Contractors are often called upon to locate leaks and sources of inflow in sanitary sewers, or to identify faults in mains, laterals, and house plumbing, including roof and yard drains. They may be asked to find sources of odors, locate cross-connections, trace plumbing and power plant piping, and analyze onsite treatment systems.
Smoke and dye testing are simple, inexpensive, yet effective methods for conducting those kinds of investigations. Smoke-generating devices (SGD) using candles, bombs, and liquid agents help pinpoint leaks in sewer pipes. Fluorescent dyes make it easy to trace errant flows of water to the source. By knowing what to use, and how, and in which situations, contractors get the desired results as efficiently, quickly, and productively as possible.
Smoke-testing protocol
Contractors usually perform smoke testing on behalf of municipalities or sewer utilities. As part of the protocol, members of the public and fire and police departments must be notified before a test begins. The usual notification procedure is to distribute leaflets door to door, and sometimes use the news media to spread the word.
“Smoke may enter buildings through faulty plumbing, and if smoke can enter, so can dangerous sewer gases,” says Bob Rothenberg, vice president and general manager of PrimeLine Products Inc., a provider of smoke testing products. “Building owners are usually thankful that defects are discovered during testing, and not after someone falls ill from escaped gases.”
Sections of pipe to be tested are usually plugged. Then a gasoline-driven blower pushes smoke through the lines with enough force to penetrate leaks. A negative test doesn’t mean the results are conclusive. Sagging laterals can trap water, blocking and preventing the smoke from reaching roof leader connections or driveway drains. Debris collecting in stormwater basins or lodging in pipes also prohibits the passing of smoke.
Sometimes smoke is observed escaping from grassy areas or through cracks in the pavement, indicating damaged pipes or open joints. “Smoke testing should not be used to locate these defects, as high groundwater and tight soil conditions can trap smoke below ground,” advises Rothenberg. “For these reasons, contractors should choose blowers with high airflow outputs.”
Bombs and candles
Contractors can choose time-tested solid smoke-generating devices or the more recently developed liquid smoke. Both products have their place.
Scott Jensen, western region sales manager for Cherne Underground, notes that solid devices seem more intuitive — just light the fuse, place the product in the smoke blower, and begin testing. “Some contractors say that solids produce better-quality smoke, but someone has to light them,” he says. “The work involved in maintaining a continuous flow of smoke could mean additional labor.”
Typical smoke bombs last three minutes, but 60- and 30-second varieties are available. One possible solution is to use double-wick devices that tie together, increasing the smoke-generating time. The products do have a shelf life and can be adversely affected by humidity.
Classic smoke candles generate a highly visible, uniform white smoke that travels farther and shows leaks that some systems may miss, says James A. Kovacs, general manager of Superior Signal Company Inc. The candles, with a total obscuring power 10 times greater than crude oil, fit most blowers, including those designed for liquid smoke.
Fuse ignitions can be dangerous in the presence of volatile sewer gasses, and the National Institute for Occupational Safety and Health (NIOSH) requires workers to wear respirators in areas where smoke can be inhaled, notes Lyndon “Lynn” Hurley, president of Hurco Technologies Inc. The smoke contains high concentrations of zinc chloride, which attacks the respiratory system. “Proper smoke-testing programs should include laboratory-tested products and trained two-man crews,” he says.
Bottled smoke
Liquid agents also generate dense smoke. “They have a longer shelf life than SGDs and seem to be gaining in acceptance,” says Jensen. “Because the product creates a continuous flow of smoke, crews spend less time monitoring the blowing equipment.”
Liquid smoke, in one-gallon, five-gallon, or drum-size containers, is poured into a pressurized tank connected to the blowing machine. One disadvantage, according to Jensen, is that operators may initially need extra time dialing in the blower to generate the optimum smoke.
“Choosing one system over the other depends on the quality of smoke, economics, and the consulting engineer’s specifications,” says Kovacs. “Smoke fluid systems can be custom-engineered to produce the maximum dry smoke using insulated liquid smoke conversion chambers and precision injectors.”
Liquid agents, because they do not require a fuse for ignition, appear safer. However, Hurley advises contractors to obtain independent laboratory tests on the smoke being generated, not on the liquid as covered in MSDS sheets. “That’s the only way to determine which agents are safe,” he says.
Air and smoke blowers from Superior Signal come in squirrel cage and propeller configurations with various air flows and static pressures. Cherne Industries, for example, makes a lightweight, cast- aluminum smoke blower that generates more than 3,700-cubic-feet- per-minute of air flow. A 1/2-inch, foam-cell gasket provides a leak-free seal on manholes and minimizes vibration. Contractors can use the blowers with the smoke bomb box holder or add a pressurized tank and hose to accommodate fluid smoke.
Fluorescent dyes
Fluorescent dyes act like a coloring label on each drop of water, tracing its travels until the dye reaches extreme dilution. The visual aspect of fluorescent dyes refers to normal reflected light as color. The fluorescent aspect refers to chemical properties that absorb certain wavelengths, then emit, rather than reflect, light.
Technicians can see fluorescent emissions by using black (ultraviolet) light or precisely measure the emissions with fluorometers. Reflected and emitted light have different wavelengths and are, therefore, not the same colors.
“Fluorescent properties are of greatest value when tracing where there is no sun, or where the artificial light source is insufficient, precise quantified data is required, or minute amounts of tracing material are allowed,” says Tim Muldoon, vice president of Kingscote Chemicals Inc., and dye producer.
Blue dyes have the highest degree of light stability, and reds are recommended for yellow and green backgrounds such as algae-rich water. FWT red and blue and FLT yellow-green are for waters that bear heavy sediment loads or that pass through soil with high clay content.
The dyes, which are temporary and degrade in sunlight, come in tablets, liquids, powders, and wax forms such as cakes, cones, and doughnuts. “For small quantities of water, tablets are easy to use and require no measuring,” says Muldoon. “Technicians can drop or flush them into the system, where they dissolve in three to five minutes. They also can be dissolved in water to form a calculated concentration.”
Powders and liquid concentrates are better suited for larger bodies of water. In situations of long-term flow or ongoing coloration, wax products provide optimum dissolution rates in large systems. Doughnuts can be suspended from a string into water. Cakes and cones are used in medium and small systems.
Color wheel
Muldoon says deciding which dye color to use depends on the color, type, water turbidity, and the suspended solids in it. “Any color dye works in clear water,” he says. “If the liquid is yellow or green, FWT red (rhodamine WT) is best, especially if using visual methods to estimate dye concentration. Visually, the dye appears bright pink to red, depending on its concentration, and bright orange under ultraviolet light.”
Muldoon recommends FLT yellow-green (fluorescein) for murky brown water. It appears yellow-green visually or lime-green under UV light. “Yellow-green dye is more resistant to absorption by suspended material in the water and is significantly less resistant to photo degradation than red dye,” he says. “Red dye stands out more clearly from normal background fluorescence and in the presence of green algae.” The absorption-emission wavelengths also are different.
Blue dyes are only visually detected, appearing aqua to royal blue, depending on the concentration and the activity of the water. Blue has the highest light stability, while red is recommended for yellow and green backgrounds, such as algae-rich water.
The dyes are nontoxic, bio-degradable, and certified to meet ANSI/NSF Standard 60 for use in and around drinking water. How-ever, technicians should wear gloves and goggles, as dyes may cause skin irritation and staining.
Simple, low-cost testing programs save taxpayers money and reduce unnecessary maintenance chores, while sustaining the public’s health and the environment.
