Gas Leak Detection: Signs and What to Do
If you smell gas right now, stop reading. Get everyone out of the building, including pets. Do not switch lights on or off, use a landline phone, start a car, or do anything else that could create a spark. From outside, call Puget Sound Energy at 1-888-225-5773 or 911. Do not go back in until the utility or fire service says it is safe.
Natural gas has no smell of its own. The rotten egg odor people associate with it is mercaptan, added by the utility precisely so that leaks can be noticed. That single fact tells you most of what you need to know about gas leak detection: the system depends on you catching something, and the margin for missing it is thin.
By Ramin Shahbaziasl, Owner, Eastside Repipe & Plumbing · Last updated October 02, 2025
This guide covers the signs, what to do about them, how professional detection actually works, and where the line sits between a scheduled call and an evacuation.
What to Do If You Suspect a Leak
Signs of an active leak:
The rotten egg or sulphur odour
Hissing or whistling near a line, meter, or appliance
A patch of dead or dying vegetation over a buried line
Dirt, dust, or bubbles blowing up from the ground
Headache, dizziness, nausea, or fatigue that eases when you go outside
The sequence, in order:
Leave the building. Everyone, including pets. Do not stop to open windows or investigate
Create no ignition source. No light switches, no phones indoors, no appliances, no vehicle ignition, no garage door opener. A switch is a spark
Call from outside. PSE at 1-888-225-5773 or 911
Stay out until the utility or fire service clears it
The utility comes first, not a plumber. PSE responds to gas emergencies and can shut the service down. A contractor handles the repair afterwards, once the situation is safe. Anyone telling you to call them before the gas company has the priority backwards.
Do not attempt to locate the leak yourself. That includes the soap and water bubble test. It is a technique used by technicians on isolated, depressurized lines during controlled work — not something to do while gas is escaping into your house.
Non-Urgent Signs Worth Investigating
These warrant a scheduled call rather than an evacuation:
A gas bill that climbed with no change in usage
Visible corrosion or rust on exposed pipe or fittings
Yellow or orange burner flames instead of blue, which can indicate incomplete combustion
Soot marks around an appliance
Appliances that underperform when several run at once, which usually means undersized piping rather than a leak
A pilot light that will not stay lit
None of these are emergencies. All of them are worth looking at, because they sit upstream of the ones that are.
Why Leaks Happen
Aging pipe. Older steel corrodes, particularly where it passes through walls or contacts soil
Poor previous work. Loose fittings, incorrect materials, and unpermitted alterations are common findings on older systems
Appliance connections. Flex connectors and appliance valves fail more often than the fixed piping does
Ground movement. Settling, saturated soil, and seismic activity all stress buried lines
Undersized systems. Adding appliances over the years without upsizing the line stresses joints and starves burners
How Professional Detection Works
Detection is instrumented rather than sensory. That is the whole point, since a leak too small to smell is still a leak.
Combustible gas detectors. Handheld instruments that register methane concentration in air, sensitive well below the level a person would notice.
Pressure testing. The line is isolated and held under pressure. A drop confirms a loss and quantifies roughly how fast.
Infrared imaging. Escaping gas is visible on thermal equipment under the right conditions.
Ultrasonic detection. Picks up the frequency of gas escaping under pressure, useful where access is limited.
Fixed gas detectors. Household units that monitor continuously and alarm. Worth installing, particularly near gas appliances and in basements.
One clarification on detectors: carbon monoxide detectors do not detect natural gas. CO is a product of incomplete combustion; a gas leak is unburned gas. Both cause headaches and nausea, which is why people conflate them, and both are worth having. They are not substitutes for each other.
What Repair Involves
Isolation. The affected line is shut down before anything is opened
Location. Instruments pinpoint the fault rather than an approximate area
Repair or replacement. A fitting, a section, or a run, depending on what is found. Material is set by the Washington State Fuel Gas Code, which adopts the International Fuel Gas Code with state amendments under WAC 51-52, plus local amendments
Pressure test. The system is held under pressure to confirm integrity
Inspection. Permitted work is signed off by the jurisdiction before gas returns
Our guide to gas line repair covers the process and cost drivers in more detail.
Why This Is Not a DIY Job
Gas piping is permitted work in Washington and must be performed by certified tradespeople employed by a licensed contractor. Beyond the legal requirement, the failure modes are fire, explosion, and carbon monoxide, and none of them give warning.
Verify any contractor's licence, bond, and insurance for free through the state Department of Labor and Industries. Our guide to choosing a gas piping contractor covers what else to check.
Prevention and Your Household Plan
Prevention:
Annual inspection, and any time a gas appliance is added or replaced
Keep gas appliances serviced. Appliance connections fail more often than fixed piping
Install both CO and natural gas detectors, and test them monthly
Note buried line locations before digging or planting
Keep the area around gas appliances and their venting clear
PSE provides free safety checks on gas appliances, which is worth using for a non-urgent concern.
The household plan. Everyone in the house should know three things:
The smell. Rotten eggs means leave, not investigate
The number. PSE 1-888-225-5773, or 911. Put it in phones now
The exit. Out of the building, no switches touched, call from outside
Where the gas shutoff is matters too, but only reach it if it is on your way out. Getting out is the priority.
A whole home plumbing inspection covers gas appliance connections alongside the rest of the system.
Frequently Asked Questions
What does a gas leak smell like?
Rotten eggs or sulphur. Natural gas is odorless on its own; utilities add mercaptan so leaks can be detected by smell. If you notice it, leave and call from outside.
Who do I call first, the gas company or a plumber?
The gas company. PSE at 1-888-225-5773, or 911. They respond to emergencies and can shut the service off. A contractor handles the repair once it is safe.
Can I check for a leak myself with soap and water?
No. That technique is used by technicians on isolated, depressurized lines. If you suspect a live leak, leave the building and call the utility rather than trying to locate it.
Will a carbon monoxide detector alert me to a gas leak?
No. CO detectors sense carbon monoxide from incomplete combustion, not unburned natural gas. Install both types.
How often should gas lines be inspected?
Annually, and any time you add or replace a gas appliance. New appliances often exceed what an older line was sized to carry.
What if I only smell it faintly and it goes away?
Treat it as real. Intermittent odors are common with small leaks and with appliance connections that leak only under certain conditions. Call PSE for a check, or book an inspection if it is not currently present.
Book a Gas Safety Inspection
If you have noticed corrosion, an unexplained bill increase, yellow burner flames, or appliances struggling when run together, an inspection is the right next step. We assess the system, establish whether the issue is a leak or a sizing problem, and quote in writing, including permit and testing.
Book an inspection or call 425-331-2011. See our specialized plumbing services for the full scope of gas work we handle.
We serve Bellevue, Kirkland, Redmond, Seattle, and the wider Eastside service area.
For a suspected leak right now: leave the building, touch no switches, and call PSE at 1-888-225-5773 or 911 from outside.
