Russell Dunne explores the types, common uses and lifecycle of machine-made mineral fibres (MMMF), looking at how the COSHH Regulations specifically apply, and suggesting practical advice for the different occasions when workers will be exposed to MMMF.

As a result of the mandatory reduction in the use of asbestos, and its subsequent prohibition, the use of machine-made mineral fibres (MMMF) has become widespread. These fibres have been developed to mirror the properties of asbestos and so are used in acoustic, thermal, fire protection and reinforcement applications.

Much research has been carried out into MMMF in an effort to predict the likelihood of these newer fibres also causing similar pulmonary diseases to asbestos. However, because they are less likely to be inhaled into the lung, and those that are will be biologically removed much quicker, the risk of fibrosis, lung cancer and mesothelioma is very small (see panel below). Indeed, Wilson et al1 predict the risk of death to a worker blowing glass wool into loft spaces as being 5.6 in a million each year. In context, being president of the Unites States has a risk of one in 80 (three presidents have been shot dead in 240 years), and a US police officer will have a risk of three in 10,000.

Nonetheless, refractory ceramic fibres (RCF), a small subset of MMMF, are classified as potentially carcinogenic to humans (see table 1 overleaf). All forms of MMMF are classed as irritants, mainly affecting the skin and eyes, although in dusty conditions the throat can be irritated. It should come as no surprise that all forms of MMMF come under the Control of Substances Hazardous to Health (COSHH) Regulations.

As table 1 shows, MMMF have many applications. Practitioners will normally encounter them in buildings, so the COSHH Regulations need to be considered. While inhalation exposure should always be as low as reasonably practicable, the Maximum Exposure Limit (MEL) should not be exceeded over a time-weighted average (TWA) eight-hour period. Because the different forms of MMMF and work processes produce very different types of dust, the MEL is expressed in two ways:

• Gravimetric limit: mass of milligrams per cubic metre (mg/m3) of the total inhalable dust – this method generally applies to mineral wools, RCF, and continuous filament fibres; and
• Airborne fibre limit: number of fibres per millilitre of air (f/ml) – generally applies to special-purpose fibres.

The MEL that is likely to be reached first is the one that should not be exceeded. For example, some forms of MMMF will produce large clumps of dust rather than individual fibres, so the gravimetric MEL will be reached much quicker than the airborne fibre MEL. As a rule of thumb, the gravimetric limit should always be used, except for special-purpose fibres.

Finally on this MEL subject, from EH404 the gravimetric limit for all MMMF is 5mg/m3. The airborne fibre limit for mineral wools and continuous filament fibres is 2f/ml, and for RCF and special purpose fibres it is 1f/ml, because the latter are potentially carcinogenic. The advice must be to keep well below the MELs to avoid confusion!

For work with MMMF, a COSHH assessment will need to be produced, setting out the duration of the work, the type of material (to estimate fibre release), and the location, i.e. whether at head height, or in an enclosed space. Based on this information, control measures can be put in place, such as using a dust suppressant, providing exhaust ventilation, and/or respiratory protective equipment.

Health surveillance of those who work with MMMF products is also required under COSHH, in that health records for workers must be collected, maintained and kept for 40 years from the last entry.

The Approved Code of Practice to the Regulations5 specifies what the record should contain, but it is also a good idea for workers to be trained in self-examination for dermatitis.

Monitoring is required where the MEL may be exceeded. It is worth remembering that while the MEL may not have been exceeded, the enforcing authorities may still take action if they believe that exposure levels could have been reasonably lower. For a repetitive task it may be worth considering monitoring as part of the assessment process. Following analysis, the results can be used to check that the initial fibre and dust estimates were accurate, or to adjust the COSSH assessment, if necessary. Low readings will also provide reassurance for workers carrying out similar activities.

MMMF in practice

As with asbestos, the risks from MMMF arise when they are disturbed and become airborne. Left alone in situ, the possible risk to the general population is very low, as the products do not readily release fibres.6 However, they can degrade over a period of time, particularly in quilt form. Anyone who has lifted a perforated ceiling tile forming part of an old Frenger radiant-heated ceiling would likely have received a face full of fibres, and probably made sure they were masked up the second time! Interestingly, researchers at Cornell University have suggested that MMMF dust may even contribute to ‘sick building syndrome'.

