Fuel Leak Discovered, Response

Purpose

This procedure guarantees that any fuel leak found on a standby generator's supply, whether discovered during a PM visit, reported as a smell by the customer, or found mid-repair, ends with the actual leak point located, isolated, and repaired, and a clean pressure retest completed before gas service is restored. It never ends with "tightened it and the hiss stopped." Fuel gas reaches an explosive concentration in an enclosed mechanical room, garage, or crawlspace well before most people notice enough odor to react, especially with propane, whose added odorant fades with distance and can mask a real concentration behind a mild smell.

Scope

Covers the response to a discovered or confirmed fuel gas leak, natural gas or LP, on a standby generator's supply line, regulator, or connection at the unit, residential or light commercial. A liquid-fuel weep at a diesel day tank follows the same isolate, contain, repair, and retest shape but without the explosion hazard driving the entry stop, so treat any spill as an environmental containment issue and skip the LEL steps below. Does not cover diagnosing an ambiguous smell with no confirmed source, owned by the fuel-smell-at-enclosure decision tree, or telling a fuel puddle apart from coolant or condensation, owned by that sibling decision tree; this procedure starts once a leak is confirmed. Does not cover line sizing or a new connection, owned by the gas supply sizing and connection standard, whose pressure-test method this procedure reuses for the post-repair retest.

Roles and responsibilities

Stop before anything else moves

No ignition sources: no light switches, no phones or radios used inside, no starting the generator or any vehicle near it, no doorbells. Evacuate everyone from the area, upwind if outdoors, entirely out of the structure if indoors, and do not let anyone re-enter. If the odor is strong, a hissing sound is audible, or anyone reports feeling unwell, call the gas utility's or propane supplier's emergency line immediately, and add 911 if the odor is strong or anyone is symptomatic. This applies before any diagnosis, before any attempt to find the source, and before touching any valve.

The procedure

1. Evacuate and hold a perimeter before any investigation begins. Acceptance: everyone clear at a set distance, no one investigating alone in an unventilated space. Wrong looks like the tech going in alone to "just take a quick look." Stop rule: if the odor is immediately noticeable at the property line, or a hissing sound is audible, this is a call-the-utility situation, not an investigate-and-report one; the tech does not enter until instructed. Hazard: an unknown-concentration gas atmosphere; do not enter without a calibrated combustible gas detector running.
2. With a combustible gas detector running continuously, take LEL readings working from clean air toward the suspected source, not a single reading at the enclosure. Acceptance: percent LEL recorded at increasing proximity, logged at each point. Wrong looks like walking straight up to the unit before the meter is running. Stop rule: any reading at or above 10 percent LEL, the fire and explosion hazard criterion 29 CFR 1910.146 sets for a confined space, applied here as the same operational floor, is a full evacuation and utility-call trigger; do not proceed past that reading, back out immediately. Hazard: a combustible atmosphere; the meter's alarm is the authority here, not the tech's nose, since odorant fades with distance and can undercount true concentration.
3. Isolate fuel supply at the nearest accessible shutoff; if the specific leak path is unclear, isolate at the main or tank valve rather than guessing at a downstream one. Acceptance: a valve closed, confirmed by the LEL reading trending down at the source afterward. Wrong looks like shutting off electrical power to the generator and assuming that stops a gas leak; fuel flow and electrical power are independent, and de-energizing the unit does nothing to gas already escaping. Stop rule: if closing the identified valve does not reduce the reading, a different or additional path is feeding the leak; stop, do not proceed to source identification until the actual isolation point is confirmed by the reading itself. Hazard: operating a valve in a potentially explosive atmosphere; use a manual ball or gate valve only, nothing that can spark, and no powered tool near the leak source.
4. Ventilate the space from outside, mechanically where possible, before any closer investigation resumes. Acceptance: the reading trending toward 0 percent LEL over a stated ventilation period, not a single dip. Wrong looks like going back in to "find the exact spot" while the space is still elevated. Stop rule: the reading must hold at or near 0 percent LEL, sustained, before source identification resumes; a temporarily lower reading during active venting is not the same as a stable clear. Hazard: entering a space still venting risks disturbing a pocket of trapped gas that a stable reading has not yet accounted for.
5. With the space clear, identify the specific leak point, a fitting, a regulator, a flex connector, a corroded run, using soap solution or an electronic leak detector, not smell alone. Acceptance: a specific, photographed leak point with the detector's response recorded at that exact spot. Wrong looks like tightening the nearest fitting and calling it fixed without confirming that was the actual source. Stop rule: no repair proceeds until the leak point is confirmed by a positive detector response, not assumed from "it's usually the regulator." Hazard: none new here if the prior clearance held; any fresh spike during this closer work is treated as a return to step 2's conditions, back out and reassess.
6. Repair the leak by the method matching the component, remaking a fitting, replacing a corroded section, replacing a failed regulator, with material and rating matched to the existing system, not a mismatched substitute. Acceptance: a completed repair with the material and pressure rating documented. Wrong looks like a temporary fix, tape, an undersized cap, left standing as the final answer. Stop rule: no leak point gets a temporary repair as the final one; a part that cannot be matched on site routes to a return visit with the correct part, and gas stays isolated until then. Hazard: hot work is never performed on a line that has carried gas without purging and testing it inert first per the applicable code; use mechanical or compression fittings instead if this repair calls for a joint.
7. Pressure and leak test the repaired section and every disturbed joint, at code test pressure and duration, using the same method the gas supply sizing and connection standard specifies, before restoring service. Acceptance: the gauge holds with zero drop for the full stated duration. Wrong looks like a quick soap check on only the one repaired joint. Stop rule: any drop is a hard stop; re-repair and retest from zero, gas does not get restored on a failed or partial test. Hazard: the same pressurized-system hazard as the original leak; keep ignition sources clear for the full duration of this test, the space is not automatically safe just because a repair was made.
8. Restore service gradually, purge air per the appliance's own procedure, restart the unit, and take a final LEL reading at the enclosure and any previously affected opening before leaving. Acceptance: a final reading at 0 percent LEL, sustained, with the unit confirmed running normally. Wrong looks like restoring gas and walking away before confirming the unit itself restarts clean. Stop rule: any residual odor or reading above zero stops final sign-off; the site is not left with gas restored and an unresolved reading. Hazard: purging air from the line releases a small, controlled volume of gas at the vent point; do this outdoors or per the appliance manual, never into an enclosed space.
9. Document the event fully, notify the utility or supplier if the leak met their reportable threshold, confirmed with that specific provider rather than assumed, and brief the customer on cause and repair. Acceptance: a written record complete, notification made where required, customer briefed. Wrong looks like a one-line closing note. Stop rule: the job does not close without the record, and without a confirmed answer on whether notification was required, not a guess.

