© 2006 by Taylor & Francis Group, LLC

82 Corrosion Control Through Organic Coatings
4.6.2 WHAT FORMS OF SILICA CAUSE SILICOSIS?
Not all forms of silica cause silicosis. Silicates are not implicated in the disease,
and neither is the element silicon (Si), commonly distributed in the earth’s crust and
made famous by the semiconductor industry.
Silicates (-SiO 4) are a combination of silicon, oxygen, and a metal such as aluminum,
magnesium, or lead. Examples are mica, talc, Portland cement, asbestos, and fiberglass.
Silica is silicon and oxygen (SiO 2). It is a chemically inert solid that can be
either amorphous or crystalline. Crystalline silica, also called “free silica,” is the
form that causes silicosis. Free silica has several crystalline structures, the most
common of which (for industrial purposes) are quartz, tridymite, and cristobalite.
Crystalline silica is found in many minerals, such as granite and feldspar, and is a
principal component of quartz sand. Although it is chemically inert, it can be a
hazardous material and should always be treated with respect.
4.6.3 WHAT IS A LOW-FREE-SILICA ABRASIVE?
A low-free-silica abrasive is one that contains less than 1% free (crystalline) silica.
The following are examples of low-free-silica abrasives used in heavy industry:
• Steel or chilled iron, in grit or shot form
• Copper slag
• Boiler slag (aluminium silicate)
• Nickel slag
• Garnet
• Silicon carbide (carborundum)
• Aluminium oxide
4.6.4 WHAT HYGIENIC MEASURES CAN BE TAKEN
TO PREVENT SILICOSIS?
The best way to prevent silicosis among abrasive blasters is to use a low-free-silica
abrasive. Good alternatives to quartz sand are available (see Section 4.2). In many
countries where dry blasting with quartz sand is forbidden, these alternatives have
proven themselves reliable and economical for many decades.
It is possible to reduce the risks associated with dry abrasive blasting with silica.
Efforts needed to do so can be divided into four groups:
• Less-toxic abrasive blasting materials
• Engineering controls (such as ventilation) and work practices
• Proper and adequate respiratory protection for workers
• Medical surveillance programs
The National Institute for Occupational Safety and Health (NIOSH) recommends
the following measures to reduce crystalline silica exposures in the workplace and
prevent silicosis [28]:
• Prohibit silica sand (and other substances containing more than 1% crystalline
silica) as an abrasive blasting material and substitute less hazardous materials.
• Conduct air monitoring to measure worker exposures.
© 2006 by Taylor & Francis Group, LLC