An asbestos fibre is a thin, long and strong fibre of a silicate mineral that has crystallised in fibrous form in nature. A single asbestos fibre is many times thinner than a human hair and cannot be seen with the naked eye. What sets asbestos apart is that its fibre bundles split lengthwise into ever thinner strands. That is why asbestos-containing material that breaks releases respirable fibres, which can travel deep into the lungs.
This article explains how an asbestos fibre is built and how small it is, why it was added to building materials, when fibres are released into the air, how asbestos fibres differ from mineral wool and other fibres, and how a laboratory identifies them.
What does an asbestos fibre look like?
Asbestos is not a single mineral but a collective name for six silicate minerals that have crystallised in nature as fibres. This fibrous growth habit is called asbestiform. The same mineral can also occur as ordinary, non-fibrous rock, and in that form it is not asbestos. The difference between the mineral groups is explained in the article serpentine and amphibole, and the six asbestos types are presented on the page types of asbestos.
Bundle, fibre and fibril
An asbestos strand that you might see in the raw mineral is actually a bundle of a huge number of parallel fibres. When the bundle is bent, rubbed or crushed, it splits lengthwise into thinner fibres and eventually into individual fibrils. This property sets asbestos apart from most other fibres and explains why it so easily forms dust that can be inhaled.
How small is an asbestos fibre?
Air measurements and occupational health use the World Health Organization (WHO) definition, under which a countable fibre is longer than 5 micrometres, thinner than 3 micrometres, and has a length-to-width ratio greater than 3:1. Fibres of this size are respirable. Many asbestos fibres are much thinner still, and the thinnest cannot be resolved with an ordinary light microscope. That is why identifying asbestos fibres takes a laboratory.
Why was asbestos fibre used in building materials?
Asbestos fibre was mixed into a very wide range of products during manufacture because of its properties.
- Heat and fire resistance: asbestos does not burn and withstands high temperatures, so it was used in insulation, gaskets and fire protection.
- Tensile strength: the fibres reinforced cement, fillers, mortars, adhesives and plastics, much as steel bars reinforce concrete.
- Chemical and wear resistance: asbestos fibre resists many chemicals and wear, which suited floor coverings and roofing products, for example.
In a finished product the fibres are bound into cement, bitumen, adhesive, filler or plastic and cannot be made out by eye. An asbestos-containing product looks the same as an asbestos-free one, as explained in the article how to identify asbestos.
When are asbestos fibres released into the air?
Intact, undisturbed asbestos material does not usually release fibres into the air, because the fibres stay bound in the material. Fibres come loose when the material is broken mechanically. Typical situations are:
- sanding, drilling, sawing, chiselling and grinding
- removing and breaking tiles, floor coverings and boards
- touching or wearing friable material, such as old pipe lagging or sprayed insulation
- the weathered surface of asbestos cement that has been exposed to the elements for a long time, if it is pressure-washed or brushed, for example
Hard materials such as asbestos cement, vinyl tiles and hardened adhesives release fibres mainly when they are worked on, but sanding and sawing do release fibres from them too. Soft and friable materials, such as some pipe insulation and sprayed fire protection, can shed dust from a light touch.
Thin fibres are light, stay airborne for a long time and are carried to other rooms by air currents. That is why possible asbestos dust is not swept or vacuumed with an ordinary vacuum cleaner; surfaces are wiped with a damp cloth instead. Fibres in the air of a room are established with an air sample.
Why are asbestos fibres dangerous?
Inhaled thin fibres can reach the deepest parts of the lungs and as far as the pleura. Their long, thin shape and their durability make it hard for the body to clear them, and some of the fibres remain in the tissues for a long time. All types of asbestos are carcinogenic. Asbestos-related diseases typically appear only long after exposure. They are described in the article symptoms of asbestos exposure.
If you are worried about possible exposure, talk to a doctor or your occupational health service.
How do asbestos fibres differ from other fibres?
Buildings contain many kinds of fibres, and not everything fibrous is asbestos.
- Glass wool and stone wool: industrially made fibres produced from molten glass or rock. Their fibres usually break across rather than splitting lengthwise into thinner strands. Mineral wool can irritate the skin and airways, but it is not asbestos. Read more in the article is there asbestos in wool insulation.
- Organic fibres: cellulose, paper, wood, cotton, hair and plant fibres are entirely different in composition from mineral fibres.
- Other fibrous particles: asbestos-free materials can also contain fibrous or needle-like particles that resemble asbestos under a microscope. That is why shape alone is not enough for identification; the chemical composition is needed too.
How does a laboratory identify an asbestos fibre?
Onelab examines samples with a JEOL SEM-EDS electron microscope. The scanning electron microscope shows the shape and proportions of a fibre at high magnification, including very thin fibres. Elemental analysis (EDS) measures the chemical composition of the fibre, such as its content of magnesium, silicon, iron, calcium and sodium. From the shape and composition together, the fibre can be identified as asbestos and matched to one of the six asbestos types. Material samples are analysed in accordance with ISO 22262-1.
The different analysis methods are compared in the article asbestos analysis methods, and the instrument is described on the page asbestos sample analysis.
If you take a material sample yourself, remove a small piece without breaking the material more than necessary, and wear a respirator of at least class FFP3. Instructions are in the article how to take an asbestos sample.
What does the result tell you?
The result is sent by email, typically on the day the sample arrives. It tells you whether asbestos fibres were detected in the sample and which type of asbestos they are. If asbestos is detected, removing or working on the material is planned as asbestos work, and the removal is carried out by a company authorised for asbestos removal work. The next steps are covered in the article positive asbestos result. If no asbestos is detected, the result applies to the sampling spot and similar material.
How much does an asbestos analysis cost?
The analysis costs €39.90 + VAT per sample, and the price is the same for 1–100 samples. Orders of more than 100 samples can be priced separately. Postage is not included. You can order the analysis online and send the sample to the laboratory by post.