Black dust

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The fogging effect , also known as black dust or magic dust , is the term for unexplained discolouration of rooms. The effect usually occurs in heated apartments in winter. Flat black coverings that stick to the ceiling or a wall are typical. In severely affected apartments, the effect is similar to the damage caused by a smoldering fire . The word fogging was taken from English for fogging to describe the diffuse deposits.

causes

The causes of black dust or the fogging effect are still unclear. So far, different mechanisms and causes have been suspected.

  • Separation of non-volatile organic compounds (such as plasticizers ) that escape from building materials, electrical cables, packaging materials and furnishings and combine with dust and soot particles to form a greasy film. In order to be able to advertise their products as “solvent-free”, manufacturers use non-declarable, non-volatile organic substances as solvent additives. Electronic devices or cleaning agents are also gradually emitting chemical components that are suitable for black dust into the surrounding air; cosmetics, deodorant sprays, hairsprays and kitchen fumes can also be used as emitters .
  • Condensation of condensable volatile organic substances on cold walls.
  • Migration of chemical material additives to the component surface with the formation of a sticky film, which also holds on to dust.
  • Adhesion effects, dust floating in the air and other particles stick to damp component surfaces. However, not all particles form permanent bonds. Particles previously held by water molecules loosen during drying and fall off (or are carried away with the air during ventilation).
  • Sorption of pollutants on fibers or mineral granules that have a large surface area or large absorbency.
  • Effects of thermophoresis , a specialty of aerosol physics .
  • Cold carbonization.

Delimitation and superimposition with other similar effects

  • The phenomenon of black dust is usually not with the occurrence of black mold spores associated, but sometimes confused with, or "lumped." However, the effects can overlap, as both occur on cold components. Black mold thrives on walls that are damp as a result of thermal bridges . Condensation of air humidity leads to an accumulation of moisture in the interior plaster and on wall paints , the mold fungi "consume" organic components of the paints. Mold growth can be identified or ruled out by means of a microbiological examination.
  • A gray veil on the outside of window lintels when the apartments are opened by smokers for ventilation should not be regarded as a black dust effect. True fogging occurs in both smoking and non-smoking apartments.
  • Because they cannot be detected in all cases, industrial and traffic emissions, soot deposits from stoves, chimneys, candles, torches or fires, tobacco smoke, ammonium salts and abrasion from carbon electrodes are usually excluded .

Semi-volatile organic compounds

Fogging over socket

According to a statistical study by the Federal Environment Agency (1996), this black coloration was found almost exclusively during the heating period in apartments that had previously been renovated or newly occupied. In 34% of the cases floor work (including carpet laying) was carried out, in 52% painting work. The vapors were associated with non-volatile organic compounds (SVOC = "Semi Volatile Organic Compounds"), they mainly come from building products such as paints, varnishes, wallpaper , coffered ceilings made of Styrofoam, radiator varnishes , laminate floors , PVC panels and insulating foams , electrical cable sheaths and Foils. Production errors have become known, for example, through which oily plasticizers leaked out of installation cables in large quantities (“sweaty cables”).

Other sources are carpeting with a back made of foamed styrene-butadiene rubber , wood imitation panels and plastic decorative panels as well as various adhesives , e.g. B. of floor coverings and plastic surfaces of furnishings and furniture (see the article indoor air ). In the case of various materials (e.g. plastic wallpaper), such low-volatile organic compounds can migrate to the surface and thus form an adhesive film.

Plasticizers, various phthalates such as bis (2-ethylhexyl) phthalate (DEHP) or dibutyl phthalate (DBP), are often found in house dust because they are used frequently and in large quantities (annual production in Germany was around 400,000 tons in 1993) The proportion of plasticizers in PVC products (floors, coatings, tablecloths, shower curtains, vinyl foam wallpapers, etc.) can be up to 70%. However, plasticizers are also contained in food (as an impurity); the risk is controversial.

Sometimes volatile organic compounds accumulate on other dusts (soot particles from chimneys, dust particles in the air drawn in from the garage).

history

According to the Federal Environment Agency, the effect was unknown before 1995 and has only been widely noticed since a questionnaire by the Federal Environment Agency in 1997/98.

Federal Environment Agency

Since the Federal Environment Agency (UBA) is sticking to the term “fogging effect”, further investigations into the complex of terms are to be expected, and it is unlikely that the observation of the phenomenon (if it is more of a psychological effect) will decrease in the near future becomes. Despite years of preoccupation with the phenomenon, experts at the office did not want to disclose any information on how to prevent the effect, as so far not even preventive measures could be verified (let alone the failure could be explained). The UBA sees thermophoresis as only a minor contribution to fogging, if at all. The topic has passed since the 2010s.

Cold carbonization as a hypothesis for the formation of black dust

During the examination of an affected apartment, indications of “cold carbonization” were found as a possible cause. Such an effect has been described as an explanation for the smog catastrophe in the London fog in 1952. The "cold charring of paper" caused by concentrated sulfuric acid is clear . There were ideas about mechanisms similar to those used in the production of biochar .