• The lifecycle of MMMF is typically:
• MMMF is typically: manufacture;
• installation;
• maintenance; and
• removal

Manufacture is likely to be the least risky stage because, even though the hazard level will be high, the control measures should be good. Most manufacturing plants incorporate dust-suppression systems and local exhaust ventilation (LEV) to minimise the need for personal protective equipment. (Remember that the LEV must be subjected to a near-annual thorough examination and test, while daily, weekly and monthly checks as regards satisfactory operation and maintenance should be recorded in a procedural document, in the use of which the operator, supervisors and managers have been trained.)

Protection during installation will depend on the form that the MMMF product takes, and its location; a data sheet should be provided by the manufacturer. For example, loose-blown material installed in an enclosed loft space will generate high dust levels. Hopefully, this will have been considered at the design stage, and rigid-form or coated insulation specified. If not, ask why not and what control measures are required.

Most rigid insulation comes in variable s so it can be selected
to minimise cutting. If cutting is required it should be done before
installation and in a screened-off and locally-ventilated space. The
method statement should clearly require this, and that ventilation
ducts be blocked off to prevent the spread of MMMF dust.

As there will be some fibre release during installation workers should be provided with disposable overalls, gloves, eye protection, and a face mask. The type of mask required will depend on the fibres involved, and the manufacturer should detail the requirements but, if in doubt, a disposable P3 mask, which conforms to BS EN 143:2000, should generally be appropriate.8

Try not to use overalls with elasticated neck, wrist and ankle coverings, as the fibres can be attracted to these points and exacerbate any irritation. Reusable overalls (e.g. a boiler suit) may be practical but need to be stored and washed separately from other clothes.

During maintenance operations it may be necessary to disturb MMMF products to access materials or services. As during installation, the level of precautions required will depend on the type of MMMF product, the location, and the duration of the task. Working above the head poses a greater risk, as any released fibres will be in the breathing zone.

When removing MMMF from a building, either in a ceiling void or partition wall, the product will generally be an older material that has degraded substantially. Prolonged exposure to heat and vibration will exacerbate this. Depending on the condition, it may be appropriate to screen off areas and block off any duct openings to prevent contamination of adjacent areas. For material in particularly poor condition it is a good idea to follow asbestos-removal procedures, using a sealed enclosure area and negative-pressure unit.

Personal monitoring should be seriously considered in the first instance. The MMMF may need wetting to minimise dust disturbance. Sweeping up MMMF dust should be avoided as this will cause even more dust and fibres to become airborne. The most efficient method for removing dust is by vacuuming.

Final thoughts

The widespread use of MMMF products has had a positive effect on energy savings and environmental protection without the deadly risks associated with asbestos. Modern manufacturing techniques for MMMF are resulting in the production of fibres that are less likely to be inhaled and less durable in the lung. While there is no need to replace installed MMMF with newer versions, neither is it the time to take the foot off the gas and advocate less control over exposure.

The sensible approach is for organisations to have:
• policy and general procedures for working with MMMF through their lifecycle;
• training for workers on the hazards and procedures to follow to reduce them;
• job-specific COSHH assessments and method statements;
• appropriate PPE and training in its effective use;
• health surveillance and monitoring, where appropriate; and a regular review of the arrangements.
• In this way, we can maximise the benefits and minimise the risks from MMMF.

References
1 Wilson R, Lamger AM, Nolan RP (1999): ‘A Risk Assessment for Exposure to Glass Wool' in Regulatory Toxicology and Pharmacology, Vol.30, pp96-109
2 Guidance Note (EH)46: Man-made mineral fibres, HSE
3 Rushton, T (2007): Investigating Hazardous & Deleterious Building Materials, RICS Books
4 Guidance Note (EH)40: Workplace Exposure Limits, HSE
5 www.hse.gov.uk/coshh/further/publications.htm
6 Institute for Environment and Health (1997): ‘Fibrous materials in the environment. A review of asbestos and man-made mineral fibres'
7 ‘Effects of man-made mineral fibers in settled dust on Sick Building Syndrome in air-conditioned offices', Proceedings of Indoor Air 1993, Vol.1 p291
8 BS EN 143:2000 – Respiratory protective devices. Particle filters. Requirements, testing, marking specifies particle filters for use as components in unassisted respiratory protective devices, with the exception of escape apparatus and filtering facepieces
9 For more on the potential risks posed by carbon nanotubes, see the article by Jim Noonan in the January 2009 issue of SHP, entitled ‘Shrinking certainty', (Vol.27 No.1) – www.shponline.co.uk/article.asp?pagename=archive&article_id=8300