Does your shop cut, grind or hone stone dry? If so, you should consider the fact that the dust created from cutting and grinding certain types of stone will emit silica in the air. If you or your workers are not using the proper respiratory protection, you could be exposing yourself and your workers to serious health problems - and potentially devastating lawsuits. Breathing silica dust can cause a disease known as silicosis. More than 250 people each year die from this disease, and over 1 million workers in the U.S. are exposed to silica dust.

Although concerns regarding silicosis in the stone industry have been on the rise lately, the problem is certainly not a new one. In 1998, the Washington State Department of Labor and Industry specifically cited the stone fabrication industry as being at risk of silicosis. Its report read, in part, as follows:
  • "Fabricating granite countertops and other silica-containing materials may expose workers to levels of respirable crystalline silica above state limits, as was found recently by the Department of Labor and Industries and the University of Washington. Workers who inhale excessive amounts of crystalline silica can develop silicosis, a serious and potentially fatal lung disease. Methods for controlling exposure to silica are available."

The really bad news is that there is no cure for silicosis. The good news, however, is that the disease is very preventable. The following are some answers to common questions regarding silica in the stone fabrication shop:

What is crystalline silica?

Crystalline silica is a natural component of the earth’s crust, and it is a basic component of sand, quartz and granite rock.

What stone types contain silica?

All granites, as well as certain slate varieties and some marbles, may contain harmful silica. I would make the assumption that all granites and slates contain silica. Most marbles, except for a few green varieties, have silica. Limestone generally will not contain silica, although there are a few which may. All quartzites and stone containing quartz will also have silica.

What are the health hazards of exposure to silica dust?

Crystalline silica inhaled in excessive amounts can cause a serious and potentially fatal lung disease called silicosis. Silica is also capable of causing lung cancer with prolonged heavy occupational exposures. Workers with impaired lung function due to silica exposure are also more susceptible to other respiratory diseases, such as tuberculosis. The health hazards of silica are not new; silicosis is one of the world’s oldest known occupational diseases, with reports dating back to ancient Greece. These serious health hazards can be caused by short-term exposure to very high levels of silica as well as long-term exposure to levels of silica that aren’t quite as high, but still exceed state limits.

What activities in stone fabrication expose workers to silica dust?

Activities common to stone countertop fabrication - grinding, cutting, routing, drilling, chipping or polishing granite and other stone materials containing crystalline silica - can create airborne dust and the potential for health hazards to workers.

High silica exposures have also been found in other stoneworking operations, such as firms which fabricate stone memorials.

Worker exposure to silica-containing dust is dependent on a number of factors, including the amount of crystalline silica in the material, which tasks are being done, length of time performing dusty tasks, work practices (e.g. dry work or wet work), type of ventilation in use and specific tools utilized.

What are some examples of limits on silica exposure?

In Washington State, for example, the permissible exposure limit (PEL) for exposure to respirable crystalline silica is 0.1 milligrams silica per cubic meter of air (0.1 mg/cu.m), averaged over an eight-hour workshift. This limit can be exceeded in just 10 minutes of “dry” work on stone products that contain silica. Employers with workers exposed to silica dust above the legal limit must reduce exposure through a variety of control options. Employers also need to explain to workers the health risks of silica exposure and methods they use to eliminate or reduce exposures.

Most states will have their own exposure limits for silica, and I would encourage you to check with your state’s Department of Labor. OSHA also has some excellent information on silicosis on its Web site:

What methods can be used to reduce exposure to silica?

Methods for reducing exposure to silica dust are available. Using water to suppress dust is perhaps the most effective and often-used control method. Purchasing water-fed tools, or finding ways to use water at the point of operation (e.g. a directed water spray or trickling water on the working surface from a soda bottle with a small hole at the bottom) should always be considered. Grinders can produce the most dust, and they have been successfully adapted with a water-feed system. Another control option would be to purchase or equip grinders and saws with ventilation devices that capture and route dust to an industrial type vacuum.

Respirators may be used as a control for very infrequent tasks or where no feasible engineering controls (e.g. using water or ventilation) can be found for a particular task. Where respirators are used (in most cases a half-face respirator equipped with HEPA type filters), a complete respirator program must be put in place. Such a program includes proper selection, fit testing, cleaning and maintenance, supervision, training and written procedures.

What other hazards need to be addressed?

When using water for dust suppression, floor drainage and appropriate clothing must be considered. Also, the use of electrical equipment with water requires grounded equipment, ground fault circuit interrupters (GFCI), electrical cords routed overhead and sufficient maintenance of electrical tools. The use of air-powered tools can eliminate the electrical hazards. Handling large pieces of stone necessitates specific safe work practices to prevent back injuries and potentially fatal material crashes. An effective accident prevention program addresses these and other hazards associated with the stone fabrication industry.