Hydrogen sulfide (H₂S) gas sources in buildings:

Don't overlook these possible sources of sewer gas smells or hydrogen sulfide gas odors: here are the causes, sources, & cures for often overlooked sources of sewer gas smells. This article series explains how to diagnose, find, and cure odors in buildings including septic or sewage or sewer gas smells or "gas odors" in buildings.

Hydrogen Sulfide or Rotten Egg Smells: building sources, causes, dangers, advice

Watch out: both HYDROGEN SULFIDE GAS discussed here

and METHANE & SEWER GAS HAZARDS (both of these are present in sewer gases) are potentially explosive

In addition, exposure to high levels of these gases can be harmful, even fatal, as we detail below.

Because sewer gas contains methane gas (CH₄) there is a risk of an explosion hazard or even fatal asphyxiation.

Sewer gases also probably contain hydrogen sulfide gas (H₂S) In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation). Hydrogen is extremely flammable (easily set fire or explodes).

Depending on the sewer gas source and other factors such as humidity and building and weather conditions, mold spores may also be present in sewer gases.

Sources of Hydrogen sulfide (H₂S) or Septic System or Sewer Gas Odors at Buildings

Here are some key places to look:

• Batteries:
  
  leaky or failing batteries, such as 12V or 24V car batteries, or batteries used to power a backup sump or sewage pump may produce a sulphur or rotten-egg odor.
• Drain waste vent piping clogs or leaks 
  
  like the leak shown in our photo at above left. See
  
  CONCRETE CORROSION DUE TO HYDROGEN SULFIDE
  
  DRAIN LINE PIPE LEAKS (drain line or sewer line breaks, leaks, seeps)
  
  DRAIN ODOR SOURCES
  
  DRAIN PIPING & SEWER ODORS
  
• Sewage backup 
  
  or spill inside or outside of a building. See
  
  SEWAGE BACKUP, WHAT TO DO
  
  SEWAGE CONTAMINATION in BUILDINGS
• Failing septic system 
  
  causing effluent breakout at ground surface. See
  
  DRAINFIELD ODORS, FAILURES
  
  LAGOON SEPTIC SYSTEMS Septic lagoon systems produce normal "musty" odors that are distinguised from abnormal lagoon smells requiring action
  
  
• Septic tank leakage to the surface, also an indicator of failing septic system or septic tank damage. See
  
  SEPTIC TANK LEAKS
  
  SEPTIC TANK INSPECTION PROCEDURE - home
  
  SEPTIC TANK LEVELS of SEWAGE - separate article
  
  May also cause damage to concrete septic tanks -
  
  See HYDROGEN SULFIDE CORROSION: CONSEQUENCES, DETECTION & CONTROL [PDF], U.S. Environmental Protection Agency, retrieved 02/20/2023, ttps://nepis.epa.gov/Exe/ZyPDF.cgi/200048ZZ.PDF?Dockey=200048ZZ.PDF
  
  
• Sewage grinder pump failures,
  
  backups, leaks.
  
  SEWAGE EJECTOR / GRINDER PUMPS
• Table of Sources of Septic or Sewer Odors
  
  SEPTIC / SEWER ODOR SOURCE TABLE
• Other sewer gas-like odors that are not due to building wastewater or drains - listed below
  
  at OTHER H2S ODORS
• Plumbing vent system defects - see
  
  BACKDRAFTING & SEWER/SEPTIC ODORS
  
  PLUMBING VENT PIPING

Other H2S Odors, sewer-gas-like odors or sulphur odors may be hydrogen sulfide (H₂S)

and may occur from these conditions which you may not have considered.

• Inspect the building water heater:
  
   if the "sewer gas smell" is noticed particularly when hot water is being run at a sink, tub, or shower, have your plumber check for a bad water heater sacrificial anode.
  
  This rod is intended to slow corrosion in the water heater tank but when the anode deteriorates it can cause a "rotten egg" smell in the hot water supply which may be mistaken for sewer gas. We discuss the hot water tank sacrificial anode and dip tube in more detail
  
  at ANODES & DIP TUBES on WATER HEATERS
  
  Watch out: Hydrogen sulfide gas is potentially explosive, can catch fire, and if it is mixed with or originating from sewer gases, it may contain pathogens or be harmful to humans and other animals.
  
  But in addition, water heaters can be a source of this sulphur or rotten egg smell due to bacterial growth or anode deterioration as we just cited. Water heater manufacturers, including American Water Heater Co., advise,
  
  Hydrogen gas is produced in a hot water system served by this heater that has not been used for a long period of time (2 weeks or more). Hydrogen is extremely flammable.
  
