# En 508.04 Leakage Surveys and Inspections

**Citation:** N.H. Admin. R. En 508.04  
**Type / status:** regulation / current  
**Agency:** New Hampshire Department of Energy  
**Effective:** 2023-10-25  
**Published:** 2023-10-25

En 508.04 Leakage Surveys and Inspections.

## Document text

En 508.04 Leakage Surveys and Inspections.

(a) For purposes of this section, "business districts" means the principle business areas in the urban portion of a community.

(b) The presence of certain factors shall indicate the presence of a business district, as follows:

(1) The general public regularly congregates in this area for economic, industrial, religious, educational, health or recreational purposes;

(2) The majority of the buildings on either side of the street are utilized for commercial, industrial, religious, educational, health or recreational purposes;

(3) Gas facilities are under continuous paving that extends either from the center line of the thoroughfare to the building wall or from the gas main to the building wall; and

(4) Other locations or sites in the urban portion of a community which contain a similar density or mix of buildings and services as provided in (1) through (3) above.

(c) Each utility shall survey distribution mains in business districts on an annual basis.

(d) Each utility shall conduct a leakage survey of cast iron main lines in business districts on a repeated basis during the months when frost is in the ground, but not in conjunction with the survey referred to in (c) above.

(e) Each utility shall conduct a leakage survey of all unprotected steel services at least once during each 3-year period and of all protected steel and plastic pipe at least once during each 5-year period.

(f) Each utility shall inspect gas mains once each calendar year in locations or on structures where known physical movement or external loading could cause failure or leakage and shall patrol such locations at least 3 times each calendar year.

(g) A gas detector survey of buildings used for public assembly, including schools, churches, hospitals, theaters, municipal buildings and downtown areas shall be conducted each year during the period March 1 to December 1.

(h) In completing a gas detector survey of buildings used for public assembly, as referred to in (g) above, a utility shall:

(1) Test areas around service entrances, inside the foundation wall, at conduit or cable entrances below grade and at cracks or breaks in the foundation wall where gas seepage might enter the basement; and

(2) Test exposed piping from the service entrance to the outlet side of the meter.

(i) If, when investigating a leak, it is determined that the perimeter of a leak area extends to a building wall, the investigation shall continue into the building unless public safety or identifiable exigent circumstances prohibit entry.

(j) Once public safety or identifiable exigent circumstances no longer prohibit entry, the investigation, as provided in (i) above, shall continue into the building, if the leak has not yet been resolved.

(k) The utility shall establish a leak repair priority based on its evaluation of the location and the magnitude of a leak.

(l) The applicable lower explosive limits (LELs) shall be determined according to Table 508-1 below:

TABLE 508-1

Utility Lower Explosive Limits &

Equivalent Percent Gas/Air Ratios

% LEL

Natural Gas % gas/air

Propane % gas/air

10

0.5%

0.2%

20

1.0%

0.4%

30

1.5%

0.6%

40

2%

0.8%

60

3%

1.2%

80

4%

1.6%

100

5%

2%

(m) A utility shall assign a classification of leaks as follows:

(1) A Class I leak shall be a leak that represents an existing or probable hazard to persons or property, and requires immediate repair within 24 hours or continuous action until the conditions are no longer hazardous, consistent with the following:

a. A Class I leak shall include but not be limited to:

1 Any leak which, in the judgment of operating personnel at the scene, is regarded as an immediate hazard;

2 Escaping gas that has ignited unintentionally;

3. Any indication of gas, which has migrated into or under a building, or into a tunnel;

4. Any reading within 5 feet of the outside wall of a building, or where gas would likely migrate to an outside wall of a building;

5. Any reading of 40% LEL or greater in accordance with Table 508-1, in an enclosed space including but not limited to manholes, vaults, and catch basins;

6. Any leak that can be seen, heard, or felt, and which is in a location that may endanger the general public or property; and

