SoCalGas - Don't Rely on Just Your Nose
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Don't Rely on Just Your Nose

Included in this section:

The distinctive odor of natural gas

Southern California Gas Company (SoCalGas) adheres to United States Department of Transportation (DOT) and California Public Utilities Commission (CPUC) rules and regulations regarding the odorizing of natural gas. For your protection, SoCalGas adds an odorant to give natural gas a distinctive odor so leaks can be more readily detected. However, you should not rely on your sense of smell alone to determine if you have a gas leak.

Don't rely on just your nose

Even though a distinctive odor is added to natural gas to assist in the detection of leaks, you should not rely on just your nose to alert you to the presence of natural gas. There are a number of reasons why your sense of smell may not always let you know that gas is leaking or has been released. For example, some people may not be able to smell the odor because they have a diminished sense of smell, or are experiencing olfactory fatigue (normal, temporary inability to distinguish an odor after prolonged exposure to it). Some physical conditions including common colds, sinus conditions, allergies, eating certain foods, inattentiveness, and the use of tobacco, alcohol, drugs and certain medications may also lessen the ability to smell the odor. In addition the odor may be masked or hidden by other odors that are present, such as cooking, damp, musty or chemical odors. And, certain conditions in pipe and soil may cause odor fade - the loss of odorant so that it is not detectable by smell. See natural gas odor fade (loss of odorant).

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Natural gas odor fade (loss of odorant)

Odor fade (loss of odorant) refers to the phenomenon in which physical and/or chemical processes cause the loss of odorant in natural gas so that its distinctive odor may no longer be detectable by smell. The processes that cause odor fade include adsorption, absorption, oxidation, or any combination thereof. Adsorption occurs when odorant molecules adhere to an exposed surface, such as the interior wall of a steel pipe. In absorption, odorant molecules are dissolved into or combined with another substance – such as cutting oil, pipeline liquids, or pipe thread compound – causing the odorant to have less odor. Oxidation occurs when rust or other compounds react with the odorant to change its chemical composition so that it is less odorous.  

In gas piping systems, odor fade occurs predominantly in new, steel pipe - steel pipe that has either been recently manufactured or which has not been previously used for odorized natural gas. Odor fade can also occur in previously used or existing gas pipe under certain conditions, such as where rust is present or when gas flow is limited or intermittent. Odor fade may also occur in pipe made of other materials. While it is often more pronounced in installations of larger and longer pipe, odor fade can also occur in smaller and shorter pipe configurations.

A number of factors can cause or contribute to odor fade. For example, odor fade is more likely to occur in gas piping systems using higher gas pressure, and where there is little, intermittent or no gas flow. The presence of rust, mill scale, moisture, air, cutting oil, pipe thread compound, liquids, condensates and other substances in pipe and other components of gas piping systems can cause odor fade. Care should be taken in the selection and use of pipe to be utilized in gas piping systems. Such systems should be designed and configured to ensure that there is a continuous flow of gas though the entire system. In addition, care should be taken in the construction of such systems or when fabricating gas pipe to prevent the introduction of substances that may contribute to odor fade.

New pipeline installations or additions of new piping segments may require the odor conditioning of the pipe before it is placed into service to prevent occurrences of odor fade. This may be accomplished by extended purges of natural gas through the pipe or by direct odorant injection. (See section on Safe Purging.) Where necessary, the gas piping system may require repeat instances of conditioning and/or modification of the system – such as by stepping down pressure or reconfiguring the piping to ensure continuous gas flow – to prevent repeat occurrences of odor fade. Odor conditioning, purging and other releases of natural gas should only be performed by qualified gas professionals.

If a gas leak occurs in underground piping, the surrounding soil or fresh concrete can absorb or oxidize the odorant so that the gas no longer has an odor. As a result, gas leaking from an underground pipe may not be detectable by smell.

For a printable copy about odor fade and safe purging practices, please refer to our Safety Bulletin.

If you have additional questions or concerns regarding pipe conditioning or odor fade, call SoCalGas at 1-800-427-2200 or contact a licensed, qualified professional.


Do not rely on your sense of smell alone to alert you to the presence of natural gas.

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Updated 10/2012

What to do if you smell gas

What to do if you smell gas

Use your senses of sight, hearing or smell to be alerted to the presence of a gas leak.

Report Any Pipe Damage

Evacuate the area and from a safe location, call SoCalGas at


to report any pipeline damage. No damage is too small to report.