UNI EN 13725:2022 : how did the standard change?

Detailed study
26 January 2023

News on fixed source emissions and the determination of odor concentration and flow rate by means of dynamic olfactometry

As of March 17, 2022, standard EN 13725:2022-replacing EN 13725:2004-came into force, which defines in detail how to determine odor concentration and flow rate with the help of human evaluators

Let us have a closer look at details tounderstand what has changed with the updating of thestandard


What is UNI EN 13725:2022 defining?

UNI EN 13725:2022 is a European technical standard that explains the method to be used for determining the concentration and flow rate of an odor sample with the help of human evaluators. This method is based on the concept that odor concentration is proportional to the number of dilutions an odor sample must undergo, in order not to be perceived any longer by a panel of selected examiners.

According to this standard, the most effective "tool" for assessing odor emissions is the human nose.

Therefore, to obtain a result as numbers, it is necessary to use:

•an olfactometer: an instrument capable of diluting an odor sample, collected in a special bag, with neutral air;

•selected examiners: suitable persons according to very specific requirements described in the standard, who distinguish themselves because they have an average and constant olfactory sensitivity over time with respect to a reference odor.

It also enhances the method for determining the odor rate of fixed source emissions, thus excluding measurement in ambient air and referring specifically to:

•point sources (piped or ducted emissions);

•active areal sources (e.g., biofilters).

The primary purpose of this standard is to provide a common basis for the assessment of odorigenic emissions.

Summary of the new standard features

As a summary, changes introduced by the new standard EN 13725:2022 cover the following aspects:

  • revision of the scope of the standard;
  • compilation of sampling plan by the customer;
  • possibility of using a secondary odorizer in addition to n-butanol;
  • revision of materials allowed for olfactometry equipment;
  • performance of leak tests prior to the use of bags with sample;
  • definition of temperature and relative humidity ranges;
  • specification of uncertainty calculation method and detection thresholds;
  • request to avoid temperature changes during sampling;
  • approvalof collection of "blank" samples.

UNI EN 13725/2022 : major changes

Let us have a look at more details of the main changes introduced.

Standard purposes: which ones have been excluded

The update of standard EN 13725:2022 excluded the following purposes:

  • direct olfactometry;
  • static olfactometry;
  • determination of odor flow rate from volumetric sources (emissions from building doors, windows, naturally ventilated ducts);
  • determinationof odor rate from fugitive sources (emissions that are difficult to detect andquantify, originating from tank vents, valve leaks, etc.).

Sampling plans: expected to be established by the customer

It is required to draw up customer-endorsed sampling plans according to UNI EN 15259:2008 "Air quality - Measurement of fixed source emissions: requirements for measurement sections and sites, as well as purpose of the measurement report plan."

But what is meant by sampling plan? 

Thesampling plan is a form containing themain information about the sampling points. 

In fact, having a clear picture ofthe characteristics of the plant, before starting the activity, makes itpossible to operate safely and use the appropriate instrumentation (e.g., inthe presence of high temperatures, accessibility of sampling points).

Secondary odorant in addition to n-butanol

Provision is also made for the laboratory to have a SROM (Secondary Reference Odor Mass), which is a second reference odorant in addition to n-butanol, the primary odorant.

Materials for olfactometry equipment: glass and rubber prohibited

Permitted materials for olfactometry equipment have been revised. 

As specified in the previous version of the standard (discussed in this Geonose blog article), materials used for sampling must comply with given requirements. Currently, the sample is collected in bags using instrumentation made of plastic material.

The EN 13725:2004 standard also provided for the use of other materials, such as:

  • aluminum;
  • glass;
  • titanium, only for static hoods;
  • stainless steel, only if properly passivated to avoid interactions with H2S. 

On the other hand, UNIEN 13725:2022 does not allowthe use of glass, while rubber remains prohibited.

New bag and sampling line leak tests

It is planned to perform:

  • leakage tests on the bags containing the sample before use;
  • integrity testing of the sampling lines.

Temperature and relative humidity ranges defined by the standard

Temperature (T) and relative humidity (RH) ranges within which to carry out analyses have been defined. 

The temperature cannot exceed or be 2 °C below the set-point temperature, which must be >21 °C in any case.

Relativehumidity must range from 20to 80%.

Calculation of uncertainty and detection thresholds: calculation method

The calculation method of uncertainty and detectability thresholdsLoD (limit of detection or detectability) and LoQ (limit of quantification) isexplicitly stated.

Condensation inside the sample bag: avoid temperature variations

Condensation inside the bag should be avoided during sampling and transport in order not to affect the odor load of the sample.

Itis no longer necessary to keep the sample below 25 °C, but it has been morecorrectly required to avoid temperature variations that may cause condensation inside thebag.

In the case of sources with particularly high temperatures, ormoisture-laden effluent, the sample is diluted with neutral air or nitrogen

“Blank" sample collection approved.

It isplanned to collect "blank" samples, called field blanks, every yearand for each type of sampling instrument used. What isa field blank?

Thefield blank is a sample that is retrieved before and after sampling takes place, in order to quantify anyodorigenic contamination due to the sampling line used, and verify its linearity over time.

How to apply the standard correctly

The RSE guidelines - which LOD helped drafting - are usefulrecommendations for the properapplication of UNI EN 13725:2022.

In particular, aspects related to sampling and technicalcharacteristics of the instrumentation to be used when performing olfactometrictests are taken intoconsideration.


Dynamic olfactometry: LOD accredited laboratory

LOD is accredited by ACCREDIA according to the UNI CEI EN ISO/IEC 17025:2018 standard for the performance of tests to determine odor concentration by means of dynamic olfactometry.

Dynamic olfactometry is the only internationally accepted methodology for measuring odor concentration.

It is regulated by Technical Standard UNI EN 13725:2022 "Fixed source emissions - Determination of odor concentration by dynamic olfactometry and odor flow rate", which we discussed in previous paragraphs.


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LOD: Laboratorio Olfattometria Dinamica

Spin-off dell’Università degli Studi di Udine