Construction Solutions - Masonry, Cement & Plaster - Mixing cement, mortar, plaster, or grout



Hazard Analysis


	Work Activity:	Masonry, Cement & Plaster
	Task:	Mixing cement, mortar, plaster, or grout
	Hazard:	Silica

Problem:

Silica is found in many construction products, including sand, some aggregates, cement, mortar, plaster and grout. Prolonged exposure to silica causes chronic lung disease (silicosis) this is untreatable and can be fatal.

In mixing operations, the highest silica dust exposure tasks typically involve work near rock crushers that may be used to size aggregate, and bag breaking where paper bags of dry cement are broken or poured. Bag breaking operations in manufacturing have long been the target of local dust control.

Risk Description:

Quartz (silica) is found naturally in almost all rock, sand and soil. It is also found in concrete products and bricks. It is sometimes found in sandblasting (abrasive blasting) grit and is called "silica sand". When dust is generated from cutting, grinding, drilling, sanding or sandblasting on or with rock, gravel and sand, the dust will usually contain silica. A lung disease called "silicosis" is caused by breathing of dust containing silica. The dust causes "fibrosis" or scar tissue formation in the lungs. This reduces the lung's ability to extract oxygen from the air. Silicosis may develop after very short periods of high exposure, but more commonly it develops after many years of lower levels of exposure. Silicosis also increases susceptibility to other lung diseases and infections such as tuberculosis, and increases the likelihood of getting lung cancer.

More Detail

When workers inhale crystalline silica, the lung tissue reacts by developing fibrotic nodules and scarring around the trapped silica particles. This fibrotic condition of the lung is called silicosis. If the nodules grow too large, breathing becomes difficult and death may result. A worker's lungs may react more severely to silica sand that has been freshly fractured, as happens when silica containing products are sawed, hammered, or treated in a way that produces airborne dust. This factor may contribute to the development of acute and accelerated forms of silicosis.

A worker may develop any of three types of silicosis, depending on the airborne concentration of crystalline silica:

Chronic silicosis, which usually occurs after 10 or more years of exposure to crystalline silica at relatively low concentrations

Accelerated silicosis, which results from exposure to high concentrations of crystalline silica and develops 5 to 10 years after the initial exposure

Acute silicosis, which occurs where exposure concentrations are the highest and can cause symptoms to develop within a few weeks to 4 or 5 years after the initial exposure

Complications

Initially, workers with silicosis may have no symptoms. As silicosis progresses, there may be difficulty in breathing and other chest symptoms such as cough. IIndividuals with silicosis are also at high risk of developing tuberculosis, which causes fever, weight loss, and night sweats. Tuberculosis or other infections are believed to result when the lung cells (macrophages) that fight these infections are overwhelmed with silica dust and are unable to kill the TB bacteria. About half of the mycobacterial infections are caused by Mycobacterium tuberculosis (TB), with the other half caused by M. kansasii and M. avium-intracellulare. Nocardia and Cryptococcus may also cause infections in silicosis.

Evidence indicates that crystalline silica is a potential occupational carcinogen.

Less Detail

Level of Risk:

Exposures are of such a magnitude and character that a significant number of workers risk developing serious long or short term health effects.

More Detail