Man-made mineral fibres, MMF for short, are the most widely used fibrous insulation in Austria (BRANCHENRADAR 2025). Glass wool is spun from molten glass, stone wool from molten rock, slag wool from blast-furnace slag (LfU 2018). Whether such insulation is harmless does not depend on the material as such, but on a single, measurable property of its fibres: how quickly the body dissolves them again. That property shifted over time: around the year 2000 the changeover to biosoluble fibres was complete. Mineral wool from production before that contains long-lived, biopersistent fibres and is classified as suspected of causing cancer; today's biosoluble wool is not. Anyone who finds yellowish, brittle insulation mats in a suspended ceiling or roof during a renovation therefore faces a single question: old or new? The year alone does not answer it; in the end the fibre decides, not the building's age.
Why biosolubility decides the risk
A fibre becomes a problem for the lung only when it meets two conditions: it must be respirable, and it must persist. A fibre is respirable if it is thin enough to reach the alveoli. The measure is geometry: a critical, so-called WHO fibre is longer than 5 µm, thinner than 3 µm and more than three times as long as it is wide (WHO 1988). Old and modern mineral wool share this geometry. The difference lies in the second condition, the residence time.
Short and thin fibres the lung can clear mechanically; for long fibres this route fails, because the lung's scavenger cells can no longer fully engulf them (WHO 1988). What remains is chemical dissolution: the fibre thins, breaks into shorter pieces and is cleared. How fast this happens is a material property, and it can be captured in a single figure, the biopersistence, measured as the half-life of the long fibres in lung tissue. For modern, biosoluble mineral wool this half-life is a matter of a few days; for old glass wool around 40, for traditional stone wool about 70 to 90 days; amphibole asbestos, the other extreme, lies orders of magnitude above this, with half-lives of over one to over two years (IARC 2002; the figures in the fold-out). It is this persistence, not the mere presence of fibres, that drives the cancer risk.
Because persistence depends on the chemical composition (see the fold-out), it could be lowered deliberately: modern wools are formulated so that their fibres dissolve quickly. The legal framework builds on exactly this. Fibre dusts from old, biopersistent mineral wool are classified across the EU as suspected of causing cancer (CLP Regulation 2008, Annex VI, entry 650-016-00-2: Carc. 2, "suspected of causing cancer"; originally Directive 97/69/EC). The decisive point is Note Q: the carcinogen classification does not apply if a biopersistence test shows that the fibres dissolve sufficiently quickly (Dir. 97/69/EC). Modern mineral wool meets this condition and is therefore not classed as suspected of causing cancer; on the German market, only such products are available today. They are identified by the EU-wide EUCEB mark and, in Germany, by the RAL quality mark "Erzeugnisse aus Mineralwolle" (EUCEB; LfU 2018). Austrian waste law, too, names both marks explicitly as proof of harmlessness (AVV 2020).
Two assessments of these fibres stand side by side and are often confused. The International Agency for Research on Cancer (IARC) lists the common insulation wools, that is glass, stone and slag wool, as not classifiable (Group 3); only special-purpose glass fibres and refractory ceramic fibres does it class as possibly carcinogenic (Group 2B) (IARC 2002). Group 3 is not an acquittal, but means that the available data are insufficient for a classification. In any case, what governs the handling of old mineral wool is not the IARC group but the European substance classification, which treats biopersistent fibres as suspected of causing cancer and makes them a hazardous substance in law. The two assessments measure different things; the second fold-out sets out their relationship.
The year of manufacture is only a rough guide, not proof. On the German market, only RAL-certified, biosoluble products have been available since June 2000; the changeover ran in the years before (LfU 2018). The German rules draw two year-lines from this: mineral wool installed before 1996 counts as old, biopersistent wool; the production of biosoluble products began around 1996, but between 1996 and 2000 old products could still be installed (TRGS 521). These are milestones of the market and of regulation, not a test of the specific material. Whether a particular insulation is biopersistent is decided by the fibre, not the building's age, and in case of doubt only an analysis settles it.
Where old MMF was installed
In buildings constructed roughly between 1965 and 2000, old mineral wool typically sits in these places:
- rafter insulation in the roof structure
- cavity insulation in lightweight partition walls
- pipe insulation in the basement
- impact-sound insulation under screed
- suspended ceilings in offices and commercial buildings
Visually, the material is often discoloured yellowish, brittle and gives off dust when touched. This dust carries the released fibres into the room air, and that is where exposure arises. The colour is no help in telling them apart, however: modern glass wool is yellow too. Old and new cannot be separated by appearance.
