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1.0 Introduction: Silica On Construction Projects

  • Issued: September 2004
  • Content last reviewed: April 2011

Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. For further information please see full disclaimer.


Employers have a duty to protect their workers from silica exposure on construction projects. This Guideline has been prepared to raise the awareness of employers and workers in the construction industry of the hazards posed by silica in construction and the measures and procedures that should be taken to control those hazards

For the purposes of this guideline, silica refers to crystalline silica in a respirable [ 1 ] form.

Silica in Construction

Silica (SiO2) is a compound resulting from the combination of one atom of silicon with two atoms of oxygen. It is the second most common mineral in the earth's crust and is a major component of sand, rock and mineral ores. Silica exists in several forms, of which crystalline silica is of most concern. The best-known and most abundant type of crystalline silica is quartz. Other forms of crystalline silica include cristobalite, tridymite, and tripoli.

In construction, worker exposure to silica is of particular concern because silica is the primary component of many construction materials. Some commonly used construction materials containing silica include:

  • abrasives used for blasting
  • brick, refractory brick
  • concrete, concrete block, cement, mortar
  • granite, sandstone, quartzite, slate
  • gunite
  • mineral deposits
  • rock and stone
  • sand, fill dirt, top soil
  • asphalt containing rock or stone.

Many construction activities can generate airborne silica-containing dust. In construction, abrasive blasting generates the most dust. Exposure to silica from abrasive blasting can result if the abrasive contains silica and/or if the material being blasted contains silica. Other activities that generate airborne dust include:

  • chipping, hammering, and drilling of rock
  • crushing, loading, hauling, and dumping of rock
  • sawing, hammering, drilling, grinding, and chipping of concrete or masonry structures
  • demolition of concrete and masonry structures
  • dry sweeping or pressurized air blowing of concrete, rock, or sand dust
  • road construction
  • sweeping, cleaning, and dismantling equipment
  • tunnelling, excavation, and earth moving of soils with high silica content.

[ 1 ] "Respirable" means that size fraction of the airborne particulate deposited in the gas-exchange region of the respiratory tract and collected during air sampling with a particle size-selective device that,

  1. meets the American Conference of Governmental Industrial Hygienists (ACGIH) particle size-selective criteria, and
  2. has the cut point of 4 microns at 50 per cent collective efficiency.

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Disclaimer: This web resource has been prepared to assist the workplace parties in understanding some of their obligations under the Occupational Health and Safety Act (OHSA) and the regulations. It is not intended to replace the OHSA or the regulations and reference should always be made to the official version of the legislation.

It is the responsibility of the workplace parties to ensure compliance with the legislation. This web resource does not constitute legal advice. If you require assistance with respect to the interpretation of the legislation and its potential application in specific circumstances, please contact your legal counsel.

While this web resource will also be available to Ministry of Labour inspectors, they will apply and enforce the OHSA and its regulations based on the facts as they may find them in the workplace. This web resource does not affect their enforcement discretion in any way.