Odor dosing systems

Metal oxide sensor (MOX) for VOC detection
© Fraunhofer IBP
Trained test person analyzing odor-active compounds.

Evaluation of odor intensity by a professional sensory panel

Our experts in “Odor Dosing Systems” focus on the intensity of odors emitted by building products and other materials. Odor intensity describes the relative strength of an odor above the so-called odor threshold. To evaluate odors, Fraunhofer IBP uses its own test persons (sensory panels), who are trained to make assessments using various descriptive verbal and numerical comparison scales.

So-called verbal scales assign intensity values based on attributes. For example, the DIN ISO 12219-7 standard, which is used to evaluate the intensity of odors inside road vehicles, uses a six-point scale graded as follows:

  1. imperceptible odor
  2. slightly perceptible odor
  3. distinct odor
  4. intense odor
  5. highly intense odor
  6. intense and unbearable odor.

When evaluating odors from building products and interiors, comparative scales are used to make an objective assessment: For this, the intensity of odors in the evaluated air is compared with a so-called concentration series of reference odors. DIN ISO 16000-28 employs the pi-value scale (“perceived intensity”) to compare an increasing concentration of acetone, which is presented to the test persons on the panel via a specially-developed odor dosing system.

Fraunhofer IBP uses either a commercially-available system with eight funnels, through which different acetone concentrations are continuously emitted, or a single-funnel system developed in-house that allows different acetone concentrations or pi values to be adjusted individually.

The test persons assign verbal attributes to the pi values, thus enabling the intensity to be assessed as follows:

0-1 pi barely perceptible odor

2-3 pi very faint odor

4-5 pi faint odor

6-7 pi distinct odor

8-9 pi strong odor

10-12 pi very strong odor

> 13 pi extremely strong odor