When it becomes an exposure
The risk does not arise from the presence of the insulation but from the fibres' route into the breathed air. That is what the three practically relevant cases turn on:
- Old MMF in a closed cavity (wall, roof, under screed): As long as the insulation stays undisturbed, that is neither drilled into nor torn open, and there is no open connection to the living space, the transmission route is missing. There is no acute need to act.
- Old MMF in open contact with the room air (open ceilings, visible, dusting insulation): Here the route is open, and fibre dust suspected of causing cancer can reach the breathed air. The material should be sealed off, permanently covered or professionally removed. A room-air measurement determines the current fibre concentration, but it is a snapshot and does not anticipate the remediation.
- A planned renovation in which old MMF is removed: Removal is the moment of greatest release. It is subject to a minimisation requirement (below), and the material is hazardous waste.
Two questions, two investigations that should not be confused: whether an insulation consists of old, biopersistent wool at all is answered by a material sample; how high the fibre concentration in the room air currently is, is answered by an air measurement. One does not replace the other.
Telling old from new
Since colour and age of construction are not enough, a material sample establishes the finding. An accredited laboratory does not measure biopersistence itself, since that is a behaviour of the fibre in body tissue and not a quantity that can be taken directly from a material sample. What is determined is fibre type, geometry and chemical composition, and from these the sample is assigned to old (biopersistent) or modern (biosoluble) mineral wool (LfU 2018). Taking one's own samples from the dry material and tearing it out without protection are counterproductive, because that is precisely what generates the respirable dust one wants to investigate; sampling, like the later remediation, is therefore carried out under controlled conditions with containment and extraction.
One point that is often missed: modern, biosoluble mineral wool gives off dust too, and this dust irritates skin, eyes and the upper airways mechanically. It is a physical irritation by the fibres, not a chemical one, and the former irritant labelling was consequently withdrawn, because the effect rests on the fibre shape and not on the chemistry (EU-OSHA). Biosoluble therefore does not mean irritation-free: when installing and cutting new insulation, gloves, safety goggles, an FFP mask and ventilation are appropriate, even though there is no cancer risk here.
The legal framework
Old, biopersistent mineral wool is classified across the EU as suspected of causing cancer (CLP Regulation 2008, Annex VI, directly applicable in Austria; originally Dir. 97/69/EC). Handling it at the workplace is governed by the Austrian Limit Values Ordinance (Grenzwerteverordnung, GKV), which lists such fibres as a carcinogenic working substance. Work on such material is therefore subject to a minimisation requirement: fibre release is to be kept as low as possible, with containment, extraction and personal protective equipment (AUVA 2018; Occupational Health and Safety Act, ASchG §§ 42, 43, 45). The removed material must be disposed of as hazardous waste, not via household waste; in the Austrian waste catalogue it carries the key number 31437 41 (man-made mineral fibre waste with hazard-relevant fibre properties), and the European waste code 17 06 03* (AVV 2020). Modern, biosoluble mineral wool with EUCEB or RAL certification is not subject to these special cancer-protection requirements; it is classed as non-hazardous waste (key number 31416, EU waste code 17 06 04; AVV 2020). Mechanical dust protection during installation is unaffected by this.
The comparison with asbestos
The comparison with asbestos is obvious, and the differences are essential. Asbestos is more persistent and finer: it splits lengthwise into ever finer fibrils, whereas mineral wool breaks transversely, producing no finer fibres (WHO 1988; LfU 2018). Above all, asbestos is orders of magnitude more persistent: its half-lives run to over one to over two years, against roughly one to three months for old mineral wool (the figures in the first fold-out). This is reflected in the classifications, kept separate by system: IARC lists asbestos as unequivocally carcinogenic (Group 1; IARC 2012) and the common insulation wools as not classifiable (Group 3; IARC 2002). The European substance classification treats old, biopersistent mineral wool as suspected of causing cancer (Carc. 2), while modern, biosoluble wool is exempt (CLP Regulation 2008). Accordingly, asbestos demands stricter procedures (→ Identifying asbestos); with old mineral wool the risk and the effort are lower. That does not make it insignificant, especially during a loft conversion or a full renovation, when a lot of old material is moved.
