What is crystalline silica?
Crystalline silica is a basic component of soil, sand, granite, and
many other minerals. Quartz is the most common form of crystalline
silica. Cristobalite and tridymite are two other forms of crystalline
silica. All three forms may become respirable size particles
when workers chip, cut, drill, or grind objects that contain
What are the hazards of crystalline silica?
Silica exposure remains a serious threat to nearly 2 million U.S.
workers, including more than 100,000 workers in high risk jobs
such as abrasive blasting, foundry work, stonecutting, rock drilling,
quarry work and tunneling. Crystalline silica has been classified as a
human lung carcinogen. Additionally, breathing crystalline silica dust
can cause silicosis, which in severe cases can be disabling, or even
fatal. The respirable silica dust enters the lungs and causes the
formation of scar tissue, thus reducing the lungs’ ability to take in
oxygen. There is no cure for silicosis. Since silicosis affects lung
function, it makes one more susceptible to lung infections like
tuberculosis. In addition, smoking causes lung damage and adds
to the damage caused by breathing silica dust.
|What are the symptoms of silicosis?
Silicosis is classified into three types: chronic/classic, accelerated,
Chronic/classic silicosis, the most common, occurs after 15–20
years of moderate to low exposures to respirable crystalline silica.
Symptoms associated with chronic silicosis may or may not be
obvious; therefore, workers need to have a chest x-ray to determine
if there is lung damage. As the disease progresses, the worker may
experience shortness of breath upon exercising and have clinical
signs of poor oxygen/carbon dioxide exchange. In the later stages,
the worker may experience fatigue, extreme shortness of breath,
chest pain, or respiratory failure.
Accelerated silicosis can occur after 5-10 years of high exposures
to respirable crystalline silica. Symptoms include severe shortness
of breath, weakness, and weight loss. The onset of symptoms takes
longer than in acute silicosis.
Acute silicosis occurs after a few months or as long as 2 years
following exposures to extremely high concentrations of respirable
crystalline silica. Symptoms of acute silicosis include severe
disabling shortness of breath, weakness, and weight loss, which
often leads to death.
For more information, contact your local OSHA office (listed in the
telephone directory under United States Government-Department
of Labor-Occupational Safety and Health Administration) or visit
OSHA’s website at www.osha.gov.
Where are general industry employees
exposed to crystalline silica dust?
The most severe exposures to crystalline silica result
from abrasive blasting, which is done to clean and smooth
irregularities from molds, jewelry, and foundry castings,
finish tombstones, etch or frost glass, or remove paint, oils,
rust, or dirt form objects needing to be repainted or treated.
Other exposures to silica dust occur in cement and brick
manufacturing, asphalt pavement manufacturing, china and
ceramic manufacturing and the tool and die, steel and foundry
industries. Crystalline silica is used in manufacturing, household
abrasives, adhesives, paints, soaps, and glass. Additionally,
crystalline silica exposures occur in the maintenance, repair and
replacement of refractory brick furnace linings.
How is OSHA addressing exposure
to crystalline silica?
OSHA has an established Permissible Exposure Limit, or
PEL, which is the maximum amount of crystalline silica to
which workers may be exposed during an 8-hour work shift
(29 CFR 1926.55, 1910.1000). OSHA also requires
hazard communication training for workers exposed to
crystalline silica, and requires a respirator program until
engineering controls are implemented. Additionally, OSHA
has a National Emphasis Program (NEP) for Crystalline Silica
exposure to identify, reduce, and eliminate health hazards
associated with occupational exposures.
What can employers/employees do to
protect against exposures to crystalline silica?
- Replace crystalline silica materials with safer substitutes, whenever possible.
- Provide engineering or administrative controls, where feasible, such as
local exhaust ventilation, and blasting cabinets. Where necessary to
reduce exposures below the PEL, use protective equipment or other
- Use all available work practices to control dust exposures, such as water
- Wear only a N95 NIOSH certified respirator, if respirator protection
is required. Do not alter the respirator. Do not wear a tight-fitting
respirator with a beard or mustache that prevents a good seal between
the respirator and the face.
- Wear only a Type CE abrasive-blast supplied-air respirator for abrasive
- Wear disposable or washable work clothes and shower if facilities are
available. Vacuum the dust from your clothes or change into clean
clothing before leaving the work site.
- Participate in training, exposure monitoring, and health screening and
surveillance programs to monitor any adverse health effects caused by
crystalline silica exposures.
- Be aware of the operations and job tasks creating crystalline silica exposures
in your workplace environment and know how to protect yourself.
- Be aware of the health hazards related to exposures to crystalline silica.
- Smoking adds to the lung damage caused by silica exposures.
- Do not eat, drink, smoke, or apply cosmetics in areas where crystalline
silica dust is present. Wash your hands and face outside of dusty areas
before performing any of these activities.
- Remember: If it’s silica, it’s not just dust.