Silicosis - Silica Dust Exposure & Prevention

Crystalline silica may be of several distinct types.Quartz, a form of silica and the most common mineral on earth, is contained in many types of rocks and is the major component of sand. Concrete and masonry products contain silica and rock and rock containing silica.Therefore it is easy to recognize how industrial workers may be exposed to free crystalline silica while in the following work activities:

1)  Sandblasting operations in which sandblasters use silica sand for blasting

2)  Crushing, loading, hauling, and dumping of rock containing high percentage of quartz

3)  Abrasive blasting using silica sand as the abrasive

4)  Abrasive blasting of concrete (regardless of abrasive used)

5)  Sawing, hammering, drilling, grinding, and chipping of concrete or masonry

6)  Demolition of concrete and masonry structures

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

8) Chipping, hammering, and drilling of rock

Other workers may be exposed to crystalline silica in the following occupations:

•   Sandblasting of Buildings
•   Sandblasting of oil field equipment
•   Shipbuilders
•   Surface Miners
•   Underground Miners Tunnel workers
•   Ceramic, Clay, Pottery Workers
•   Glass Manufacturing
•   Railroad Workers - (setting & laying track, engine rebuilding)
•   Foundry Workers - (grinding, molding, shakeout & core room)
•   Manufacturers of Abrasives
•   Grinders, Polishers
•   Tombstone Sandblasters
•   Boiler Scalers
•   Maritime/Offshore Rust Removal/Sandblasters
•   Welders
•   Soap and Detergent Workers
•   Nuclear Testing Sites

How Does Silica Become Free Silica ?

When Silica (SiO2) combines with other cations to form Silicates, then the SiO2 is no longer "free". Free Silica exists in three forms, amorphous, cryptocrystalline and polymorphic crystalline.

Mining or quarrying of any rock that contains siliceous material may produce hazardous exposures to "free" Silica. Thus, the mining of copper, gold, platinum, tin, uranium or even coal may produce high exposures. Tunneling in rock containing high concentrations of quartz may produce severe exposures. The quarrying, rock drilling, chipping and cutting of granite,sandstone and slate may produce high exposures of silica from the quarry face where modern flame cutters may have increased exposure through all aspects of cutting, dressing, and polishing the quarried stone. Abrasive blasting and other uses such as scouring and polishing where Silica flows may be used may cause rapidly progressive disease. Other significant exposures may occur in glass manufacture, production of pottery, porcelain and lining bricks, boiler scaling, and enameling.

The production and use of refractory brick (firebrick) containing silica may pose significant health hazards particularly after they have been exposed to high temperatures as a significant major proportion of the Silica is transformed to cristobalite or tridymite. Bricklayers and others who maintain and dismantle the refractory brick of ovens, furnaces and other similar devices are exposed to a serious silica hazard.

Foundry work is still a major source of "free" Silica exposure. In all stages of the foundry process from core making through "shake-out" to maintenance and repair, "free" Silica exposures occur along with other potentially hazardous exposures to metal fumes, asbestos and toxic gases. As the quartz-containing sand used in the molds is exposed to hot metal, formation of cristobalite may occur. It is not uncommon for such sand to be used on a repeated basis leading to further increases in the concentration of cristobalite.