Alkaline Earth Silicate (AES) Wool

AES wools consist of amorphous fibres produced by melting a combination of CaO, MgO and SiO2. Key features of AES products are low thermal conductivity, low linear shrinkage and low biopersistence. Products made from AES wools are generally used at application temperatures >600°C in industrial equipment, fire protection, automotive exhaust systems and domestic appliances. See the AES section of the website for more information.

Alumino Silicate Wool (ASW)

Alumino Silicate Wools, also known as "refractory ceramic fibre" (RCF), are amorphous fibres produced by melting a combination of Al2O3 and SiO2. Key features of ASW products are low thermal conductivity, high chemical stability, and low linear shrinkage. Products made from ASW are generally used at application temperatures >900°C in industrial equipment such as furnaces and kilns, in fire protection, and in automotive exhaust systems. See the ASW section of the website for more information.



The characteristic of a fibre to persist in the lung, involving or implying resistance to both dissolution and mechanical breakage. Biopersistence can only be directly measured in in vivo test systems, i.e. following inhalation, instillation or injection in experimental animals. The rate of removal of fibres is typically expressed as "half life" – the time it takes for the number of fibres in the lungs to be reduced by 50%.

Man Made Vitreous Fibres (MMVF; see below) have low biopersistence compared with most natural mineral fibres. Understanding the biological significance of biopersistence has resulted in the development of materials such as AES wools that have very low biopersistence. See also Durability and Biosolubility and the Health & Safety section of the website for more information.


A measure of the solubility of a fibre in biological aqueous media (e.g. lung fluid, macrophage cytoplasm), quantifiable in in vitro test systems.


CARE Programme

Standing for "Controlled and Reduced Exposure", CARE is a cross-industry industrial hygiene programme initiated by ECFIA in 1996. It comprises exposure monitoring and risk assessment for all HTIW. Workplace control methods are evaluated and personal concentrations of fibrous dust monitored in both manufacturing and user company sites. The programme forms the basis for the production of ‘best practice’ guidance documents. See the Exposure Control / CARE section of the website for more information.

CLP Regulation

The Classification Labelling and Packaging Regulation (CLP-Regulation (EC) No 1272/2008) on the classification, labelling and packaging of substances and mixtures aligns existing EU legislation to the United Nations Globally Harmonised System (GHS). It replaces the former Dangerous Substances and Preparations EU Directives.


Cristobalite is a type of crystalline silica that can form when MMVFs devitrify following heating to sufficiently high temperatures for a sufficient duration (depending on chemical composition). See Devitrification.


See Devitrification.


The 3Ds Paradigm

This is the general paradigm for fibre toxicity referring to Dose (the amount reaching the lung), Dimension (fibre length and diameter) and Durability. These parameters are crucial in determining both the ability of a fibre to reach the deep lung and its pathological effects once there. See also Dose, Dimension, Durability and Biopersistence and the Health & Safety Section of the website for more information.


The process by which prolonged high temperatures can alter the physicochemical properties and crystalline structure of amorphous HTIWs (AES and ASW), resulting in reduced resiliency and mechanical strength. Various crystalline phases can be formed by devitrification, including mullite, enstatite, wollastonite and cristobalite (a form of crystalline silica, see above). Crystalline phases produced when heating polycrystalline wools at high temperature (1400°C - 1600°C) are mullite (main phase) and corundum (secondary phase). Crystalline silica (including cristobalite) is not formed on heating PCW.


While this may seem a simple concept, the diameter of fibres in mineral wools is complex. Mineral wools contain fibres with a wide range of diameters; if these are to be measured in any type of microscope the mineral wool must usually be ground, milled or broken up in some other way. When this is done the thin fibres tend to break more easily than thick ones. This also happens when working with mineral wools, so that in workplace dusts length and diameter are correlated, with finer diameter fibres tending to be shorter than coarser fibres. If the diameter of a number of fibres is measured and a simple mean diameter calculated, then this figure will depend on how many thin fibres are created which, in turn, depends on the way the fibres have been handled. Therefore to obtain a meaningful and reproducible measure of mineral wool fibre diameter, independent of the preparation method, the so called "length weighted geometric mean diameter (LWGMD)" concept has been devised. As the diameters usually vary so that their logarithms are normally distributed then the geometric mean should be used; 50% of the total length of fibres present will be less than the LWGM. This value is also close to the median diameter. The vast majority of man-made mineral fibres are fairly coarse, with most fibres having LWGMD well above 1µm.