  To reduce the risk of injury under these conditions, it is recommended that the hot water faucet be opened for several minutes at the kitchen sink before using any electrical appliance connected to the hot water system.
  
  When hydrogen is present, there will be an unusual sound such as air escaping through the pipe as the water begins to flow. There should be no smoking or open flame near the faucet at the time it is open. [5]
  
  More details about dangers of hydrogen sulfide gas exposure are
  
  at HYDROGEN SULFIDE EXPOSURE and
  
  at HYDROGEN SULFIDE GAS DANGER
• Check the building water supply:
  
  if the "sewer gas smell" is a "rotten egg smell" and if it is noticed particularly when hot or cold water are being run at a sink, tub, or shower, your water supply may contain excessive hydrogen sulphide or H₂S.
  
  This is not likely to be the case if you are on a municipal or community water supply but could occur if your water is supplied by a private well. Have the water tested for sulphur and H2S. If this condition is confirmed, the H2S is not a health concern but remains an aesthetic one.
  
  It can be corrected by installation of a proper water treatment system such as a chlorine injection system, a potassium permanganate filtration system, or by other methods. More information about causes of and cures for hydrogen sulfide odors in water is
  
  at IDENTIFYING ODORS in DRINKING WATER
• Chlorine solution preparation 
  
  during well disinfection or for water treatment equipment disinfection involves steps that can produce hydrogen sulfide. Watch out for hydrogen sulfide (H₂S) during the mixing procedure.
  
  If there is H₂S in the water you will need to aerate the water to dissipate that gas before adding vinegar (or chlorine) to the water.
  
  See CHLORINE SAFETY WARNING where we discuss both H₂S and chlorine gas hazards.
  
  Well shocking & disinfection are discussed
  
  at WELL CHLORINATION & DISINFECTION
• U.S. Army Field Manual FM-8-285-NOXIOUS CHEMICALS [PDF] discusses Ammonia, Carbon Monoxide, Hydrogen Sulfide, Oxides of Nitrogen, Hazards caused by fire
• Use of improper or excessive cleaning chemicals
  
   in the building, or perhaps excessive use of antibiotics (such as by a nursing home served by a septic tank and whose residents consume a lot of antibiotics) can kill off bacteria in the septic tank. This is an unusual condition unlikely to occur in a normal homeowner environment.
• Drywall outgassing:
  
  see CHINESE DRYWALL HAZARDS & ODORS for an explanation.
• Septic system, sewer system, & building drain defects 
  
  are common sources of sewer gases and hydrogen sulfide odors in buildings - but not if everything is working properly.
  
  But a loose toilet, blocked plumbing vent, improperly-maintained aerobic septic system, or a failing septic drainfield can be a source of sewer gas odors observed both indoors and outside.
  
  See SULPHUR & SEWER GAS SMELL SOURCES
• For help in tracking down sulphur or sewer odors to their source:
  
  read this page and also
  
  see SMELL PATCH TEST to FIND ODOR SOURCE

Hydrogen Sulfide Gas H₂S Explosion Dangers

Watch out: both hydrogen sulfide gas and methane gas (both present in sewer gases) are potentially explosive. Hydrogen sulfide gas is heavier than air, poisonous, corrosive, flammable (will burn), and depending on its concentration in air, it can explode.

My older sister Linda and later my best friend David Hoff both led experiments in attempts to light ... well, politely put, human flatulence gases.

Results were amazing. But in buildings, an accumulation of hydrogen sulfide gas H₂S is not funny, it is potentially catastrophic, or fatal should an explosion occur. In dangerous mixtures with air or if put into direct contact with nitric acid, H₂S explodes. (Fletcher 1999)

Compound is heavier than air and may travel a considerable distance to source of ignition and flash back.

Hydrogen sulfide forms explosive mixtures with air over a wide range. Also reacts explosively with bromine pentafluoride, chlorine trifluoride, nitrogen triiodide, nitrogen trichloride, oxygen difluoride, and phenyl diazonium chloride.

When heated to decomposition,

Hydrogen sulfide emits highly toxic fumes of oxides of sulfur. Incompatible with many materials including strong oxidizers, metals, strong nitric acid, bromine pentafluoride, chlorine trifluoride, nitrogen triiodide, nitrogen trichloride, oxygen difluoride and phenyl diazonium chloride.

Avoid physical damage to containers; sources of ignition; storage near nitric acid, strong oxidizing materials, and corrosive liquids or gases. (Chemcial Book, Hydrogen Sulfide CAS No. 7783-06-04)

Hydrogen Sulfide Gas H₂S Exposure Dangers

The following information about hydrogen sulfide gas H₂S hazards is adapted from information from U.S. Army Field Manual 8-285 Chapter 10, Noxious Chemicals:

10-4. Hydrogen Sulfide Gas Danger Information

Physical Properties of Hydrogen Sulfide Gas:

This colorless gas in low concentrations has the odor of rotten eggs. In high concentrations it may dull the sense of smell and be difficult to recognize.

