Odour testing

Several factors must be taken into account when performing an odour test as the tests themselves are subjective, and, as the perception of odours within a population is also subject to considerable variability, the test must be carried out by several testers (a so-called “odour panel”) in order to obtain a statistically validated odour assessment. The ‘odour panel’ must be able to verify that an odour is present, and also what type of odour it is. Furthermore, they must be able to determine the intensity of the odour and whether it is disturbing or not.

The GUT odour test is carried out in accordance with the Swiss standard (SNV 195651) for determining the disturbance (nuisance) level of the odour of textiles. A circular sample of material approx. 144 cm² is stored for at least 15 hours in an airtight desiccator (with an approximate volume of 2L)  and held at 37°C with 50% relative humidity. The air humidity is adjusted using a saturated magnesium nitrate solution (approx. 100 ml). Under these conditions, at least 7 (preferably 9) testers are asked to assess the nature, intensity and disturbance of the perceived odour by briefly opening the desiccator. The intensity of the odour is graded on a scale from 1 (no odour) to 5 (very strong odour). Whether an odour is perceived as disturbing or not is also graded on a scale from -3 (very disturbing) to +3 (not disturbing). After a tester has made a judgement, the desiccator must be closed again and kept under the previously described conditions for at least another 30 minutes. The test is considered to have been passed if the mean value of the assigned intensity grades is at least grade 3 and the odour is classified as not disturbing on average.

Geruchsprüfung für textile Bodenbeläge

Within an interior, there are typically three different odour types each with specific causes which can be identified, and which are directly related to the installation of textile floor coverings:

Odour profile 1: There is a “New odour” immediately after installing a new floor covering which diminishes over time and within a few weeks.

Cause 1: The familiar “new odour” of textile floor coverings can largely be traced to emissions that may arise due to the application of coatings onto raw materials during production. These by-products are substances which are easily detectable during an investigation into VOC’s. GUT has defined limit values which are below the respective odour threshold (see VOC emissions) for these substances.

Odour profile 2: An odour that is only noticeable after a few weeks or months and which develops into a persistent, partly weather- and temperature-dependent, basic odour. In most cases, the odour does not subside.

Cause 2: If old adhesive is not completely removed or the new substrate is insufficiently primed, a delayed degradation reaction may occur after application of the new adhesive. This produces so-called secondary emitters (mainly aldehydes), which have a strong inherent odour even in low concentrations.

Odour profile 3: A typically unpleasant odour with a slightly acidic, pungent base note and which does not have a clearly perceptible decay behaviour. This type of odour will spread and develop further over time.

Cause 3: In this case, once the indoor air is analysed, isododecenes are often detected and whilst it has been found (cf. Schmidt, 2018; Vankann, 2018) that they themselves do not contribute significantly to the overall odour, they are a good indicator that degradation processes may have taken place in SBR ? polymers. Therefore, the odour is influenced by a number of partly unstable precursors (sulphur compounds) or degradation products (aldehydes, alcohols, acids).

Further information on the three odour patterns described and their causes can be found in the article “Störgerüche in Innenräumen – Beispiel textile Bodenbeläge“

During new build and refurbishments, many different types of materials are used, and a typical “new building or refurbishment smell” cannot be avoided. However, these odours usually fade after a short time as they are replaced with other odours which develop as the building is used.

One reason for the recent increase in odour complaints is due to the fact that many buildings are constructed to be ‘airtight.’ in an effort to reduce energy, however this is also often accompanied by a hygienically inadequate air exchange. Most odours can be effectively reduced and eliminated by ensuring there is correct and adequate ventilation. Many new products contain olfactorily active substances, whose initial concentrations are high before diminishing over time. In these cases, a sufficient air exchange will minimise the odour and significantly its reduction.

Experience shows that new odours from textile floor coverings, used in areas with appropriate ventilation, decrease significantly after the first four weeks and thereafter barely perceptible if at all.

If there is an unpleasant odour following the installation of a new textile floor covering, the carpet can be examined to establish the cause. Not all unpleasant odours are directly attributable to a defect in the floor covering supplied

Experience has shown that there are essentially three causes of unpleasant odours as described previously.

If you have further questions, please contact our office in Aachen directly:
Tel. +49 241 96843411
E-mail: mail@gut-ev.de

Odour testing for textile floorcoverings is an important addition to standard chemical analysis during laboratory tests. Despite testing methods being constantly optimised, the data obtained does not usually adequately reflect the whole situation. This is because, although the human sense of smell is less developed than that of other mammals, it is still sensitive enough to detect numerous odour-active substances present in concentrations below those limits which would be detected during analysis. This is particularly prevalent with odours relating to complex mixtures of substances. In principle, the following applies: an unpleasant odour does not necessarily mean increased VOC’s (volatile organic compounds) emissions and conversely, if the limit value for VOC’s is exceeded, it doesn’t necessarily mean that there is an unpleasant odour present.