Fibre dimension is critical in terms of possible health effects as only fibres of a certain size can reach the lungs. Mineral fibres with a diameter >3µm are regarded as essentially "non respirable" in humans. While respirability is determined predominantly by fibre diameter, fibre length is also important. Short fibres can be cleared by the normal mechanisms of phagocytosis by lung macrophages, but long fibres (e.g. >20µm) can frustrate this mechanism and are also more biologically active. See also The 3Ds Paradigm, Diameter and the Health & Safety section of the website for more information.


The amount of material (fibrous dust) reaching the lungs during a certain period of time. Often referred to as "lung burden" it is usually expressed in F/ml*year or F/ml*month. With chronic exposures, lung burden is the result of ongoing deposition (driven by workplace exposure levels and fibre dimensions) and clearance (determined by fibre biopersistence). If the exposure is high enough and clearance slow, then a sufficiently large dose may accumulate for adverse health effects to result. See the Health & Safety section for more information.


A general term, as used in the '3Ds paradigm', referring to the ability of a material (in this case a fibre) to resist dissolution and so persist in the lung. See also Biopersistence.


EU Directive 97/69/EC

A technical amendment to the Dangerous Substances Directive 67/548 EU concerning the hazard classification and labelling of man-made vitreous (silicate) fibres as carcinogens. It exonerates thick fibres (see Note R) and then divides the rest into two groups according to their alkaline and alkaline earth oxide composition. Those containing more than 18% alkaline and alkaline earth oxides by weight are called mineral wools and may be exonerated from classification and labelling if certain bioassays guarantee either their low biopersistence or lack of pathogenicity (see Note Q).


Specifically in this context, exposure is the measure of airborne fibrous dust or other material that reaches the deep lung in exposed persons (or animals in the case of bioassays). Exposure is not the same as airborne fibre concentration, which is often evaluated according to the WHO definition of fibres. See the Risk Management Obligations of the website for more information.



A fibre is any particle longer than it is wide. Material scientists normally call objects fibres when their length is more than 10 times their width (i.e. their ‘aspect ratio’ >10), although the WHO definition of a fibre refers to an aspect ratio of 3. To be useful in most applications, fibres must have aspect ratios very much greater than this. See also Diameter and Length and WHO Fibres.

Fibrous dusts

Dusts that are comprised of, or predominantly contain fibres.



The Globally Harmonized System of Classification and Labelling of Chemicals, or GHS, is an internationally agreed system set to replace the various different classification and labeling standards used in different countries. See Labelling.


High Temperature Insulation Wool (HTIW)

High Temperature Insulation Wools are synthetic mineral wools used in high-temperature industrial applications, typically in the range 600°C to 1800°C. They include three different types of wool: Polycrystalline Wools (PCW), Aluminium Silicate Wools (ASW/RCF) and Aluminium Earth Silicate (AES) wools. HTIW are specialist materials and account for only about 2% of the total synthetic mineral wool production in Europe. See the HTIW section of the website for more information.



In the past, classification and labelling of hazardous substance and preparations had to be done following Directive 67/548/EEC and 1999/45/EEC. In order to harmonise classification and labelling regulation, the European Union decided to adopt and adapt the Global Harmonised System (GHS) proposed by the United Nations. As a consequence, a new Regulation (EC) No 1272/2008 has been published aiming at replacing the former above listed Directives. Substances and mixtures will have to be labelled according to these new European regulation CLP-rules. In addition to the labelling of classified substances, ECFIA members are voluntarily labelling articles made of these substances. See the Classification & Labelling section of the website for more information.


Another simple variable describing fibre dimension that conceals a degree of necessary complexity (c.f. Diameter). The length of fibres in mineral wools is highly variable, ranging from a few micrometers to some centimetres (e.g. 25cm). When fibres are handled, dust liberated into the air will include some non-fibrous particles as well as fibres with lengths up to some tens of mm. Fibre length is a key determinant of hazard. See also Fibre and Dimension.

