What is Silica dust?

This is a form of the naturally occurring substance silica which consists of the two most abundant elements in the earth’s crust; silica and oxygen. Each silica molecule consists of one atom of silicon and two oxygen atoms giving the chemical formula SiO2. As fine dust, it is commonly known as respirable crystalline silica because of its exposure routes which affect the respiratory and pulmonary systems leading to different health hazards such as silicosis. Silicosis is a lung disease caused by inhalation, retention and pulmonary reaction to crystalline silica and when it becomes symptomatic, the primary symptom is usually difficulty in breathing and shortness of breath, first noted with activity or exercise and later as the functional reserve of the lung is also lost it happens at rest. Silicosis increases the risk of tuberculosis, and it has been linked with other diseases such as chronic obstructive pulmonary disease, and kidney and autoimmune disease. Prolonged or repeated breathing of silica dust may cause permanent lung damage and other diseases even if it does not cause immediately noticeable injury or illness.

Previously we have penned articles on silica dust industries at risk with a broader discussion touching on the different aspects of those industries. In the Australian context which extends to the global silica dust crisis we have written on workplace exposure standards for silica dust in Australia and silica dust exposure in Australian workplaces. In this article we delve deeper into understanding:

  • Types of silica dust and how it is formed. 
  • Routes to silica dust exposure and its symptoms. 
  • How much silica dust can cause silicosis and other health hazards?

What are the types of silica dust?

Silica can exist in two forms namely crystalline and amorphous. In the crystalline state the silica molecules form a three-dimensional repeating pattern. In the amorphous state the silica molecules form a random pattern. In our discussion the focal point will be the crystalline form of silica. In its crystalline form silica is found in almost every type of rock and, as quartz, it is the second most common form of naturally occurring mineral. Volcanic rocks such as granite can contain up to 33% quartz. Sedimentary rocks such as sandstone can contain up to 80% quartz. Sand and silt can contain up to 95% quartz.

How is silica dust formed?

Silica dust forms during road and building construction, sandblasting, stone cutting, mining, abrasive manufacturing, glass manufacturing, quarrying, tunnelling and working with certain metal ores. Materials that contain crystalline silica are not hazardous unless they are disturbed, generating small-sized particles that can get in your lungs as respirable crystalline silica. Activities such as blasting, cutting, chipping, drilling and grinding materials that contain silica can result in silica dust that is hazardous for mining and quarry industries. In agriculture cultivation of arable land can cause significant exposure to respirable crystalline silica dust, the level of exposure will depend upon the concentration of crystalline silica in the soil type. In the construction industry, the crystalline silica comes from materials such as concrete, mortar, bricks, tiles, stone and fibre cement products.

What causes silicosis?

Respirable crystalline silica is the type of crystalline silica dust that is of most importance when assessing the risk to health of exposed workers and communities within the vicinity of silica dust-generating activities. Respirable dust consists of very small particles that can penetrate the deep parts of the lungs. These particles are less than 10 microns which in perspective is less than one seventh the diameter of a human hair. Respirable particles penetrate the alveolar region of the lung. This is the deep part of the lung where the blood takes the oxygen from the air we breathe. It is progressive lung damage caused by inhalation of dust containing silica particles. The problem arises from the fact that particles small enough end up in the alveoli, parts of the lungs devoted to gaseous exchange. The areas of so-called lower lungs cannot be cleared by coughing and so-called mucus escalator because the ciliated epithelium ends way before the gas exchange begins, and the mucus ends even earlier. The only way to remove contaminants from is by the macrophages, that patrol the lower lung environment and phagocytize the particles. They try to do it with silica, but here a major problem begins. Silica is lethal for macrophages. Macrophages that consume silica die before they can get to a point where they can move up, passively or actively, so they die in the alveoli. Prior to their death, they secrete compounds that activate other cells, and this initiates inflammation. Lung tissue does not regenerate, the inflammation causes the proliferation of fibrocytes, that lay down fibers, and create scar tissue.

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What are the symptoms of silicosis?

The symptoms range from:

  • Shortness of breath
  • Weight loss 
  • Eye irritation
  • Lung and throat irritation
  • Trouble breathing
  • Lung cancer

Who Gets Silicosis?

People get silicosis due to exposure to silica dust at work or living in nearby localities. Most of the silicosis cases are recorded due to working in high-risk jobs such as:

  • Mining
  • Steel industry
  • Construction
  • Masonry
  • Roofing
  • Farming
  • Plaster or drywall installation
  • Glass manufacturing
  • Road repair

How much silica dust can cause silicosis and other health hazards?

It only takes a very small amount of the very fine respirable silica dust to create a health hazard. Recognizing that very small, respirable particles are hazardous. There are three types of silicosis namely chronic, accelerated and acute silicosis. Chronic silicosis, results from long-term exposure of more than 20 years to low amounts of silica dust. The silica dust causes swelling in the lungs and chest lymph nodes. The silica dust causes swelling in the lungs and chest lymph nodes. This disease may cause people to have trouble breathing which is the most common form of silicosis. Accelerated silicosis, which occurs after exposure to larger amounts of silica over a short period of time from 5 to 15 years. Swelling in the lungs and symptoms occur faster than in simple silicosis. Acute silicosis, which results from short-term exposure to very large amounts of silica. The lungs become very inflamed and can fill with fluid, causing severe shortness of breath and a low blood oxygen level. There is no specific treatment for silicosis. Removing the source of silica exposure is important to prevent the disease from getting worse. People with silicosis are at high risk of developing tuberculosis. Silica is believed to interfere with the body’s immune response to the bacteria that cause tuberculosis. Effectively, lungs cannot heal from silicosis the only form of prevention is eliminating any further exposure at its source because lungs will flush some out before it settles in. The damage is irreversible. Silica dust kills and there is no cure so prevention only delays the effects of a detrimental situation. End dust in mining, quarrying and construction to save lives.

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