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Silica Air Sampling and Controls

Crystalline silica is a naturally occurring mineral most commonly found as quartz. Silica is present in substantial quantities in sand, sandstone, granite, stone and rock aggregates, clay, shale, and slate. When crystalline silica is released into the air as fine dust, workers may inhale the dust, putting them at risk for illness.

When breathing in very small (“respirable”) crystalline silica particles, workers are at an increased risk of developing multiple diseases, including:

  • Silicosis, an incurable lung disease that can lead to disability and death;
  • Lung cancer;
  • Chronic obstructive pulmonary disease (COPD); and
  • Kidney disease.
In Alberta, the 8-Hour Occupational Exposure Limits for silica is 0.025 mg/m3 for Respirable Crystalline Silica (Cristobalite) and Respirable Crystalline Silica (Quartz).

Importance of Silica Air Samples

When dust-creating activities are happening, the best way to determine the concentration of dust in the air is to take silica air samples. There are two types of air sampling: personal (occupational) sampling and area sampling.

1. Occupational air sampling: 
Personal air monitoring is necessary to ensure exposures do not exceed the occupational exposure limit (OEL), verify engineering controls are working effectively, and select the proper respirator if one is needed.
 
The respirator is worn by the worker and used to evaluate work procedures and worker techniques. Also, it helps to identify exposures and adequacy of controls. If problems with the project occur, occupational sampling will show higher concentrations.
 
2. Area Sampling: 
Area samples are placed on the perimeter of the work area. The location and the number of the samples are determined by the size and complexity of work tasks. Area samples help to assess contaminant migration.

What do we need for a sample?

  • Match-weighted 5µm 37mm PVC Cassette
  • Cyclone (Respirable Silica)
  • Cyclone Calibrator-Adapter or Calibration-Jar
  • Low Flow Sampling Pump (1-4 LPM)

What are the Key Steps?

1. After the discussions with workers, a professional industrial hygienist (IH) will determine the number of the samples and the typical work activities and worst-case exposures to collect the air sample. It would be throughout the work shift or specific task length.
 
2. Samples were submitted immediately following collection and were analyzed by an accredited laboratory where the total amount of dust and silica dust will be measured.
 
3. Based on the sample results and silica content, dust control options for the material and task will be conducted.

What Exposure Controls are Neccessary?

For controlling silica dust, follow the hierarchy of controls for the basic approaches:

Hierarchy of Controls image 1. Elimination is the best method of controlling silica exposure but not always feasible for all operations.
 
2. Wet methods include wet processes, wet blasting, and wet cutting can keep the cutting or grinding surface moist to prevent silica from becoming airborne. Proper ventilation, such as local exhaust, is another way to protect workers as it keeps air moving and prevents them from inhaling airborne silica. 
 
3. Administrative controls such as educating and training the workers to ensure that they fully understand the hazardous nature of their work materials. Exposure Control Plan for Crystalline Silica (Quartz) and Respirable Particulate should be prepared and implemented if one isn’t already available. It should include, but not be limited to, roles and responsibilities of site personnel, hazard/risk assessments, and controls; 
 
4. If practical engineering controls cannot be implemented, having workers wear respirators is another option. However, workers must each have a properly fitting mask that they wear throughout their shift.

It is an employers’ responsibility to protect their workers’ health and safety. Workers who may be exposed to silica are required to undergo a health assessment no more than 30 days after a worker becomes exposed and every 2 years after the initial assessment.

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