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Last changed: 24.08.2011
The average person in Central Europe spends today about 90% of his or her time indoors. Humans breathe 10-20 m3 of air daily depending on age and activity level. This volume is equal to a mass of 12-24 kg of air which is far more than a person’s daily intake of food and water! It is therefore important that precautions be taken to ensure good indoor air quality. This requires developing and deriving guide values above which concentrations of a substance is considered “harmful” in indoor air.
The German Advisory Council on the Environment (Environmental Council – SRU) defines 'indoor environment’ as dwellings with living rooms, bedrooms, hobby rooms, exercise and basement areas, kitchens and baths, working areas in buildings which are not subject to the Ordinance on Hazardous Substances (GefStoffV), e.g. offices. Furthermore, it refers to indoor spaces in public buildings (hospitals, schools, kindergartens, sports facilities, libraries, restaurants, theatres, cinemas, and other public event venues), and the interior of motor vehicles and public means of transport.
Whereas limit values as per the Hazardous Substances Ordinance are in effect for work areas where hazardous substances are handled, they do not apply to the indoor spaces listed above. For example, formaldehyde contamination PDF / 381 KB, in German in the air of an office which occurs through emissions from furniture containing chipboard is considered similar to contamination of living rooms and not seen as workplace exposure, e.g. in the chemical industry.
Indoor air guide values for individual substances are developed by an ad-hoc working group composed of members of the Federal Environment Agency's Indoor Air Hygiene Commission (IRK) and the Permanent Working Group of the Highest State Health Authorities(AOLG). The setting of indoor air guide values is founded on a basic scheme PDF/ 317 KB, in German published in the Bundesgesundheitsblatt in 1996. In accordance with this, two guide value categories have been established.
Guide value II (RW II) is an effect-related value based on current toxicological and epidemiological knowledge of a substance's effect threshold that takes uncertainty factors into account. It represents the concentration of a substance which, if reached or exceeded, requires immediate action as this concentration could pose a health hazard, especially for sensitive people who reside in these rooms over long periods of time. Depending on the mode of action of the substance, guide value II may be defined either as a short-term value (RW II K) or a long-term value (RW II L).
Guide value I (RW I – precautionary value) represents the concentration of a substance in indoor air for which, when considered individually, there is currently no evidence that even life-long exposure is expected to cause any adverse health impacts. Concentrations higher than RW I are deemed to constitute an exposure that is higher than normal and therefore undesirable. As a precaution, action should also be taken in the concentration range between RW I and RW II, whether in the form of technical and construction measures (the responsibility of the building manager) or a change in the user’s behaviour. RW I can be considered as a target value during rehabilitation efforts. The guide values apply to individual substances and provide no indication of any possible combined effects with different substances. Up to the end of 2011, the following guide values were established by the IRK/AOLG Ad-hoc Working Group (detailed rationales are given in the publications listed below the table).
Guide values (I and II, in milligrams per cubic meter of air) for the concentration of specific substances in indoor air
| Compound | Guide value II1) (mg/m3) |
Guide value I1) (mg/m3) |
Year of establishment |
| Benzaldehyde | 0.2 |
0.02 |
2010 |
| Benzyl alcohol | 4 |
0.4 |
2010 |
| Monocyclic monoterpenes (Lead substance d-Limonene) |
10 |
1 |
2010 |
| Aldehydes (C4-C11, saturated acyclic aliphatic) | 2 |
0.2 |
2009 |
| C9 – C14-Alkanes / Isoalkanes (dearomatized) |
2 |
0.2 |
2005 |
| Naphthalene | 0.020 |
0.002 |
2004 |
| Bicyclic terpenes (Lead substance α-Pinen) |
2 |
0.2 |
2003 |
| Tris(2-chlorethyl)phosphate (TCEP) | 0.05 |
0.005 |
2002 |
| Diisocyanates (DI) | see following text |
2000 |
|
| Mercury (as metallic vapor) | 0.00035 |
0.000035 |
1999 |
| Styrene | 0.3 |
0.030 |
1998 |
| Nitrogen dioxide (NO2) | 0.35 (30 Min-Wert) 0.06 (7 Tage-Wert) |
- |
1998 |
| Dichlormethane | 2 (24 h) |
0.2 |
1997 |
| Carbon monoxide | 60 (½ h) 15 (8 h) |
6 (½ h) 1.5 (8 h ) |
1997 |
| Pentachlorphenol (PCP) | 0.001 |
0.0001 |
1997 |
| Toluene | 3 |
0.3 |
1996 |
| Phenol | 0,2 |
0,02 |
2011 |
| 2-Furaldehyd | 0,1 |
0,01 |
2011 |
| Zyklische Dimethylsiloxane D3-D6 (Summenrichtwert) | 4 |
0,4 |
2011 |
1)These are usually long-term values. Deviating averaging periods are given in brackets, e.g. 24 h.
The working group did not consider the establishment of a guide value II for diisocyanates (DI) useful. Despite initial higher concentrations in the air during application of paints and adhesives containing diisocyanates (concentrations within the MAK range), they quickly decrease and long-term exposure is not likely after hardening. As a rule, use of products containing DI should take place in well-ventilated rooms.
