Exposure to fine particles of silica has been shown to cause silicosis, a serious and sometimes fatal lung disease. Construction employees who inhale fine particles of silica may be at risk of developing this disease.
Silicosis is classified into three types: chronic/classic, accelerated, and acute.
Chronic/classic silicosis, the most common, occurs after 15-20 years of moderate to low exposures to respirable crystalline silica. Symptoms associated with chronic silicosis may or may not be obvious: therefore, workers need to have a chest x-ray to determine if there is lung damage. As the disease progresses, the worker may experience shortness of breath upon exercising and have clinical signs of poor oxygen/carbon dioxide exchange. In the later stages, the worker may experience fatigue, extreme shortness of breath, chest pain, or respiratory failure.
Accelerated silicosis can occur after 5-10 years of high exposures to respirable crystalline silica. Symptoms include severe shortness of breath, weakness, and weight loss. The onset of symptoms takes longer than in acute silicosis.
Acute silicosis occurs after a few months or as long as two years following exposures to extremely high concentrations of respirable crystalline silica. Symptoms of acute silicosis include severe disabling shortness of breath, weakness, and weight loss, which often leads to death.
Silica dust can be generated when materials such as ceramics, concrete, masonry, rock and sand are mixed, blasted, chipped, cut, crushed, drilled, dumped, ground, mixed or driven upon.
Employees at construction sites may be exposed to silica dust during general housekeeping activities such as sweeping, emptying vacuum cleaners and using compressed air for cleaning. Silica exposures may also occur whenever silica-containing dusts are disturbed, such as during material handling. The small particles generated during these activities easily become suspended in the air and, when inhaled, penetrate deep into employees’ lungs.
Visible dust contains large particles that are easy to see. The tiny, respirable-sized particles (those that can get into the deep lung) containing silica pose the greatest hazard and are not visible.
Most dust-generating construction activities produce a mixture of visible and respirable particles.
General Rule: If dust containing silica is visible in the air, it’s almost always more than the permissible limit.
Time-weighted average (TWA) limit: The employer must ensure that no employee is exposed to an airborne concentration of silica dust in excess of 0.1 fiber per cubic centimeter of air as an eight (8) hour time-weighted average (TWA).
A trained specialist, such as a certified industrial hygienist, will use a device called a cyclone assembly and a sampling pump to trap tiny respirable silica particles from the air in the work environment.
To control exposure to silica dust and fibers, avoid dry sweeping and the use of compressed air on concrete. Both these activities can stir up large amounts of dust. Use a vacuum with high efficiency filters when possible. When these activities cannot be avoided, respirators must be worn.
Best practices to help protect employees against exposures to silica include:
It’s important for the employer to train all employees who might have exposure to silica while performing demolition operations. Make sure employee training includes:
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