There's a hazardous substance that most of the construction workers are exposed to on a daily basis that doesn't look hazardous at all. It looks like common materials such as bricks or stone, and it's called silica. Silica, also called silicon dioxide, is a family of minerals with the chemical formula SiO2. It's one of the main components that make up the earth's crust and abounds in a variety of natural, everyday materials. It comes in two basic forms - Noncrystalline and crystalline silica. Noncrystalline silica is found in materials like silicon carbide, glass and silicone. This type of silica is not as much of a health concern. Crystalline silica is termed as “respirable crystalline silica” as this silica particles are small enough to be inhaled and more of a health concern than noncrystalline silica. It's most prevalent in the form of quartz. This natural substance is found in many different types of rock and building materials, such as sand, gravel, granite, sandstone, clay, concrete, asphalt, bricks and more. Exposure to silica dust can lead to the development of lung cancer, silicosis (an irreversible scarring and stiffening of the lungs), kidney disease and chronic obstructive pulmonary disease. It is estimated that 230 people develop lung cancer each year as a result of past exposure to silica dust at work. Not all exposed workers will develop cancer; cancer risk increases with long term or repeated high level exposure.
SILICA AND SILICOSIS
Quartz is abundant in most rocks, sands, and soils. The extensive natural occurrence of quartz and the wide uses of the materials that contain quartz are directly related to potential occupational exposures to quartz for workers in many industries and occupations. Virtually any process that involves movement of earth (e.g., mining, farming, construction), disturbance of silica-containing products such as masonry and concrete, or use of sand and other silica-containing products (e.g., foundry processes) may potentially expose workers to quartz. Exposure of workers to respirable crystalline silica is associated with elevated rates of lung cancer. The strongest link between human lung cancer and exposure to respirable crystalline silica has been seen in studies of quarry and granite workers and workers involved in ceramic, pottery, refractory brick, and certain earth industries. Consequentially, exposure to crystalline silica remains a problem in both developed and developing nations.
Silicosis is the result of the body's response to the presence of silica dust in the lung(s). Exposure to silica occurs by inhaling airborne particles of silica dust, typically ranging from 5.0μm to 0.5μm. The respirable fraction of the dust (particles generally considered to be smaller than ve-millionth of a meter) can penetrate to the innermost layers i.e. the alveoli (airsacs) where the exchange of oxygen and carbon dioxide occurs. When workers inhale crystalline silica, they land on the alveoli, and white blood cells (macrophages) try to remove them. However, the particles of free crystalline silica cause the macrophages to break open. The lung tissues react by developing brotic nodules and scarring around the trapped silica particles.
Formation of large numbers of "scars" following prolonged exposure causes the alveolar surface to become less elastic. This is noticed as shortness of breath following exertion. Symptoms seldom develop in less than ve years and, in many cases, may take more than 2 years to become disabling or cause death.
Figure 1: Image Showing A Healthy Lung And Lung With Silicosis
TYPES OF SILICOSIS
Figure 2: Chest X-ray of Patients with simple silicosis and Complicated silicosis
2. Accelerated silicosis which results from exposure to high concentrations of crystalline silica and develops ve to ten years after the initial exposure.
3. Acute silicosis, which occurs where exposure concentrations are the highest and can cause symptoms to develop within a few weeks to four or ve years after the initial exposure.