In common usage, a gas leak refers to a leak

Leak

A leak is a hole or other opening, usually unintended and therefore undesired, in a container or fluid-containing system, such as a tank or a ship's hull, through which the contents of the container can escape or outside matter can enter the container...

 of natural gas

Natural gas

Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

, from a pipe

Pipeline transport

Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....

 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 rather dangerous.

Safety

Although natural gas is by nature colorless and odorless, scents in the form of traces of mercaptans are usually added, to assist in identifying leaks. This odor

Odor

An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...

 commonly takes the form of rotting eggs. If this scent is detected, it is recommended to evacuate the area immediately, usually to the outside. Do not light fires/cigarettes, and do not operate electrical appliances/light switches/phones, as these may act as points of ignition. Once in a safe area, contact your natural gas provider.

As a result of the Pipeline Safety Improvement Act of 2002 passed in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, Federal Safety Standards require companies providing natural gas to conduct safety

Safety

Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...

 inspection

Inspection

An inspection is, most generally, an organized examination or formal evaluation exercise. In engineering activities inspection involves the measurements, tests, and gauges applied to certain characteristics in regard to an object or activity...

s for gas leaks in homes and other buildings receiving natural gas. The gas company is required to inspect gas meter

Gas meter

A gas meter is used to measure the volume of fuel gases such as natural gas and propane. Gas meters are used at residential, commercial, and industrial buildings that consume fuel gas supplied by a gas utility. Gases are more difficult to measure than liquids, as measured volumes are highly...

s and inside gas piping from the point of entry into the building to the outlet side of the gas meter for gas leaks. This requires entry into private homes by the natural gas companies in many cases.

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:

1. Any leak which, in the judgment of operating personnel at the scene, is regarded as an immediate hazard. And the Chemistry show that biological operating systems are impacted by synthetic methane and other compounds in the admixture of natural gas; combined with toxic products in the environment. Humans and animals exposed to these toxins are at risk of biological dysfunction, the problem posed is that theses compounds are constractants and or dehydrators which block or prevent bio generation i.e. cell growth.. Human Security must be placed on the agenda.

1. Escaping gas that has ignited.
2. Any indication of gas which has migrated into or under a building, or into a tunnel.
3. Any reading at the outside wall of a building, or where gas would likely migrate to an outside wall of a building.
4. Any reading of 80% LEL, or greater, in a confined space.
5. 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.
6. 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:

A. 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.

B. Leaks Requiring Action Within Six Months

1. 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.
2. 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.
3. 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.
4. Any reading between 20% LEL and 80% LEL in a con-fined space.
5. 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.
6. Any reading of 80% LEL, or greater, in gas associated sub-structures.
7. 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 a leak that is non-hazardous at the time of detection and can be reasonably expected to remain non-hazardous.

Examples of a Grade 3 Leak are:

1. Any reading of less than 80% LEL in small gas associated substructures.
2. 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.
3. Any reading of less than 20% LEL in a confined space.

Other contexts

If working with other dangerous gases (such as in a lab or industrial setting), a gas leak can refer to a leak of some other gas

Gas

Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

. The identity of the gas in question is usually obvious from context, and requires the same response: evacuate, and seek help from someone equipped to deal with that particular gas. Other details depend on the gas in question.