Before we start

What does an odour assessor actually do?


14 November 2017

If something literally stinks to high heaven, then it’s time to call on odour expert Thomas Liebich. The TÜV NORD expert explains in this interview why the job doesn’t involve his nose and how you can dilute a stench.

#explore: What does an odour tester actually do?
Thomas Liebich: There are odour testers and odour assessors. The odour testers are the subjects, who act, as it were, as our noses. My job, on the other hand, is that of odour assessor. I carry out odour measurements and write reports on issues that have to do with smells. If you want to operate a plant in Germany, regardless of its size, you have to stick to a sophisticated set of rules and get permission, just like anyone who wants to build a house needs planning consent. And if the plant releases emissions, which, in layman’s terms, are things like gases or dust, then the application for a permit also requires you to submit an odour assessment, whose purpose is to clarify whether the emissions are within official tolerances or if measures are needed to counteract the stink. Existing plants also need to be monitored – and we perform the necessary regular measurements. Court proceedings are a third important element. In this context, we help resolve questions like is there an unreasonable level of odour pollution in a room? Is an item of furniture responsible for this odour? Or has a renovation failed?

“We don’t look for supernoses that are capable of distinguishing between the most subtle nuances; all we need is a tried-and-tested average European nose.“

Thomas Liebich

#explore: How do you actually measure smells?
Thomas Liebich: Smells are still measured using your nose - in our field there aren’t any technical innovations that can relieve us of this job. We basically only measure the strength of the smells. To do this we work with dilutions. To start with, the subject is exposed to a highly diluted version of the odour, which becomes stronger and stronger until the tester says: Stop, now I can smell something. Conversely, what this means is that the more we have to dilute the smell until it is no longer discernible, the more intense it is. To capture the smells in the first place we work with bags made of the same material as completely normal oven bags. When we get to the site we use these bags to trap air from flues, exhaust gas scrubbing plants, open surfaces and other sources. We then take them to the odour laboratory and work with the subjects to assess them. It’s a similar principle to working with hazardous substances - in these cases you also analyse samples, such as dust, in the lab.

#explore: Do the noses of your subjects have to be as good as those of a parfumier?
Thomas Liebich: No, not at all. We don’t look for supernoses that are capable of distinguishing between the most subtle nuances; all we need is a tried-and-tested average European nose. If you want to become a subject, you need to pass a whole raft of tests with standard odorants and have a sense of smell that lies in a particular range. Our “noses” also need to be able to pick up the odour once it has been lost. The values need to lie within a pre-set spectrum so that the results don’t differ too much from one nose to the next. I’m a certified subject myself but only use my nose to gain an impression. This is especially the case if we aren’t working in the lab but are out on site, for example on a field. I then head up the measurement team and use my nose at the same time.


Thomas Liebich has been responsible for odour assessments at TÜV NORD for the last 25 years. “I always used to take little forays into other fields of work, but the focus of my job has always been on smells,” says the expert.


TÜV NORD helps plant operators identify the causes of odour emissions. The experts also offer advice on measures to reduce odours and draft court reports on cases of odour pollution. You can read more about the odour investigations, technically known as olfactometry, here.