Nose Testing

The Nose Knows

Despite best practices and sophisticated equipment, factories occasionally will generate odors that reach local communities and become a nuisance. Why these odors occur and how to prevent them is an issue factories grapple with across the country and around the world. Investigating and mitigating community nuisance odors is a challenge because conventional instrumentation has a limited ability to detect odorous compounds at very low levels.

Professionally trained odor panelists can provide the detection sensitivity and guidance needed to help companies understand and control their industrial odors. These professionals have completed an intense training program (typically about a year long), in which they have learned how to consistently measure the strength and type of odors. Their training includes many hours of practice with odor reference standards that help calibrate them to a standard intensity scale while building their descriptive vocabulary. At the completion of the training, they must pass a rigorous final exam to qualify as a professional odor panelist. Odor panels usually consist of three to four of these professionals.

Facility managers must first ask the questions that will help them discover the source of the problem:

  • When and where does the odor occur in the community?
  • What does it smell like and how strong does it get?
  • How often does it happen and how long does it last?

Odor panelists can provide answers where instruments fail. For example, instruments rarely help measure odors in communities located near factories. Odor panelists often help assess odors in these areas by conducting community odor surveys. During these surveys, they travel through the community assessing and documenting the location, intensity, and character of odors they detect. They record critical weather conditions such as wind speed and direction, temperature, humidity, and cloud cover. Using these data, odor professionals can determine sources and track down a factory that is causing a problem.

Once the site is found, the panelist must sift through the complex maze of odors emanating from various roof stacks, exhaust fans, and fugitive emission sources such as open doors and windows. Even though something smells bad at a plant, it may not be causing a problem in the community. In fact, many odorous emissions at industrial sites never make it to local neighborhoods because of factors such as natural dispersion.

Conventional testing (collecting air samples at each source and analyzing them with instruments, such as gas chromatographs) can sometimes identify what is being released but often fails to measure important odor compounds at levels lower than 1 part per billion. The best way to assess odor emission sources at a factory is to collect air samples and use a professional odor panel to evaluate the intensity and characteristics of odors at various dilutions using a dynamic olfactometer. This instrument provides a known flow of clean air and meters in set volumes of air samples to achieve a range of dilution levels.

This approach creates a number representing the strength of the odor or how many dilutions it takes to reduce the intensity of the odor from the emission source to below known complaint levels. Odor release rates (ORRs) are then generated by multiplying the strength of the odor by the volume of air released at the plant source. Guidelines currently exist to use the ORR to predict if an emission source at an industrial plant is at risk of negatively impacting a local community. For example, if the ORR for a point emission source such as a roof vent or wall fan is less than 1 x 106, it has a low risk of causing odor complaints in a typical neighborhood. However, if that same source has an ORR greater than 10 x 106, it has a high risk of causing odor complaints.

In addition to generating risk potential numbers, odor panelists can smell source samples at various dilutions. Often, an odor changes with dilution and what an emission smells like in the community can be very different from how it smells at the industrial site. Panelists can determine which specific plant sources produce odors that when diluted match those found in the community.

Lastly, the professional odor panel can guide the plant by evaluating odor control technologies as they are applied to various sources on the industrial site. By conducting professional odor analysis on inlets and exhausts to these odor control systems, the panel can determine the percent reduction in odor, and more importantly, the risk of the new emission to cause community odor problems.

Whether a company produces food and beverages, chemicals, packaging materials, or just uses smelly ingredients, the stakes are high. Community nuisance odors can result in a decrease in property values, an increase in health problems, and/or the reduction of a neighbor’s overall quality of life. Sometimes this results in angry telephone calls. In more extreme cases, it can lead to litigation and pressure from government agencies. In worst case scenarios, plants are shut down.

Professionally trained odor panelists can help you understand and control your industrial odorous emissions, and they can help you monitor local communities to ensure that you are not having a negative impact. In addition, they can protect you from being blamed for odors that are not from your plant.

Other EPonline articles on odor:

The Science of Smell

Pima County Wastewater Plant Installs 6 E-Noses

Firm Files Suit Involving Landfill Odors in Ohio

About the Author

Roy Desrochers is the sensory practice leader at Boston-based GEI Consultants, Inc., a geotechnical, environmental, water resources, and ecological science and engineering consulting services firm. Desrochers specializes in sensory analysis related to odor and taste and its practical application to environmental and consumer challenges. For more information, visit

comments powered by Disqus