Look for signs of a possible leak:
• Persistent bubbling in standing water
• Discolored or deadvegetation around the pipeline area
• Dense white cloud or fog
• Slight mist of ice
• Unexplained frozen ground near the pipeline
Listen for any unusual noise:
• Whistling, hissing or roaring sound
• Distinctive, strong odor, often compared to rotten eggs or sulfur
*Some persons may not be able to smell the odor because they have a diminished sense of smell, olfactory fatigue (normal, temporary inability to distinguish an odor after prolonged exposure to it) or because the odor is being masked or hidden by other odors that are present in the area, such as cooking smells or damp, musty, or chemical odors.
In addition, under certain rare circumstances, odor fade (the loss of odorant so that it is not readily detectable by smell) can occur. Odor fade is caused by physical and chemical processes. Other factors that may cause odor fade include: construction and configuration of the customer’s gas facilities; presence of rust, moisture, liquids, or other substances in the pipe; gas composition, pressure, and flow; intermittent, little, or no gas flow over an extended period that normally lasts until the gas flow increases or becomes more frequent; new pipe installations; steel and larger pipes; and certain types of dry soil.
Source: Center Point Energy