The silica dust hazard – what is it and why should I be concerned?


    By Nayab Sultan

    Every year an estimated 2.3 million workers out of a global workforce of approximately 3.5 billion die as a result of work-related accidents and incidents. An estimated 160 million suffer as a consequence of work-related diseases with some two million dying from these diseases annually. It is estimated five per cent of all cancer cases may be work-related.

    Silica dust: Regulations and controversy challenge construction industry/government relationships

    In terms of the deaths from work activities about eight per cent can be directly attributed to respiratory diseases namely silicosis, pneumoconiosis, asbestos related diseases (ARD), chronic obstructive pulmonary disorders (COPD), occupational asthma, metal-lung disease and organic dust diseases.

    Respirable Crystalline Silica (RCS) is an abundantly found naturally occurring substance found in stone, rocks (marble, sandstone, flint, slate), sand and clay as well as ranging from brick, concrete, tiles, some composite materials and some metallic ores as well as in shingles mortar, plaster.

    Less harmful forms of silica dust is amorphous form such as with diatomaceous earth, synthetic amorphous silica or silica gel. These are not believed to lead to silicosis, lung cancer or other known common disease associated with RCS.

    However, it is possible to chemically change amorphous silica above 1300oC into RCS such as when calcining (roasting or exposing to strong heat) or welding using acetylene at over 3100oC. Diatomaceous earth as well as burning agricultural waste can at these temperatures change into a harmful form. This is important in scenarios where demolishing silos or receptacles which may have been used to store rice husk.

    When and at what quantity is RCS harmful?

    RCS is harmful to health when it is inhaled deep into the lungs therefore activities such as drilling, cutting, crushing are where we have to be more careful. The dust that is particularly harmful is smaller than a fine grain of sand. To put this into prospective, the size of a full stop is about 200-300μm (micrometres) in diameter whereas the RCS dust is about 5μm. These particles are so small that these cannot be seen with the naked eye.

    Those involved in demolition of older building and facilities can be exposed to bricks which have higher silica content due to high levels of sand and limestone such as sand-lime bricks, concrete blocks, cellular concrete, masonry rubble, natural stone and blast furnace slag bricks.

    If a person is exposed to high level of RCS, the effects of harm and onset of silicosis can start from as little as a few weeks of exposure as in the case of the Hawks Nest Tunnel Disaster in the 1930s. In this case thousands of workers were exposed to particularly high grades of silica dust during the construction of a tunnel in restricted areas with no personal protection. These lead many workers developing an acute form of silicosis within a matter of weeks resulting in their untimely deaths. This figure is an under-estimate and the actual number could have been many thousand workers from one incident.

    The table below gives a range of RCS content in certain materials found on demolition sites either in pure form or within other materials. In the case of *plastic composites silica may be as filler:

    Type of Material Crystalline

    Silica (%)

    Tripoli 95+%
    Sandstone 70 – 90%
    Plastic Composites* 19 – 90%
    Road Rock Up to 80%
    Concrete / Mortar 25 – 70%
    Shale 40 – 60%
    China Stone Up to 50%
    Granite 20 – 45%
    Tile 30 – 45%
    Slate 20 – 40%
    Clay Up to 40%
    Brick Up to 30%
    Ironstone Up to 15%
    Basalt / Dolerite Up to 15%
    Limestone Up to 2%
    Marble Up to 2%


    Regulatory authoriies have se standards based on the maximum exposure levels before there is likely to be significant harm.

    In the UK this is defined as a Workplace Exposure Limit (WEL) of 0.1mg/m3 based on an 8 hour working shift whereas this is lower in countries such as Canada where the occupational exposure limit at a federal level is 0.025mg/m3.

    Exposure need to be monitored and health of workers kept under surveillance to ensure levels are not harmful.  You cannot simply use visual sight to determine dangerous levels –  as by the time you observe a dust cloud, levels are already likely to be far in excess of the WEL of 0.1mg/m3.

    What happens to those exposed?

    Unlike asbestos where it may take anywhere between 10 to 50 years to manifest, symptoms for silicosis can start within extremely short periods. Individual susceptibility is based on a number of factors such as amount of dust, its size, respiratory protective equipment worn, the indivdual’s overall health status, and whether the person is a smoker – to name but a few.

    Type of Silicosis Exposure Latency before symptoms develop
    Acute Silicosis* Heavy exposure over short periods 2 weeks – 5 yrs.
    Accelerated Silicosis** High exposure over a period of time 5 – 10 yrs.
    Chronic Simple Silicosis Relatively low to moderate exposure over a long period of time 10+ yrs.


    Silica dust is one of the world’s most significant causes of occupational disease with an estimated 46,000 deaths globally in 2013.

    Below image shows the progressive worsening of lung tissue in black lung which is also a form of pneumoconiosis like Silicosis Image Source: Google

    Occupational respiratory diseases – Silicosis  

    The name silicosis is derived from the Latin word Silex or flint. However it has been known under many other previous names including ‘grinder’s asthma’, ‘potters rot’ and ‘miner’s phthisis’.  Its recognition goes back to the time of the Greeks and Romans, who spoke of respiratory problems from breathing in dust.

