Accredited Environmental Technologies, Inc.         





Data Archiving and Management

What's That Smell?  Sewer Gas

Odor Investigations

Standard IAQ Procedures

Health Effects: Odor Threshold of Hydrogen Sulfide

Explosion/Fire Hazards

Case History: Connect the Dots

Inspirational Quotes

"There's nothing common about common sense" Voltaire

"Most people would die sooner than think and they usually do" Bertrand Russell

"If you fail to plan, you plan to fail"
Ben Franklin


  • Shorter is Better
  • Targeted is Better




Data Archiving and Management


Recently, AET was contacted by a lending institution regarding the Phase I ESA that AET completed at a Florida property in Feb. 2005. The lending institution was in a panic since they were restructuring their client's debt and accepting as collateral, the FL property among other assets. The lending institution needed a copy of the report and the lending officer stated that "restructuring would not be achieved if a copy of the report was not available, and if not, a new ESA would have to be completed immediately".


In 2005, AET installed a data management system for our work product. Full copies of report texts are stored on the company server by year and project number. Hard copy files are also maintained. As a result of these data management procedures, AET was able to access the text of the 2005 report while taking the initial phone call. Within ten minutes, the original client was emailed a memorandum to endorse so that the records could be released. The lending institution had a copy of the report text within 20 minutes. Within 40 minutes, a hard copy of the full report had been placed in shipment to the client as requested. AET believes that full service includes data management and that our services do not end at the conclusion of the project.

What's That Smell? Sewer Gas

     Sewer gas is a complex mixture of gases produced by the decomposition/decay of organic household or industrial waste. Highly toxic components of sewer gas include hydrogen sulfide in ammonia. Sewer gas can also contain methane, carbon dioxide, sulfur dioxide and nitrogen oxides. The odor of sewer gas is most often described as a rotten egg smell primarily associated with hydrogen sulfide.

Odor Investigations to Locate/Eliminate Source

     Sewer gas can enter a home or commercial property through open floor drains, leaking or blocked roof vent stacks or through cracks in basement foundations. Odors are often intermittent and correspond to changes in relative air pressures. Building HVAC system operation can create negative pressure within the interior space and draw/accelerate the release of sewer gas. Many of the components of sewer gas are heavier than air and tend to settle/accumulate in basements or the lower level of structures. The methane component is less dense than air and tends to rise in structures.

Standard IAQ Procedures

Check components of plumbing systems for traps (i.e. curved sections that collect water). Water in traps acts as an airtight seal that blocks the odor. Dried out traps allow floor gas to escape. Fixtures without traps should be changed.
  • Check basement floor drains and other potential sources with direct reading instrumentation. Track the septic odor according to strength to its source.
  • Look for abandoned lines, uncapped cleanouts, etc. in crawl spaces.
  • Check the roof to verify the plumbing vents are not blocked with debris, bird's nest, or snow/ice and that the vents extend up through the roof surface. In freezing climates, water vapor passing through the vent can freeze inside the pipe; listen for gurgling sounds.
  • Check locations of plumbing vent discharge for potential re-entrainment into the building HVAC system or a window.
  • Trace the sanitary lines through the building to verify its condition (no rust or corrosion leaks) which could allow sewer gas to escape. Rusting typically occurs along the top portion of the pipe allowing for gas release without the telltale liquid spill.

Keep Water in All Traps

     Water should be added regularly to plumbing fixtures, especially in any sinks, toilets or floor drains which may have dried out. Look for abandoned, infrequently used fixtures; water in the water-seal traps will evaporate. This allows sewer gas and odors to enter your home or business. For seasonal structures or hibernated buildings, use of a propylene based anti-freeze (RV or marine type) in traps, or application of a surface coating of mineral oil atop the water can minimize evaporation rates. Based on the quantities involved, check compatibility with local sewer authorities or on-site systems.

Health Effects, Odor Threshold of Hydrogen Sulfide

     In general, the odor of sewer gas is primarily a nuisance. The extremely low odor threshold (i.e. 10 ppb) of hydrogen sulfide provides the home/business owner a warning to find its source and control gas release. The OSHA PEL ceiling standard for hydrogen sulfide is 20 ppm. A ceiling standard is a concentration that should not be exceeded at any time. Inhalation of low concentrations of hydrogen sulfide can cause eye and upper respiratory tract irritation, cough, headache and nausea. Remember! Hydrogen sulfide is heavier than air, travels along the ground, and accumulates in confined areas... significantly increasing health concerns.

     Don't Rely on Your Nose!

Inhalation of Hydrogen Sulfide at concentrations of 50 ppm or above can cause olfactory nerve fatigue (loss of the ability to smell the gas). A level of hydrogen sulfide gas at or above 100 ppm is Immediately Dangerous to Life and Health (IDLH). High concentrations (>600 ppm) can cause loss of consciousness, respiratory failure and death. Each year people die from entering tanks, vessels, trenches, sewers, manholes, vaults and other confined spaces where hydrogen sulfide has accumulated. See OSHA Standard for Confined Space on AET's website under links.

Explosion/Fire Hazards

     Methane and hydrogen sulfide gas are flammable and highly explosive. Both tend to travel to sources of ignition and flashback. If you suspect this problem, evacuate the area, restrict entry and contact your local fire department for assistance. Avoid creating an ignition source such as a spark from an electrical appliance, switch, match or cigarette lighter.

Case History: Connect the Dots... Intermittent Odor... Intermittent Flush?


: In a past case, AET was contacted regarding an intermittent foul odor within a large commercial office facility. The building was converted from a former office/printing facility to an office-only building complex with multiple tenants. HVAC design incorporated a common air return plenum for each of the tenant spaces. Building construction was slab-on-grade with a single occupied level. The reported concern consisted of an isolated open cubicle area in which periodic odors were reported to occur. No specific time correlation was established for the occurrence.


: Review of the building renovation construction techniques identified several small capacity waste water transfer lift stations associated with kitchenette facilities. AET discovered one vent line for the plumbing in these lift systems was left open within a wall cavity space. This 2 inch vent was concealed within interior drywall partitioning and did not extend through the roofing system. The odor occurred as a result of line pressurization (a flush) during the intermittent operation of the lift systems forcing the accumulated sewer gas out of the piping system and into the wall cavity and ceiling interstitial space. As a result of the common air plenum and open grate returns, the odor migrated into the occupied space.


: Once identified, corrective action was relatively simple, the line was extended up through the roof which allowed venting of the sewer gas to the outdoor environment. Installation required coordination of both plumbing and roofing trades.

Call 800-9696-AET or 610-891-0114 
to discuss any environmental concerns


Alan Sutherland has been a Certified Industrial Hygienist since 1978 with over 30 years of CIH-related environmental consulting experience. He has a Masters Degree in Environmental Science from Drexel University and is the founder/owner of Accredited Environmental Technologies, Inc. (In 1984). He is uniquely trained and licensed as an Environmental Professional in both the field and laboratory. He has been the founder of two AIHA Accredited Laboratories and a mentor to six (CIHs). Mr. Sutherland is also a Certified Hazardous Material Manager. He can be reached directly at 610-891-0114 or email

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