Respirable Crystaline Silica

Is Not Just Dust

Silica

Silica is synonymous with silicon dioxide (SiO2). Silicon and oxygen are the two most abundant elements in the earth’s crust. Silica is commonly found in nature as sand. Silica exists in many different forms that can be crystalline as well as non-crystalline (amorphous).

Breathing silica can cause Silicosis

autoimmune diseases tuberculosis (TB) and other chest infections

pulmonary hypertension

heart failure

arthritis

kidney disease

chronic obstructive pulmonary disease (COPD)

lung cancer and more

Silicosis - NHS

Forms

Silica exists in nine different crystalline forms or polymorphs with the three main forms being quartz, which is by far the most common, tridymite and cristobalite. It also occurs in a number of cryptocrystalline forms. Fibrous forms have the general name chalcedony and include semi-precious stone versions such as agate, onyx and carnelian. Granular varieties include jasper and flint. There are also anhydrous forms – diatomite and opal.

Crystalline Silica

Crystalline silica is hard, chemically inert and has a high melting point. These are valued/important properties in various industrial uses. Quartz is the most common form of crystalline silica and is the second most common mineral on the earth’s surface. It is found in almost every type of rock i.e. igneous, metamorphic and sedimentary. Since it is so abundant, quartz is present in nearly all mining operations

Cristobalite

Cristobalite is scarce in nature. Some volcanic rocks and meteorites may contain small amounts of it. Cristobalite may also form when quartz is heated at high temperatures starting at 450°C. This is especially true during production and use of refractory materials and/or during calcination of silica (between 800 and 1110°C). As a result, there is a likelihood of exposure to cristobalite in occupational settings

Tridymite

Tridymite is also a scarce mineral that is only found in nature in volcanic rocks and meteorites. Tridymite, however, differs from cristobalite in that it is not stable during quartz and refractory materials heating processes at conventional process temperatures. As a result, exposures are very unlikely to occur in occupational or other settings.

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Types Of Dust

Fibrogenic Dust

Fibrogenic dust, such as free crystalline silica (FCS) or asbestos, is biologically toxic and, if retained in the lungs, can form scar tissue and impair the lungs’ ability to function properly.

Nuisance Dust

Nuisance dust, or inert dust, can be defined as dust that contains less than 1% quartz. Because of its low content of silicates, nuisance dust has a long history of having little adverse effect on the lungs. Any reaction that may occur from nuisance dust is potentially reversible. However, excessive concentrations of nuisance dust in the workplace may reduce visibility (e.g., iron oxide), may cause unpleasant deposits in eyes, cars,and nasal passages (e.g., portland cement dust), and may cause injury to the skin or mucous membranes by chemical or mechanical action.

From an occupational health point of view, dust is classified by size into three primary categories:

Respirable Dust

Inhalable Dust

Total Dust

Respirable Dust

Respirable dust refers to those dust particles that are small enough to penetrate the nose and upper respiratory system and deep into the lungs.

Particles that penetrate deep into the respiratory system are generally beyond the body’s natural clearance mechanisms of cilia and mucous and are

more likely to be retained.

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