Please be advised that the City and our consultant will be conducting sewer and drain smoke testing tomorrow Thursday 9/7 in the area of Exchange and West Streets (near the American Legion Post 452) to determine actual connections of mains. Smoke testing is a commonly used practice and poses no safety hazards. State transportation and law enforcement officials have also been notified. For questions, please call Chicopee Waste Water at 594-3585 or the DPW at 594-3557.

"In plumbing a smoke test forces non-toxic, artificially created smoke through waste and drain pipes under a slight pressure to find leaks. Plumes of smoke form where there are defects. This test can be performed when the plumbing is brand new, but more often it is used to find sewer gas leaks that may plague a building or an area. Any sign of smoke escaping can be considered a possible site for sewer gas to escape. Sewer gas typically has a rotten egg smell and can contain methane gas, which is explosive, or hydrogen sulfide gas, which is deadly.

Plumbing smoke tests are also used to find places where pipes will spill fluid, and to check sanitary sewer systems for places where ground water and storm runoff can enter. Smoke testing is particularly useful in places such as ventilated sanitary sewer systems, where completely sealing the system is not practical.

When smoke testing a sanitary sewer system it is helpful to partially block off the section of sewer to be tested. This can be done by using a sand bag on the end of a rope. The sand bag is lowered into the manhole and swung into position to partially block lines. Completely blocking the line can cause water to back up and prevent smoke from escaping through defects. Smoke testing may not be done after rain or when ground water is unusually high as this may also prevent detection of defects.

Large downdraft fans, usually powered by gasoline engines, are placed on top of open manholes at either end of the section to be tested. If possible all lines in the manholes except for the line between the manholes are partially blocked. Smoke is created using either a smoke bomb or liquid smoke. Smoke bombs are lit and placed on a grate or in a holder on top of each fan, while liquid smoke is injected into the fan via a heating chamber. The fans create a pressure differential that forces the smoke into the sewer at a pressure just above atmospheric. With properly installed plumbing, the traps will prevent the smoke from entering the house and redirect it out the plumbing vents. Defective plumbing systems or dry traps will allow smoke to enter the inside of the house

The area around the section being tested is searched for smoke plumes. Plumes coming from plumbing vents or the interface between the fan shroud and manhole rim are normal; however, smoke plumes outside of the manhole rim are not. Plumes are marked, usually with flags, and defects are noted using measurements from stationary landmarks like the corners of houses. The plumes or markers may also be photographed."

https://en.wikipedia.org/wiki/Smoke_testing_(mechanical)