Cancer-Causing
Substances in the Workplace and Home -Crystalline Silica
What is crystalline silica?
Crystalline silica
is a basic component of soil, sand, granite, and many other minerals. It is used extensively in many industrial
applications because of its unique physical and chemical properties. 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 crystalline silica. During the last few years, thousands of
workers have been exposed to crystalline silica during hydraulic fracturing
activities because several thousand tons of pure crystalline silica are
injected into the subsurface at every single gas well to keep the shale
fractures open.
Sand, the most
common size fraction of natural crystalline silica, has many applications. For
example, it may be used in foundry castings, Portland cement, abrasives and
sandblasting materials, and hydraulic fracturing. It may also be used as a raw material for the
production of silicon and ferrosilicon metals, or as a filter for large volumes
of water, i.e. in municipal water and sewage treatment plants. When sand has more than 98% silica and low
iron content it can be used for glass and ceramic production. Flours are formed by the grinding or quartz,
quartzite, sand and sandstone. Flours are very fine grades of crystalline
silica and are used in the ceramic and pottery industry, in the manufacturing
of chrysotile cement, as a filler in rubber and paints and as an abrasive in
soaps and cleaners.
What are the hazards of crystalline silica?
Silica exposure
remains a serious threat to more than 2 million U.S. workers, including more
than 100,000 workers in high risk jobs such as abrasive blasting, hydraulic
fracturing, foundry work, stonecutting, rock drilling, quarry work and
tunneling. The seriousness of the health
hazards associated with silica exposure is demonstrated by the fatalities and
disabling illnesses that continue to occur in sandblasters and rockdrillers. 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, and acute.
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.
Where are construction workers exposed to crystalline
silica?
Exposure occurs during many different construction
activities. The most severe exposures generally
occur during abrasive blasting with sand to remove paint and rust from bridges,
tanks, concrete structures, and other surfaces. Other construction activities that may result
in severe exposure include: jack hammering, rock/well drilling, hydraulic
fracturing, frac sand mining and loading and unloading, concrete mixing,
concrete drilling, brick and concrete block cutting and sawing, tuck pointing, tunneling
operations.
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.
In the maritime industry, shipyard employees are
exposed to silica primarily in abrasive blasting operations to remove paint and
clean and prepare steel hulls, bulkheads, decks, and tanks for paints and
coatings.
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 protection
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 protective
measures.
■ Use all available work practices to
control dust exposures, such as water sprays.
■ 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 blasting.
■ 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.
How can I get more information on safety and health?
OSHA has various
publications, standards, technical assistance, and compliance tools to help
you, and offers extensive assistance through workplace consultation, voluntary
protection programs, strategic partnerships, alliances, state plans, grants,
training, and education. OSHA’s Safety
and Health Program Management Guidelines (Federal Register 54:3904-3916, January
26, 1989) detail elements critical to the development of a successful safety
and health management system. This and other information are available on
OSHA’s website.
■ For one free copy of OSHA
publications, send a self-addressed mailing label to OSHA Publications Office,
200 Constitution Avenue N.W., N-3101, Washington, DC 20210; or send a request
to our fax at (202) 693–2498, or call us toll-free at (800) 321–OSHA.
■ To order OSHA publications online at
www.osha.gov, go to Publications and follow the instructions for
ordering.
■ To file a complaint by phone, report
an emergency, or get OSHA advice, assistance, or products, contact your nearest
OSHA office under the U.S. Department of Labor listing in your phone book, or
call toll-free at (800) 321– OSHA (6742). The teletypewriter (TTY)
number is (877) 889–5627.
■ To file a complaint online or obtain
more information on OSHA federal and state programs, visit OSHA’s website.
This is one in a
series of informational fact sheets highlighting OSHA programs, policies, or
standards. It does not impose any new compliance requirements. For a
comprehensive list of compliance requirements of OSHA standards or regulations,
refer to Title 29 of the Code of Federal Regulations. This information will be
made available to sensory-impaired individuals upon request. The voice phone is
(202) 693–1999. See also OSHA’s website at www.osha.gov.
