Odour testing principles
Until today, electronic noses can be fine for measuring odours of the same characteristics, but they are challenged by measuring and comparing odours of widely different nature.
Therefore, odour testing mostly is performed by presenting a product to an odour testing panel (group of testing persons), and then averaging the individual test results.
- The more people are included in the odour panel, the more independent the result will be from individual vote.
- The more the odour panel members will be trained against know odour sources, and selected for individual performance, the more independent the result will be from individual vote.
Odour of a product can be tested in a
- Static test:
The product is placed in a closed canister at controlled temperature and humidity until equilibrium is reached. Odour panellists open the lid, rate the odour, and close the lid again.
GUT odour test (textile floorings),
Austrian ecolabel UZ 56 (for textile floorings only),
Blue Angel RAL UZ 128 (textile floorings).
- Dynamic test:
The product is placed in a ventilated canister or test chamber at controlled temperature and humidity. After a specified time (for simulating ageing of the odour emissions), odour panellists evaluate the exit air of the test chamber, presented as an air stream fast enough that no side-air is diluting the odour when taking a breath.
Danish Indoor Climate Label.
If a VOC emission testing chamber is used, then the outlet air is collected in Tedlar gas bags.
These then are subjected to odour testing by a panel.
Alternatively, special glass chambers can be used that are not suited for VOC emissions testing (chambers of type CLIMPAC or similar). Here the outlet air is evaluated by the odour panel directly.
German BAM placed a description of ISO 16000-28 and VDI 4302-1 techniques in the Web and reported results of a related round robin test that was performed in 2012.
Several experts raise questions on the reliability of such tests, and on the validity of chamber tested odours for odours of the same products after realistic application. This was investigated in a validation project. See also recent discussions in LinkedIn.
Possible scales for rating odours can include one or several of these:
- Odour Intensity (best if rated against known standards)
- Odour Hedonics (character of the odour)
- Odour Acceptance
- The above parameters are treated as independent from each other even though this independency is discussed controversial.
Calibration of an odour panel will occur via selection of the panel members by their individual performance until the response of the total panel responds to expectations.
There is a multitude of units to measure the odour intensity; all of these have different historical background, are not directly interchangeable, and are limited to a distinct testing methodology:
- European Odour Reference Unit
- Application: Odour testing of outdoor air, EN 13725
- Calibration: One European Odour Reference Unit is equivalent to the physiological response from a trained panel to 123 mg n-butanol (CAS-Nr. 71-36-3) evaporated in 1 cubic metre of neutral gas.
- The numerical value of the odour concentration is equal to the dilution factor that is necessary to reach the odour threshold.
- Application: Odour testing of emissions test chamber air, ISO 16000-28.
- 0 pi is equivalent to the odour threshold concentration of an acetone-air mixture (e.g. 20 mg acetone/m³ air) at which 50 % of a trained panel can perceive the odour of acetone.
- 1 pi is equivalent to the perceived odour concentration of an acetone-air mixture of 20 mg acetone/m³ air on top of the baseline of 0 pi.
- Danish semi-quantitative scale
- Application: Odour testing of emissions test chamber air for Danish Indoor Climate Label.
- The sensory evaluation of the material emission is made by an untrained panel of at
least 20 persons, who rate the air quality by marking the acceptability and odour
intensity on continuous scales between 0 = "no odour", 1 = "slight odour", 2 =
"moderate odour", 3 = "strong odour", 4 = "very strong odour", and 5 = "overwhelming
- Olf and decipol
- Application: Odour testing of indoor air, performed mostly at research level. These were used by some researchers at the end of 20th century, but these units still are found in some publications.
- One olf is the sensory pollution strength from a standard person defined as an average adult working in an office or similar non-industrial workplace, sedentary and in thermal comfort, with a hygienic standard equivalent of 0,7 baths per day and whose skin has a total area of 1,8 square m².
- One decipol (dp) is the perceived air quality (PAQ) in a space with a sensory load of one olf (one standard person) ventilated by 10 L/s.
- At least 20 naive (= untrained) panelists individually enter an air space with a measured rate of ventilation and a measured rate of human bioeffluents emissions, and decide whether the air quality was satisfactory or unsatisfactory. A correlation curve of percent dissatisfied panelists against ventilation rate is derived from that exercise.