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Measures and procedures for working with silica
Protective measures and procedures should be implemented when working with silica. Specific measures and procedures will depend on how the work is classified. This section of the guideline outlines the general measures and procedures for all work with silica, followed by specific recommendations for Type 1, Type 2 and Type 3 operations.
6.1 General Measures and Procedures for Type 1, Type 2, and Type 3 Operations
The following is a list of general measures and procedures that should be followed for all work with silica:
- Clean-up after each operation is encouraged to prevent dust containing silica from spreading;
- Compressed air or dry sweeping should be avoided when cleaning a work area;
- Compressed air should not be used for removing dust from clothing;
- Workers exposed to silica should be provided with or have access to washing facilities equipped with clean water, soap, and individual towels.
- Silica dust on personal protective clothing and equipment should be removed by damp wiping or HEPA vacuuming;
- Contaminated personal protective clothing and equipment should be handled with care to prevent disturbing the silica dust and the generation of airborne silica dust
- Washing facilities and laundering procedures must be suitable for handling silica contaminated laundry.
Preparation of the Work Area
Warning signs should be posted in sufficient number to warn of the hazard. If it is an indoor operation, signs should be posted at each entrance to the work area. The signs should display the following information in large, clearly visible letters:
- There is a silica dust hazard.
- Access to the work area is restricted to authorized persons.
- Respirators must be worn in the work area.
Dust Control Measures
The generation of airborne silica-containing dust should be controlled with a mechanical ventilation system, wetting, or the use of a dust collection system. If silica-containing airborne dust is generated, mechanical ventilation with an air flow sufficient to remove airborne contaminants from workers' breathing zone should be provided. The air flow of the mechanical ventilation system should be at least 50 cubic feet per minute per square foot of face area
- Risk to workers using wetting or a dust collection system.
- Likelihood of damage to equipment if wetting or a dust collection system is used.
- Frequency and duration of the operation.
If compressed air is being used to remove silica-containing dust outdoors, the operator and workers within 25 metres of the work area who may be exposed to the dust must either be removed from the path of the dust cloud or provided with respirators (see Table 1: Respirator Requirements).
Where effective dust control measures are in place and where an employer can demonstrate on a continual basis that the silica exposure levels are below the OEL, respirators may not be required.
6.2 Measures and Procedures for Type 1 Operations
A half-mask particulate respirator with N-, R-, or P-series filter and 95, 99 or 100 per cent efficiency should be provided for workers performing Type 1 operations. Respirators should also be provided when:
- entering a dry mortar removal area with visible airborne dust for less than 15 minutes for the purposes of inspection and/or sampling purposes.
- work is being performed within 25 metres of an outdoor area where silica-containing dust is being removed with compressed air.
6.3 Measures and Procedures for Type 2 Operations
Respirators with a NIOSH APF of 50 (see Table 1: Respirator Requirements) should be provided for workers performing Type 2 operations. In addition, the generation of silica-containing airborne dust should be controlled by thoroughly wetting the area prior to and/or during drilling or cutting operations and during the loading, scraping or moving of rock.
Other workers entering a work area where Type 2 operations are being performed should remain at least 10 metres away. Ropes or barriers should be set up to prevent unauthorized personnel from entering the work area. If this is not possible and there are workers within the 10-metre limit, the Type 2 operation should be enclosed to prevent the escape of airborne silica-containing dust (see Section 6.4.1: Barriers, Partial Enclosures and Full Enclosures).
6.4 Measures and Procedures for Type 3 Operations
The operator of the abrasive blasting nozzle should wear a Type CE abrasive blast supplied air respirator operated in a pressure demand or positive pressure mode with a tight-fitting half-mask or full facepiece.
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. (View CSA standards) Where an oil-lubricated compressor is used to supply breathing air, a continuous carbon monoxide monitor/alarm should be provided.
While abrasive blasting is in progress or the airborne dust from abrasive blasting is visible,
- any worker entering the work area where abrasive blasting is being carried out for less than 15 minutes for inspection and/or sampling purposes should wear a half-mask particulate respirator with N-, R-, or P-series filter and 95, 99 or 100 per cent efficiency.
