Health and Safety
Executive / Commission
Freedom of Information
Author unit / section: Metals and Minerals
Target audience: All HSE and LA visiting staff
1 There has been a long history of respiratory disease associated with exposure to respirable crystalline silica. Improvements in workplace standards of control have led to a marked improvement in ill-health statistics in the UK since the 1930s. However, although silicosis is no longer a major industrial disease in this country, it has not been completely eliminated. Since 2003 there have been 295 assessed cases of silicosis and typically each year between 10 and 30 deaths are recorded with silicosis being an underlying cause. The annual incidence has shown no sign of a decline over the last few years.
2 Crystalline silica is one of the most abundant minerals in the earths crust and consists of silicon and oxygen atoms (SiO2). There are different crystalline forms of silica, with the most common one being quartz. Quartz is found in varying amounts in almost all types of rock, sands, clays, shales and gravel. For example, sandstone is more than 70% quartz, whereas granite might contain 15-30% quartz. In the high temperatures of industrial furnaces and kilns, quartz may convert to another crystalline form of silica known as cristobalite.
3 Crystalline silica is also a major constituent of construction materials such as bricks, tiles and concrete. Many common workplace activities such as cutting, drilling, grinding and polishing, produce fine dust containing respirable crystalline silica (RCS). Silica flour (up to 100% RCS) is produced and used for a wide variety of purposes.
4 An increasing amount of new evidence on the health risks of RCS has become available in recent years. HSE published a review of the evidence in two phases;
Phase 1 was published in 2002 and Phase 2 in 2003.
5 The aims of the Phase 1 review were to:
6 In 2005 Disease Reduction Programme initiated a baseline occupational hygiene survey to characterise current exposures and control practices in the brick making, quarries, stonemasonry and construction sectors. The aims included obtaining up to date RCS exposure data and to determine the standard of control practices being employed. The initial findings suggested that exposure levels were higher than the estimates made by the relevant industries. The report is expected to be published in the first half of 2008.
7 RCS is harmful to the lungs, causing the disease silicosis in which the lungs develop small, hard nodules of scar tissue resulting in coughing and breathing difficulties. The speed of onset of silicosis depends on the exposure. Although low-level chronic exposure to RCS may take many years to produce the disease, intense daily exposure can cause severe illness much more quickly. Exposure to RCS is also a potential cause of chronic obstructive pulmonary disease (COPD) which interferes with air movement in and out of the lungs, often associated with a chronic cough. Heavy and prolonged exposure to RCS may also cause lung cancer once silicosis is established.
8 An evaluation of the scientific evidence on RCS by HSE in 2002 showed a 20% risk of developing silicosis after 15 years of exposure at a level of 0.3mg.m-3 (averaged over 8 hours). At 0.1mg.m-3, the risk would be down to 2.5%, and at 0.04mg.m-3, the risk would be 0.5%. These levels of RCS are very low and RCS is always a part of any dust cloud created by working on silica-containing materials.
9 These risk estimates are based on findings in workers who breathed in dust containing RCS that was produced by mechanically cutting into sandstone. The surfaces of the RCS particles to which the workers were exposed had been freshly cut (fractured) and were relatively uncontaminated by other minerals.
10 The HSE Phase 2 review findings showed considerable variability; some studies suggested no increased risk of lung cancer due to RCS, but others showed an excess of lung cancer deaths that could only be explained by exposure to RCS. Alternative explanations such as cigarette smoking, asbestos, or socio-economic status could not adequately explain the lung cancer findings.
11 The observed excess risks of lung cancer were all seen in workers who commenced employment (usually in the granite and other stone industries) in the 1930s and 1940s before modern dust control systems, when workplace dust exposures were likely to have been considerably higher than current levels. These workers generally stayed in these industries for all of their working lives. It is difficult to judge retrospectively what the historical levels of exposure would have been in these industries. However, the pattern of evidence suggests that an increased risk of lung cancer would only be apparent with very heavy and prolonged occupational exposures. It was also strongly suggestive, but not entirely definitive, that an increased risk of lung cancer will only occur in workers with silicosis.
12 Research Report 595 The burden of occupational cancer in Great Britain was published in 20073. It identifies silica as one of the major contributors to the burden of lung cancer estimates attributable to occupational exposure.
13 The HSE Phase 1 review concluded that for any particular level of exposure, there is likely to be some variability in the risks of silicosis according to the circumstances of the exposure conditions. The highest risks are predicted to result from exposures to very fine particles, and to dry freshly fractured particles of RCS. Somewhat lower risks are predicted from exposure to aged particles that have not been freshly fractured, and where the particle surfaces are contaminated with aluminium-containing minerals. Appendix 1 summarises the position.
14 A 3-year pan-European research project known as Siliceram started in October 2004 involving 8 national Trade Associations, 22 SME manufacturers of ceramic products and 8 research organisations. The project objectives included increased understanding of how the chemistry, size and surface properties of different RCS forms affects their toxicity; and to identify potential and practical ways to render RCS safer. Training materials have been produced to assist in raising worker awareness of the health effects of exposure to RCS.
