Siliosis

BACKGROUND

Types of Silica

Crystalline silica may be of several distinct types. Quartz, a form of silica and the most common mineral in the earth's crust, is associated with many types of rock. Other types of silica include cristobalite and tridymite.

Potential for Exposure During Construction

Concrete and masonry products contain silica sand and rock containing silica. Since these products are primary materials for construction, construction workers may be easily exposed to respirable crystalline silica during activities such as the following:

* Chipping, hammering, and drilling of rock

* Crushing, loading, hauling, and dumping of rock

* Abrasive blasting using silica sand as the abrasive

* Abrasive blasting of concrete (regardless of abrasive used)

* Sawing, hammering, drilling, grinding, and chipping of concrete or masonry

* Demolition of concrete and masonry structures

* Dry sweeping or pressurized air blowing of concrete, rock, or sand dust

Even materials containing small amounts of crystalline silica may be hazardous if they are used in ways that produce high dust concentrations.

HEALTH EFFECTS OF CRYSTALLINE SILICA EXPOSURE

Description of Silicosis

When workers inhale crystalline silica, the lung tissue reacts by developing fibrotic nodules and scarring around the trapped silica particles [Silicosis and Silicate Disease Committee 1988]. This fibrotic condition of the lung is called silicosis. If the nodules grow too large, breathing becomes difficult and death may result. Silicosis victims are also at high risk of developing active tuberculosis [Myers et al. 1973; Sherson and Lander 1990; Bailey et al. 1974].

A worker's lungs may react more severely to silica sand that has been freshly fractured (sawed, hammered, or treated in a way that produces airborne dust) [Vallyathan et al. 1988]. This factor may contribute to the development of acute and accelerated forms of silicosis.

Types 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