Gas leak

In common usage, a gas leak refers to a leak of natural gas, from a pipe or other containment, into a living area or any other area where the gas should not be. As natural gas may explode when exposed to flame or sparks, this situation is dangerous.^[1] In addition to causing fire and explosion hazards, leaking flammable gases can kill vegetation, including large trees, and contributes powerful greenhouse gases to the atmosphere.

Fire and explosion safety

Pure natural gas is colorless and odorless, and is composed primarily of methane. Unpleasant scents in the form of traces of mercaptans are usually added, to assist in identifying leaks. This odor may be perceived as rotting eggs, or a faintly unpleasant skunk smell. Persons detecting the odor must evacuate the area and abstain from using open flames or operating electrical equipment, to reduce the risk of fire and explosion.

As a result of the Pipeline Safety Improvement Act^[2] of 2002 passed in the United States, federal safety standards require companies providing natural gas to conduct safety inspections for gas leaks in homes and other buildings receiving natural gas. The gas company is required to inspect gas meters and inside gas piping from the point of entry into the building to the outlet side of the gas meter for gas leaks. This may require entry into private homes by the natural gas companies to check for hazardous conditions.

Harm to vegetation

Gas leaks which are too small to pose an explosive hazard may still affect vegetation, causing the decline and death of lawns or large shade trees.^[3][4] In addition to leaks from natural gas pipes, methane and other gases migrating from landfill garbage disposal sites can also cause chlorosis and necrosis in grass, weeds, or trees.^[5] In some cases, leaking gas may migrate as far as 100 feet (30 m) from the source of the leak to an affected tree.^[6]

Legislation proposed in 2013 would require gas suppliers to make greater efforts to control some of the 20,000 documented leaks in the state of Massachusetts. The new rules would require even minor leaks to be repaired if the street above a gas pipe is dug up, if it is in a school zone, or if the leaking gas is killing trees.^[7] An attorney for the Conservation Law Foundation stated that the leaks are worth $38.8 million in lost natural gas, which also contributes 4% of the state's greenhouse gas emissions.^[7]

Leak grades

Most state and federal agencies have adopted the Gas Piping and Technology Committee (GPRTC) standards for grading natural gas leaks

A Grade 1 leak is a leak that represents an existing or probable hazard to persons or property, and requires immediate repair or continuous action until the conditions are no longer hazardous. Examples of a Grade 1 leak are:

• Any leak which, in the judgment of operating personnel at the scene, is regarded as an immediate hazard.
• Escaping gas that has ignited.
• Any indication of gas which has migrated into or under a building, or into a tunnel.
• Any reading at the outside wall of a building, or where gas would likely migrate to an outside wall of a building.
• Any reading of 80% LEL, or greater, in a confined space.
• Any reading of 80% LEL, or greater in small substructures (other than gas associated sub structures) from which gas would likely migrate to the outside wall of a building.
• Any leak that can be seen, heard, or felt, and which is in a location that may endanger the general public or property.

A Grade 2 leak is a leak that is recognized as being non-hazardous at the time of detection, but justifies scheduled repair based on probable future hazard. Examples of a Grade 2 Leak are:

• Leaks Requiring Action Ahead of Ground Freezing or Other Adverse Changes in Venting Conditions. Any leak which, under frozen or other adverse soil conditions, would likely migrate to the outside wall of a building.
• Leaks Requiring Action Within Six Months
• Any reading of 40% LEL, or greater, under a sidewalk in a wall-to-wall paved area that does not qualify as a Grade 1 leak.
• Any reading of 100% LEL, or greater, under a street in a wall-to-wall paved area that has significant gas migration and does not qualify as a Grade 1 leak.
• Any reading less than 80% LEL in small substructures (other than gas associated substructures) from which gas would likely migrate creating a probable future hazard.
• Any reading between 20% LEL and 80% LEL in a confined space.
• Any reading on a pipeline operating at 30 percent SMYS, or greater, in a class 3 or 4 location, which does not qualify as a Grade 1 leak.
• Any reading of 80% LEL, or greater, in gas associated sub-structures.
• Any leak which, in the judgment of operating personnel at the scene, is of sufficient magnitude to justify scheduled repair.

A Grade 3 leak is non-hazardous at the time of detection and can be reasonably expected to remain non-hazardous. Examples of a Grade 3 Leak are:

• Any reading of less than 80% LEL in small gas associated substructures.
• Any reading under a street in areas without wall-to-wall paving where it is unlikely the gas could migrate to the out-side wall of a building.
• Any reading of less than 20% LEL in a confined space.

History

Catastrophic gas leaks are well-recognized as problems, but the more-subtle effects of chronic low-level leaks have been slower to gain recognition.

Other contexts

In work with dangerous gases (such as in a lab or industrial setting), a gas leak may require hazmat emergency response, especially if the leaked material is flammable, explosive, corrosive, or toxic.

See also

• Gas detector
• Gas leak detection
• Soviet nuclear well collapses

References