Silica

Silica is a natural substance found in most rocks, sand and clay and in products such as bricks, tiles, concrete and mortar. Silica is also used as filler in some plastics. In the workplace these materials create dust when they are cut, sanded, carved, crushed, etc. Some of this dust may be fine enough to breathe deeply into your lungs and cause harm to your health. The fine dust is known as Respirable Crystalline Silica (RCS) and is too fine to see with normal lighting. It is breathed in through the nose and mouth and can stay in the lungs for many years. It can cause irreversible lung damage before any symptoms develop. The illness it causes may continue to worsen even after exposure stops.

Health Effects of Respirable Crystalline Silica (RCS):

Silica is the biggest risk to construction workers after asbestos. Heavy and prolonged exposure to RCS can cause silicosis, chronic obstructive pulmonary disease (COPD), lung cancer, and other serious respiratory diseases.

• Silicosis is a disease of the lungs due to the breathing of dust containing crystalline silica particles. This dust can cause fibrosis or scar tissue formations in the lungs that reduce the lung's ability to work to extract oxygen from the air. Silicosis usually follows exposure to RCS over many years, but there is also an acute form of silicosis that occurs at very high exposures. This can start within a short time and can kill within a few months of first exposure. There is no cure for this disease, thus, prevention is the only answer. Early stages may go completely unnoticed. The main symptoms are cough and difficulty in breathing. Workers with silicosis are at increased risk of tuberculosis and lung cancer and may also develop kidney disease, arthritis and related diseases. 

• Chronic obstructive pulmonary disease (COPD) is a group of lung diseases, including bronchitis and emphysema, resulting in severe breathlessness, prolonged coughing and chronic disability. It can be very disabling and is a leading cause of death. Around 4000 deaths are estimated annually due to COPD resulting from past workplace exposures in the past. Construction workers are a significant at risk group within this.

• Lung cancer: Heavy and prolonged exposure to RCS can cause lung cancer. When someone already has silicosis, there is an increased risk of lung cancer. 

The health risks from RCS are insignificant when exposure to dust is adequately controlled – you do not need to become ill through work activities.

How to Recognize Silica Hazards:

Crystalline silica is a common mineral found in the earth's crust. Materials like sand, stone, concrete, mortar, ceramics, bricks, and glass all contain crystalline silica. Simply being near sand or other silica-containing materials is not hazardous. There is potential for danger ONLY when crystalline silica particles are in the air. Materials may contain silica but if the operations on those materials do not generate dust, there is little chance of inhaling the silica. Likewise, there may be silica particles in the air even though you don't see any dust.

Respirable crystalline silica is generated by high-energy operations like cutting, sawing, grinding, drilling and crushing stone, rock, concrete, brick, block and mortar; or when using industrial sand. Activities such as abrasive blasting with sand; sawing brick or concrete; sanding or drilling into concrete walls; grinding mortar; manufacturing brick, concrete blocks, or ceramic products; and cutting or crushing stone generates respirable dust.

In workplaces, the following can happen: 

• Leaks or spillages cause a build-up of dust containing RCS; 

• Dust containing RCS is not cleaned up safely, eg by dry sweeping rather than wet cleaning; 

• Clothing and surfaces are contaminated with dust containing RCS; 

• Accumulated dust containing RCS is raised from the ground or other surfaces by moving vehicles and people; 

• Fine dusts remain in the air from work activities.

Common construction materials and their silica content:

• Sandstone 70–90% 

• Concrete / mortar 25–70% 

• Shale 40–60%

• Tile 30–45% 

• Granite 20–45% 

• Slate 20–40% 

• Brick (Up to) 30% 

• Limestone, Chalk, and Marble 2%

Action Plan if Silica is Believed to be Present:

Consider Silica Substitutes: The most sure way to eliminate the silica hazard is to eliminate the silica. Eliminating the silica means using a different, safer material in place of the silica-containing substance. It is true that in many cases it is not possible to use a substitute in place of silica, but for some operations, such as abrasive blasting, there are possible substitutes.

Use Engineering Controls: When working with materials containing silica, limit the ways silica dust can enter the air. Some examples of engineering controls are:

• Install a water hose to wet down the dust at the point of generation

• Install local exhaust ventilation

• During rock drilling flow water through the drill stem

• Install dust collection systems onto machines or equipment that generate dust

• Use concrete/masonry saws that provide water to the blade

Once installed, engineering controls must be properly operated and maintained.

Work Practices: If workers know about silica and understand the severity of its health hazard, they will be more likely to do the following:

• Know which work operations can lead to silica exposure.

• Participate in any air monitoring or training programs offered.

• If possible, change into disposable or washable work clothes at the worksite; shower (where available) and change into clean clothing before leaving the worksite.

• Do not eat, drink, use tobacco products, or apply cosmetics in areas where there is dust containing crystalline silica.

• Wash your hands and face before eating, drinking, smoking, or applying cosmetics outside of the exposure area.

• If using respirators, do not alter the respirator in any way. 

• Use type CE positive pressure abrasive blasting respirators for sandblasting.

• For other operations where respirators may be required, use a respirator with a high level particulate filter.

• Avoid dry sweeping. If necessary, use a dust suppressant such as water.

Personal Protective Equipment (PPE): A good option as a temporary control, but the last choice as a permanent control. PPE against silica includes respirators and masks.  Respirators should be used only when the dust controls cannot keep dust levels below the recommended exposure levels. Safety goggles are the only effective type of eye protection from dust because they create a protective seal around the eyes.

When assessing the risks, consider:

• How long workers are exposed to the dust;

• How much they are exposed to; and

• How much crystalline silica there is in the dust.

More information can be found at:

OSHA - Determining Silica Exposure

OSHA - Taking Action to Protect Against Silica

OSHA - Health Effects of Silica

UK Health and Safety Executive - Control of Exposure to Silica Dust

UK Health and Safety Executive - Silicosis

Canadian Centre for Occupational Health and Safety - Silica FAQ

Operations Portal - Dust Hazards