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Frequently Asked Questions Smoke Test
What does the test involve?
Blowing of harmless "smoke" into parts of the sewer system to find where rainwater may be entering.

What can I expect to see?
You may see smoke coming out of roof vent pipes, open plumbing outlets, manhole covers, or infrequently used drains.

What is the purpose of smoke testing?
We will locate possible leaks in the sewer system and improper drain connection which may flood the sewer system when it rains. In addition, smoke testing can help locate bad connections that home owners or occupants are not aware of. Remember, if the smoke can get into your house, so can harmful sewer gas. You should correct the problem as soon as possible.

Is the smoke harmful?
No. It is clean and harmless to humans, pets, food, clothing, drapes, and furniture.

What should I do if smoke comes out of a plumbing fixture in my house?
Smoke should not enter your home if it is properly plumbed and vented, and water traps under drains contain water. However, should you have smoke entering your home, you should first open windows for ventilation. Then tell the crew chief working in the area. Keep these facts in mind:
  • The smoke is a non-toxic substance which is clean and harmless to humans, pets, food, and material goods.
  • The testing operation takes only 10 to 15 minutes. If smoke can enter, it will do so during this period.
  • If smoke does enter, it will usually clear within about 15 to 20 minutes once windows and doors are opened. Please advise a testing crew member of any smoke in your home.
  • Help prevent smoke leakage through dry water traps by turning on plumbing fixtures for a few seconds at this time.

We have a sick person in the house. What should we do if smoke gets into the building?
Open windows for ventilation. This will allow the smoke to dissipate. Contact the crew chief in the area. If it would make you feel more at ease, the crew chief will appoint someone to stand by at, or in, your home, if desired. If the sick person can stay in a well ventilated room during the testing the chance of encountering a high smoke concentration will be less.

Should I be at home during the testing?
Your presence at home is not required during the test. Public Safety authorities (Police, Fire) have been notified. We appreciate your cooperation and understanding.

I will not be at home during smoke testing and have pets in the house. What should I do?
The smoke is not harmful to pets. It would be a good idea to leave several windows partially open for ventilation, should any smoke enter the building. If the building is properly plumbed and vented and all of the traps have water in them, there should not be any problems.

If smoke gets into the house, how long does it take for the smoke to dissipate?
This will depend upon how much smoke enters the building, and how much ventilation you can provide. It usually takes only a brief time.

Can smoke stop up the sewer?
There is no way that smoke can stop up a sewer. The smoke is made up of a vaporous substance, mostly water, like fog.

What happens if you find a bad sewer or lack of traps in a building?
All test information will be recorded for the City of San Mateo, Public Works Department. The City will determine what steps are necessary to remedy any problems. The contractor will make recommendations for solutions.



San Mateo City Hall – 330 West 20th Avenue, San Mateo, CA 94403

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