The National Institute for Occupational Safety and Health (NIOSH) issued a safety advisory to fire departments concerning fading odorants during natural gas and propane leaks.
NIOSH’s Fire Fighter Fatality Investigation and Prevention Program (FFFIPP) urged fire departments to ensure that 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 in natural 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.
The FFFIPP investigated a September 16, 2019, incident in which a firefighter died in the line of duty and six others were hospitalized. 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.
FFFIPP investigators determined the odor fade of mercaptan as a key contributing factor. They learned that some fire departments may not fully understand odor fade. Fire departments 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, according to NIOSH.
Mercaptan, a sulfur-containing compound, which is described as smelling like a rotten egg or rotten cabbage, is added to natural gas, n-butane, and propane to give it a distinct odor. The odorant alerts building occupants to a gas leak.
Because natural gas and propane are odorless, a volatile liquid odorant is added to natural gas and propane before distribution in pipelines as a safety precaution. The two most common odorants are methyl mercaptan (for natural gas) and ethyl mercaptan (for propane and n-butane), according to NIOSH.
The odor of mercaptan may fade for several reasons:
- Due to 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.
Odor fade is generally most common in new large-diameter steel pipes and storage tanks, according to NIOSH. However, odor fade also may occur in smaller-diameter gas lines made of polyethylene.
Some gas installation companies perform pipeline conditioning to saturate the new gas installations before use to guard against odor fade. New storage tanks or new components of natural gas or propane installations also may need to be conditioned before use.
Underwriters Laboratories (UL) and gas suppliers recommend that firefighting personnel use gas detection equipment to detect natural gas or propane leaks.