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3/29/2021 - Odor Surveys and Assessments - 2021

If you ever had an odor or indoor air quality issue within your facility you can appreciate the difficultly in identifying the sources or causes and responding to questions from employees.

Summary of Odor Issues

Wednesday, May 13, 2009
Summary of Odor Issues

If you ever had an odor issue within your facility, you will know the difficultly in identification of a source(s) and cause(s). The following summary and recommendations have proven to be successful in the identification and mitigation of odor sources.

Chemical compounds from chemical products or microbiological activity typically cause odors. Odors can be perceived with olfactory senses even when the contaminant concentration cannot be detected by sensitive analytical instrumentation. Compounds that cause odors can oxidize and change chemically making their detection difficult and / or impossible.

The release of an intermittent odor from an indoor cause and source is generally regulated by a change in its pathway(s) and driving force(s). Driving forces determine the pathway from an odor source. Building pressure, system pressures, temporary or permanent blockages causing pressure build-up, HVAC systems, and the effects of weather conditions on a building are examples of driving forces.

Odors are from sources:

  • external to a building, i.e. not related to a buildings systems, or processes and occupants within a building
  • internal to a building, i.e. related to a buildings systems, or processes and occupants within a building


Outdoor entrainment can occur through:

  • outdoor air intakes
  • uncontrolled leakage due to negative building pressure and / or system pressure

Outdoor causes and sources can be extensive, but general categories include:

  • Vehicle emissions
  • Fugitive emissions from nearby facility(s)
  • Fugitive emissions from other parts of facility
  • Ground gases from soil contamination


Indoor dispersion can occur via the HVAC system(s), and other controlled and uncontrolled airflow, which are caused by many factors.

Indoor causes and sources include:

Building systems

Sanitary sewage discharge and venting systems

  • Re-entrainment of vented gases (methane / hydrogen sulfide), this would tend to distribute odors throughout all areas served by an HVAC unit
  • Breach in vent stack / vent stack joints located within the structure (methane / hydrogen sulfide) intensity of odor would depend on system use, size of breach, draft within vent, pressure differential between vent pipe and surrounding area, back pressure caused by discharge flow volume variations and interception point flow restriction,
  • Broken seals around water closets and urinals
  • Dry or unsealed drain traps
  • Broken discharge pipe resulting in odor accumulation under the slab. Intensity of the odor would vary with building pressure in relation to under slab pressure, cracks in the concrete flooring, floor penetrations for conduits
  • Grease traps that are improperly maintained
  • Insufficient pitch of sanitary sewage lines under the floor

HVAC systems

    • Condensation pan and drain
    • Wet insulation, in duct or mix box
    • Mold growth in the HVAC system and associated ductwork
    • Insufficient or excessive exhaust air
    • Entrainment of kitchen exhaust air
    • Fuel fired boilers

Electrical systems

  • Overheating ballasts with melted insulation
  • New computers or other electronic equipment
  • Emergency generators


  • Breach in roof integrity which would allow water liquid flow and allow for the growth of bacteria and mold in the roofing system
  • Odors from chemicals, tar, and other products used during roof replacement

Windows and walls

  • Water intrusion around windows resulting in hidden mold and bacteria growth and decomposition of materials
  • Water absorption and transfer through brick and mortar resulting in hidden mold and bacteria growth and decomposition of materials
  • Water intrusion around flashing etc resulting in hidden mold and bacteria growth and decomposition of materials

Floor systems

  • Cracks and floor penetrations allowing soil gases to enter the building. Intensity of the odor would vary with building pressure in relation to under slab pressure, cracks in the concrete flooring, and floor penetrations for conduits. Subsurface conditions and or pollution can be a source.
  • Floor penetrations between floors that allows transfer of odors from one floor to another
  • Raise flooring allows for collection of debris and rodents
  • Cabling channels in floor covered with steel plated. May dead end at an odor source, or receive and hold water


Personal hygiene product use

  • Level of personal care
  • Perfumes and colognes


  • Intentional release or application of an odor or irritant causing substance

Food storage

  • Food storage in closets, desk drawers, and waste cans


  • Processing equipment
  • Manufacturing equipment
  • Maintenance procedures / chemicals
  • Housekeeping
  • Trash storage and disposal systems
  • Loading docks

Furniture systems

    • Off-gassing of new furniture
    • Odors from stored or used furniture

In order to assist in the resolution of odor issues, it is beneficial to gather some information first to assist in determining what types of sampling and where the sampling needs to be conducted within the facility. Questions such as the following need to be answered prior to conducting any type of sampling or assessment.

  • When odor is present, what are its boundaries?
  • We know where the odor does not appear?
  • What is the pattern associated with the odors presence?
  • Is odor present above ceilings?
  • What does the odor smell like?
  • Does weather affect the presence or intensity of the odor?
  • Is odor present throughout an entire areas served by an AHU?
  • Is odor present before employee's come into building?
  • Are HVAC systems shutdown overnight?
  • Are there any janitor closets in the areas?
  • Is odor present during the night?


  • Get answers to the above noted questions
  • Begin keeping a log for a few weeks. This might allow us to look back at what was occurring in the building at that time.
  • When odor is present shut down systems and conduct air sampling and olfactory evaluations to identify areas of low and high intensity. This will assist in focusing in on the point source, as contaminants tend to migrate in a rolling fashion from a source.
  • Evaluate air prior to employees coming in to work.
  • Conduct air sampling with various direct reading and sampling media.

Need more information, or a proposal? Please send us an information request.