CANCER-CAUSING SUBSTANCES IN THE WORKPLACE AND HOME -CRYSTALLINE SILICA

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.