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Machine Made Mineral Fibres (MMMF) & Refractory Ceramic Fibres (RCF): Assessment & Measurement

Updated: May 15, 2020

Asbestos fibres are capable of causing serious conditions such as fibrosis of the lungs and lung / pleura cancer. Over time, further concerns have been raised regarding possible effects caused by the inhalation of synthetic fibrous material which has been used to replace asbestos.

What are MMMFs and RCFs: Processes and General Uses

Synthetic fibres are widely used across the building industry. They're also known as Machine-made Mineral Fibres or Man-made Mineral Fibres. The materials include continuous glass fibres (MMMF), installation wools made of glass, rock or slag fibres.

Refractory ceramic fibres, on the other hand, are generally formed with aluminium silicates.

Glass fibres are generally used to reinforce other materials, such as resins and plastics. Whereas, the installation wools are generally utilised due to their thermal and acoustic properties. Rockwool. For example is great for lining the inside of sound enclosures, as it is great at absorbing sound energy. Simular types of materials are used as loft or wall insulation for thermal reasons.

Refractory ceramic fibres are used mainly in high-temperature insulation products.

How Materials Are Made

Synthetic vitreous fibre manufacturing involves a process whereby continuous glass fibres are formed by extruding molten glass through small diameter holes. The fibre diameters are usually fairly large in comparison to insulation wools. Often, the size of these fibres means they are not inhaled deep into the lung or lower respiratory tract, eliminating many potential chronic respiratory effects.

Insulation wools and refractory ceramic fibres are manufactured by dropping molten material into a series of spinning disks or wheels where the material is drawn off by blowing the product with steam or hot gasses. This process generates fibres of various sizes and diameters. In addition, some fibres with diameters of less than 3 microns could be formed. These can become respirable penetrating the lower respiratory tract and deep lung tissue. It's often these types of fibres that pose a specific health risk due to their ability to enter deep into the lungs, similar to asbestos.


In 1988, the International Research on Cancer (IARC) had originally categorised glass wool, rock wool and slag wool into IARC Group 2B (Possibly Carcinogenic to Humans). This was based on a lack of evidence proving that cancer could be formed in humans. However, sufficient evidence was found that cancer could form in animals. It placed continuous filament glass into Group 3 (Not Classifiable as to Carcinogenicity to Humans). This was based on inadequate carcinogenicity in humans and animals.

A review was conducted in 2001 and as a result, new research and evidence placed rock wool, insulation glass wool, slag wood and continuous filament glass into IARC Group 3 because of the inadequate evidence of carcinogenicity to humans. However, the International Agency for Research on Cancer (IARC) categorised RCF as Group 2B: Possibly Carcinogenic to Humans due to the seemingly high biopersistence.

Workplace Exposures

Refractory Ceramic Fibres have separate workplace exposure limits (WELs) in the EH40 Workplace Exposure Document, away from Machine/Man-made Mineral Fibres. This is due to the carcinogenicity of RCF.

Fibres can become airborne during the initial manufacture of the fibrous products. That said, there's a foreseeable risk of exposure to airborne fibres during building installations, removals and construction processes. Concentrations can depend on how confined the work area is as well as the duration and type of work.

High-level exposures can occur during furnace wrecking and demolition work involving vitreous synthetic fibres. These processes may present particular problems with some refractory ceramic fibres where the products have been heated to temperatures in excess of 1000 degrees celsius. The materials can undergo partial conversion to cristobalite, a crystalised form of silica which can be extremely harmful if inhaled.

Skin and Respiratory Tract Irritation

All fibres are known to be irritating to the skin and respiratory tract. Exposures may lead to itchy and irritated skin along with an irritated throat leading to coughing. Exposures should be reduced to an acceptable level.

Quantifying Exposures

Exposures can be quantified by undertaking personal exposure monitoring. This should be undertaken by a competent occupational hygienist. With this method,

airborne respirable fibres are collected by drawing a measured volume of air through a membrane filter mounted in an open-faced filter holder fitted with an electrically-conducting cowl. This method is outlined in the HSE Methods for the Determination of Hazardous Substances (MDHS) 59/2.

Controlling MMMF and RCF

Control measures can be put in place to reduce exposures to MMMF and RCF. By combining a number of control strategies, a residual risk can be achieved sufficiently.

During the cutting and machining of the products containing these fibres, local exhaust ventilation (LEV) should be utilised. The LEV should comply with the COSHH Regulations and meet the criteria set out in HSG258. Extracting at the source of emission is best practice.

Workers should Limit the use of power tools unless they are equipped with local exhaust ventilation/on-tool extraction and dust collection systems.

Where possible, workers could dampen down the workpiece to prevent fugitive emission, depressing the fibres and dust. If working with a fibrous material, such as rock wool or glass wool, dampening the material with a water sprayer could reduce exposures dramatically.

Work areas should be cleaned and maintained frequently. Dampening down floor areas may help suppress the fibres. dry sweeping should be prohibited and instead, a vacuum cleaner fitted with a HEPA filter.

Long sleeve protective clothing should be provided and worn to help prevent the fibres from coming into contact with the skin.

Where respiratory protective equipment (RPE) is required. The face pieces should be fit for purpose and have undergone routine checks prior to use along with a suitable and sufficient face fit test. Respiratory protective equipment should be worn as a last resort, or in combination with other methods of control such as LEV, water suppression, staff rotation, provisions of information, instruction and training and so on.

Do You Need Support with COSHH?

It is hoped that this article goes some way to providing a brief overview of COSHH. If you wish to know more on this subject or need support with your COSHH assessments, exposure monitoring or the testing of your LEV systems, RPE Fit Testing then please feel free to get in touch with us through social media or our website (, by email at or simply give us a call on 01709 931299.

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