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 hair and cannot be seen with the naked eye. What makes asbestos fibres special is that the fibre bundles split lengthwise into ever thinner strands. That is why damaged asbestos material releases respirable fibres that can reach deep into the lungs.
In this article you will learn how an asbestos fibre is structured and how big it is, why it was added to building materials, when fibres get into the air, how asbestos fibres differ from mineral wool and other fibres, and how the laboratory identifies them.
What does an asbestos fibre look like?
Asbestos is not a single mineral but a collective term for six silicate minerals that have crystallised in fibrous form in nature. Such a fibrous growth form is called asbestiform. The same mineral can also occur as ordinary, non-fibrous rock, in which case it is not asbestos. The differences between the mineral groups are described in the article Serpentine and amphibole, and the six types of asbestos are presented on the page Types of asbestos.
Bundle, fibre and fibril
An asbestos strand, such as one you might see in a raw mineral, is in reality a bundle of an enormous 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 distinguishes asbestos from most other fibres and explains why respirable dust is created so easily.
How small is an asbestos fibre?
Air measurements and occupational safety use the definition of the World Health Organization (WHO): a countable fibre is longer than 5 micrometres and thinner than 3 micrometres, and the ratio of length to width is greater than 3:1. Fibres of this size are respirable. Many asbestos fibres are much thinner still, and the thinnest cannot be seen with an ordinary light microscope. That is why a laboratory is needed to identify asbestos fibres.
Why was asbestos fibre used in building materials?
Because of its properties, asbestos fibre was mixed into a great many products during manufacture.
- Heat and fire resistance: asbestos does not burn and withstands high temperatures. That is why it was used in insulation, seals and fire protection.
- Tensile strength: the fibres reinforced cement, filler, mortar, adhesives and plastics in the same way that reinforcement strengthens concrete.
- Chemical and wear resistance: asbestos fibre resists many chemicals and wear, which suited, for example, floor coverings and roofing products.
In the finished product, the fibres are bound in cement, bitumen, adhesive, filler or plastic and cannot be seen by eye. A product containing asbestos looks exactly like an asbestos-free one.
When do asbestos fibres get into the air?
An intact, undisturbed asbestos material generally does not release fibres into the air, because the fibres are bound in the material. Fibres come loose when the material is mechanically destroyed. Typical situations are:
- sanding, drilling, sawing, chiselling and milling
- removing and breaking boards, floor coverings and sheets
- touching and wear of crumbling materials such as old pipe insulation or sprayed insulation
- weathered surfaces of asbestos cement that have long been exposed to wind and weather, for example during pressure washing or brushing
From hard materials such as asbestos cement, vinyl tiles and hardened adhesives, fibres are released mainly when they are worked on, but sanding and sawing release fibres from them too. Soft and crumbling materials such as some pipe insulation and sprayed fire protection can create dust even with a light touch.
Thin fibres are light, float in the air for a long time and are carried to other rooms by air currents. So do not sweep up possible asbestos dust or vacuum it with an ordinary vacuum cleaner; instead, wipe the surfaces with a damp cloth.
Why is asbestos fibre dangerous?
Inhaled thin fibres can reach the outermost parts of the lungs and the pleura. The long, thin shape of the fibres and their durability make it difficult for the body to get rid of them, and some of the fibres remain in the tissue for a long time. All types of asbestos cause cancer. Asbestos-related diseases usually only appear a long time after exposure.
If you are worried that you have been exposed, talk to your doctor or your occupational health service.
How does asbestos fibre differ from other fibres?
There are many kinds of fibres in buildings, and not everything fibrous is asbestos.
- Glass wool and rock wool: industrially produced fibres made from molten glass or rock. The fibres usually break across and do not split lengthwise into thinner fibres. Mineral wool can irritate the skin and airways but is not asbestos.
- Organic fibres: cellulose, paper, wood, cotton, hair and plant fibres have a completely different composition from mineral fibres.
- Other fibrous particles: asbestos-free materials can also contain fibrous or needle-shaped particles that resemble asbestos under the microscope. That is why shape alone is not enough to identify asbestos; the chemical composition is needed too.
How does the laboratory identify an asbestos fibre?
Semlab examines samples with a JEOL SEM-EDS electron microscope. The scanning electron microscope shows the shape and proportions of the fibre at high magnification, even for very thin fibres. The elemental analysis (EDS) measures the chemical composition of the fibre, for example the proportions of magnesium, silicon, iron, calcium and sodium. Shape and composition together make it possible to identify the fibre as asbestos and determine which of the six types of asbestos it is. Material samples are analysed in accordance with ISO 22262-1.
Different analysis methods are compared in the article Analysis methods for asbestos, and how the instrument works is described on the page Analysis of asbestos samples.
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. You will find instructions in the article How to take an asbestos sample.
What does the result show?
You receive the result by email in English, usually on the same day the sample arrives at the laboratory. It shows whether asbestos fibres were detected in the sample and which type of asbestos it is. If asbestos is detected, demolition and working on the material are planned as asbestos work under the occupational safety rules, and the demolition is carried out by a contractor specialising in asbestos removal. What to do after the result is described in the article Positive asbestos result. If no asbestos is detected, the result applies to the sampling location and identical material.
How much does an asbestos analysis cost?
The analysis costs €49.99 incl. VAT per sample, and the price is the same for 1–100 samples. For orders of more than 100 samples we can make a separate arrangement. Postage is not included in the price. You can order the analysis online, pay by card and send the sample as a letter or small parcel with your national postal service to the laboratory in Finland.