Purpose-made plumbing test smoke is described by its manufacturer as non-toxic when used as directed. Dense or prolonged exposure can irritate people, and those with respiratory sensitivity should avoid it. Follow product instructions and ventilate if smoke enters; clearing time depends on the site and conditions.
What the makers and cities say
The smoke used for this work is described as "non-toxic and harmless. It is light in color, leaves no residue, and does not create a fire hazard," by Superior Signal, which sells it. Erie County describes its sewer-test smoke as non-toxic and advises ventilation if it enters a building. Product formulation and instructions still matter. An engineering firm notes that "extended exposure may cause some skin irritation" (SEH).
Who should stay out
Superior Signal also says people with "particular respiratory sensitivity should avoid exposure to all types of smoke." That covers asthma, COPD and similar conditions. If someone in your building has one, have them leave for the test, the same as they would for any smoky day.
What to do if smoke gets inside
Open doors and windows and run fans, and if the building has monitored detectors, see whether smoke tests set off fire alarms. The smoke should clear on its own, and Erie County advises to "open windows or doors and use a fan for ventilation". Then tell the crew, because smoke indoors is a finding. It means the same path can pass sewer gas. If anyone feels dizzy or sick, get them outside. For symptoms of actual sewer gas exposure, see the first signs of sewer gas poisoning.
The part people miss
Test smoke itself can cause irritation. Unexpected smoke also identifies an air path that could admit sewer gas, but does not prove the duration, concentration or exact cause of past exposure. Document the finding and have the crew confirm it before choosing a repair. Learn what to do next in what smoke in the wrong place means.
What it means for you
Give occupants notice, keep sensitive people away for the test, ventilate if smoke appears, and never improvise with a fire or a smoke bomb inside a building. Use a plumber with equipment made for the job. If you want a smoke test done by a licensed, insured plumber, HQ Plumbing and Air uses professional liquid-smoke equipment, gives free estimates and upfront pricing, and takes emergency calls 24/7.
For a site-specific test plan, see HQ's plumbing smoke-testing service.