Faint Gas and a Strong Sewer Smell in a Crawlspace-Height Basement
You are the only plumber on call for a small Wisconsin service company. At 9 p.m. you arrive at a 1920s two-story house where the homeowner reports a strong sewer odor in the basement and bubbling at the floor drain whenever the upstairs tub drains. The basement is a low, crawlspace-height area with a gas-fired water heater, a floor drain, and a sump pit; the only access is a 24-inch by 30-inch hatch. Your phone shows one bar of signal. You smell gas faintly near the water heater and see standing water on the floor by the sump. The homeowner wants you to just snake the drain and says the last plumber did it in twenty minutes.
1. List, in order, what you do in the first fifteen minutes and explain why that order cannot be rearranged.
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The order is fixed by hazard hierarchy: life safety, then property, then the repair.
- Do not enter. Stop at the hatch. Methane and hydrogen sulfide from the sewer and a possible natural-gas leak are all invisible, and you cannot tell them apart by smell.
- Remove ignition sources. No light switches, no phone use inside, no shop vacuum, no torch. Step outside to call the gas utility; call the fire department if the odor is strong or anyone feels ill.
- Evacuate and account for occupants. A lone worker with one bar of signal and a 24 x 30 hatch cannot self-rescue. Treat the space as a permit-required confined space: no entry without an attendant and a four-gas meter (O2, LEL, H2S, CO).
- Shut gas only if qualified and only with utility agreement.
- Ventilate from outside the hatch with a non-sparking fan, re-test, and only then diagnose the drain.
Snaking first puts your head inside an unmonitored atmosphere with an ignition source and no rescue plan.
2. How do you decide whether the faint gas odor lets you keep working, and what do you leave behind in writing?
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The test is not whether you can still smell it; it is whether you can prove it is not gas.
- Sniff-testing is not a test. Use a calibrated combustible-gas meter at the appliance connection, the draft hood, and the low point by the floor drain. Any reading above zero, or any doubt, ends the drain work for the night.
- Never use a flame or a lighter to look for a leak, and never treat a bubble test as the only confirmation while you are standing in the space.
- If readings are clear and the utility agrees, document the time, the instrument used, the reading at each location, what you did, and the customer's instructions.
Leave a written notice at the appliance and on the invoice stating that gas was not verified by the utility and that the drain work is deferred, plus a referral. If the customer refuses to leave the house, call the utility anyway and record it: the duty to warn is not discharged by a verbal exchange.
3. The blockage turns out to be roots in the building sewer. What safety controls apply to the rodding operation?
Read the worked answer
Once the machine is running, the machine is the hazard.
- PPE and entanglement: face shield over safety glasses, fitted gloves, no loose cuffs, and never a rag wrapped around a spinning cable.
- Machine: foot-actuated switch, GFCI-protected grounded cord, cable fed with the machine in forward only. If it binds, stop, reverse, and re-feed - do not force it.
- Backflow: shield or cone over the cleanout. A backed-up line can return a pressurized plug of water, roots, and debris at your face.
- Atmosphere and rescue: an attendant outside the hatch watching the meter and the access point, with forced ventilation running.
- Chemical history: ask what was poured into the line before you start, and have water available for flushing eyes. Caustic drain cleaner plus a splash is a much worse injury than the clog.
Confirm where the cleanout discharges before you feed cable - if the main is surcharged, the cable can bring the surge into the basement.