15 From the emerging results of toxicity testing of factory dusts containing RCS it appears the UK ceramic industry will continue to criticise the HSE risk estimates described above as being worst case and not representative of typical industrial exposures. A summary of the project findings and the training materials can be viewed on the British Ceramic Confederation website.
History of the OEL for Respirable Crystalline Silica
16 A MEL for RCS of 0.4 mg.m3 (8-hr TWA) was introduced in 1992, replacing the earlier OES of 0.1 mg.m3. In 1997, the value of the MEL was adjusted to 0.3 mg.m3 following adoption of the ISO/CEN EN481 sampling convention for respirable dusts. This change reflected a modification in measurement methodology, not an increased stringency of control.
17 When the system of MELs and OESs was replaced by a new system with a single type of OEL known as a Workplace Exposure Limit (WEL), the MEL of 0.3 mg.m3 for RCS was converted to a WEL of the same value.
18 Following public consultation by means of Consultative Document CD203 [604KB]
a revised WEL of 0.1mg.m3 for RCS was adopted on 1 October 2006.
19 There is widespread occupational exposure to RCS in a diverse range of industry sectors including mining and quarrying, construction, ceramics, heavy clay (brick & tile manufacture), refractories, foundries and stonemasonry. HSE estimates that at least 100,000 workers are regularly exposed, but many more workers may be exposed on a less regular basis.
20 A list of many of the relevant processes and activities is given in Appendix 2.
21 Control of substances hazardous to health should be in accordance with COSHH Regulation 7. Control will only be treated as adequate if the principles of good control practice set in the eight bullet points listed in Schedule 2A are applied.
22 Practical guidance on securing adequate control is given in COSHH Essentials which includes control guidance sheets on more than 50 tasks/processes across a range of industries where exposure to RCS occurs. The relevant guidance sheets can also be found on the HSE Website
23 In April 2006, the European Network on Silica (NEPSI) signed an Agreement on Workers Health Protection through the Good Handling and Use of Crystalline Silica and Products containing it under the Social Dialogue Agreement (SDA). The signatories were European trade unions and employer associations of the aggregates, cement, ceramics, foundry, glass, industrial mineral wool, natural stones and pre-cast concrete sectors. They undertook to apply the agreement and practices, conduct risk assessments, organise training, dust monitoring and health surveillance and to monitor the agreement. Many of the good practice guidance sheets are based on Silica Essentials but the range of sheets is far wider. For further details, see Appendix 3. The construction sector is not a signatory to this agreement.
24 HSE welcomes the SDA as a positive step towards improving control over worker exposure to RCS in the workplace. Duty-holders can follow either Silica Essentials or the good practice guidance under the SDA to establish the benchmark for good practice. As with all such guidance, it is not compulsory, but if followed it will normally help to demonstrate compliance with the law.
25 Where an employer opts to follow the SDA guidance, HSE Inspectors will continue to assess compliance against the COSHH Regulations.
26 Both COSHH and the SDA require health surveillance for silicosis where appropriate. Current HSE guidance is set out in COSHH Essentials Sheet G404 [57KB] An occupational health professional must assess the benefits of chest x-rays against the radiation health risk.
27 Work with stakeholders is in progress to develop further guidance on this issue.
28 Inspectors are asked to assess whether all reasonably practicable precautions have been taken to control RCS exposure in accordance with COSHH Reg 7, Schedule 2A, the ACoP and relevant guidance. In cases of doubt refer to the relevant Sector.
29 The exposure benchmark for inhalation of RCS is considered to be 0.1 mg.m3 (8-hour TWA) (established standard).
30 The control measures given in guidance establish the standards that can be used to meet the benchmark.
31 Absence of compliance with the benchmark standard is considered to create a risk of "serious health effect" (see OC 130/5). Non-compliance with the benchmark will produce a "substantial" risk gap giving an initial enforcement expectation of at least an Improvement Notice.
32 Where exposure is considered to be gross (defined as >1.0 mg.m3 8-hour TWA) there may be a greater risk of acute silicosis and a Prohibition Notice should be considered. In cases of doubt consult the relevant Sector or SG.
33 The Sector contacts are:
34 HSE has established an international Silica Exposure web community to provide a centralised place to capture and share information about publicly available reports, documents and links on RCS. It helps people communicate with others managing, delivering and contributing to work on control of exposure to RCS.
35 The topic packs on Migrant Working [220KB] Duty to Manage Asbestos [676KB], and Worker Consultation and Involvement [263KB] may be relevant and useful when engaging with this sector, and also the Diversity & Delivery pages.
