Gas Leak Detection and Odor Fade

Natural gas is colorless and odorless, but a distinct rotten-egg or sulfur smell known as Mercaptan is added for easy detection. Not all transmission lines are odorized.

During a gas leak, you may smell something, you may notice dead vegetation in a moist area, or you may see a white cloud, mist, or bubbles in standing water. You may also hear unusual sounds such as roaring, hissing, or whistling.

Move to a safe location and dial 911 immediately or call us at 1-800-640-1595. Do not smoke or use electrical devices, including e-cigarettes and vape pens, as they could cause a spark and ignite the gas.

When reporting the gas leak, provide the exact location, including cross streets, and mention any nearby digging or sewer construction. Do not assume someone else will report the leak.

Odor fade is the reduction or loss of the distinct rotten-egg smell added to natural gas, making it harder to detect leaks. This often occurs in large steel pipes with low gas flow, but it can also affect smaller pipes and materials used in commercial and industrial settings.

During a process called “purging,” air in a pipe is replaced with natural gas. Normally, sulfur compounds are added to natural gas to give it a noticeable smell for safety. However, these compounds can sometimes get filtered out or absorbed by the materials in the pipes, making it harder to detect gas leaks by smell. It can also be harder to detect gas leaks due to:

• A diminished sense of smell for some people
• The odor being masked by other strong smells
• Moisture, rust, or other contaminants in the piping system
• Absorption of the odorant by soil, concrete, and piping materials
• Oxidation of the sulfur compounds
• Variations in gas pressure

Rhode Island Energy regularly tests its systems to ensure that natural gas meets state and federal odorization standards. However, once the gas leaves our distribution system, the odor can diminish. This poses a safety risk if installers of new equipment or appliances rely only on smell to detect gas leaks.

Odor fade is the reduction or loss of the distinct rotten-egg smell added to natural gas, making it harder to detect leaks. This often occurs in large steel pipes with low gas flow, but it can also affect smaller pipes and materials used in commercial and industrial settings.

During a process called “purging,” air in a pipe is replaced with natural gas. Normally, sulfur compounds are added to natural gas to give it a noticeable smell for safety. However, these compounds can sometimes get filtered out or absorbed by the materials in the pipes, making it harder to detect gas leaks by smell. It can also be harder to detect gas leaks due to:

• A diminished sense of smell for some people
• The odor being masked by other strong smells
• Moisture, rust, or other contaminants in the piping system
• Absorption of the odorant by soil, concrete, and piping materials
• Oxidation of the sulfur compounds
• Variations in gas pressure

How to help prevent odor fade:

• Design piping systems for the expected flow rate and avoid oversizing
• Design piping systems in a loop to keep gas flowing and minimize dead ends

General precautions:  

• Always use gas detection equipment (such as combustible gas indicators) when purging or if gas may be leaking
• Never purge natural gas into a confined space — vent it outdoors
• Ensure the area is well-ventilated during purging operations
• Do not rely solely on your sense of smell to detect gas leaks
• Follow local plumbing, mechanical, and fuel gas codes during purging
• Adhere to manufacturer instructions when installing appliances or gas equipment

Only licensed, qualified professionals should perform purging operations. If you suspect odor fade, consider shutting off the affected piping.