Occurrence of hydrogen sulfide gas in military operations. This gas is produced during the decomposition of sulfur containing compounds in sewers, waste, coal bins or stacks, holds of ships, and waterfront excavations.

Occurrence of hydrogen sulfide gas in Military Operations as well as in civilian and residential conditions

Hydrogen sulfide gas is produced during the decomposition of sulfur containing compounds in sewers, waste, coal bins

Pathology of Hydrogen Sulfide Gas Exposure

In low concentrations (less than 0.15 mg per liter), hydrogen sulfide may produce inflammation of the eyes, nose, and throat if breathed for periods of 1/2 to 1 hour.

Watch out: higher concentrations of hydrogen sulfide (H₂S) gas (0.75 mg per liter or greater) are rapidly fatal, presumably by combination of the hydrogen sulfide with the respiratory tissue pigments and the subsequent paralysis of the respiratory center.

Symptoms of Hydrogen Sulfide Gas Exposure

The symptoms depend upon the concentration of the gas. At the lowest concentrations, the effects are chiefly on the eyes; that is, conjunctivitis, swollen eyelids, itchiness, smarting, pain, photophobia, and blurring of vision. At higher concentrations, respiratory tract symptoms are more pronounced.

Rhinitis, pharyngitis, laryngitis, and bronchitis may occur. Pulmonary edema may result. At very high concentrations, unconsciousness, convulsions, and cessation of respiration rapidly develop.

Details about H₂S exposure effects & limits are at

HYDROGEN SULFIDE EXPOSURE EFFECTS

HYDROGEN SULFIDE GAS EXPOSURE LIMITS

Treatment for Hydrogen Sulfide Gas Exposure

Immediately remove the casualty from the contaminated atmosphere and administer assisted ventilation with oxygen, if possible. Treatment of pulmonary edema is the same as for that caused by CG (chap 5).

Reader Comment: Hydrogen Sulfide Gas H₂S health hazards warning & citation of HUD Dictionary of Deficiency Definitions

Not a question just a comment.

HUD regulates how to keep those in living in subsidized housing from the dangers of sewer gas inhalation but the state of Georgia (Georgia Dept. of Community Affairs a HUD area housing administrator) does not follow that HUD mandate and that is why myself and my child have severe lung disease that is caused from our prolonged exposure to sewer gas within and about a Bremen, GA rental.

See page 305 Sewer Odor Detected (Air Quality) quoted below:

Deficiency:
You detect sewer odors that could pose a health risk if inhaled for prolonged periods.

- SB4Justice - 4/4/2013

Reply:

SB4Justice

Thanks I've posted your remark above so that I could include a link to

the HUD DEFICIENCIES DEFINITIONS [PDF] document provided by U.S. HUD.

Also below in our references we include citations [3][4][5][6][7][8] describing the health hazards of breathing hydrogen sulfide gas H₂S, and of course methane can be a more immediate hazard - that of explosion.

Details about Hydrogen Sulfide gas and advice about tracking down such odors are on this page in the article above.

Details about methane gas hazards are given separately

at METHANE GAS, SEPTIC / SEWER.

Watch out: while H₂S can be dangerous, readers should keep in mind that both H₂S and more commonly methane gas (a significant component in sewer gas) is dangerously explosive and at sufficient concentrations can also be fatal. So both can be an immediate hazard, not just a health hazard.

The same HUD Deficiencies document you cite, back up on page 304 also warns:

Propane/Natural Gas/Methane Gas Detected (Air Quality)

Deficiency: You detect strong propane, natural gas, or methane gas odors that could:

• pose a risk of explosion/fire
• pose a health risk if inhaled

And from HUD Pass/Fail deficiencies p. 302 we have more general advice

Air Quality (Health and Safety)

Indoor/Outdoor spaces must be free from high levels of sewer gas, fuel gas, mold, mildew, or other harmful pollutants. Indoors must have adequate ventilation.

The following deficiencies can be noted:

Mold and/or Mildew Observed

Propane/Natural Gas/Methane Gas Detected

Sewer Odor Detected

Which is in error only that mildew is never found in buildings, only mold, unless the mildew is growing on a plant (my photo at left).

Mildew is an obligate parasite that only grows on plants. Of course normal people don't know that and the word "mildew" is used by lay persons interchangeably (if incorrectly) with "mold".