Old insulation rarely comes alone. Buildings of the same decades often also contain PCB in flexible joint sealants and, in buildings from before 1990, asbestos in boards and adhesives.
For experts, or those who want to become one: From oxide composition to half-life, why the chemistry determines persistence
A mineral fibre is a solidified silicate glass, and its persistence in tissue is at heart a question of glass chemistry. The network is built by silicon dioxide (SiO2); aluminium oxide (Al2O3) acts as a stabiliser and raises the chemical durability. Network modifiers, on the other hand, above all the alkali and alkaline-earth oxides (Na2O, K2O, CaO, MgO), loosen the network and accelerate dissolution; a higher share of such modifiers lowers durability (IARC 2002). This is where solubility can be tuned. The special case is boron trioxide (B2O3): structurally a network former, but biologically a solubility driver, which is why it was raised in modern glass wools.
The typical compositions differ accordingly (mass fractions, IARC 2002): glass wool contains 55 to 70 % SiO2, 12 to 20 % alkali oxides, up to about 12 % B2O3 and only 0 to 7 % Al2O3; stone wool has considerably more Al2O3 (6 to 15 %) and alkaline-earth oxides (CaO and MgO together 16 to 41 %), plus iron oxide, at a low alkali content; slag wool has very high calcium and magnesium oxide. The move to biosoluble products consisted chemically of exactly this, shifting these ratios in favour of solubility.
The dissolution itself runs in two lung environments: in the near-neutral tissue fluid (about pH 7.4) and in the acidic phagolysosome of the scavenger cell (about pH 4.5). The dissolution rate measured there, the mass loss per fibre surface and time, correlates with the half-life determined in animal studies (IARC 2002). This half-life, measured for the long fibre fraction above 20 µm, orders the materials: modern biosoluble glass and stone wools about 6 to 9 days, older glass wool around 37 days, traditional stone wool 67 to 91 days; for comparison, amphibole asbestos with amosite around 418 and crocidolite around 817 days (IARC 2002). The European Note Q draws its line exactly here: the carcinogen classification does not apply if, among other things, a short-term inhalation biopersistence test gives a weighted half-life below 10 days for fibres longer than 20 µm (Dir. 97/69/EC). A second, separate exemption route is Note R, which exempts coarse fibres with a length-weighted geometric mean diameter above 6 µm, because they are not respirable (Dir. 97/69/EC).
For experts, or those who want to become one: Why IARC lists glass and stone wool in Group 3 while the substance classification treats them as suspected of causing cancer
The apparent contradiction dissolves once both assessments are taken for what they are. IARC assesses the strength of the scientific evidence for a carcinogenic effect in humans. In 1988 it had still listed glass and stone wool as possibly carcinogenic (Group 2B) (IARC 1988). In 2002 it downgraded both to Group 3, not classifiable: the large cohorts of workers in mineral-wool production, European and US alike, had shown no consistent increase in lung cancer attributable to the fibre (IARC 2002). Group 3 does not mean "harmless", but "the available data do not permit a classification".
The European substance classification, by contrast, is a precautionary, legal classification: biopersistent fibres of the critical geometry count as suspected of causing cancer (Carc. 2) as long as they do not pass the biopersistence test, and are exempted via Note Q once they pass it (Dir. 97/69/EC; CLP Regulation 2008, Annex VI). A purely chemical shortcut to this exists, the carcinogenicity index (KI): the sum of the mass fractions of Na2O, K2O, B2O3, CaO, MgO and BaO minus twice the mass fraction of Al2O3; from a KI of 40 the fibre counts as not to be classified (TRGS 905; LfU 2018). The KI estimates persistence from the composition; decisive for the exemption, however, is the actual biopersistence test of Note Q, and the two can diverge. The LfU points out that the KI can wrongly rate modern, demonstrably biosoluble wool as suspect (LfU 2018). One assessment asks: what do the data in humans show? The other: how does one treat a fibre of this geometry and persistence as a precaution? For handling old, untested mineral wool, the precautionary answer is the one that governs. The distance to asbestos nonetheless remains large: asbestos is unequivocally carcinogenic (Group 1; IARC 2012), and its half-lives run to over one to over two years; old mineral wool, by contrast, counts in Europe as suspected of causing cancer (Carc. 2), remains not classifiable for IARC (Group 3) and is broken down in months (IARC 2002).
