Quick Answer
If you smell rotten eggs or natural gas, treat it as an emergency. Leave the building immediately without touching lights, switches, or electronics. Extinguish any flames as you exit. From a safe location outside, call your gas utility’s 24-hour emergency line or 911. Do not re-enter until officials say it’s safe. If you know how and it’s safe, you can shut off gas at the meter (or propane tank) from outside.
Why the Rotten Egg Smell Matters
Natural gas and propane are odorless; utilities add a sulfur-like odorant (mercaptan) so leaks are detectable. Even a faint smell can indicate a leak that could build to an explosive concentration. You can’t reliably gauge “how bad” a leak is by smell alone, so err on the side of caution.
Note: Sewer gas can also smell like rotten eggs. If you’re unsure, act as if it’s natural gas until proven otherwise.
Step-by-Step: What To Do Right Now
Leave immediately
- Don’t use light switches, electrical outlets, doorbells, or phones inside.
- Don’t smoke, light matches, or use lighters.
- Get everyone out, including pets. Help neighbors if you’re in a multi-unit building.
Avoid creating sparks
- Don’t start vehicles in an attached garage.
- Don’t operate appliances or fans. Even static discharge can be risky in a concentrated leak.
Vent only if it’s already safe to do so
- If a door is already open on your way out, you can leave it open. Don’t stay inside to open windows.
Call for help from a safe spot
- Move at least 100 feet away and upwind if possible.
- Call your gas company’s emergency number (on your bill or company website) or call 911. For propane, call your supplier.
- Describe the odor, where you smelled it, and any hissing sounds.
Optional: Shut off gas from outside if you’re trained and it’s safe
- Natural gas meter: Turn the shutoff valve a quarter-turn so it’s perpendicular to the pipe.
- Propane tank: Turn the service valve clockwise to close.
- Only do this if the meter/tank is easily accessible outdoors and you won’t pass through the odor to reach it.
Wait for clearance
- Do not re-enter until the utility or fire department says it’s safe. They’ll test the air and locate the leak.
Tools and Materials (Preparedness)
- Adjustable wrench (10–12 inch) or dedicated gas shutoff wrench
- Combustible gas leak detector (methane/propane) for non-emergency checks: $30–$80
- Gas-rated leak detection spray or dish soap/water solution for fittings (use only after pro clears re-entry)
- Battery-powered lantern or glow sticks for emergency lighting (store near exits)
- Natural gas/propane detector and carbon monoxide (CO) alarms (CO ≠ natural gas): $25–$60 each
How to Shut Off Gas at the Meter (If Trained and Safe)
Only from outside and only if you can do so without passing through the odor.
Natural Gas Meter Valve:
- ON: Valve slot/handle aligned with pipe
- OFF: Valve slot/handle perpendicular (90°) to pipe
- Turn with an adjustable wrench; it’s a quarter-turn valve
For propane tanks, turn the main service valve clockwise to close fully. Never turn gas back on yourself—only the utility or a licensed professional should restore service and relight appliances.
After the Emergency: What Happens Next
- Utility or fire officials will check for gas levels and source.
- A licensed plumber or HVAC technician may be required to repair leaks in piping, connectors, or appliances.
- Typical costs for non-emergency repair visits run $150–$300+, parts extra. Utility emergency response is usually free.
- Appliances with pilots (furnaces, water heaters, stoves, fireplaces) may need professional relighting and safety checks.
Common Causes and Prevention
- Loose flare fittings or old flexible appliance connectors
- Damaged or improperly routed gas lines (including CSST that lacks proper bonding)
- Faulty valves on stoves, water heaters, or furnaces
- Pilot lights out or burners not fully igniting
- Sewer gas confusion: Dry P-traps in seldom-used drains can release odors
Preventive steps:
- Schedule annual inspections for gas appliances.
- Replace old uncoated flexible connectors with new, listed gas connectors.
- Ensure CSST is properly bonded by an electrician.
- Keep P-traps wet (run water weekly in seldom-used sinks/floor drains). Add a tablespoon of mineral oil to slow evaporation.
- Install gas and CO detectors near appliances and sleeping areas.
- Keep a shutoff wrench secured near the meter (outdoors).
Tips for Best Results
- Treat any rotten egg odor as a potential gas leak first. Once cleared, investigate sewer odors if needed.
- If you occasionally smell gas when using the stove, have a pro check burner ignition and valve seals—don’t rely on “airing it out.”
- If you hear hissing near gas lines, that’s urgent—evacuate immediately and call for help.
- In multi-unit buildings, knock on neighbors’ doors as you evacuate. Avoid using building intercoms or alarms that require electricity unless they’re designed for emergency use.
Common Mistakes to Avoid
- Flipping lights on/off while leaving
- Using a phone inside the building to call for help
- Starting a car in an attached garage
- Trying to find the leak with a lighter or match (never do this)
- Ventilating with box fans or opening multiple windows before leaving
- Turning gas back on yourself after shutoff
When to Call a Professional
- Any time you detect a gas odor—contact the utility or 911 first.
- After clearance, hire a licensed plumber or HVAC tech for repairs and to test with calibrated instruments.
- Call a plumber if odors recur near drains; they can address dry or faulty traps and venting issues.
Staying calm and following these steps protects your household and helps responders fix the problem quickly and safely.