Details are at MILDEW in BUILDINGS ?

Thank you again SB4Justice for pointing out these dangers. Working together we're smarter. - Daniel F.

Note: For a helpful discussion of just what constitutes "adequate venitlation", see

• Offermann, Francis (Bud) J., P.E., C.I.H., ASHRAE & Mark Nicas, Ph.D., MPH, C.I.H., USE WITH ADEQUATE VENTILATION ? [PDF], ASHRAE Journal, May 2018.

 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2019-09-02 by Jared Raymer - house inundated with sewer gas (H₂S) for 4 months

My Mother has a house that was inundated with sewer gas (H2S) for a period of about 4 months. There is still some kind of smell that is in the house years later. Do you know of any ways to treat this house to keep items in the house from off gassing? like seal the walls and repaint?

Is there any way to know that this house is safe to live in?

The house was aired out after the incident happed. There was a ozoneator also ran in the house for a long period of time.

There is proof that the H2S was there due to the copper wiring in the walls by the outlets turning black and silver. Any advice on this problem would be greatly appreciated. Thanks, Jared

On 2019-09-03 by (mod) -

Jared

Before prescribing a "cure" for the indoor odor AND before deciding if the house is safe to live-in, it would be best to

1. Identify the odor source - so that removal, cleaning, or sealing are effectively focused - See the ARTILE INDEX to find

SMELL PATCH TEST to FIND ODOR SOURCE - an easy way to do that

2. Have the property's electrical and mechanical systems inspected for corrosion that could make electrical wiring, controls, or HVAC equipment unsafe - as H2S may have caused harmful corrosion: put safety ahead even of odor mitigation

See this example of such damage:

CHINESE DRYWALL HAZARDS where other links will suggest further investigation and mitigation.

On 2017-09-02 by Pamela Pawlowski - What does hydrogen sulfide smell like

What does hydrogen sulfide smell like

On 2017-09-02 by (mod)

Hydrogen sulfide gas or H₂S smells like Rotten eggs

On 2017-07-25 by ray scott - flickering lights, lost electrical power, then rotten egg smell

We had a bad rain during the night when we woke up several lights were flickering and power to bathroom went off.

An electrician was called and he found the copper wire in a light fixture to be not connected tight. He fixed the problem and the lights started working. several hours later returned home to have a strong rotten egg smell in several rooms of the house.

Don't know what caused this. Any comments on problem. Thanks

On 2017-07-26 by (mod) -

Not sure what would be the connection, Ray, but to be very safe you could turn off that circuit on the theory that a wire or component may be overheating.

Then see if you can track down where the odor is strongest - that'd be diagnostic.

Odors of sewage or sulphur often are due to a drain backup or septic failure that might show up in wet weather.

On 2017-03-27 by Smithe438 - compliment

Usually I do not read writeup on blogs, nevertheless I wish to say that this writeup extremely forced me to take a look at and do so! Your writing taste has been amazed me. Thanks, really wonderful post. ffefekefcbdfbdef

On 2017-03-27 by (mod) -

Thank you, SmithE. Assuming you're not kidding me, I'll add that we work hard to provide researched, unbiased data so I'm happy when a reader finds our information useful.

Daniel

...

Continue reading at HYDROGEN SULFIDE EXPOSURE EFFECTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see HYDROGEN SULFIDE GAS FAQs - questions & answers about H₂S posted originally on this page.

Or see these

Recommended Articles

• ANIMAL DAMAGE to BUILDINGS
• CHINESE DRYWALL HAZARDS & ODORS
• CONCRETE CORROSION DUE TO HYDROGEN SULFIDE
  
• GAS DETECTION INSTRUMENTS
• HYDROGEN SULFIDE GAS
  • HYDROGEN SULFIDE EXPOSURE EFFECTS
  • HYDROGEN SULFIDE GAS EXPOSURE LIMITS
• METHANE & SEWER GAS HAZARDS
• METHANE GAS SOURCES
• PLUMBING SYSTEM ODORS - home: explore this link to track sulphur odors traced to the plumbing system, drains, toilets, vents
• SEPTIC SYSTEM ODORS - home: explore this link to track sulphur odors traced to septic system failures, septic tank trouble, backups
• SEWER GAS ODORS - home: explore articles at this lik to diagnose sources of sewer gases in buildings from all sources
• SULPHUR & SEWER GAS SMELL SOURCES - home
• WATER ODORS, CAUSE CURE - home: follow this link to correct sulphur odors in the water supply coming from a well or from contamianted hot water heater tanks or similar sources

Suggested citation for this web page

HYDROGEN SULFIDE GAS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ODOR DIAGNOSIS & CURE

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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