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Man-Made Vitreous Fibres (MMVF)
Man-Made Vitreous Fibres (MMVF) is a collective term used to describe synthetic fibres like glass wool, rock wool and refractory ceramic fibres. Previously, these fibres were known as Synthetic Mineral Fibres (SMF). The biological effects of these fibres are determined by the fibre diameter and length, chemical nature and biopersistence in the body when inhaled.
Safe Work Australia has now adopted an 8-hour time-weighted average (TWA) respirable workplace exposure standard (WES) of 0.5 fibres per millilitre (f/mL) to be applied to MMVF belonging to the group of refractory ceramic fibres, special purpose glass fibres and fibres with high biopersistence. In situations where almost all the airborne material is fibrous, a complementary inhalable dust exposure standard of 2 mg/m3 (8-hour TWA) shall be applied to minimise mechanical irritation from largely non-respirable fibre. This inhalable dust exposure standard also applies to glass wool, rock (stone) wool, slag wool, continuous glass filament and low biopersistence MMVF and is not to take precedence over the respirable fibre standard, where the respirable fibre standard is applicable.
For those applications where MMVF is combined with other material such that the proportion of respirable fibres is extremely low or is difficult to measure because of the larger portion of non-fibrous MMVF material, it is appropriate to apply the exposure standard for nuisance dusts of 10 mg/m3, measured as inhalable dust (8-hour TWA). See the Safe Work Australia publications Workplace Exposure Standards for Airborne Contaminants(1) and Guidance on the Interpretation of Workplace Exposure Standards for Airborne Contaminants(2) for more information.
The airborne fibre concentration of MMVF should be determined in accordance with the National Occupational Health and Safety Commission (NOHSC) Guidance Note on the Membrane Filter Method for the Estimation of Airborne Synthetic Mineral Fibres(3). The airborne concentration of inhalable fibrous dust can be determined in accordance with, for example, Australian Standard AS 3640: Workplace atmospheres – Method for sampling and gravimetric determination of inhalable dust.
No exposure standard should be applied without reference to the Guidance on the Interpretation of Workplace Exposure Standards for Airborne Contaminants(2), and to the related documentation.
DEVELOPMENT OF EXPOSURE STANDARDS
At its meeting on 8 March 1990, the NOHSC recommended an 8-hour TWA exposure standard of 0.5 f/mL be applied to all forms of MMVF and, in addition, where almost all the material is fibrous, a complementary exposure standard of 2 mg/m3 (TWA) of inspirable dust shall be applied to minimise upper respiratory tract irritation from largely non-respirable fibres. This exposure standard was declared taking into account the cost to industry and the community from suffering encountered by individuals and their families as a result of past uncontrolled exposures to other fibrous materials like asbestos and reflected the level of community concern and expectation that appropriate controls should be implemented to avoid future problems with MMVF. Given the uncertainty at the time as to exactly what levels of MMVF exposure would lead to adverse health effects and that compliance with the proposed exposure standard could in most cases readily be achieved, the National Commission recommended an 8-hour time-weighted average exposure standard of 0.5 f/mL be applied for all forms of MMVF.
In 2002, the International Agency for Research on Cancer (IARC) published an evaluation of new and more complete epidemiological studies and animal experimentation(4) available since the original NOHSC review in 1990. In their evaluation, the IARC stated glass wool, continuous glass filament, rock (stone) wool and slag wool were ‘not classifiable as to their carcinogenicity to humans’. This was considered a downwards re-classification from IARC Group 2 to Group 3. Refractory ceramic fibres (RCF) and special purpose fibres remained classified in IARC Group 2B as ‘possibly carcinogenic to humans.’
Following this decrease in concern for adverse health effects resulting from exposure to some MMVF and development by industry of fibres which are less persistent in the lung following inhalation, Safe Work Australia agreed to conduct a review of the workplace exposure standard for MMVF to take into account the IARC assessment(4) and the EU removal of carcinogen classification for new, less biopersistent products(5).
A public consultation period was held by Safe Work Australia from 16 April to 8 June 2012 followed by discussion with key industry stakeholders to refine the text of the listing in the Workplace Exposure Standards for Airborne Contaminants. Safe Work Australia also consulted with the Australian Institute of Occupational Hygienists (AIOH) who supported the assessment by IARC.
The revised exposure standard was approved by Safe Work Australia Members at their meeting in Melbourne on 21 November 2012.
1. Safe Work Australia, Workplace Exposure Standards for Airborne Contaminants.
2. Safe Work Australia, Guidance on the Interpretation of Workplace Exposure Standards for Airborne Contaminants.
3 National Occupational Health and Safety Commission (NOHSC), ‘Guidance Note on the Membrane Filter Method for the Estimation of Airborne Synthetic Mineral Fibres’ in Technical Report on Synthetic Mineral Fibres and Guidance Note on the Membrane Filter Method for the Estimation of Airborne Synthetic Mineral Fibres, AGPS, Canberra, 1989.
4. International Agency for Research on Cancer, IARC Monographs on the Evaluation of the Carcinogenic Risks to Humans, Volume 81: Man-made Vitreous Fibres, International Agency for Research on Cancer, Lyon, 2002.
5. European Union Annex VI to Regulation (EC) No 1272/2008, updated by the 1st Adaption to Technical Progress to the Regulation.