What is Silica?
Silica is a crystalline (crystal-like), naturally occurring, mineral commonly found in materials such as rock, sand, quartz, clay, granite, and concrete.
When these materials are cut, ground, or otherwise disturbed (for example, during activities like construction, mining, or sandblasting), fine dust particles of crystalline silica can be generated.
Silica dust, that is produced from a work process, can enter the body by inhalation through the nose and mouth. This is referred to as ‘total inhalable dust’.
Total inhalable dust consists of two separate fractions. ‘Inhalable dust’ and ‘respirable dust’.
Inhalable dust which consists of larger, heavier particles, tend to get trapped in the nose, mouth, throat or upper respiratory tract where they can cause damage.
Dust which contains particles that are small enough to be breathed deep into the lungs are called respirable dusts. These dusts can build up in the lungs and can lead to lung damage.
Respirable crystalline silica (RCS) refers to tiny particles of silica dust that are small enough (typically less than 10 micrometres in diameter) to be inhaled into the lungs, where they can cause serious health problems.
The table below details several different types of stone and the percentage of silica they may contain.
| Type of stone | Percentage of silica |
|---|---|
| Sandstone, gritstone, quartzite | Above 70% |
| Mortar, concrete | 25% - 70% |
| Shale | 40% - 60% |
| China stone | Up to 50% |
| Granite | 20% - 45% (typically 30%) |
| Slate | 20% - 40% |
| Ironstone | Up to 15% |
| Basalt, dolerite | Up to 5% |
| Limestone, chalk | Up to 5% (typically less than 2%) |
| Marble | Up to 5% (but can contain veins of crystalline silica so the overall content may be a lot higher) |
Table note: Information sourced from HSE publication 'HSG201: Controlling exposure to stone dust' - (hse.gov.uk)
Health effects from RCS exposure
Long-term exposure to RCS can lead to a variety of serious health issues, including:
- silicosis - a chronic lung disease caused by the inhalation of silica dust, leading to inflammation, scarring, and difficulty breathing
- lung cancer - studies have shown a higher risk of lung cancer for people with long-term exposure to RCS
- chronic obstructive pulmonary disease (COPD) - a group of lung diseases, including bronchitis and emphysema, that cause obstructed airflow and breathing difficulties
Some artificial stone products, including work tops for kitchens, have been linked to silicosis in workers when precautions to prevent exposure to the dust have not been in place.
The risk from exposure
Am I at risk?
Occupations with potentially high levels of exposure to RCS include:
- quarrying
- slate works
- foundries
- potteries
- stonemasonry
- construction (when cutting or breaking stone, concrete or brick)
- industries using silica flour to manufacture goods
Industries and processes that can generate RCS
Abrasive blast cleaning
Abrasive blast cleaning, known as direct pressure blasting (DPB) is a process where surfaces are cleaned by the action of particles of grit striking at high velocity.
It's important to use alternative abrasives instead of silica-based abrasives. The use of non-silica grits as substitutes is accepted industrial practice, although they themselves can also pose a risk to health depending on their composition.
Use of sand alternatives
The UK has moved towards alternatives to traditional sand, however, some (for example garnet) may contain crystalline silica impurities, in which case they will be subject to the prohibition unless these amount to less than one percent of the total, but even if below this limit they may still be hazardous in some other way.
The Control of Substances Hazardous to Health Regulations (Northern Ireland) 2003 (as amended) (COSHH NI) provides specific prohibitions which includes a prohibition on the use of sand or other substance containing free silica for the blasting of articles.
COSHH NI does not define a concentration at which a substance is regarded as silica free, so it has been necessary, in practice, to apply a pragmatic limit of one percent. If a substance contains one percent or more of free silica, it is subject to the prohibition.
The Health and Safety Executive’s (HSE (GB)) operational guidance circular OC 273/18:The control of substances hazardous to health regulations blasting using silica sand explains further:
What is the risk to construction workers?
RCS dust is generated during many common construction tasks. These include cutting, drilling, grinding and polishing. HSE (GB) have produced an e-tool specific to the construction sector to help employers comply with COSHH NI to control exposure to RCS and protect employees health.
For more information, please see the following link:
What is the risk to quarry workers?
One of the health risks from working in the quarry industry is that of exposure to fine dust containing crystalline silica (otherwise known as quartz). Quartz is found in almost all kinds of rock, sands, clays, shale and gravel.
Workers exposed to fine dust containing quartz are at risk of developing a chronic and possibly severely disabling lung disease known as "silicosis".
For more information, please see the following link:
What is the risk to stone masons?
Stoneworkers can suffer ill health and disease caused by RCS in the stone dust that they breathe in. These include silicosis, lung cancer and chronic obstructive pulmonary disease (COPD).
The amount of dust you are exposed to depends on several factors including:
- the type of stone being worked (including both natural and artificial/engineered stone)
- the type of tool you are using and whether it is powered or handheld
- how long you are working with the tool
- how well you are using any extraction system (local exhaust ventilation)
- the effectiveness of your mask (respiratory protective equipment)
- how your workshop is organised (including segregation of dusty activities and housekeeping arrangements)
HSE (GB) have produced an e-tool specific to the Stoneworkers to help employers comply with COSHH NI to control exposure to RCS and protect employees health.
