The short answer
Why Sewer Gas Is Flammable
Sewer gas is a mix of gases that forms when waste breaks down. Methane is the main flammable part. Methane ignites when it reaches a certain concentration in the air and meets a flame or spark. Common household ignition sources include water heater pilot lights, furnaces, and electrical switches.
The risk depends on how much gas has built up and whether it is trapped. A small leak in a ventilated room may not reach dangerous levels. A larger leak in a closed basement or crawl space can create a serious hazard. If you smell rotten eggs, that odor is added to warn you of danger.
Signs of a Sewer Gas Leak
The most obvious sign is the smell. It often resembles rotten eggs or sulfur. You might notice it near drains, toilets, or in basements. Other clues include gurgling sounds from plumbing fixtures or slow-draining sinks, which can mean a vent pipe is blocked.
You should not ignore the smell even if it seems faint. Open windows and doors to ventilate the area. Leave the house if the odor is strong. Do not use electrical switches or light matches until the area airs out. The next step is to find where the gas is entering your home.
- Check floor drains for dry traps
- Look for cracked or loose toilet seals
- Inspect vent pipes on the roof for blockages
- Listen for gurgling in sink drains
- Feel around pipe joints for moisture
Where Sewer Gas Enters
Sewer gas usually enters through plumbing failures. A dry floor drain trap is a common culprit. When the water in the trap evaporates, gas can flow freely into the room. Toilet seals and wax rings can fail over time, allowing gas to escape around the base.
Cracked pipes or loose joints in the drain system also let gas seep into walls or under floors. Blocked vent stacks on the roof can cause pressure changes that push gas out of fixtures. A plumber can inspect the system to find the exact entry point.
What to Do Right Away
Your first move is to ventilate. Open windows and doors to push fresh air through the affected area. Leave the house if the smell is overpowering or if you feel dizzy or sick. See a doctor if you feel unwell after exposure.
Do not try to locate a gas leak with a flame. Do not operate electrical appliances near the smell. Write down where you noticed the odor and any plumbing sounds. This information helps a plumber or a water damage pro find the source faster.
- Open all windows and exterior doors
- Evacuate if the odor is strong
- Avoid using light switches or appliances
- Note the location and time of the smell
- Keep children and pets away from the area
When to Call for Help
A plumber can repair the specific plumbing issue, such as a broken pipe or a dry trap. If the leak has caused water damage to walls, floors, or subflooring, you may need a water damage pro to assess the extent of the moisture. Water damage inspection can reveal hidden problems.
If you live in Redmond, keep your plumbing maintenance in mind. The mild marine climate with wet winters can affect drainage systems. Local water damage pros can help with drying and dehumidification if moisture has soaked into building materials.
Water damage does not wait
Call (425) 407-5186 any time, day or night, and describe what happened.
Call Now (425) 407-5186Frequently asked questions
Can sewer gas explode without a flame?
No, methane needs an ignition source to burn. It will not explode on its own. The danger comes when gas accumulates and meets a spark or pilot light. Ventilating the area reduces the concentration and lowers the risk.
How long does sewer gas stay in a house?
It depends on ventilation and how much gas entered. With open windows and fans, the smell can fade within hours. If the leak continues, the gas will keep returning. You must fix the source to stop the problem permanently.
Is sewer gas harmful to breathe?
Yes, in high concentrations it can cause headaches, nausea, and dizziness. The rotten egg smell comes from hydrogen sulfide, which can be toxic at high levels. Leave the area and seek fresh air if you feel unwell.