Industrial Odor Measurement: How to Interpret the OUE/m³ Value?
Introduction
One of the most frequently asked questions during environmental inspections is: "What is our odor value — are we compliant?" To answer this, you first need to understand what the OUE/m³ unit means and how it is measured.
Many facility managers try to assess their odor situation by looking at whether stack emissions are visible or by gauging the volume of nearby complaints. Yet odor measurement is an entirely different science — and the results may surprise you.
What Is OUE/m³?
OUE/m³ stands for "Odor Unit per cubic meter" and is a unit of measurement defined by European Standard EN 13725. It is also the reference unit used in Turkey's environmental legislation for industrial stack emissions.
By technical definition: 1 OUE/m³ is the dilution ratio at which an odor sample is just barely detectable by the human nose. This means a value of 1,000 OUE/m³ indicates that the odor must be diluted one thousand times before it becomes undetectable.
The higher this value, the more intense the odor — and the harder it is to dilute.
What Is the Legal Limit in Turkey?
Under the Regulation on Control of Industrial Air Pollution (SKHKKY), the stack emission odor limit for industrial facilities is set at 1,000 OUE/m³.
Facilities that exceed this threshold may face:
- Administrative fines
- Loss of environmental permits
- Suspension of operations
- Legal proceedings due to complaints from neighboring communities
How Is Odor Measured?
Unlike standard emission measurements, odor measurement is carried out in a laboratory setting using a human panel. This method is called olfactometry.
The process consists of the following steps:
- Sample Collection — Gas samples are collected from the stack or source into specialized sample bags (Tedlar or Nalophan) by accredited measurement firms.
- Olfactometer Analysis — In the laboratory, a trained panel (minimum 4 people) smells the sample at different dilution ratios to determine the detection threshold.
- Calculation and Reporting — The OUE/m³ value is calculated from panel data using statistical methods, and an accredited report is produced. This report serves as an official document in environmental inspections.
Typical OUE/m³ Values by Sector
Typical values measured at stack outlets across different industrial sectors are as follows:
- Feed mill (rendering process): 3,000 – 10,000 OUE/m³
- Slaughterhouse and meat processing: 2,000 – 6,000 OUE/m³
- Textile dyehouse: 1,500 – 4,000 OUE/m³
- Wastewater treatment plant: 1,000 – 5,000 OUE/m³
- Plastics and rubber processing: 2,000 – 8,000 OUE/m³
- Food processing (general): 500 – 3,000 OUE/m³
As these figures show, the starting values in the majority of these sectors are 2 to 10 times above the legal limit — requiring significant system capacity for effective odor removal.
Factors That Affect OUE/m³ Values
Even within the same facility, odor values can vary considerably throughout the day. The main factors driving this variation are:
Raw material quality: Particularly in facilities using animal-based raw materials, the freshness of the input directly affects odor intensity.
Process temperature: Higher temperatures release more volatile organic compounds, driving odor values up.
Weather conditions: High humidity, low wind speed, and temperature inversions increase odor dispersion. Complaint risk reaches its peak under these conditions.
Production capacity: A facility running at full capacity generates significantly higher odor values compared to partial capacity operation.
How Does an Ozone System Reduce OUE/m³ Values?
Ozone (O₃), with its powerful oxidizing properties, chemically breaks down odor compounds. Sulfur-based compounds (H₂S, mercaptans), nitrogen-based compounds (ammonia, amines), and fatty acids react with ozone and are converted into odorless end products.
In the systems we implement at OCS Ozon, we commit to bringing stack outlet OUE/m³ values below the legal limit of 1,000 OUE/m³. To achieve this, we first map the facility's odor profile, then determine the appropriate ozone dose and application method.
Conclusion
The OUE/m³ value is both a legal requirement and a critical indicator of environmental neighborliness for industrial facilities. Facilities operating with high odor values face risks of fines, shutdown orders, and reputational damage.
If you do not know your facility's current odor value, the first step is to commission an accredited measurement. At OCS Ozon, we offer free consultancy on navigating the measurement process and designing the right system based on the results.