PART I. CASE STUDY

Question 1. How did epidemiologists find out what caused a silicosis outbreak in Texas?

In November 1988, a doctor in Texas reported three cases of silicosis to his local health department. These workers went to the doctor because they were becoming very short of breath. All three men worked at a facility where they sandblasted oil-field drilling pipes. One of the workers (aged 34) died of acute silicosis. The doctor reported the cases to the health department because silicosis is a very serious occupational disease. The doctor knew that the facility where these people worked might be hazardous. The doctor wanted the facility to be checked by the local health department to protect other people from developing silicosis. Recognition of silicosis usually signals a serious problem in the workplace.

The county health department and the Texas Department of Health contacted other local doctors and identified seven more workers who had suffered from silicosis since 1985. Thus the health departments identified a total of 10 workers who had been diagnosed with silicosis. Epidemiologists from the Texas Department of Health conducted an investigation of the workers with silicosis. The investigators reviewed personal and occupational histories from each worker who had been diagnosed with silicosis. They reviewed lung biopsy reports and inspected the facility for hazardous agents. The workers' chest X-rays were examined for lung diseases.

Each of the 10 workers had been exposed to crystalline silica at the workplace. Their chest X-rays were all abnormal and showed pneumoconiosis. Nine of the workers had abnormal lung biopsy reports of silicotic nodules or acute silicosis. The workers' ages ranged from 24 to 50 at the time of diagnosis. Seven workers were under age 30.

All 10 workers had used sandblasting machines for periods of 18 months to 8 years (the average was 4.5 years). Nine workers reported no silica exposure before working at the current site. The other worker had sandblasted oil-field drilling equipment for 3 years before working at the current site for 5 years. The epidemiologists from the Texas Department of Health consulted with occupational safety and health experts (called industrial hygienists) to learn more about the industrial processes that could have caused silicosis at this facility.

The sandblasting process at the facility used a blasting rod with a sandblasting agent containing 20.5% crystalline silica sand. The rod, which was connected to a high-pressure air supply hose, was held by the worker and directed through the drilling pipe. The abrasive silica sand from the rod was air-blasted against the inner walls of the pipe. This process removed contaminants to create a cleaner, smoother interior surface for application of a protective plastic coating. Although the sandblasting operation was enclosed by blasting cabinets connected to exhaust systems, the cabinets were in poor condition and permitted clouds of dust to be released throughout the work area. Workers stood inside booths intended to protect them from inhaling crystalline silica. However, the booths actually increased the workers' inhalation of crystalline silica by drawing their air from surrounding areas with high silica contamination. Workers then shoveled the used sandblasting mixture into the machinery for reuse.

In March 1989, air samples collected in the workers' breathing zones showed high concentrations of crystalline silica in the sandblasting area.

 

PART II. UNDERSTANDING SILICOSIS

Question 2. What is silica and what are the possible dangers of working with silica?

Silica may be of several distinct types. For example, quartz is a crystalline form of silica and is the most common mineral in the earth's crust. When rock containing quartz is chipped, hammered, drilled, crushed, loaded, hauled, or dumped, small particles of silica are released into the air and can be inhaled by workers.

Silica sand containing quartz is used in sandblasting equipment to clean surfaces. The outsides of buildings and bridges and the insides of storage tanks and pipes are some of the surfaces that are cleaned by sandblasting.

The silica sand used in sandblasting breaks into fine particles that stay in the air (Figure 1). If these particles are small enough to be inhaled deeply into the lungs, they are known as respirable crystalline silica. Inhaling these fine silica particles causes more lung damage than inhaling larger particles. This process causes rapid and severe forms of silicosis in sandblasters.

 



Figure 1. Detailed microscopic view of silica particles on a filter. (Scanning electron micrograph by William Jones, Ph.D.)

Question 3. What is silicosis?

When workers inhale crystalline silica, the lung develops scar tissue around the silica particles. This process results in a lung disease known as silicosis. As more lung tissue is damaged by silica dust, breathing becomes more difficult, chest pain occurs, and death may result. Silicosis patients suffer shortness of breath, fever, and cyanosis. Some patients are diagnosed incorrectly as having pulmonary edema, pneumonia, or other lung diseases.

