31 August 2017

What is silica?

Silica is the common term used for the mineral compound silicon dioxide (SiO2), and it is one of the most common naturally-occurring elements in existence. Silica comes in two forms: crystalline and noncrystalline. It is primarily the crystalline (RCS) form that we will be addressing in this briefing.

Silica and construction

Common construction materials that contain silica include brick, cement, sand, stone, tile, mortar, grout, drywall and asphalt. Left in solid form, these materials don’t pose a respiratory threat; however, the dust that is created by activities such as mixing, cutting, drilling, blasting, grinding, chipping, etc. is extremely hazardous. It doesn’t take much, and exposure over the long term can lead to permanent debilitating conditions and premature death.

Dangers of dust


One respiratory condition that can come on rather quickly when exposed to any kind of construction dust, including lower toxicity dusts like gypsum (plasterboard) and marble, is asthma. Asthma is a long-term chronic disease that must be actively managed. Common symptoms include difficulty breathing, shortness of breath, tightness in the chest, coughing (especially at night and when exercising or laughing), and a wheezing sound when breathing in and out.


Extended or intensive exposure to RCS can result in silicosis, which is the hardening and/or scarring of lung tissue. Symptoms include shortness of breath, to the point that sufferers can find it difficult or impossible to walk up a flight of stairs or even short distances.

Chronic silicosis typically occurs after several years of consistent exposure to low concentrations.

Accelerated silicosis happens when someone is exposed to higher concentrations, with symptoms developing as much as five to 10 years after initial exposure.

Acute silicosis is the result of short term exposure to a very high concentration of silica. Symptoms can develop anywhere between a few weeks and a few years after the exposure event.

Once someone develops the condition, it is irreversible, with the sufferer usually becoming house or bed bound and dying prematurely from heart failure.

Chronic obstructive pulmonary disease (COPD)

COPD is a term that covers several different lung conditions that are the result of narrowing of the airways. These includes chronic bronchitis, emphysema, bronchiectasis, and chronic airway obstruction. Symptoms include shortness of breath, coughing, wheezing, and increased production of phlegm and sputum. Side effects also include loss of appetite resulting in weight loss and swollen ankles. Whereas with asthma airways are narrowed for a period of time, often as the result of a “trigger”, with COPD airways are permanently narrowed.

Lung cancer

RCS has also been linked to lung cancer, although, the exact extent of its role still remains controversial. According to research by Imperial College London, approximately 800 people in the UK die per year from lung cancer that is the result of prolonged RCS exposure, and there are approximately 900 new cases diagnosed annually.


Other conditions that have been lined to silicosis include tuberculosis, arthritis, and kidney disease.



According to silica-safe.org, the estimated number of annual, newly recognised cases of silicosis in the USA is somewhere between 3,600 and 7,300. As with the UK, this number is deemed to fall short of the true figure, as so many cases are either not reported or not properly diagnosed.


CAREX Canada and Occupational Cancer Research Centre fact sheet attributes 570 cases of lung cancer per year to occupational exposure to RCS (based on 2011 statistics). This is approximately 2.4% of total lung cancer cases diagnosed annually. The fact sheet also states that construction workers make up majority of those most affected (56%).


HSE statistics for cases of and fatalities attributed to RCS include:

  • From 2005–2007, there were 80 cases on average per year reported via the Industrial Injuries Disablement Benefit system.
  • In the period of 2013–2015, that number was approximately 40 cases per year.
  • There were more than 50 new cases identified by specialists in both 2014 and 2015.
  • In the last 10 years, there have been between 10 and 20 deaths per year attributed to RCS.
  • Analysis of cases reported via THOR (The Health and Occupational Reporting network) showed that the construction industry was most susceptible, constituting 51% of total reported cases. More specifically 26% stonemasons and bricklayers and 25% other construction-related occupations.

While IIDB cases have consistently dropped since 2005, THOR-SWORD (surveillance of work-related and occupational respiratory disease) cases have risen, and deaths have remained consistent.

HSE publication Silicosis and coal workers pneumoconiosis [AC317473] also states that:

“Both the IIDB and THOR data sources are likely to substantially underestimate the incidence of silicosis. Estimates of annual lung cancer cases due to past exposures to silica (nearly 800 deaths per year) imply that the extent of underestimation of silicosis by IIDB and THOR was substantial, since many such lung cancers would be expected to develop from among highly exposed workers who were also developing silicosis. Estimates of the risk of silicosis following long-term exposure , together with information about the likely extent of past exposures in Britain, also suggest that silicosis incidence could be much higher than recorded in the available IIDB and THOR statistics.”