- any worker entering a work area where abrasive blasting is being carried out for more than 15 minutes should wear a respirator with a NIOSH APF of 50 (see Table 1: Respirator Requirements).
- workers engaged in cleaning dust from abrasive blasting operations, should wear a respirator with a NIOSH APF of 50 (see Table 1: Respirator Requirements).
Where abrasive blasting is conducted, barriers, partial enclosures and full enclosures should be in place to prevent other workers from being exposed to silica-containing dust and to prevent the spread of dust to other work areas.
6.4.1 Barriers, Partial Enclosures and Full Enclosures
Barriers, partial enclosures, and full enclosures are used to separate the work area from the rest of the project, and in some cases, to prevent silica exposure to other workers not directly involved in the operation. Partial and full enclosures can also prevent or reduce the dispersion of silica into the surrounding work area and environment. Barriers should only be used where full and partial enclosures are not practicable.
Ropes or barriers do not prevent the release of contaminated dust or other contaminants into the environment. However, they can be used to restrict access of workers who are not adequately protected with proper PPE, and also prevent the entry of workers not directly involved in the operation. Ropes or barriers should be placed at a distance far enough from the operation that allows the silica-containing dust to settle. If this is not achievable, warning signs should be posted at the distance where the silica-containing dust settles to warn that access is restricted to persons wearing PPE. For example, the removal of mortar and cutting operations, ropes or barriers should be located at least 10 metres away. All workers within the barrier or warning sign zone must be adequately protected.
Partial enclosures allow some level of emission to the atmosphere outside of the enclosure. Partial enclosures may consist of vertical tarps and floor tarps so long as the tarps are overlapped and securely fixed together at the seams. A partial enclosure is not a recommended containment system if significant dust is being generated.
Full enclosures are tight enclosures (with tarps that are generally impermeable and fully sealed joints and entryways). Full enclosures allow minimal or no fugitive emissions to reach the outside environment.
For full enclosures, the following requirements should be met:
If, as outlined above, a Type 3 operation should be enclosed, the enclosure should meet the following requirements:
- entry ways in the enclosure should be equipped with air locks, overlapping door tarps or doors
- the enclosure should be supported by a secure structure
- all joints in the enclosure should be fully sealed
- the escape of abrasive and debris from the enclosure should be controlled, at air supply points, by the use of baffles, louvers, flap seals and filters
- general mechanical ventilation should be provided to remove contaminated air from the enclosure and replacement air should be provided to replace the exhausted air
- the air pressure within the enclosure should be negative relative to the outside
- equipment venting such air shall be equipped with filters adequate to control vented air to provincial environmental standards
- the air velocity within the enclosure should provide an average minimum cross-draft or down-draft past each worker during abrasive blasting operations as follows:
- cross-draft velocity of 0.5 m/sec (100 ft/min)
- down-draft velocity of 0.25 m/sec (50 ft/min)
If the enclosure is located outdoors these additional requirements should be met:
- the enclosure should be made of windproof materials that are impermeable to dust
- the enclosure should be supported by a structure that prevents more than minor movement of the enclosure.
If abrasive blasting is being conducted indoors and persons other than those doing the abrasive blasting may be exposed to silica-containing dust, the abrasive blasting area should be separated from the rest of the project by an enclosure that will confine the dust within the abrasive blasting area. When an indoor abrasive blasting operation is completed, dust and waste should be cleaned up and removed by vacuuming with a HEPA-filter-equipped vacuum, wet sweeping or wet shovelling.
If abrasive blasting is being conducted outdoors and persons other than those doing the abrasive blasting may be exposed to silica-containing dust, the work area should be identified by ropes or barriers located at least 25 metres from the abrasive blasting area, to prevent entry by workers not directly involved in the operation.
If it is not possible to locate the ropes or barriers at least 25 metres from the abrasive blasting operation, the employer should ensure that the abrasive blasting area is separated from the rest of the project by an enclosure that will confine the dust within the abrasive blasting area.