    With the dawn of industrialization say many new devices introduced such as pneumatic hammer drills in 1897 and sandblasting in 1904 which lead to a steady rise in silicosis prevalence. While we don’t have specific data for Canada overall, here are some numbers from other countries.

    Industrial Countries
    UK 800 die annually from lung cancer caused with RCS with 900 new cases of lung cancer diagnosed as a result of RCS exposure
    EU 7000 cancers of lung cancer are due to RCS
    Germany 400 new cases annually (1990’s)
    France 300 cases annually
    Australia 1,010 cases predicted
    Japan 1,000 cases annually
    USA 3,600-7,300 cases annually / 2m exposed; 10% at risk
    Developing Countries
    China 5000 annual deaths with 20m exposed with

    Pneumoconiosis 72% of all work-related diseases

    India 10m exposed to RCS
    Brazil 6.6m exposed
    Latin America 37% prevalence amongst miners
    Columbia 1.8m workers at risk
    South America 1m former miners with silicosis. 30-50% prevalence in some industries


    Silicosis is defined as an occupational lung disease classed as a pneumoconiosis and is marked by inflammation and scaring of the in the upper lobes of the lungs in the form of nodular lesions.

    In acute (short term, severe or sudden) form the symptoms are typically bluish skin, breath shortness, cough and fever. It is not uncommon for this to be misdiagnosed as pulmonary oedema (water on the lungs), pneumonia or Tuberculosis. Symptoms can continue to develop even after exposure has stopped.

    Exposure to RCS dust can also cause:

    • Chronic bronchitis;

    • lung cancer;

    • pulmonary fibrosis;

    • rheumatoid arthritis;

    • scleroderma;

    • systemic lupus erythematosus;

    • autoimmune antibodies;

    • and a variety of other conditions associated with exposure.

    Based on the above conditions it is conceivable many persons exposed to RCS dust may go on to develop other conditions other than silicosis.

    So how can we work safely without being harmed?

    So we know that RCS is harmful to health and also know that there is a level that is considered safe.  If the threat of exposure to RCS cannot be eliminated altogether then there are a few control measures that may work. It is estimated that silica related lung cancer could drop to 100 a year (currently circa 800 in the UK) if more legal compliance was instigated such as the points raised below.

    To ensure compliance with your various legislative requirements you should follow the local rules. Here we will adopt guidelines from the UK Health & Safety Executive based on compliance with the Control of Substances Hazardous to Health Regulations 2002 (COSHH) requirements:

    1. Assess

    2. Control

    3. Review  

    Assess (the risks) Assess the risks linked to the work and materials. High dust levels are caused by one or more of the following:

    • Task – high-energy tools like cut-off saws, grinders and grit blasters produce a lot of dust in a very short time;

    • Work area – the more enclosed a space, the more the dust will build up. However, do not assume that dust levels will be low when working outside with high-energy tools;

    • Time – the longer the work takes the more dust there will be;

    • Frequency – regularly doing the same work day after day increases the risks

    Control (the risks)

    For operatives tasked with specific activities where RCS could become airborne options of using mechanical equipment such as remote controlled rock-breaker or other means to provide some degree of separation between the workers can be used. In some cases the means can be as simple as dousing with a water stream and standing upwind. Other techniques such as hydro-demolition can be adopted and certainly from safety and an environmental element can be beneficial in terms of dust suppression can introduce a number of other hazards.

    Use the following measures to control the risk.

    Stop or reduce the dust before work starts, look at ways of stopping or reducing the amount of dust you might make.

    Use different materials, less powerful tools or other work methods.

    For example you could use:

    • The right size of building materials so less cutting or preparation is needed;

    • silica-free abrasives to reduce the risks when blasting;

    • a less powerful tool; or

    • a different method of work altogether.

    Control the dust  

    Even if you stop some dust this way, you may do other work that could still produce high dust levels.

    In these cases the most important action is to stop the dust getting into the air.

    There are two main ways of doing this:

    Water – water damps down dust clouds.

    However, it needs to be used correctly.  This means enough water supplied at the right levels for the whole time that the work is being done. Just wetting the material beforehand does not work.

     On-tool extraction – removes dust as it is being produced. It is a type of local exhaust ventilation (LEV) system that fits directly onto the tool. This ‘system’ consists of several individual parts – the tool, capturing hood, extraction unit and tubing. Use an extraction unit to the correct specification (i.e. H (High) M (Medium) or L (Low) Class filter unit).

     Do not sweep use an industrial vacuum cleaner with a high efficiency HEPA filter –

    Don’t use a general commercial vacuum.

    Respiratory protective equipment (RPE)

    Before considering RPE there are various considerations ranging from the type and duration of activities. It is far easier and more efficient generally speaking in using engineering controls to protect a wider range of workers than ill-fitting RPE which may give a false sense of security and actually endanger the lives of wearers.