The three types of silicosis are as follows:

• Chronic silicosis, which occurs after 10 or more years of exposure to low concentrations of crystalline silica.
  
  
• Accelerated silicosis, which occurs 5 to 10 years after exposure to high concentrations of crystalline silica.
  
  
• Acute silicosis, which occurs a few weeks to 5 years after exposure to very high concentrations of crystalline silica.
  
  

Question 4. How many workers are exposed to dusts containing crystalline silica?

More than 2 million U.S. workers are potentially exposed to dusts containing crystalline silica. More than 100,000 of them are in high-risk occupations, including sandblasting. Most sandblasters work in construction and shipbuilding. Workers may be exposed to crystalline silica in many other industries, including surface and underground mining, pottery, drywall hanging, glassmaking, foundry work, quarry work, work with sandblasting materials, agriculture, and automotive repair.

PART III. PREVENTION OF SILICOSIS

Question 5. What fields of occupational health protect workers from occupational hazards?

Industrial hygiene is the science of recognizing, evaluating, and controlling hazards in the workplace and environment. Industrial hygiene practices protect workers from hazards. Other professionals important for protecting workers' health include occupational health physicians and nurses as well as engineers.

Question 6. What practices are used to protect workers from silicosis?

Industrial hygiene practices are used to protect workers from silicosis and other workplace hazards. These practices include the use of substitution, engineering controls, work practices, respiratory protection, and air monitoring. Employers are responsible for implementing these practices when they are needed to provide safe and healthful workplaces.

Substitution

NIOSH has studied several abrasive agents that might be used as substitutes for silica sand during sandblasting. Some of the abrasives studied are steel grit, specular hematite, nickel slag, copper slag, crushed glass, garnet, staurolite, olivine, and coal slag. Most of these abrasives work as well as silica sand and cost about the same or even less. However, the use of a substitute may have other adverse effects. Regardless of the type of abrasive, NIOSH recommends the use of engineering controls, work practices, respiratory protection, and air monitoring (all described below) to reduce hazards to workers during sandblasting. Figure 2 illustrates good work practices and the proper use of personal protective equipment for abrasive blasting.

Engineering Controls

Engineering controls are hazard controls designed into equipment and workplaces. Examples of engineering controls are

—automated equipment operated from an enclosed booth,
—enclosed blast-cleaning machines and cabinets,
—tools with dust collection systems, and
—local exhaust ventilation.

Engineering controls are sometimes called source controls when they are designed to eliminate or reduce exposures at the source.

Figure 2. Sandblaster using proper respiratory protection inside a ventilated booth. Note that the worker is supplied with two separate air lines—one to supply fresh air for the worker to breathe and the other to supply air for sandblasting.

Work Practices

Work practices are procedures followed by both employers and workers to control hazards in the workplace. Examples of work practices are

—wet drilling or sawing of silica-containing materials,
—showering and changing into clean clothing before leaving work, and
—avoiding smoking, eating, and drinking in dusty areas.

Respiratory Protection

Respiratory protection prevents workers from inhaling pollutants. Appropriate respiratory protection equipment and programs should be provided whenever engineering controls and work practices cannot keep concentrations of airborne silica at or below safe limits.

Respirators—Workers can wear special protective equipment called respirators to protect them from inhaling respirable crystalline silica. Respirators are a good option as protective equipment, but they should be used only when controls (such as substitution, automation, enclosed systems, and local exhaust ventilation) cannot keep exposures at or below safe limits.

Workers who perform sandblasting must use the type of respirator recommended by NIOSH for their particular job. Regardless of the abrasive used, NIOSH recommends a respirator that provides a constant supply of clean air through a line that connects to a hood or helmet worn by the worker. The respirator air line must be separate from the line that supplies air for blasting. This device is known as a type CE abrasive-blasting respirator operated in the continuous-flow mode.

