How can you measure the odor

odor

The sense of smell is an evolutionarily very old sense. Smell impressions can be processed very differently, depending on their quality. We "get used" to most smells very quickly and no longer actively perceive them. Under certain conditions, e.g. B. If a smell is associated with fears or negative feelings, the odor perception can also intensify. That can be z. B. Observe many smells with a warning function (burning smell, smells of mold, rot or decay), but also unusual product smells or chemical smells in rooms can trigger such an effect.

The human nose is a sensitive organ and can detect many substances in extremely low concentrations. The concentration from which a substance is perceived by smell is known as the odor threshold and varies greatly from substance to substance.

There are many sources of odorous substances in interiors. Many cosmetic articles and cleaning agents have fragrances added to them that are supposed to convey a smell of freshness. Furniture and building materials are another source of odorous substances. Some structural damage (water damage, mold, unsuitable product combinations) are also initially noticeable through the smell.

An unpleasant or noticeable smell does not in itself represent a health risk, but can be an indication of problems in the interior (e.g. an overheating electrical device). If a person is permanently and involuntarily exposed to an odor, this can lead to severe annoyance and thus also to health impairments. Anyone who quickly feels disturbed by smells should pay attention to low-odor materials for furniture, furnishings, cosmetics and cleaning agents. Regular ventilation helps to keep the concentrations of odorous substances in the room low.

The Federal Environment Agency has published a guide for dealing with fragrances, which provides further information on the subject.

While there are now established methods for determining the concentration of many air pollutants, quantitative determination of odors is still difficult. There are two main reasons for this:

The human nose perceives a number of odorous substances in extremely low concentrations. This means that it is sometimes significantly more powerful than the most sensitive chemical measurement methods. As long as no better measuring techniques are available, the odor assessment must be carried out by humans.

Since humans do not have an absolute measure of strong, weak, unpleasant or pleasant smells, the smell of a room or a product cannot be assessed by a tester alone. The sense of smell is too individual for that. So many people have to judge the same odor and thus an average value for the odor strength or odor note must be determined. Such measurements are therefore very complex.

Which properties can be assessed for a smell?

Theintensityis a measure of the strength of an odor.

TheHedonicsevaluates the quality of an odor, i.e. it is a measure of how unpleasant or pleasant an odor is.

Theacceptanceindicates how people can deal with a certain odor, i.e. whether it is acceptable or unacceptable.

The odor intensity is the strength of the sensation triggered by an olfactory stimulus. The odor intensity depends on the substance concentration, but can also change significantly due to the type of inhalation / smell. There are two approaches to determining the intensity of an odor:

Intensity determination using a category scale

In this procedure, the intensity is assessed using a whole number based on a seven-point scale from imperceptible (0) to extremely strong (6). Since the test persons rate “freely”, that is to say, everyone decides for himself what a strong and a weak odor is, this method shows a high degree of variation. The intensity determination must therefore be carried out with at least 15 test persons. According to VDI 4302 Part 1, the intensity determination using a category scale is only used for the assessment of indoor air.

Perceived intensity

By using a benchmark, this form of assessment can be carried out with a smaller group of trained examiners (at least 8 people). The comparative standard according to ISO-16000-28 is a device for generating odors with a defined strength. With the help of these comparative smells, the test persons can better assess the odor strength of a building product. The use of the comparative standard thus enables the intensity evaluation to be standardized and should thus lead to a reduction in the spread of the measured values ​​through the standardization of the evaluation criterion. In the current version of the ISO standard 16000-28, acetone is specified as the reference substance for the comparative scale. The result of the evaluation is given in pi, the unit of the perceived intensity Π. Values ​​of 0-4 pi are weak odors, strong odors are present at values ​​above 12 pi.

The method of perceived intensity according to DIN ISO 16000-28 is used to determine the intensity of emissions of odorous substances from building products and interior materials. In addition, this evaluation method is also used for odor tests of indoor air.

The hedonic effect provides information about the annoyance of an odor and is strongly influenced by personal and cultural factors. In general, the rating depends on the situation in which an odor is smelled for the first time.

At least 8 trained or at least 15 untrained examiners are to be used for the evaluation of hedonics. »Trained« examiners means that the test persons were trained according to the method of »perceived intensity« or the intensity assessment with a category scale. The test persons rate the sample air using a nine-part scale from "extremely pleasant" (+4) to "extremely uncomfortable" (-4).

Acceptance is an assessment variable for the dissatisfaction to be expected from room users. The minimum size of an examiner group is 15 untrained examiners. These test subjects are asked the question “Imagine being exposed to the air in this room for several hours a day. How acceptable is the air quality? ”The rating is based on a scale from“ clearly acceptable ”(1) to“ clearly unacceptable ”(-1).

An empirical connection can be used to infer an expected percentage of dissatisfied room users (“percent dissatisfied”, pd) from the measured acceptance. Such pd values ​​are often used for the planning and design of ventilation systems in large buildings.

Facts

Although people are said to have a bad sense of smell, the nose is a very powerful organ.

The nose can perceive a number of substances (e.g. the unpleasant / foul-smelling thiols) more sensitively than sensitive chemical measuring methods. Therefore, not all off-odors in products can be cleared up with chemical analysis technology.

Tips & recommendations

Cleaning and airing are better than scenting. Bad air should not be covered with odorous substances in the office or at home.

When buying furnishings, look for low-odor materials.