    Water or on-tool extraction may not always be appropriate or they might not reduce exposure enough. Often respiratory protection (RPE) has to be provided as well. You will need to make sure that the RPE is:

    ■ Adequate for the amount and type of dust – RPE has an assigned protection factor (APF) which shows how much protection it gives the wearer. The general level for RCS dust is an APF of 40 based on the activity – this means the wearer only breathes one fortieth of the amount of dust in the air;

    Common RPE for use with construction dust

    **APF level for common RPE types for construction dust Common type of RPE for use Possible activity during construction/ demolition work
    10 FFP2 disposable mask or half mask with P2 filter §  Clearing and removing rubble
    20 FFP3 disposable mask or half mask with P3 filter

    Or for longer duration work

    §  Cutting and polishing


    40 Full face powered respirator with airline and constant air flow §  Abrasive blasting

    §  Hand and pneumatic chiselling

    §  Drilling and coring with handheld rotary power tools

    §  Concrete scabbling

    §  Tunnelling and shaft sinking


    ■ Suitable for the work – disposable masks or half masks can become uncomfortable to wear for long periods. Powered RPE helps minimize this. Consider it when people are working for more than an hour without a break;

    ■ Compatible with other items of protective equipment;

    ■ Fits the user. Face fit testing is needed for tightfitting masks;

    ■ Worn correctly. Anyone using tight-fitting masks also needs to be clean shaven.

    Remember: RPE is the last line of protection. If you are just relying on RPE you need to be able to justify your reasons for this.

    Review (the controls)

    You may already have the right controls in place, but are they all working properly? Check the controls work by:

    ■ Having procedures to ensure that work is done in the right way;

    ■ Checking controls are effective. Does the work still seem dusty? You might need to carry out dust exposure monitoring;

    ■ Involve workers. They can help identify problems and find solutions;

    ■ Maintaining equipment: follow instructions in maintenance manuals; regularly look for signs of damage. Make repairs; replace disposable masks in line with manufacturer’s recommendations; properly clean, store, and maintain non-disposable RPE. Change RPE filters as recommended by the supplier; carry out a thorough examination and test of any on-tool extraction system at least every 14 months (or as specified).

    ■ Supervising workers – make sure they use the controls provided; follow the correct work method and attend any health surveillance where it is needed.

    Air monitoring

    Carry out air monitoring to measure the overall amount of silica dust created at various positions on the worksite and the maximum level of worker exposure (given the use of dust control methods, respirators and other measures). Monitoring will enable the correct selection of dust control methods and respiratory protection.

    Carry out air monitoring on a regular basis to ensure dust control methods in place remain effective and provide adequate protection for your workers. It is particularly important to carry out air monitoring when new work methods are introduced.

    Health surveillance

    A health surveillance programme will be important to verify that controls are protecting staff. The surveillance programme should be under the direction of a suitably qualified medical personnel and can include pre-employment health screening questionnaire and occupational history questionnaire to set a baseline coupled with suitable lung function testing and biological effect monitoring to monitor actual exposure levels.

    As a disease it is possible to diagnose using patient history, chest x rays and also ruling out other possible underlying illnesses that may display similar symptoms such as pulmonary oedema, pneumonia and TB (tuberculosis).

    Protective clothing  

    It is vital that dusty clothes do not contaminate cars, homes and other areas outside of the worksite. Ensure your workers have disposable or washable clothes to change into at the worksite.

    Ensure that before your workers leave the worksite they shower (if possible) or wash with water, and then change into clean clothes. Do not allow your workers to take dusty clothing home to wash as it is possible to expose family to harmful levels of RCS dust.


    Provide your workers with training on silica dust. All training should include information about: the health effects of exposure to silica dust; work practices to follow when silica dust is created at a worksite; the appropriate use and care of protective equipment (including protective clothing and respiratory protection).

    We should all adopt the principals stated below based on the new global harmonisation standards requirements for RCS exposure which can be merged into regular tailboard meetings/ tool box talks.

    Prevention is the best form of protection against silicosis and other illnesses by either complete elimination of the silica dust hazard or by introducing suitable engineering controls such as dust control strategies using dry air filtering and water spray where dust emanates.

    That said, each worksite needs to have a comprehensive review of the hazards (risk assessed/ hazard analysis/ field level hazard assessment/ job safety analysis – whatever technique is used) and establish suitable and effective risk control measures such as development of an ECP – exposure control plan coupled with a health surveillance program for all those exposed to respirable crystalline silica (RCS) dust based on local legislative requirements relating to workplace exposure limits/ occupational exposure limits.

    In conclusion

    Exposure to RCS is common in a number of sectors and particularly prevalent in demolition and decommissioning operations.

    Nayab Sultan

    The reality is that silicosis is non-reversible but avoidable disease. Once you have it the only cure is therapy to lessen its effects on the body therefore prevention of exposure is the key.

    For further insights, see

    Nayab Sultan has been researching the prevalence of acute, accelerated and chronic silicosis and silico-tuberculosis across Canada.


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