Workplace exposure limit (WEL)

The UK exposure limit for silica is 0.1 mg/m3 average per eight hours, which is the level currently proposed by the European Commission. The EC believes that, by adopting this level as standard for maximum RCS exposure, 98,670 deaths could be avoided across member states. (European Commission – Fact Sheet, 13 May 2016)

Case studies

USA – World Trade Center

In 2001, after the World Trade Center’s twin towers fell, just under 16,000 emergency crew worked over a period of 10 months to deal with the aftermath. There were unprecedented amounts of aerosolised dust and fumes, which included pulverised cement and glass, asbestos, lead, dioxins and silica. While masks and respirators were available, there weren’t always enough for everyone and, they weren’t always consistently worn. Within the first year, over 70% of firefighters developed breathing problems. There were also a proportionately large number of cases of autoimmune disease reported. While the dust on the site was a complex mix, breathing in asbestos and/or silica is known to make the immune system more reactive.

South Africa – Gold mining

On 13 May 2016, a South African High Court ruled that gold mine workers who had contracted silicosis and, often as a result, tuberculosis could join together in a class-action suit against 32 mining companies whose negligence contributed to making them sick in the first place. It is estimated that as many as 500,000 former miners and/or their dependents could benefit.

Health and Safety Laboratory

In an HSL case study, the amount of RCS construction workers cutting roof tiles were exposed to was assessed, particularly when cutting valley tiles. In the study, workers performed the work at rooftop level using hand held power tools without wet dust suppression systems (which create an additional safety hazard when working from a roof). The result showed that, if a worker cut two roof edges worth of valley tiles in a single shift, they would exceed the eight hour time weighted exposure limit, putting no only themselves but nearby co-workers at significant risk. The solution was to change working practices so that valley tiles are marked at roof level but then taken to a fixed location where they can be cut using water suppression and other engineering controls.

No Time to Lose campaign

Representatives from the construction, rail and mineral products industries have joined with IOSH, HSE, and others to action a 12-month plan to raise awareness of the dangers of RCS and champion change. All who have signed up agree to work together to:

  • Use effective monitoring and dust management to reduce RCS exposure
  • Increase awareness and understanding of associated health risks
  • Share good management practice across industries

Minimising the risk

When it comes to controlling the risk presented by silica dust, the most important element is knowledge. Employers have a responsibility to educate their workers on the extensive dangers of breathing in silica dust and implement best practice policies to minimise exposure. Workers should also take it upon themselves to remain alert and aware; protecting not only themselves, but others in and around the job site. Suggestions include:

Have a good on-site health and safety programme

Have a written exposure plan – At minimum, this should include:

  • A description of the tasks to be performed that are known to create dust.
  • Methods that will be used to minimise dust creation and exposure during each of those tasks.
  • The clean-up and housekeeping procedures to be used.
  • Measures that are to be put into place to minimise incidental exposure in and around the construction site.

Don’t let the dust get airborne – Whenever possible, use water and/or a HEPA vacuuming system to supress or capture dust at the source. Also avoid dry sweeping or brushing during clean-up, again opting for wet or HEPA vacuuming methods.

Require workers to use an approved rated respirator at all times.

Consider using alternative materials wherever possible – for instance, using aluminium oxide instead of sand for abrasive blasting.

Be aware, and take care

Understand the risks of breathing silica dust and what tasks generate it – By staying informed about the risks and causes, you will be better able to respond appropriately when risks present themselves.

Wear your respirator and insist that co-workers wear theirs – Make sure that it’s fitted properly and carries the appropriate rating.

Be safe with personal hygiene – Wash your hands and face before eating, drinking or smoking, and never eat/drink/smoke in a dusty area.

Avoid taking dust home – Whilst focus is on minimising risk at the construction site, it is also important to be aware of the dangers of bringing silica dust home on equipment and clothing. Things that can help minimise that risk include:

  • Changing into and out of work clothes at the work site.
  • Showering (if possible) before changing into clean clothes and heading away from the work site.
  • Parking cars far enough away from the job site to prevent silica contamination.

It is also advisable to get regular health checks.

This article has been edited and repurposed from “The dangers of silica dust”, written for the Construction Information Service.