The record this produces

Time reported and initial LEL readings by location, the isolation point and how it was confirmed, the leak point identified with photos, the repair performed with material and rating, the pressure test result, the final restore reading, the utility or supplier notification status, and the customer briefing. Filed with the unit's service history so a repeat leak call at the same address starts from what was already found and fixed.

Worked pass: a moderate odor after the weekly exercise

A customer calls reporting a gas smell near their LP-fed 22 kW unit's enclosure shortly after the weekly exercise cycle ended, no hissing, no symptoms reported. Dispatch evacuates the area by phone and dispatches a licensed tech same-day with the meter-first instruction, since the description does not meet the strong-odor or symptomatic threshold that would trigger an immediate utility call.

On arrival, step 2's readings climb from 0 percent LEL at the property line to 4 percent at the enclosure door, below the 10 percent hard-stop, so the tech proceeds carefully. Step 3 isolates at the local shutoff on the generator's own gas train, the nearest valve, but the reading at the enclosure does not drop after several minutes. The stop rule fires: closing that valve did not reduce the reading, meaning the leak sits upstream of it, not downstream. The tech escalates to the main tank valve, closes it, and the reading drops to 0 percent, confirming the correct isolation point.

Step 4 ventilates until the reading holds stable at zero. Step 5 finds the actual leak: a corroded flare fitting on the copper run between the regulator and the local shutoff, upstream of the valve closed first, exactly consistent with why that first attempt did not work. Step 6 remakes the fitting with a new flare nut sized to the line, mechanical connection only, no hot work. Step 7's pressure test holds clean at the code test pressure for the full duration.

Step 8 reopens the main valve, then the local shutoff, purges the short run per the generator's manual, and confirms a clean restart; the final reading at the enclosure and the door holds at 0 percent LEL. Step 9's documentation notes the leak did not meet the propane supplier's own reportable-release threshold, confirmed by a call to that supplier, so no external report was required beyond the shop's own file. The customer is briefed on the corroded fitting and given a reminder to have exposed copper runs checked at future PM visits.

References

• See related: Fuel smell at enclosure, no leak found, regulator versus line versus tank decision tree, for the ambiguous-smell diagnostic branch this procedure does not cover.
• See related: Condensation versus coolant versus fuel puddle under unit decision tree, for telling a fuel puddle apart from other fluids before this procedure's leak-confirmed response begins.
• See related: Gas supply sizing and connection standard, for the pressure and leak test method this procedure reuses for the post-repair retest.
• NFPA 54 National Fuel Gas Code, current locally adopted edition, for pressure test requirements and leak-repair methods.
• NFPA 58 Liquefied Petroleum Gas Code, current locally adopted edition, for LP-specific response and reporting.
• 29 CFR 1910.146, for the 10 percent LEL threshold used here as the evacuation and full-stop trigger.
• The gas utility's or propane supplier's own emergency and reportable-release requirements, confirmed with that specific provider.