7. Any leak in a small substructure, which shall include but not be limited to conduits, pipes, pedestals and other small enclosures, when a sustained combustible gas indicator reading of 70% LEL or greater in accordance with Table 508-1 is measured; and

b. In the event of a Class I leak, the utility shall take action immediately to eliminate the hazard and make repairs, including, as necessary, one or more of the following actions:

1. Implementation of an emergency plan;

2. Evacuation of premises;

3. Blocking off an area;

4. Rerouting traffic;

5. Elimination of sources of ignition;

6. Venting the area by removing manhole covers, barholing, installing vent holes, or other means;

7. Stopping the flow of gas by closing valves or other means; or

8. Notification to emergency responders;

(2) A Class II leak shall be a leak that is recognized as being non-hazardous at the time of detection, but requires scheduled repair within 6 months or before the end of the calendar year based on probable future hazard of any degree, evaluated as follows:

a. When evaluating Class II leaks, each operator shall consider criteria such as the following:

1. The amount and migration of gas;

2. The proximity of gas to buildings and subsurface structures;

3. The extent of pavement, including wall-to-wall paving that includes areas covered in gravel or grass; and

4. Soil type and conditions, such as frost cap, moisture, and natural venting;

b. A leak shall be considered a Class II leak when a sustained combustible gas indicator reading of 40% LEL or greater in accordance with Table 508-1 is measured under a sidewalk in a wall-to-wall paved area that does not qualify as a Class I leak;

c. A leak shall be considered a Class II leak when a sustained combustible gas indicator reading of 100% LEL or greater in accordance with Table 508-1, is measured under a street in a wall-to-wall paved area that has significant gas migration and does not qualify as a Class I leak;

d. A leak shall be considered a Class II leak when a sustained combustible gas indicator reading of less than 70% LEL in accordance with Table 508-1 is measured in small substructures. A small substructure shall include but not be limited to conduits, pipes, pedestals and other small enclosures;

e. A leak shall be considered a Class II leak when a sustained combustible gas indicator reading less than 40% LEL in accordance with Table 508-1 is measured in a confined space including but not limited to manholes, vaults, and catch basins;

f. A leak shall be considered a Class II leak when a sustained combustible gas indicator reading is measured on a pipeline operating at 30 percent specified minimum yield strength (SMYS), or greater, in a class 3 or 4 location, as defined in 49 C.F.R. § 192.5, which does not qualify as a Class I leak;

g. A leak shall be considered a Class II leak when, in the judgment of operating personnel at the scene, it is of sufficient magnitude to justify scheduled repair;

h. All Class II leaks shall be rechecked at intervals no greater than every 60 days during the months of April through, and including, December; and no greater than every 30 days during the months of January through, and including, March; and

i. Each utility shall take action ahead of ground freezing or other adverse changes in venting conditions with respect to any leak which, under frozen or other adverse soil conditions, would likely allow gas to migrate to the outside wall of a building; and

(3) A Class III leak shall be a leak that is non-hazardous at the time of detection and can be reasonably expected to remain non-hazardous, as evaluated in accordance with the following:

a. Each utility shall survey and re-evaluate each Class III leak no less than once per calendar year, but at least one re-evaluation of each Class III leak shall be performed between September 1 and December 15 each calendar year until the leak is repaired;

b. A leak shall be considered a Class III leak when a sustained combustible gas indicator reading less than 40% LEL in accordance with Table 508-1 is measured under a street or sidewalk in areas without wall-to-wall paving where it is unlikely the gas could migrate to the outside wall of a building. Wall-to-wall paving shall include areas covered in gravel or grass, in accordance with (m)(2) above;

c. A leak shall be considered a Class III leak when a sustained combustible gas indicator reading of less than 100% LEL in accordance with Table 508-1, is measured under a street in a wall-to-wall paved area that does not have significant gas migration and does not qualify as a Class II leak. Wall-to-wall paving shall include areas covered in gravel or grass, in accordance with (m)(2) above; and

d. Any leak that does not classify as a Class I or Class II leak shall be considered a Class III leak.