Silica risks
Potency factors |
Comment |
Some relevant circumstances |
High proportion of respirable particles of very small size |
Enhanced potency compared with exposure to the same mass of larger size respirable particles |
High energy, sustained grinding and abrasive processes, e.g. dry polishing and cutting. Exposure to finely divided, high purity, silica powders e.g. silica flour. |
Production of dry, freshly created particles, of respirable crystalline silica |
This is the reference state of RCS against which other conditions and circumstances are compared. |
Drilling, blasting and the lower energy abrasive processes |
Freshly created surfaces are wetted |
Reduced potency compared to dry freshly created surfaces |
Wet extraction or handling processes. Wet cutting of stone or solids containing crystalline silica. |
Respirable dust particles are aged i.e. they were created sometime ago and then made airborne later |
Reduced potency compared with reference state - freshly created particles |
Re-suspension of settled respirable dust. Release of old particles during processing e.g. unloading powdered product. |
Presence of aluminium-containing clay minerals intimately mixed with silica particles |
Reduced potency compared with reference state - freshly created particles. |
Some processes involving clay extraction and handling. Mines extracting low-rank coals. |
Silica is in the form of cristobalite |
Cristobalite has equivalent potency to quartz, the most common form of silica. Note: For decades cristobalite was believed to be twice as toxic as quartz but this is not the case. |
Heating of quartz-containing materials e.g. furnaces and kilns. Some naturally occurring rocks contain cristobalite. |
Quarry |
Slate |
Stonemasonry work |
Foundry |
Potteries |
Brick and Tile |
Construction |
Drilling |
Slate stone extraction |
Wet sawing (Primary circular saw) |
Sand handling and reclaim |
Body preparation (Blunger?) |
Milling |
Drilling |
Extraction of stone (inc background exposure and vehicle driver exposure) |
Wet sawing (Primary circular saw) |
Hand chiselling |
Shotblasting |
Casting |
Sand addition to mix |
Cutting (various) |
Primary and secondary crushing |
Splitting |
Pneumatic chiselling |
Shakeout |
Fettling |
Addition of surface sand (brick only) |
Scabbling |
Conveyors and screens |
Dressing |
Handheld powered rotary tools (cutting and polishing) |
Fettling |
Loading and unloading kiln |
Movement of dry bricks |
Abrasive cleaning |
Packaging of final product (inc lorry loading and sack filling) |
Packing |
Polishing (Dry) |
Furnace lining removal |
Assembly and packing |
Dehacking |
Drilling and Boring |
Stock piles |
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Cleaning |
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Chasing using hand-held tools |
Coating plants |
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Spraying glazes |
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Crushing and screening |
Sand drying |
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Abrasive use |
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Tunnelling |
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Pneumatic breaker indoors |
The SDA for Silica is an autonomous multi-sectoral bi-partite agreement signed by employer and employee organisations involving all 27 EU member states covering a total of 15 industries including aggregates, cement, ceramics, foundries, glass fibre, special glass, container glass, flat glass, industrial minerals, minerals wool, mines, mortar, natural stone and pre-cast concrete.
Its full title is Agreement on Workers Health Protection through the Good Handling and Use of Crystalline Silica and Products containing it" and HSE was one of three official observer organisations to this EC-funded process.
The agreement covers the production and use of crystalline silica and materials/ products/ raw materials containing it and is intended to secure control over silica by:
It is important to note that only those workers employed by an organisation which, through its trade body, is a signatory to the agreement are covered by the SDA. Within a sector not all trade bodies will be signatories and therefore workers of an organisation which is a member of a trade body but not signed up to the SDA, and workers of an organisation which is not a member of a trade body, may not be covered by the agreement. They may elect to act as though they were signatories and implement the requirements of the SDA voluntarily, including the reporting requirements.
Some trade bodies have agreed to alert companies who are not their members to the existence of the SDA and invite them to participate in the arrangements on a voluntary basis, e.g. foundry industry.
An electronic reporting procedure has been introduced and the information is fed into the Negotiating Platform on Silica (NePSi) Council which will forward information on to the European Commission, which is monitoring the effectiveness of this agreement. Trade bodies will be provided with the data arising from this reporting process.
The Agreement is supported by 8 Annexes which include:
Under the reporting requirements reporting will be every 2 years and collated for site, company, country and sector level.
Each company will be required at site level to:
A key feature of the SDA is the Good Practice Guide which identifies hazards and control measures. It is in two parts:
The Good Practice guide has drawn heavily upon the UKs COSHH Essentials for silica. The difference between COSHH Silica Essentials and the SDA Good Practice Task Guidance sheets is small.
HSE has welcomed the agreement as a valuable contribution to improving good practice and reducing the risk of ill health in industries where workers are exposed to RCS.
The Agreement does not override national exposure limits and the UK WEL of 0.1mg/m3 will still apply.
Industry has been advised through CHARGE, FIAC and QNJAC that Inspectors will enforce using the COSHH Regulations and expect dutyholders to comply with Regulation 7 and Schedule 2A (Principles of Good Practice).
For practical purposes, whilst Inspectors will continue to use COSHH Essentials as the benchmark for enforcement, other equally effective measures can be used and this can include the SDA Good Practice Guidance.
Consequently, to avoid duplication of effort, dutyholders may chose to follow SDA guidance rather than COSHH Essentials and this is acceptable.