If the hypothesis of “cold carbonization” applies as a possible cause of fogging and extremely hygroscopic aerosols play a role in the formation of black dust, this effect would have to occur on human tissue. In this case, living with an unsolved fogging problem would (contrary to the statement by the Environment Agency) involve considerable health risks, especially for lung diseases.

Thermophoresis as a hypothesis for the formation of black dust

Dust particles or aerosol particles are subject to thermophoresis, among other things. This means that they move in air from a warm area to colder zones and separate there. This applies to all types of suspended particles that are in the room air. In a normal apartment this is between 1000 and 5000 particles per cubic centimeter. Above warm heaters and just below the ceiling, the temperature difference between the air and the wall is particularly large, so that the effect is most evident there. The deposition of soot in a fire is largely due to the temperature gradient between the room air and the wall, i.e. through thermophoresis .

Temperature differences are particularly large at thermal bridges. For example, iron girders or other metal objects that are insufficiently insulated on the side of the room will appear colored on the wall after a few years in external walls. This can be confused with the black mold spores already mentioned.

The discoloration effect occurs preferentially in winter because the walls are particularly cold and the heating systems are particularly warm. Whether the fogging effect is more or less visible depends on how an apartment is used. In particularly warm and constantly used apartments, it should be clearer than in less frequently used and cooler living spaces. Naturally, the air in smoker's apartments contains far more aerosol particles than that of non-smoking apartments. Candles and other open fire sources also produce a lot of particles and more fogging.

Basically, this effect has been known for a long time. The Federal Environment Agency has made modern building materials responsible for the increased and changed occurrence (sticky deposits instead of easily removable dust) since the 1990s. Instead of using highly volatile solvents, they are often equipped with non-volatile organic compounds. There are also plasticizers in plastic products and possibly the increased use of oil lamps and candles. According to the UBA theory, these substances combine with the "normal" dust in the room air and thus cause the black deposits. Even slight oversaturation of the chemical from a building material is sufficient, for example in the air above radiators on the cooler wall, to lead to condensation of the chemical on the particle surface (heterogeneous condensation).

Evidence for the thermophoresis of aerosol particles

Dust deposit in a corner of the room

The first picture shows dust particles separated by thermophoresis in a corner of a room. The left and right walls are papered outside walls and accordingly cold. The top is a painted concrete ceiling. The temperature gradients (greatest temperature gradient) do not point exactly to the corners, but to the wall surfaces just in front of them. Because the dust particles follow the temperature gradient with their thermal movement, the deepest corners remain lighter than the directly adjacent wall surfaces.

Dust precipitation on a hidden thermal bridge

Thermophoresis often makes hidden thermal bridges visible . The second picture shows a build-up of dust on the outlines of a walled-in metal housing. There used to be a fan in this wall. The residents removed the fan and walled up the opening. Its continuous housing remained in the wall and dissipates heat to the outside. Thermophoresis separates dust particles from the wallpaper exactly at the metal edge. The blackening can be easily removed with an eraser, which is an important distinguishing feature between normal dust deposits and fogging or black magic dust. These deposits cannot be removed by wiping or erasing.

Dust precipitation from the room air on filters

Dust particles in the room air are black , as are the fogging patterns on the wall. The third picture shows filters from a dust collector through which between 0.5 m 3 and 10 m 3 of air from a living room has flown.

Other effects of thermophoresis

Especially at the end of winter, a film of dirt can be observed on the inside of window panes. These are dust and aerosol particles deposited on the cold pane by thermophoresis. This film is particularly visible on panes with poor thermal insulation , such as those found in old apartments, shop windows or cars.

Some sampling devices for dust particle analysis even separate particles from air samples by thermophoresis. Such a device is called a thermal precipitator .

Other causes of fogging

There are other effects of dust separation that can play a role in fogging. This includes the electrical charging of wall surfaces. Electrostatic fields separate dust particles that are electrically charged or polarizable . This applies to most aerosol particles in indoor air. Electrostatic fields on wall surfaces are quite rare. They occur, for example, on moving curtains or when a wall is rubbed in some other way.

The separation of dust on the picture tube of older television sets is quite drastic. The picture tubes of newer televisions or computer monitors are hardly charged. Older picture tubes clearly show that the covering originates from the room air. Many aerosol particles are naturally radioactive because they carry radon decay products . They accumulate on the picture tube to such an extent that the radioactivity can easily be measured (although this could also come from the screen color bodies made of rare earth compounds). Since fogging is said to have occurred more frequently after renovations, low-volatility organic compounds from paintwork and coverings, for example through the evaporation of plasticizers, are accepted.