(n) A utility shall conduct a follow-up inspection as follows:

(1) The adequacy of leak repairs shall be checked before backfilling;

(2) The perimeter of the leak area shall be checked with a combustible gas indicator (CGI) or equivalent gas detection equipment; and

(3) Where there is residual gas in the ground after the repair of a Class I leak, the utility shall conduct a follow-up inspection as soon as practical after allowing the soil atmosphere to vent and stabilize, but in no case later than one month following the repair.

(o) In the case of leak repairs other than Class I, the need for a follow-up inspection shall be determined by qualified personnel of the utility.

(p) In any calendar year, a utility shall not reclassify from Class II to Class III more than six total leaks or 5% of all outstanding leaks in a given class, whichever is less.

## Provenance

- Official: Yes
- Source: <https://gc.nh.gov/rules/state_agencies/en500.html>
- Source ID: `nh-general-court-en-500`
- SHA-256: `ad3683f655b6ba4e7e32f07d6a783c44fac1ac76cd58b1319168cd0f9398c27b`
- Retrieved: 2026-08-20T08:23:25.693Z
- Exported: 2026-08-24T05:20:34.750Z
- Document slug: `nh-admin-rules-en-508-04`

### Source metadata

```json
{
  "jurisdiction": "US-NH",
  "chapter": "En 500",
  "part": "508",
  "documentNumber": "#13796",
  "certificationScope": "intrastate-gas",
  "federalPartsReferenced": [
    191,
    192,
    193,
    198,
    199
  ],
  "fixedFederalBaseline": null,
  "laterFederalAmendmentsIncludedByText": true,
  "references": [
    {
      "citation": "En 508.04",
      "referenceType": "state_regulation",
      "url": "https://gc.nh.gov/rules/state_agencies/en500.html"
    }
  ],
  "caveats": {
    "exactScope": "Bounded current direct pipeline-safety corpus of 36 sections in New Hampshire Administrative Rules Chapter En 500, effective October 25, 2023. It includes governing scope, safety-defined terms, emergency and incident duties, pipeline standards, safety records and maps, accidents and leaks, directly associated forms, and enforcement for gas pipeline utilities.",
    "excludedScope": "This is not all New Hampshire gas or pipeline law. Seventy-nine current En 500 sections concerning service, gas quality, meters, general accounting, supply, federal filings, or specialized LPG and landfill-gas programs are inventoried but not searchable. En 511 and En 512 are adjacent because the official PHMSA evidence proves intrastate-gas certification generally but does not independently establish that every state-defined LPG or landfill operator falls within that certification. En 800 damage prevention, En 1400 pipeline-utility economic regulation, statutes, forms, orders, federal text, private standards, interstate gas, hazardous liquids, and underground storage are excluded.",
    "applicability": "Applicability depends on operator and utility status, commodity, facility, activity, intrastate or interstate status, PHMSA and FERC jurisdiction, master-meter and LPG thresholds, waivers, orders, and the text in force on the relevant date. PHMSA states that New Hampshire is certified for intrastate gas; PHMSA retains interstate gas and both intrastate and interstate hazardous-liquid inspection and enforcement. The connector does not infer hazardous-liquid or underground-storage certification.",
    "incorporation": "En 506.01 requires compliance with 49 CFR Parts 191, 192, 193, 198, and 199, including future amendments, and contains additional state requirements and incorporated private standards. The rule does not state a fixed federal edition. This connector links but does not reproduce federal or private standards and does not decide whether every later federal amendment is validly incorporated for every state-law purpose.",
    "publication": "The New Hampshire General Court administrative-rules publication is the controlling current text used here. Document #13796 adopted En 500 effective October 25, 2023. The official Puc 500 revision note confirms that former PUC safety provisions were deleted and transferred to En 500; Puc 500 is not treated as parallel current safety text. Retrieval time is publication observation, not a legal event.",
    "rights": "Official New Hampshire and federal government artifacts are retained with attribution and SHA-256 provenance. Public access does not resolve rights in site presentation, seals, agency marks, forms, linked works, or incorporated private standards; downstream redistribution requires separate review."
  },
  "region": "NH"
}
```