected cross connections, storm tie ins, or fixture specific pathways, select non staining, non toxic dyes and trace to outfalls. Step 3, use acoustic leak detection or pressure transient logging on pressurized or large diameter appurtenances where smoke dispersion is limited. Step 4, for long reaches or limited access, consider robotic inspections enhanced by explainable anomaly detection to reduce false positives, see research on deep anomaly detection for robotic sewer inspection. Step 5, where capacity or ovality is a concern, add 3D profiling to prioritize rehabilitation.
Safety controls and communications
Protect people and property throughout the test. Step 1, use only non toxic, odorless, non staining smoke and state this in public notices, consistent with guidance in the City of Toronto resource Smoke Testing Sanitary Sewer Systems. Step 2, notify affected residents and businesses in advance, instruct them to fill traps, secure pets, and report interior smoke. Step 3, coordinate with local fire and police to avoid false alarms and stage a standby crew with radios. Step 4, enforce PPE, traffic control, and ventilation protocols, monitor wind, and maintain a two person minimum crew. The expected outcome is safe, non invasive testing that accurately flags leaks and odor pathways while minimizing community disruption.
Conclusion: Benefits and Best Practices
Smoke testing sewer systems provides a fast, non-invasive, and low-cost way to expose defects across mains, laterals, and manholes. By pushing non-toxic simulated smoke through the network, crews quickly pinpoint hidden leaks, cross-connections, illicit discharges, and odor sources that would evade visual inspection. Early identification of inflow and infiltration pathways protects structures from water damage and mold growth, preserves pavement and landscaping, and reduces treatment plant loading. The method also confirms system connectivity and uncovers blockages or unpermitted ties, producing actionable maps that drive targeted rehabilitation. Compared with reactive repairs, proactive smoke testing consistently finds issues before they escalate, improving reliability and controlling lifecycle cost.
For efficient, accurate results, adopt a repeatable field protocol and QA workflow. Prerequisites include public and fire department notification, a dry-weather window, isolated test reaches, and safety controls; materials include a calibrated blower, non-toxic smoke, PPE, GIS basemaps, and a GPS-enabled camera. Follow these steps: 1) verify baseline conditions and calibrate the blower, 2) pressurize from the upstream access and confirm smoke at control points, 3) walk the reach and geotag every emission with defect codes, 4) reconcile findings with CCTV and compile a ranked repair list. Expected outcomes are a geocoded defect inventory, reduced inflow and infiltration after repairs, fewer odor complaints, and measurable O&M savings. Schedule testing annually in high-risk basins, every 3 to 5 years systemwide, and after major storms or construction to preempt failures and validate corrective work.