Prevent fogging

Black dust precipitation cannot be completely avoided because the possible separation mechanisms are natural physical effects that are not caused by environmental toxins or the like. In order to largely reduce the effect, temperature differences between the room air and cold surfaces must be kept as low as possible. This can be achieved through larger heating surfaces with a lower temperature or through even heating of the apartment. The room temperature should not be lowered below 17 degrees Celsius. In this sense, underfloor or wall heating is ideal.

A lower dust content in the room air would keep the walls cleaner. If an apartment is not cleaned regularly, black dust precipitation will increase. Regular cleaning of the apartment ensures clean floors and radiators. This in turn means that the dust is not thrown up the wall due to the heating. The wall stays clean.

If the effect is based on the vapors of non-volatile organic compounds and these have health effects, these substances should not be used. The room air can also be kept cleaner if smoking is avoided and only soot-free candles are used (even if these emissions should not lead to fogging). Only the elimination of the stress factors can lead to an exposure sstop; a full declaration of all ingredients of a component or building material, but also of cleaning agents and utensils, would be helpful.

Tenancy law issues

Since the causes are of a complex nature, the tenancy law question of who is responsible for the damage is even more difficult to answer than in the case of mold and depends on the individual investigation. According to the views of the Berlin and Ellwangen regional courts and the Federal Court of Justice , there should be a lack of rent .

In 2008, the Federal Court of Justice classified the possible causes (equipping the apartment with a customary carpet, painting the walls with customary colors and cleaning the windows in winter) as "contractual use of the rental property" based on an expert opinion.

literature

  • Fogging. In: Wolfgang Isenmann, Ralf Adam, Günter Mersson: Moisture phenomena in inhabited buildings. Verlag für Wirtschaft und Verwaltung H. Wingen, Essen 2008, ISBN 978-3-8028-0560-8 , p. 49ff.
  • Heinz-Jörn Moriske, M. Wensing: New research results on the phenomenon of "black apartments". In: Hazardous substances - keeping the air clean. No. 9, Springer-VDI-Verlag, Düsseldorf Sept. 2001, p. 387ff. (PDF; 409 kB) ISSN  0039-0771
  • Umweltbundesamt Berlin (Ed.): Attack of the black dust - The phenomenon "black apartments". Federal Environment Agency, Berlin, August 2004.

Web links

Individual evidence

  1. ↑ UBA study on the phenomenon of "black apartments" (PDF; 596 kB)
  2. ↑ What causes the fogging effect? , at labor-melzer.de
  3. ^ Gerhard Führer: Fogging: Chemistry in the interior becomes visible. In: The expert. July-August 2003, PDF file ( Memento of the original dated November 5, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed July 5, 2019. @1@ 2Template: Webachiv / IABot / www.peridomus.de
  4. ↑ labor-melzer.de: The fogging effect is a multifactorial problem
  5. ↑ Guide to the prevention, investigation, assessment and remediation of mold growth in interiors, Federal Environment Agency , PDF file , accessed on July 5, 2019.
  6. ^ Gerhard Führer: Fogging: Chemistry in the interior becomes visible. In: The expert. July-August 2003, PDF file ( Memento of the original dated November 5, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed July 5, 2019. @1@ 2Template: Webachiv / IABot / www.peridomus.de
  7. ↑ UBA study on the phenomenon of "black apartments" (PDF; 596 kB)
  8. ↑ Daniel Krull: So many particles come from laser printers. NDR report
  9. ^ [German] Federal Environment Agency for Man and the Environment: Phthalates, the useful plasticizers with undesirable properties. PDF file , accessed July 5, 2019.
  10. ^ LG Bonn · Judgment of June 2, 2004 · Az. 13 O 5/03
  11. ↑ labor-melzer.de: What causes the fogging effect? .
  12. ^ Gerhard Führer: Fogging: Chemistry in the interior becomes visible. In: The expert. July-August 2003, PDF file ( Memento of the original dated November 5, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed July 5, 2019. @1@ 2Template: Webachiv / IABot / www.peridomus.de
  13. ↑ Detlef Wölfle: Risk assessment of plasticizers in vegetable edible oils (PDF; 268 kB)
  14. ↑ "Plasticizers" in the human body
  15. ↑ Plasticizers and flame retardants ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.svb-blessing.de
  16. ↑ Tappler, Damberger, Twrdik: Determination of causes and analytical procedures when black dust pollution (fogging) occurs in buildings. In: Mushrooms in the interior. Pp. 69-77.
  17. ↑ Cf. on "Fogging" from a legal point of view, the articles by Hitpaß, Haugg ( ZMR 2002, 337) or Isenmann ( WuM 2001, 428) and Moriske (NZM 2000, 894)
  18. ^ LG Berlin ZMR 2003, 489
  19. ↑ ZMR 2001, 544
  20. ↑ juris.bundesgerichtshof.de
  21. ↑ The tenant is entitled to an advance payment for the removal of black dust deposits ("fogging"). Article on the BGH judgment. May 29, 2008. Retrieved November 14, 2012 .