For more information, please see the following link:
Other industry HSE COSHH e-tools:
- Brick and tile silica - COSHH e-tool - (hse.gov.uk)
- Ceramics silica - COSHH e-tool - (hse.gov.uk)
- Manufacturing silica - COSHH e-tool - (hse.gov.uk)
Further information on Occupational Lung Disease, is available using the following link:
Managing the risk from RCS
Silica is a substance that is hazardous to health and is classed as a carcinogen (cancer-causing substance).
Duty holders must assess the risks from silica dust and implement controls measures in line with COSHH NI and HSE’s Control of substances hazardous to health (COSHH). The Control of Substances Hazardous to Health Regulations 2002 (as amended). Approved Code of Practice and guidance L5 - (hse.gov.uk).
Hierarchy of control
Although silica is found in several industries, the basics of the COSHH hierarchy of controls apply as follows:
- elimination: physically remove the hazard - stop using silica based products (if possible)
- substitution: replace the hazard - use an alternative substance that does not contain silica
- engineering controls: isolate people from the hazard, local exhaust ventilation (LEV), dust suppression
- administrative controls: change the way people work
- personal protective equipment (PPE) - for example gloves, coveralls, aprons, face masks
- respiratory protective equipment (RPE) - for example masks, breathing apparatus
The best way to prevent this damage is to stop the dust getting into the air. If it’s not airborne, it is therefore more difficult to get into your lungs.
Dust exposure can be controlled using water suppression or dust extraction, either with an appropriate vacuum or local exhaust ventilation fitted to the hand-held equipment. It’s really important to use enough water for the duration of the work. When dust is continuously produced during a work process, it needs to be controlled/suppressed with water until the work activity stops.
Click on the following links to to watch two video clips; with water suppression and without water suppression:
With water suppression
Without water suppression
Exposure limits
Silica dust and RCS have prescribed workplace exposure limits (WELs) stated within the HSE (GB) EH40 publication - (hse.gov.uk). As such exposure must be reduced to below the WEL, to as low as is reasonably practicable (ALARP).
As RCS is capable of causing cancer and/or heritable genetic damage, RCS has a specified workplace exposure limit (WEL of 0.1 mg/m3 expressed as an eight-hour time-weighted average (TWA)).
The maximum amount of silica dust that you should be inhaling during an eight hour working day, after using the right controls, is shown next to the penny in the diagram below. The amount needed to cause damage to your health are not large, and the associated health risks are entirely preventable with the right controls in place.
Health surveillance
Health surveillance means regularly looking for early signs of work-related ill health and putting procedures in place to achieve this.
Health surveillance should be considered for workers who are involved in high-risk occupations, including construction, foundry work, brick and tile work, ceramics, slate, manufacturing, quarries and stonework.
Where workers are regularly exposed to RCS dust and there is a reasonable likelihood that silicosis may develop, health surveillance must be provided.
HSE (GB) has produced simple guidance on what health surveillance is required within the following publication:
Resources
- Appointed doctors topic page
- Control of Substances Hazardous to Health (COSHH) topic page
- COSHH (NI): A brief guide to the regulations
- Cancer and construction: Silica - (hse.gov.uk)
- Construction dust - CIS 36 - (hse.gov.uk)
- Control of exposure to silica dust (INDG463) - (hse.gov.uk)
- Control of Substances Hazardous to Health. Approved Code of Practice and guidance (L5) - (hse.gov.uk)
- Control of Substances Hazardous to Health (COSHH) - (hse.gov.uk)
- Controlling airborne contaminants at work: A guide to local exhaust ventilation (LEV) (HSG258) - (hse.gov.uk)
- Dust control on cut-off saws used for stone or concrete cutting - CIS 54 - (hse.gov.uk)
- EH40/2005 Workplace exposure limits - (hse.gov.uk)
- Health surveillance for those exposed to respirable crystalline silica (RCS) (G404) - (hse.gov.uk)
- Health surveillance for those exposed to respirable crystalline silica (RCS) - Supplementary guidance - (hse.gov.uk)
- Respiratory protective equipment at work (HSG53) - (hse.gov.uk)
- Respiratory protective equipment (RPE) selector tool - (healthworkinglives.scot)
- Silicosis: Lung disease - (hse.gov.uk)
- Using cut-off saws: A guide to protecting your lungs (INDG461) - (hse.gov.uk)
Please note HSENI is not responsible for and cannot guarantee the accuracy of information on sites that it does not manage; and the use of a hyperlink does not mean HSENI endorses the linked site.
Key legislation
- Health and Safety at Work (Northern Ireland) Order 1978 - (legislation.gov.uk)
- Management of Health and Safety at Work Regulations (Northern Ireland) 2000 - (legislation.gov.uk)
- Control of Substances Hazardous to Health Regulations (Northern Ireland) 2003 - (legislation.gov.uk)
- The Control of Substances Hazardous to Health (Amendment) Regulations (Northern Ireland) 2005 - (legislation.gov.uk)
Please note that these links are to the original legislation, visitors should verify for themselves whether legislation is in force or whether it has been amended or repealed by subsequent legislation.
Related to Silica dust
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