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5.0 Classification of Work: Silica On Construction Projects

  • Issued: September 2004
  • Content last reviewed: Insert Date Here

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.

A key feature of this guideline is the classification of work. It is the classification of the work that determines the appropriate respirators, measures and procedures that should be followed to protect the worker from silica exposure. In this guideline, silica-containing construction operations are classified into three groups, Type 1, Type 2, and Type 3 operations, and can be thought of as being of low, medium and high risk. From Type 1 to Type 3 operations, the corresponding respirator, and measures and procedures become increasingly stringent.

The classification of typical silica-containing construction tasks is based on available and published exposure data. Type 1, Type 2, and Type 3 operations, are based on the following airborne concentrations of respirable crystalline silica in the form of cristobalite, tridymite, quartz, and tripoli:

Classification of Silica-Containing Construction Operations Based on Airborne Concentrations of Respirable Crystalline Silica in the Form of Cristobalite, Tridymite, Quartz, and Tripoli.
  Type 1 Operations Type 2 Operations Type 3 Operations
Cristobalite and Tridymit > 0.05 to 0.50 mg/m3 > 0.50 to 2.50 mg/m3 > 2.5 mg/m3
Quartz and Tripoli > 0.10 to 1.0 mg/m3 > 1.0 to 5.0 mg/m3 > 5.0 mg/m3

The following section lists the typical construction operations that generate silica-containing dust:

Type 1 Operations

  • The drilling of holes in concrete or rock that is not part of a tunnelling operation or road construction.
  • Milling of asphalt from concrete highway pavement.
  • Charging mixers and hoppers with silica sand (sand consisting of at least 95 per cent silica) or silica flour (finely ground sand consisting of at least 95 per cent silica).
  • Any other operation at a project that requires the handling of silica-containing material in a way that may result in a worker being exposed to airborne silica.
  • Entry into a dry mortar removal or abrasive blasting area while airborne dust is visible for less than 15 minutes for inspection and/or sampling.
  • Working within 25 metres of an area where compressed air is being used to remove silica-containing dust outdoors.

Type 2 Operations

  • Removal of silica containing refractory materials with a jackhammer.
  • The drilling of holes in concrete or rock that is part of a tunnelling or road construction.
  • The use of a power tool to cut, grind, or polish concrete, masonry, terrazzo or refractory materials.
  • The use of a power tool to remove silica containing materials.
  • Tunnelling (operation of the tunnel boring machine, tunnel drilling, tunnel mesh installation)
  • Tuckpoint and surface grinding.
  • Dry mortar removal with an electric or pneumatic cutting device.
  • Dry method dust cleanup from abrasive blasting operations.
  • The use of compress air outdoors for removing silica dust.
  • Entry into area where abrasive blasting is being carried out for more than 15 minutes.

Type 3 Operations

  • Abrasive blasting with an abrasive that contains ≥1 per cent silica.
  • Abrasive blasting of a material that contains ≥ 1 per cent silica.

Employers, supervisors, and workers should be able to recognize and correctly classify the types of operations carried out in the workplace, in order to select appropriate respirators, and implement appropriate measures and procedures. Respirator requirements are listed in Table 1 (below) for Type 1, Type 2, and Type 3 operations.

Table 1: Respirator Requirements

Operations Required Respirator

Type 1
( > 0.05 to 0.50 mg/m3 of silica in the form of cristobalite and tridymite)
( > 0.10 to 1.0 mg/m3 of silica in the form of quartz and tripoli)

  • The drilling of holes in concrete or rock that is not part of a tunnelling operation or road construction.
  • Milling of asphalt from concrete highway pavement.
  • Charging mixers and hoppers with silica sand (sand consisting of at least 95 per cent silica) or silica flour (finely ground sand consisting of at least 95 per cent silica).
  • Any other operation at a project that requires the handling of silica-containing material in a way that may result in a worker being exposed to airborne silica.
  • Entry into a dry mortar removal or abrasive blasting area while airborne dust is visible for less than 15 minutes for inspection and/or sampling.
  • Working within 25 metres of an area where compressed air is being used to remove silica-containing dust outdoors.

NIOSH APF[ * ] = 10

Half-mask particulate respirator with N-, R-, or P-series filter and 95, 99 or 100 per cent efficiency.

Type 2
( > 0.50 to 2.5 mg/m3 of silica in the form of cristobalite and tridymite)
( > 1.0 to 5.0 mg/m3 of silica in the form of quartz and tripoli)

  • Removal of silica containing refractory materials with a jackhammer.
  • The drilling of holes in concrete or rock that is part of a tunnelling operation or road construction.
  • The use of a power tool to cut, grind, or polish concrete, masonry, terrazzo or refractory materials.
  • The use of a power tool to remove silica-containing materials.
  • The use of a power tool indoors to chip or break and remove concrete, masonry, stone, terrazzo or refractory materials.
  • Tunnelling (operation of the tunnel boring machine, tunnel drilling, tunnel mesh installation).
  • Tuckpointing and surface grinding.· Dry method dust clean-up from abrasive blasting operations.
  • Dry mortar removal with an electric or pneumatic cutting device.
  • The use of compressed air outdoors for removing silica dust.
  • Entry into area where abrasive blasting is being carried out for more than 15 minutes.

NIOSH APF = 50

Full-facepiece air-purifying respirator with any 100-series particulate filter.

Tight-fitting powered air-purifying respirator with any 100-series particulate filter.

Full-facepiece supplied-air respirator operated in demand mode.

Half-mask or full-facepiece supplied air respirator operated in continuous-flow mode.

Type 3
( > 2.5 mg/m3 of silica in the form of cristobalite and tridymite)
( > 5.0 mg/m3 of silica in the form of quartz and tripoli)

  • Abrasive blasting with an abrasive that contains ≥ 1 per cent silica
  • Abrasive blasting of a material that contains ≥ 1 per cent silica

NIOSH APF ≥ 1000

Type CE abrasive-blast supplied air respirator operated in a positive-pressure mode with a tight-fitting half-mask facepiece.

Type CE abrasive-blast supplied air respirator operated in a pressure-demand or positive pressure mode with a tight-fitting full-facepiece.

[ * ]NIOSH APF = National Institute of Occupational Safety and Health Assigned Protection Factor

Note: It is recommended that compressed air that is used to supply supplied air respirators meet the breathing air purity requirements of CSA Standard Z180.1-00. Where an oil-lubricated compressor is used to supply breathing air, a continuous carbon monoxide monitor/alarm should be provided.

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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.