Odour Measurements

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odour measurements


For sectors such as composting, food factories or waste water treatment, the management of odour as a side-product, and an awareness of the impact it can have on the local environment, is an important factor in the smooth running of the business. Odour measurements concentration is a key component to this process. The US, Australia and Europe now have regulations in place as part of a growing environmental concern to standardise the ways in which odours are measured and controlled. 

Silsoe Odours Ltd has over two decades of experience in odour analysis and management. Our team of odour scientists can provide the data and guidance you need to assess whether odour pollution is a problem, and implement effective odour controls where necessary.

We use the odour concentration measurements that comply with the European Standard BSEN13725:2003


Odour Measurements – What is Olfactometry?

This is a process used to measure odour concentration. Olfactometry determines concentration of an odour in an objective way.  The intensity, quality and hedonic tone are purely subjective and emotional responses.

The Olfactometer.

The Silsoe Odours laboratory uses a panel of six selected and screened human subjects in the process of determining the odour concentration of a gaseous sample of odorants. The odours are presented to the panel using an olfactometer; a device that dilutes the odorous sample to a known concentration for presentation to the panel. Our odour laboratory uses a ‘forced choice’ olfactometer which has two outlet ports. The diluted odour flows through one of the ports and odour-free air flows through the other.

The test subjects are presented with samples which vary in their concentration by being diluted with odourless gas. This allows us to determine the dilution factor at the 50% detection threshold (Z50 ≡ Z ITE.pan).

At that dilution factor the odour concentration is 1 ouEm-3 by definition. The odour concentration of the examined sample is then expressed as a multiple (equal to the dilution factor at Z50) of one European Odour Unit per cubic metre [ouEm-3] at standard conditions for olfactometry.


Odour measurements concentration begin by introducing a dilution of the sample large enough to make the odour so dilute that it is below the detection thresholds of the panel members. We then increase the concentration by a factor of about 1.7 in each successive presentation. Throughout this process the olfactometer port carrying the odorous flow is selected randomly by the control sequence. The assessors are asked to note, on a personal keyboard, which port is carrying the odour, and whether their choice is a guess, inkling or they are certain. The only responses considered to be ‘TRUE’ are those where the correct port was chosen and the assessor claims certainty in making that choice. The process is required to continue until each panel member has registered two TRUE responses.

The individual threshold estimate (ITE) for each panel member is determined through the geometric mean of the dilution factors of the last FALSE and the first of at least two TRUE presentations. The geometric mean of at least two ITEs for each panel member are required to calculate the odour concentration, ouEm-3, for a sample.

The resulting concentration is expressed in units of European Odour Unit per cubic meter (ouE/m3).



Professional accreditation means that our customers can have full confidence in the accuracy of our laboratory testing results, the proficiency of our odour assessors and analysts, and the integrity of our methodology.


ISO 17025


The Silsoe Odours laboratory is fully compliant with European standard BS EN 13725 performance criteria.

View our Schedule of Accreditation 

ISO 17025 Accreditation maintained

Silsoe Odours laboratory was the first in the UK to gain UKAS accreditation for odour concentration measurements by dynamic olfactometry to BS EN 13725:2003. Our surveillance visit in 2017 was successful in maintaining our current accredited status for a further 12 months.

We were pleased to receive the following feedback from our assessors:

“Once again, the way in which the activities witnessed were carried out, the knowledge of the staff employed and the performance in the external proficiency scheme…gives confidence in data produced.”

If you need help and guidance with Odour Measurements, call our team today on 01525 351 396.

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