Ad-hoc Arbeitsgruppe „Innenraumrichtwerte” der Innenraumlufthygiene-Kommission (IRK) des Umweltbundesamtes und der AOLG. Richtwerte für monocyclische Monoterpene (Leitsubstanz d-Limonen). PDF / 467 KB
Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz 53 (2010) S 1206 - 1215.
Ad-hoc Arbeitsgruppe „Innenraumrichtwerte” der Innenraumlufthygiene-Kommission (IRK) des Umweltbundesamtes und der Obersten Landesgesundheitsbehörden. Richtwerte für Benzylakohol. PDF / 235 KB
Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz 53 (2010) S 984 - 988.
Ad-hoc working group of members of the Federal Environment Agency’s Indoor Air Hygiene Commission (IRK) and the permanent working group of the Highest State Health Authorities (AOLG), Richtwerte für Benzaldehyd. PDF / 251 KB
Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz 53 (2010) S 636 -640 [Guide values for Benzaldehyde].
Ad-hoc working group of members of the Federal Environment Agency’s Indoor Air Hygiene Commission (IRK) and the permanent working group of the Highest State Health Authorities (AOLG), Richtwerte für gesättigte azyklische aliphatische C4- bis C11-Aldehyde in der Innenraumluft. PDF / 755 KB
Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz 52 (2009) S 650 -659 [Guide values for indoor air: Saturated acyclic aliphatic C4-C11 aldehydes].
Ad-hoc working group of members of the Federal Environment Agency’s Indoor Air Hygiene Commission (IRK) and the permanent working group of the Highest State Health Authorities (AOLG), Gesundheitliche Bedeutung von Feinstaub in der Innenraumluft. PDF / 466 KB
Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz 51 (2008) S 1370 -1378 [Health relevance of particulate matter in indoor air].
Ad-hoc working group of members of the Federal Environment Agency’s Indoor Air Hygiene Commission (IRK) and the permanent working group of the Highest State Health Authorities (AOLG), Gesundheitliche Bewertung von Kohlendioxid in der Innenraumluft. PDF / 795 KB
Bundesgesundheitsbl Gesundheitsforsch Gesundheitsschutz 51 (2008) S 1358 -1369 [Health-related evaluation of carbon dioxide in indoor air].
Communication of the Ad-hoc working group of the IRK (2007) Gesundheitliche Bewertung dioxinähnlicher polychlorierter Biphenyle in der Innenraumluft. PDF / 388 KB
Gesundheitsbl Gesundheitsforsch Gesundheitsschutz 50(11): S. 1455-1465 [Health-related evaluation of dioxin-like polychlorinated biphenyls in indoor air].
Ad-hoc working group of members of the Federal Environment Agency’s Indoor Air Hygiene Commission (IRK) and the permanent working group of the Highest State Health Authorities (AOLG), Beurteilung von Innenraumluftkontaminationen mittels Referenz- und Richtwerten. PDF 721 KB
Bundesgesundheitsblatt-Gesundheitsforschung-Gesundheitsschutz 50 (2007) S 990-1005 [Evaluation of indoor air contaminants by means of reference and guide values].
Sagunski, H. und I. Mangelsdorf: Richtwerte für die Innenraumluft: Aromatenarme Kohlenwasserstoffgemische (C9-C14) PDF / 764 KB.
Bundesgesundheitsblatt-Gesundheitsforschung-Gesundheitsschutz 48 (2005) 803-813 [Guide values for indoor air: Dearomatized hydrocarbon solvents (C9-C14)].
Sagunski, H. und W. Heger: Richtwerte für die Innenraumluft: Naphthalin PDF / 257 KB.
Bundesgesundheitsblatt-Gesundheitsforschung-Gesundheitsschutz 47 (2004) 705-712 [Guide values for indoor air: Naphthalene].
Sagunski, H. und B. Heinzow: Richtwerte für die Innenraumluft: Bicyclische Terpene (Leitsubstanz a-Pinen) PDF / 225 KB.
Bundesgesundheitsblatt-Gesundheitsforschung-Gesundheitsschutz 46 (2003) S. 346-352 [Guide values for indoor air: Bicyclic terpenes – lead substance: a-pinene].
Sagunski, H. und E. Rosskamp: Richtwerte für die Innenraumluft: Tris(2-chlorethyl)phosphat PDF / 132 KB.
Bundesgesundheitsblatt-Gesundheitsforschung-Gesundheitsschutz 45 (2002) S. 300-306 [Guide values for indoor air: Tris(2-chlorethyl)phosphate].
Wolf, T. und H. Stirn: Richtwerte für die Innenraumluft: Diisocyanate PDF / 140 KB.
Bundesgesundheitsblatt-Gesundheitsforschung-Gesundheitsschutz 43 (2000) S. 505-512 [Guide values for indoor air: Diisocyanates].
Seifert, B.: Richtwerte für die Innenraumluft: Die Beurteilung der Innenraumluftqualität mit Hilfe der Summe der flüchtigen organischen Verbindungen (TVOC-Wert) PDF / 147 KB.
