Utility companies like National Grid add an odorant to natural gas called mercaptan, which smells like sulfur or rotten eggs. Although mercaptan often aids in detection of natural gas leaks, you may not be able to smell this odorant if you have been exposed to it for too long, or if the mercaptan odor is masked by other odors. Mercaptan may also be stripped from the gas due to chemical and physical processes. This effect is known as “odor fade.”
You should never rely on your nose alone to detect a natural gas leak! In any gas leak incident, use a combustible gas indicator to be certain a flammable atmosphere does not exist. In addition, stay alert for any of these gas leak warning signs:
- A distinctive, sulfur-like odor
- A hissing, whistling or roaring sound
- Dirt blowing into the air from a hole in the ground
- Continuous bubbling in water
- Dead or dying vegetation (in an otherwise moist area) over or near a pipeline
- An exposed pipeline after a fire, flood or other disaster
- A damaged connection to a gas appliance
If National Grid does not distribute natural gas in your department’s response area, please coordinate your incident response with the appropriate local gas utility.