Silica, also known as Crystalline Silica*, is a naturally-occurring mineral that is found in many materials and industrial processes.

Silica is one of the most common hazards on worksites.

*Chemical Name: Silicon dioxide; formula: SiO2

Most silica is in the quartz form, so the term “quartz” is often used interchangeably with “silica".
For the remainder of this article, the health effects of silica will refer to quartz.

Most data on the hazardous effects of silica concerns quartz, but there is also an ample data on the hazardous effects of cristobalite and tridymite.

Less common forms of silica include:

•  tridymite  •  cristobalite

Rarer forms of silica include:

• keatite  •  coesite  •  stishovite  •  moganite.

Most data on the hazardous effects of silica concerns quartz, but there is also an ample data on the hazardous effects of cristobalite and tridymite.

According to CAREX Canada 153,000 Ontarians are exposed to silica
in their workplaces.

The largest occupational groups affected by silica exposure are:

Icon of a person wearing a hard hat representing construction


Icon of cart on a track representing mining


Icon of an rig in the ocean representing oil and gas


Icon of a factory representing manufacturing


Icon of hand with a plant growing in front of it representing agriculture


Other exposed occupations include iron foundry workers, and metal processing workers,
though it can occur in any workplace where silica is disturbed or processed.


Silica is naturally found in:

A photo/icon showing sand as a source of silica


A photo/icon showing amethyst crystals as a source of silica

(such as amethyst, chalcedony, citrine, onyx)

A photo/icon showing stone / rock as a source of silica


...and particularly in deposits of diatomite.

It is also found in a wide range of construction materials, such as:

An icon of a stack of rectangles representing bricks

Bricks / Concrete Blocks

Icon of a pile of stones representing gravel

Gravel / Stone / Rock
(or asphalt containing)

Concrete / Cement

Icon of a trowel mounded with mortar for spreading between bricks / concrete blocks


Icon of a square with lines running through it representing a sheet of glass


Icon of a counter top with a faucet and sink below representing artificial counter tops

Artificial Stone
(e.g. Counter Tops)

Icon of a circle of patio pavers or tiles representing granite


Icon of a bunch of small circles in a tight group representing abrasives

Some Abrasives / Cleansers

Icon of a pile of dirt representing dirt or top soil

Fill Dirt / Top Soil

Icon of ceramic roof tiles representing ceramics

Ceramics / Tiles

Icon of a roll of fibreglass

Some Types of Fibreglass

Icon showing water droplets being absorbed into a material representing fillers

(e.g., anti-caking agents, laboratory absorbents, paint, paper, etc.)


Silica-related diseases can occur from either short-term high exposures or long-term repeated exposures.

Silica damages the lung and causes scar tissue to form, which in turn causes the lung tissue to become thicker.

Inhaling silica dust can cause silicosis, a serious and irreversible lung disease.

It is possible to have silicosis without showing any symptoms at first.

The longer workers have been exposed to silica dust, the worse the symptoms will become.

As the disease progresses workers may show noticeable symptoms such as:

Icon depicting a tight chest showing the lungs with arrows surrounding them

Shortness of breath  

Icon depicting a person clenching their chest due to difficulty breathing

Severe Coughing  

Icon of a figure bent over, breathing heavy and feeling light headed representing fatigue and exhaustion

Body Weakness

Silica exposure can also cause lung cancer.

of lung cancers diagnosed in Ontario each year are caused by silica*.

That is approximately
lung cancer cases per year

* The Occupational Cancer Research Centre (OCRC) and Cancer Care Ontario (CCO)

Other diseases caused by silica exposure include:

Icon showing a pair of kidneys with a disease cell representing kidney disease

Chronic Kidney Disease 

Icon of two bones rubbing together representing arthritis

Rheumatoid Arthritis  

Icon of hand overlapped by a disease cell representing scleroderma


In addition, scientific literature has demonstrated that exposure to silica is positively associated with the development of:

•  Idiopathic Pulmonary Fibrosis (IPF)  •  Chronic Obstructive Pulmonary Disease (COPD)  •  Esophageal Cancer  •  Sarcoidosis
among several other diseases.

* The Occupational Cancer Research Centre (OCRC) and Cancer Care Ontario (CCO)

Occupational Exposure Limits

In Ontario, the time weighted average limit (TWA) for respirable crystalline silica is 0.1 mg/m3, as defined by:
O. Reg. 490/09: Designated Substances.
R.R.O. 1990, Reg. 833: Control of Exposure to Biological or Chemical Agents

Ontario has not adopted the current ACGIH Threshold Limit Values (TLVs)*.

*ACGIH TLVs are health-based and evidence-based occupational exposure limits meant to protect most workers.
The ACGIH TLV for silica is currently 0.025 mg/m3, as respirable particulate matter.


 Silica is the most common hazard on a work site.
Any activity that creates dust can expose workers to airborne silica.

 Silica becomes hazardous when it is broken into fine particles and inhaled.
These fine silica dusts are known as Respirable Crystalline Silica (RCS).

Respirable crystalline silica is much smaller than ordinary sand and is small enough to penetrate into the gas-exchange region of the lungs (alveoli).