Bundesgesundheitsblatt-Gesundheitsforschung-Gesundheitsschutz 42 (1999) S. 270-278 [Guide values for indoor air quality: The evaluation of indoor air quality by means of the sum of volatile organic compounds (TVOC value)].
Link, B.: Richtwerte für die Innenraumluft: Quecksilber PDF / 109 KB.
Bundesgesundheitsblatt 42 (1999) S. 168-174 [Guide values for indoor air: Mercury].
Sagunski, H.: Richtwerte für die Innenraumluft: Styrol PDF / 486 KB.
Bundesgesundheitsblatt 41 (1998) S. 392-421 [Guide values for indoor air: Styrene].
Englert, N.: Richtwerte für die Innenraumluft: Stickstoffdioxid PDF / 270 KB.
Bundesgesundheitsblatt 41 (1998) S. 9-12 [Guide values for indoor air: Nitrogen dioxide]
Ad-hoc-Arbeitsgruppe aus Mitgliedern der Innenraumlufthygiene-Kommission (IRK) des Umweltbundesamtes und des Ausschusses für Umwelthygiene der AGLMB. Richtwerte für die Innenraumluft: Pentachlorphenol.
Bundesgesundheitsblatt 40 (1997) S. 234-236 [Guide values for indoor air: Pentachlorphenol].
Witten, J., H. Sagunski und B. Wildeboer: Richtwerte für die Innenraumluft: Dichlormethan PDF / 499 KB.
Bundesgesundheitsblatt 40 (1997) S. 278-284 [Guide values for indoor air: Dichlormethane].
Englert, N.: Richtwerte für die Innenraumluft: Kohlenmonoxid PDF / 272 KB.
Bundesgesundheitsblatt 40 (1997) S. 425-428 [Guide values for indoor air: carbon monoxide].
Ad-hoc working group of members of the Federal Environment Agency’s Indoor Air Hygiene Commission (IRK) and the AGLMB Committee for Environmental Hygiene. Richtwerte für die Innenraumluft: Basisschema PDF / 317 KB.
Bundesgesundheitsblatt 39 (1996) S. 422-425 [Guide values for indoor air: Basic scheme].
Sagunski, H.: Richtwerte für die Innenraumluft: Toluol PDF / 447 KB.
Bundesgesundheitsblatt 39 (1996) S. 416-421 [Guide values for indoor air: Toluene].
The Ad-hoc Working Group defines a guidance value to be a hygiene-based assessment value for a substance or group of substances. Guidance values are formulated when systematic practical experience indicates that the likelihood of complaints or adverse health effects increases with increasing concentration but current knowledge is insufficient to derive a toxicology-based guide value. To date, indoor air guidance values have been established for carbon dioxide, total volatile organic compounds (TVOC) and fine particulate matter (PM2.5).
Level |
Concentration range [ppm CO2] |
Hygienic evaluation |
1 |
< 1000 ppm |
Harmless |
2 |
1000 – 2000 ppm |
Elevated |
3 |
> 2000 ppm |
Unacceptable |
In order to account for the fact that indoor air contains many organic compounds and guide values have been established for relatively few individual pollutants, the IRK/AOLG Ad-hoc Working Group developed evaluation standards for assessing volatile organic compounds in indoor air by using the sum of volatile organic compounds (TVOC). To illustrate the uncertainties involved in the derivation, concentration ranges were applied rather than individual numerical values. Five levels were defined for the evaluation of TVOC concentrations and specific measures were recommended for each level.
Level |
Concentration range [mg/m3] |
Hygienic evaluation |
1 |
≤ 0,3 mg/m3 |
No objections |
2 |
> 0,3-1 mg/m3 |
No relevant objections, provided that any guide values for individual substances or groups of substances are not exceeded |
3 |
>1-3 mg/m3 |
Hygienic aspects of concern |
4 |
>3-10 mg/m3 |
Major objections |
5 |
>10 mg/m3 |
Situation not acceptable |
Concentration [µg PM2.5/m3] |
Hygienic assessment |
|
25 µg/m3 |
The 24 h average only applies to purely residential indoor spaces in the absence of indoor-specific sources of dust |
Indoor air guide values benefit everyone. They can help in an individual case to determine whether indoor air quality might be detrimental for health. In disputes between landlords and tenants they might serve as a basis for a surveyor’s assessment of whether a dwelling is making anyone “sick”. Unlike limit values, such as exist for outdoor air or drinking water, guide values have the advantage that it might be appropriate to take measures even when concentrations are below them (here, RW II). Also, guide values account for the different conditions that may lead to thresholds being exceeded or fallen below much better than do limit values, which are usually subject to strictly defined conditions. The Ad-hoc Working Group at the Federal Environment Agency will therefore continue to derive guide values for indoor air pollutants, and to review existing values as to their validity in accordance with latest scientific knowledge.
At many institutions there is an interest to learn about the state of health assessment of indoor air pollution. The Ad-hoc Working Group has therefore decided at its 41st meeting to publish the summary minutes on the UBA website.