OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at http://www.osha.gov.

February 11, 1986

The Honorable Gary Hart
United States Senator
1748 High Street
Denver, Colorado 80218

Dear Senator Hart:

Your letter of January 9, to former Assistant Secretary Robert Rowland concerning your constituents, Mr. and Mrs. Richard Robidoux, has been referred to us for reply.

According to this recent U.S. Vital Statistics published by the National Center for Health Statistics, a total of 1,005 Americans died from silicosis during the years 1976-1980. The actual figures for each year are as follows:

Year   Deaths
1976 - 215
1977 - 193
1978 - 168
1979 - 222
1980 - 207

Silicosis, a type of pneumoceniosis, is caused by inhalation of fire dust containing crystalline silica (free silica). It is a disabling, progressive and sometimes fatal pulmonary fibrosis characterized by the presence of nudulations in the lungs. The clinical signs and symptoms of silicosis tend to be progressive with continued exposure to quantities of dust containing free silica. Signs and symptoms include cough, dyspnea, wheezing, and repeated nonspecific chest illness. Impaired pulmonary function may be progressive. In individual cases there may be little or no decrement when simple discrete nodular silicosis is present, but when nodulations become larger or when conglomoration occurs, recognizable cardiopulmonary impairment occurs. Progression of signs or symptoms usually continues after dust exposure ceases. The risk of onset and the rate of progression of the pulmonary lasion is related to the character of the exposure (dust concentration and duration). The disease occurs after an exposure is measured in years rather than months. Occasionally, exposures to very high concentrations for short periods of time cause the development of acute silicosis.

The human body has a defense mechanism against inhaled dust. Large particles (5 micrometers or larger) usually deposited in the upper respiratory tract, are removed by swallowing, or by blowing or sneezing from the nose. Particles smaller than 5 micrometers are usually deposited in the lower respiratory tracts such as the trachea-bronchial tree and the alveolar region of the lungs. Particles deposited in these regions are transported by ciliated mucous membranes to the upper respiratory tract for removal. If the inhaled dust exceeds the capacity of the clearance mechanism of the lungs, dust remaining in the lungs may cause damage. Once the nodules are formed in the lungs, it is not reversible.

Regarding the ban of silica in other countries, we are aware the United Kingdom banned the use of silica in abrasive blasting. However, in this country only the U.S. Environmental Protection Agency (EPA) has the authority to ban substances; the Occupational Safety and Health Administration (OSHA) cannot. We suggest that you direct Mr. and Mrs. Robidoux to EPA concerning this matter. Also, concerning the use of pediatric data in settling standards, we again suggest that your constituents contact EPA regarding their standards- setting process. OSHA's standards are based on adult populations that are present in the workplace. Pediatric data are not included in the setting of OSHA standards for the obvious reason that infants and children are not part of the work force. Although OSHA cannot ban the use of silica, we have set limits for its use in the workplace. OSHA has set a permissible exposure limit (PEL) for occupational exposure to crystalline silica according to the following formula (29 CFR 1910.1000 Table Z-3):

                          10 mg/m(3)
Crystalline Silica = ----------------------
 (respirable)            % Silica + 2

                          30 mg/m(3)
Crystalline Silica = ----------------------
 (total dust)            % Silica + 2

OSHA's health standards require employers to implement engineering or administrative controls to reduce employee exposure to toxic air contaminants within the PEL whenever feasible. Since it is not feasible to control silica exposure during a sandblasting operation, respirators such as supplied air respirators approved for abrasive blasting are permissible to reduce worker exposure to free silica during the blasting operation. A properly operated and maintained approved abrasive blasting respirator may provide adequate protection to the wearer.

There are many abrasive blasting materials available other than silica such as aluminum oxide, smelter slags, glass beads, plastic beads or carbon dioxide pellets. Each of these materials has specific characteristics for a given application. The use of sand with lower quartz content, or large fraction of non-respirable particles content for blasting could reduce the potential hazard associated with silica.

I am taking the liberty of forwarding a copy of your constituents' letter along with a copy of our reply to EPA's Office of Toxic Substances.

If you need further assistance, please have a member of your staff contact Mrs. Becky Morris, Special Assistant for Congressional Relations, at 523-6027.


Edward J. Baier
Directorate of Technical Support