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Crystalline Silica
Health Effects of Crystalline Silica
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Silica
occurs virtually everywhere on the earth's surface. Crystalline silica
is in most of the rocks found in the earth's crust and in gravels,
sands and soils. Industrial sand contains a very high percentage of
silica, in the form of quartz, and is distinguished by its high degree
of purity. Industrial sand must meet stringent quality requirements for
its use in ceramic products and the health effects caused by its
inhalation in a number of industries are of concern.
It is
essential to provide a safe and healthful workplace for workers exposed
to crystalline silica. Each workplace is different and only the users
of the material can know and implement the appropriate controls,
protections, policies and procedures to protect workers and customers
from the respiratory health effects of crystalline silica. Occupational
exposure to crystalline silica occurs by breathing silica-containing
dusts and inhalation of excessive amounts of these dusts is a serious
health concern. The primary and most commonly known health hazard is
silicosis, a fibrotic lung disease (development of scar tissue in the
lungs) which can be progressive and disabling, and can lead to death.
There are three different types of silicosis. Chronic silicosis may
result from prolonged inhalation of excessive levels of respirable
silica dust, and may take many years of exposure to develop.
Accelerated silicosis may occur in a relatively shorter period of time
from the inhalation of intense excessive levels of respirable silica
dust. Acute silicosis develops rapidly and has been reported in
occupations such as sand blasting and drilling through
silica-containing rock. Cases of acute silicosis and complicated cases
of chronic silicosis and accelerated silicosis can be fatal.
The occurrence of lung cancer caused by crystalline silica exposure
continues to be studied. In 1997, the International Agency for Research
on Cancer upgraded its classification of inhaled crystalline silica
from occupational sources as carcinogenic to humans. Designated a Group
1 agent, the IARC sites sufficient evidence of carcinogenicity in
humans. The human studies reviewed by the IARC included inhalation
resulting from workplace exposures. In the overall evaluation, the IARC
noted that carcinogenicity was not detected in all industrial
circumstances studied, and may be dependent on inherent characteristics
of the crystalline silica or on external factors affecting its
biological activity or distribution of its polymorphs.
Safety and health programs, policies and procedures should be
implemented and enforced to control silica hazards in the workplace and
include:
* wearing a NIOSH-approved respirator when working around silica dust;
* warning and training workers concerning hazards;
* crystalline silica dust sampling;
* engineering controls;
* good housekeeping; and
* medical surveillance of workers focusing on respiratory health.
These programs, policies and procedures must be designed to fit the
specific needs of the workplace. For further information on such
programs, contact the National Institute for Occupational Safety and
Health at (800)35-NIOSH. |
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