Sources
- ASchG: Occupational Health and Safety Act (ArbeitnehmerInnenschutzgesetz), BGBl. No. 450/1994 as amended, §§ 42, 43 and 45 (substitution, hazard prevention and limit values/minimisation for carcinogenic working substances), in conjunction with the Limit Values Ordinance (GKV). ris.bka.gv.at
- AUVA (2018): Quartz dust and man-made mineral fibres. sicherearbeit.at, issue 5/2018 (Austrian Workers' Compensation Board). Old, biopersistent MMF as a carcinogenic working substance with a TRK of 500,000 fibres/m³ (daily mean) and a minimisation requirement; new MMF at a MAK of 10 mg/m³ (inhalable fraction). sicherearbeit.at
- AVV (2020): Waste Catalogue Ordinance (Abfallverzeichnisverordnung), BGBl. II No. 409/2020, waste catalogue. Key number 31437 41 (man-made mineral fibre waste with hazard-relevant fibre properties, hazardous; EU waste code 17 06 03*) and 31416 (non-hazardous mineral wool with EUCEB/RAL certification; EU waste code 17 06 04). edm.gv.at
- BRANCHENRADAR (2025): Insulation materials in Austria. Market analysis (BRANCHENRADAR.com Marktanalyse GmbH). Market shares by volume: foams (EPS/XPS/PUR) about 56 %, mineral wool about 40 % (the largest fibrous share).
- CLP Regulation (2008): Regulation (EC) No 1272/2008 on classification, labelling and packaging of substances and mixtures, Annex VI. Mineral wool index 650-016-00-2 = Carc. 2 (H351) with Notes Q and R; refractory ceramic fibres 650-017-00-8 = Carc. 1B. eur-lex.europa.eu
- EU-OSHA: Man-made mineral fibres; Asbestos. OSHwiki, European Agency for Safety and Health at Work. Mechanical (physical) skin irritation from mineral-wool dust and withdrawal of the former irritant labelling; longitudinal splitting of asbestos versus transverse breakage of mineral wool. oshwiki.osha.europa.eu
- EUCEB: European Certification Board for Mineral Wool Products. Certification of biosolubility via the biopersistence test under Note Q. euceb.org
- IARC (1988): Man-made Mineral Fibres and Radon. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 43. International Agency for Research on Cancer, Lyon. Earlier classification of glass and stone wool as Group 2B, downgraded to Group 3 in 2002. publications.iarc.fr
- IARC (2002): Man-made Vitreous Fibres. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 81. International Agency for Research on Cancer, Lyon. Oxide compositions (Table 1.1), biopersistence half-lives (Table 2.1), group classification (glass/stone/slag wool Group 3; special-purpose glass and ceramic fibres Group 2B). inchem.org
- IARC (2012): Asbestos (Chrysotile, Amosite, Crocidolite, Tremolite, Actinolite and Anthophyllite). IARC Monographs, Vol. 100C. Asbestos Group 1 (carcinogenic to humans). ncbi.nlm.nih.gov/books/NBK304374
- LfU (2018): Man-made mineral fibres (Künstliche Mineralfasern). UmweltWissen Abfall, Bavarian State Office for the Environment. Fibre types, WHO fibre, RAL quality mark, dating, carcinogenicity index and its limits, disposal. lfu.bayern.de
- Dir. 97/69/EC (1997): Commission Directive 97/69/EC of 5 December 1997 adapting Directive 67/548/EEC. Classification of man-made mineral fibres, Note Q (biopersistence criterion) and Note R (diameter criterion). eur-lex.europa.eu
- TRGS 521: Tätigkeiten mit alter Mineralwolle (activities involving old mineral wool). German Technical Rules for Hazardous Substances, edition May 2026 (GMBl 2026 p. 300). Mineral wool installed before 1996 counts as old (biopersistent) mineral wool; new, biosoluble wools have been produced since about 1996; between 1996 and 2000 old products could still be used; German manufacture and use ban since June 2000. baua.de
- TRGS 905: List of carcinogenic, germ-cell-mutagenic or reproductive-toxic substances. German Federal Institute for Occupational Safety and Health (BAuA). Basis of the carcinogenicity index for mineral fibres. baua.de
- WHO (1988): Man-made Mineral Fibres. Environmental Health Criteria 77, International Programme on Chemical Safety, World Health Organization, Geneva. WHO fibre definition, deposition and length-limited clearance. inchem.org
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