Respirable crystalline silica is made when materials that contain silica (like concrete and bricks) go through processes such as:

Icon of circular saw representing sawing / cutting

Sawing / Cutting

Icon of a drill drilling into a wall representing drilling


Icon of a plate crushing stones into a powder repesenting crushing


Icon of a machine used for chipping


Icon of blast with a dynamite igniter overlay representing blasting


Icon of a hand-held grinding wheel representing grinding

Grinding / Sanding / Dressing

Icon of a dump truck with it's bed in the raised portion representing loading, hauling, dumping

Loading / Hauling / Dumping

Icon of a wrecking ball hitting a building representing demolition and renovation

Demolishing / Renovating

Icon of a broom sweeping up debris representing sweeping and blowing

Sweeping / Blowing

Icon of a digger removing earth representing tunnelling and excavating

Tunneling / Excavating

Icon of a bulldozer pushing a mound of dirt representing earth moving

Earth Moving

...or when the process involves the application of silica, such as:

An icon of a gun-shaped tool shooting sand, representing abrasive or sand blasting

Abrasive / Sand Blasting

Other industrial processes can lead to the generation of respirable crystalline silica, such as:

Icon of molten metal being poured representing foundry work

Foundry Work


Icon of a tower with earth cracking below representing fracking or fracturing

Hydraulic Fracturing

Icon of a tooth being drilled representing dental processes

Some Dental Processes



The best way to reduce the risk of exposure to silica dust is to eliminate the source of exposure.

If that is not possible, there are other risk controls that can be used.

If working in an industry or occupation where respirable crystalline silica can be generated, the following control measures may be needed:

Icon of a shield with a cog on the front surrounded by a dotted line leading up to a couple of hazard warning triangles

Engineering Controls

Icon of a calendar and clock representing administrative controls

Administrative Controls

Icon showing a rubber glove, hard helmet and mask depicting the use of personal protective equipment (PPE)

Personal Protective Equipment (PPE)

These controls serve to:

Icon of a shield overlayed with a gear representing prevention

silica dust from getting in the air

Icon showing dust particles passing through a filter process and the air coming out clean on the other side

existing silica dust from the air

Icon with several rows of dots diminishing in number from left to right with a downward pointing arrow representing a reduced exposure

the likelihood of workers inhaling silica dust

Diagram of the Control Methods triangle

Learn more about each control method using the dynamic bars below:

Eliminate the hazard by changing the process to avoiding cutting, grinding, or drilling, etc. (e.g. improving concrete forms). This is the most effect control method.

Ask yourself:

  • Can a process that generates less dust be used (for example, splitting rather than sawing concrete pavers)?
  • Can formwork be designed more carefully to reduce the amount of concrete finishing required?

Source and substitute a safer material (i.e. lower silica-containing products)

Ask yourself:

  • Can a less hazardous material be used (e.g., garnet instead of silica in sand-blasting operations)?

Making physical modifications to facilities, equipment, and processes such as enclosing the process; using a wet process, or using local exhaust ventilation can reduce exposure.

Ask yourself:

  • Can local exhaust ventilation be used on all equipment that generates silica dust?
  • Can water be used to prevent dust from becoming airborne?
  • Can the areas that generate large amounts of dust be enclosed, and have proper ventilation to clean the air?

These involve changing work practices and work policies. Providing awareness tools and robust training programs, proper clean-up procedures, procedures for safe work; etc., can all limit the risk of silica dust exposure.

Ask yourself:

  • Have you developed a written exposure control plan for silica?
  • Can warning signs be posted in the work area?
  • Can crews be scheduled to work as far away from silica dust-generating processes as possible?
  • Have you provided adequate washing facilities on site?
  • Have you developed safe work procedures for dealing with silica dust?
  • How will worker exposure to silica be monitored?

Using disposable protective clothing; respirator half-face respirator with a P100 cartridge, a full face with P100 cartridge, or full face with powered air-purifying respirator with P100 cartridge can all help reduce exposure...BUT REMEMBER:  This is the least effective control. When used, there must always be at least one other control in place as well.

Ask yourself:

  • Do workers have the proper respirators, eye wear, and protective clothing?
  • Has personal protective equipment been tested to make sure it is working properly?

Silica Infographic Now Available

This infographic summarizes the content of this page and is a great resource for posting in the workplace or using as a handout for workers or at training sessions:

Thumbnail image of OHCOW's Silica infographic
Note:  Click on image to preview


Learn more about Silica, the effects of exposure, and prevention methods using the following resources:

Note:  Use the dots above to view all the resources.

The following resources were used in the preparation of this page:

“Silica Control ToolTM” (OHCOW, in partnership with B.C. Construction Safety Association (BCCSA) and the Canadian Centre for Occupational Health and Safety (CCOHS)):

“The Silica Control Tool Pilot Project” (OHCOW video)

“Occupational Lung Disease: Overview, Risk, Assessment, Diagnosis” (OHCOW slides)

“Using Scientific Evidence to Drive Prevention and Compensation” (OHCOW slides)

“Practical Tools for Working on Occupational Cancer Cases: Case Studies of Lung Cancer” (OHCOW slides)

Silica (Crystalline) Profile (CAREX Canada):

Silica, Quartz Fact Sheets (CCOHS (Canadian Centre for Occupational Health & Safety)):

Silica Dust, Crystalline, in the form of Quartz or Cristobalite Monograph (IARC (International Agency for Research on Cancer)):

Silica (Occupational Cancer Research Centre (OCRC)):

Workplace Crystalline Silica Exposure Causes 200 Lung Cancers Annually (Special Edition) (Cancer Care Ontario (CCO)):

Construction Exposure Profiles: Crystalline Silica (Occupational Cancer Research Centre (OCRC)):

Crystalline Silica Burden of Occupational Cancer Fact Sheet for Construction (Occupational Cancer Research Centre (OCRC) and CAREX Canada):

Crystalline Silica Burden of Occupational Cancer Fact Sheet for Mining (Occupational Cancer Research Centre (OCRC) and CAREX Canada):

Silica (Collaborative on Health and the Environment (CHE): Toxicant and Disease Database):

OEL Tool (OHCOW Tool link):

Logo of the Silica Control Tool Pilot Program for Ontario

Silica Control Tool for Construction Industry
Coming to Ontario – November 2023