Odor Fade in Natural Gas and Propane

RECOMMENDATIONS

The NIOSH Fire Fighter Fatality Investigation and Prevention Program (FFFIPP) recommends that fire 

departments ensure all firefighters responding to natural gas

or propane incidents:

 use gas detection equipment and do not rely upon 

their sense of smell to determine if propane or 

natural gas is present

 understand that the odorant innatural gas or propane 

can fade 

 are trained on the proper calibration, maintenance,

and use of gas detection equipment to determine if 

a potential explosive atmosphere is present

 recognize that the lack of odor can result from the 

natural gas or propane contacting soil, concrete, and 

a wide variety of building materials such as drywall,

wood, and new piping storage tanks

Propane tank involved in the explosion described 

in the FFFIPP Investigation 

Photo courtesy of Maine Fire Marshal

FFFIPP INVESTIGATION 

On September 16, 2019, a fire department responded to a propane leak at a newly renovated 

office building. Several firefighters entered the building. The propane gas ignited and caused an 

explosion. The blast resulted in a line of duty death of a firefighter and the hospitalization of six 

other firefighters. The NIOSH FFFIPP investigated this incident and identified the odor fade of 

mercaptan as a key contributing factor. During this investigation, NIOSH FFFIPP investigators 

learned that some fire departments may not fully understand odor fade. They also may not 

recognize the subsequent explosion hazard that exists when responding to natural gas and 

propane incidents where there is not enough odorant in the released material to alert firefighters 

to its presence. 

QUESTIONS & ANSWERS on p. 2

 
Odor Fade in Natural Gas and Propane

QUESTIONS & ANSWERS

What is an odorant? 

Odorant is a volatile liquid that is added to natural gas 

and propane prior to distribution in pipelines as a safety 

precaution to make it smell. It helps detect a gas leak 

because natural gas and propane are odorless. The two 

most common odorants are methyl mercaptan (for 

natural gas) and ethyl mercaptan (for propane and 

n-butane).

What is mercaptan? 

Mercaptan is a sulfur-containing compound added to 

natural gas, n-butane, and propane to give it a distinct 

odor. The odor is described as smelling like a rotten egg or 

rotten cabbage.

 

Are there medical conditions that affect sense of smell? 

Anosmia (inability to smell), hyposmia (reduced sense of smell), and nasal inflammation can interfere with the 

ability to smell mercaptan odorant. 

Debris field from the propane explosion described 

in the FFFIPP Investigation 

Photo courtesy of Maine Fire Marshal

How does odorant such as mercaptan fade? 

The odor of mercaptan may fade by absorption or oxidation when leaking natural gas or propane from 

underground lines passes through soil and concrete. Materials such as drywall and plywood may also cause 

odor fade. New piping for natural gas or storage tanks for propane can remove the odorant through 

adsorption of the odorant into the interior of the pipes or tank shell.

 

Is odor fade more common in certain types of gas installations? 

Odor fade is generally most common in new largediameter steel pipes and storage tanks. However, odor 

fade can also occur in smaller diameter gas lines made of polyethylene.

What can be done to ensure odor does not fade? 

For new natural gas or propane installations, many gas installation companies perform pipeline conditioning to 

saturate the new gas installations prior to use. Likewise, new storage tanks and new components

of natural gas or propane installations should be conditioned prior to use.

 

Are there ways to detect a natural gas or propane leak when there is no odor? 

Underwriters Laboratories (UL) and gas suppliers recommend personnel use gas detection equipment to 

detect natural gas or propane leaks. 

Find NIOSH products and get answers to workplace 

safety and health questions:

1-800-CDC-INFO (1-800-232-4636) | TTY: 1-888-232-6348

CDC/NIOSH INFO: cdc.gov/info | cdc.gov/niosh

FFFIPP: cdc.gov/niosh/fire/

DHHS (NIOSH) Publication No. 2021-106 (revised 01/2022) | March 2021

DOI Number: https://doi.org/10.26616/NIOSHPUB2021106revised012022

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