Odor Fade

By Tabitha Mishra
Last updated: April 12, 2022

What Does Odor Fade Mean?

Odor fade refers to the gradual loss of odor emanating from a gas. It results from physical or chemical processes like absorption, adsorption, and oxidation.

Odor fade makes a gas more difficult to detect. To combat it, an odorant known as mercaptan can be added to ensure that leaking gases will have a detectable scent. However, even mercaptan can succumb to odor fade and gradually become more difficult to detect by smell alone.

Safeopedia Explains Odor Fade

Some causes of odor fade, including instances where an odorized may become undetectable, include:

  • Oxidation from rusting pipes
  • Presence of rust, moisture, liquids, or other substances in the pipe
  • Adsorption on iron oxide layers inside pipelines
  • Absorption into liquids
  • Intermittent, little, or no gas flow over an extended time
  • Contact with soil in underground leaks

Even without odor fade, some situations can make it more difficult to detect a gas by its oder. These include:

  • Olfactory adaptation (getting used to the smell)
  • Diminished sense of smell due to age, medication, or illness
  • Stronger odors masking the odor of the gas
  • Being asleep or heavily distracted

Unreliability of Odorants

Adding an odortant to a gas is one way to combat odor fade. However, it is not a sufficient precaution against gas leaks or gas exposure.

Certain types of piping can accelerate odor fade. It tends to occur predominantly in new installations rather than in existing ones. It is also more prevalent in new steel pipes that are longer in length and larger in diameter. To prevent odor fade, new pipeline installations and piping segments may need to be conditions before they are placed in service.

Failing to recognize a gas leak can have serious consequences, especially when purging gas. The contents of a gas line should never be purged into a confined space and purging should only be done in a well-ventilated area by a licensed, qualified professional. The use of gas detection equipment is necessary while conducting these operations, or when working on a gas piping system to ensure that no gas is present that can be a potential hazard.

Recommendation for Firefighters

The National Institute for Safety and Health (NIOSH) Fire Fighter Fatality Investigation and Prevention Program (FFFIPP) gives the following recommendations related to odor fade when dealing with natural gas and propane incidents:

  • Use gas detection equipment and not rely on the sense of smell
  • Understand that odorant can fade
  • Proper training on calibration, maintenance, and use of gas detection equipment
  • Recognizing that lack of odor may be due to contact of gas with soil, concrete, drywall, wood, and new piping storage tanks

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