Length-Weighted Geometric Mean Diameter (LWGMD)

See Diameter.


Man Made Vitreous Fibres (MMVF)

The class of materials including all the glassy fibres such as rockwool, glass wool, slagwool, AES and ASW/RCF-wools. The European Union added the term (silicate) in Directive EU/97/69 to identify a subset of these fibres. The term Synthetic Vitreous Fibres (SVF) is now often used instead of MMVF. Conglomerates made from MMVFs are called Man Made Vitreous Wools (MMVWs). Non-vitreous synthetic mineral fibres, such as PCW, are described generically as Man Made Mineral Fibres (MMMF) or Synthetic Mineral Fibres (SMF). See also Wool.


Malignant tumour of the mesothelium – the membrane lining the chest and abdominal cavities. This tumour is relatively rare in the general public and is normally associated with occupational exposure to asbestos (especially amphibole asbestos).


Note Q

A note in Directive EU/97/69 (q.v.) stating the conditions that may be used in Europe to exonerate some man-made vitreous (silicate) fibres from classification as carcinogens under this Directive.



Occupational Exposure Limit. Any of several (e.g. Threshold Limit Value, TLV; Permissible Exposure Limit, PEL; Maximum Exposure Limit, MEL) exposure levels set by regulators to control worker exposure.


Pleural plaque

A non-malignant inflammatory condition of the pleural surface detected on chest x-rays and at post mortem, especially in individuals occupationally exposed to asbestos. Plaques are relatively common in the general public and are not usually associated with symptoms of ill health.

Polycrystalline Wool (PCW)

Polycrystalline Wool is made predominantly of aluminum oxide (typically 72-99%), with the remainder consisting of silicon. It is manufactured using sol-gel technology and high temperature firing to produce fibres of well-defined dimensions. PCW is produced in relatively small quantities for very specific applications, typically from 600°C to 1700°C. See the PCW section of the website for further information.

Product Stewardship Programme (PSP)

Product stewardship is an action, or usually a series of actions, taken by industry to address and reduce environmental, health, and safety impacts of product(s) they manufacture. The PSP for HTIW products was developed by ECFIA in the 1990’s, in close cooperation with its American partner organisation the HTIW Coalition. ECFIA’s PSP follows well-established principles of risk assessment and risk management. Its components are science-based, with human health effects research a priority. The programme is designed to assist HTIW manufacturers and end-users in the evaluation, control and reduction of workplace exposures; it helps ensure the proper manufacture, storage, handling, use and disposal of HTIW products. The CARE programme (see above) is a key element of ECFIA's PSP. See the PSP section of the website for further information.


REACH (Reach, Evaluation, Authorization and Restriction of Chemicals)

REACH is a European Union Regulation introduced in December 2006. REACH addresses the production and use of chemical substances and their potential impacts on both human health and the environment inviting producers, importers and to a lesser extend users to provide extensive information on their substances, mixtures and products. REACH entered into force in June 2007, with a phased implementation over the next decade. (See also ECHA-website).

Refractory Ceramic Fibres (RCF)

Also (preferably) referred to as Aluminium Silicate Wool (ASW), which better describes the material’s composition. See Aluminium Silicate Wool (ASW) and the ASW section of the website for more information.


Capable of reaching the deep lung – i.e. the alveolar (gas exchange) region – when inhaled. The respirability of a fibre is determined predominantly by its diameter. See also Dimension.


Vitreous (Amorphous) Glassy Fibres

Vitreous fibres are amorphous rather than crystalline. They have no cleavage planes and when handled they break transversely rather than splitting into thinner fibres as asbestos does. This term has the same meaning as MMVF (see above).



For the purpose of harmonising optical fibre counting, the World Health Organization has adopted a convention to define fibre dust size. To evaluate workplace fibre concentrations, only airborne fibres with diameter less than 3µm, length greater than 5µm, and an aspect (length to diameter) ratio greater than 3 are to be counted. Such so-called ‘WHO Fibres’ are not all equally respirable; fibres with diameter <1µm are far more likely to reach the deep lung than those of 3µm diameter. See also Dimension.


Wool is the term used to describe an unordered mass of fibres of different lengths and diameters (EN 1094-1).