Finding the leak: the survey. Episode thirty-seven of the Gas Service Animated series.

A leak call is not a sniff-and-shrug. The code and the trade give you a method: work the system in order, confirm every suspect with an approved tool, and let two simple rules decide when you stop working outside and start working inside.

First, the tools the code allows. NFPA fifty-four says a leak is located with an approved combustible-gas detector, a noncorrosive leak-detection fluid that bubbles at the leak, or another approved method. And it's blunt about the one method that's forbidden: a match, a candle, an open flame — any ignition source — shall never be used to find a leak. Bubbles and electronics find gas. Flames find funerals.

Before gas even flows, tightness is proven. After any interruption of service the piping is pressure-tested — the gauge or manometer has to hold. A drop in test pressure is deemed to be a leak unless you can pin it on something else, like a temperature change. Only a system that holds gets gas, and only then do you bubble-test the accessible joints.

Now the on-site survey, in order. Start at the meter set — the connections, the regulator vent, the shutoff. Follow the service into the building. Walk the house piping: every threaded joint, union, valve, drip, and the flexible connector at each appliance. Confirm each suspect with bubbles or the detector. Fix what leaks and re-check it before you move on. A survey is a route, not a guess.

Two rules decide when the outside job becomes an inside job. The first is the five-foot rule: any sustained reading, or any indication of gas, within five feet of a building wall means you go inside and check — even a building with no gas service, because migrating gas doesn't care whose pipe it is.

Inside, you check the foundation and basement walls, floor and wall penetrations, sumps, drains, and the meter and house-line entry. And the second rule: a positive gas reading at any inside sample point means immediate evacuation, and you extend the survey to the buildings next door. A reading inside is not a data point to note — it's a reason to move people.

Don't forget the hidden highways. Storm and sanitary sewers, and phone, cable, and electric manholes and conduits, carry migrating gas straight toward buildings. Put the meter at those openings; a flammable reading there means gas is on the move and the survey just got bigger.

Put it together. Odor complaint, no obvious source inside. You bubble the meter set — clean. You bar the reading down to a service joint near the wall, inside the five-foot zone, so you go in — and the basement reads gas at the floor penetration. That's not a Grade three you schedule. That's evacuate and make safe, now.

The survey in one breath. Approved tools only — bubbles and electronics, never a flame. Prove tightness; a pressure drop is a leak. Work the system in order and confirm every suspect. Five feet from a wall, go inside. A reading inside, get people out. Next: how leaks are graded.