Silica Dust: Health Hazards

Silica or silicon dioxide (SiO2) is one of the most common naturally occurring minerals on the planet. Furthermore, forms of silica are specifically manufactured by industry for their unique chemical (generally inert), physical (strong but brittle material with relatively high melting point) and electrical properties. The intra-molecular polar covalent bonds results in tetrahedral ordered molecular structures, which can be grouped as follows:

Amorphous silica: Molecules are arranged with limited ordering relative to each other, resulting in a transparent solid. Occurring rarely in nature, amorphous silica is extensively used within industry – particularly as the main component in glass and more recently in the electronics industry.

Crystalline silica: Molecules are arranged with indefinite ordering relative to each other, resulting in distinct crystalline structures that are white or yellowish in appearance. Nine different crystalline structural forms (polymorphs) exist – the most common forms of which are quartz, followed by cristobalite and tridymite. Crystalline silica is a key component of soil, sand, granite and other naturally occurring minerals.

Respirable crystalline silica (RCS): RCS is commonly used to refer to the tiny particles (at least 100 times smaller than ordinary grains of sand) of crystalline silica that are too small to be seen by the human eye. They can remain in the air for extended periods of time and be inhaled deeply into the lungs. These particles are created when handling, using, cutting, sanding or carving materials containing crystalline silica.

According to the UK Health and Safety Executive (HSE), due to its presence in commonly used construction materials, RCS is the second biggest health risk to construction workers, following asbestos. The HSE estimates that excessive exposure to silica was responsible for between 10 and 20 deaths annually in the last 10 years.

Awareness of the dangers posed by breathing RCS is increasing, but still many workers do not fully understand health risks of RCS exposure. Respirable crystalline silica can cause irreversible fibro cardiovascular diseases such as:

• Silicosis
• Lung cancer
• Chronic obstructive pulmonary disease (COPD)
• Bronchitis and emphysema
• Other effects including autoimmune, immunological and renal diseases have been reported. In addition, there is strong link between RCS exposure, silicosis and an increased risk of tuberculosis

Silicosis is a form of pneumoconiosis, with typically a long latency period between initial exposure and onset of disease symptoms.

Crystalline silica particles enter the lung, over-load the body’s defence mechanisms and cause irritation and damage to the alveoli. The body reacts by forming fibrous tissue around the trapped silica particles, and scarring of the lungs develops.

Over time, as the extent of scarring continues, the efficiency of the lungs decreases, and symptoms of silicosis develop. Unfortunately, no specific intervention is known to halt the progression of silicosis – silicosis is incurable and can lead to significant ill health and even death.

There are 3 types of silicosis:

1. Acute silicosis: The individual will have been typically exposed to very high levels of silica dust and symptoms will result in a matter of weeks or months.
2. Accelerated silicosis: A gradual onset of shortness of breath and dry cough occurs many years after exposure to medium to high levels exposure to RCS.
3. Chronic silicosis: This is the most common type and usually occurs after > 10 years’ exposure to low level silica dust.

According to the UK Health and Safety Executive (HSE), due to its presence in commonly used construction materials, RCS is the second biggest health risk to construction workers, following asbestos. The HSE estimates that excessive exposure to silica was responsible for between 10 and 20 deaths annually the last 10 years.

Symptoms of silicosis
Symptoms of silicosis can take many years to develop. It is important that workers are aware of what these are so they know what to look out for:

• Debilitating shortness of breath
• Loud cough
• Feeling of weakness
• Weight loss
• Chest pains
• Night sweats