Respiratory Protection Program—To make sure that respirators are used properly, the employer must establish a comprehensive respiratory protection program as required in the OSHA respiratory protection standard of 1998 (see the NIOSH Guide to Industrial Respiratory Protection for guidance). The following are important elements of this standard:

• Periodic air monitoring
  
  
• Regular training of workers in respirator use
  
  
• Selection of proper NIOSH-approved respirators
  
  
• A medical determination of the worker's ability to perform the work while using a respirator
  
  
• Respirator fit testing
  
  
• Maintenance, inspection, cleaning, and storage of respirators
  
  

The respiratory protection program should be evaluated regularly by the employer.

Air Monitoring

Air-monitoring equipment measures air pollutants such as silica to assess worker exposure. Industrial hygienists and air-sampling technicians perform air monitoring. The samples from air monitoring are analyzed to identify concentrations and types of pollutants in the air. The results of air monitoring for crystalline silica are used to select and evaluate engineering controls and respiratory protection. These air monitoring results are also compared with exposure limits that have been recommended on the basis of health studies of animals and humans. NIOSH, OSHA, and MSHA have exposure limits for respirable crystalline silica. For more information about these exposure limits, see Suggested Reading List and Other Useful Resources in Question 8.

Question 7. What else is done to detect and control silicosis in a workplace?

Medical exams should be offered to all workers who may be exposed to respirable particles of silica. Each exam includes a job history, a medical history, and a physical exam. The job history questionnaire asks about all the jobs the worker has had, all the materials worked with, and all protective equipment used. These exams should occur before job placement or entry into a trade. Workers should continue to have followup medical evaluations as well as careful monitoring of their work and exposures.

Question 8. What steps can employers take to prevent silicosis in workers who work with crystalline silica?

1. Use abrasive blasting materials that are less hazardous than those containing more than 1% crystalline silica. Because substitute abrasives may also have toxic effects, NIOSH recommends the use of engineering controls, work practices, and respiratory protection for all abrasive blasting, regardless of the type of abrasive used.
   
   
2. Recognize situations in which silica dust may be generated; plan to eliminate or control dust at its source.
   
   
3. Inform workers about their exposures to crystalline silica dust, the possible health effects of this dust, and the risk of silicosis.
   
   
4. Establish effective programs for monitoring the exposure of workers to crystalline silica dust. Conduct air monitoring to measure worker exposure and check that controls are working properly.
   
   
5. Train workers about safe work practices to reduce exposure to crystalline silica. For example, workers should remove dust from equipment with a water hose instead of compressed air. Use vacuums with high-efficiency particulate air filters (HEPA filters). Use wet sweeping instead of dry sweeping.
   
   
6. Post warning signs to mark the boundaries of work areas that may be contaminated with respirable crystalline silica.
   
   
7. Provide workers with material safety data sheets (MSDSs) for silica, masonry products, alternative abrasives, and other hazardous materials to which they may be exposed.
   
   
8. Provide workers with information about safe handling, labeling, and storage of toxic materials.
   
   
9. Write all signs, labels, instructions, and other material for workers in easy-to-read English and in any other languages needed for workers' understanding of the material.
   
   
10. Provide engineering controls such as containment methods (enclosed blast-cleaning machines and cabinets). Provide equipment for wet drilling or wet sawing of silica-containing materials. Make sure workers use tools with dust collection systems. Use local exhaust ventilation to prevent release of dust into the air.
    
    
11. Provide appropriate respiratory protection for workers, including NIOSH-certified respirators and a respiratory protection program to ensure proper use and maintenance of respirators.
    
    
12. Provide regular medical exams for workers who may be exposed to respirable crystalline silica.
    
    
13. Provide either disposable protective clothes or protective clothes that are laundered at the workplace.
    
    
14. Provide areas for workers to shower and change into clean clothes before leaving the worksite. This practice prevents contamination of other work areas, cars, and homes.
    
    
15. Report all cases of silicosis to State health departments and to OSHA (1–800–321–6742) or MSHA (1–800–746–1553).

Question 9. What steps can workers take to reduce exposure to silica and prevent silicosis?

1. Use proper respiratory protection when engineering controls cannot keep silica exposures at or below safe limits.
   
   
2. Remove dust from equipment with a water hose instead of compressed air. Use vacuums with HEPA filters. Use wet sweeping instead of dry sweeping.
   
   
3. Change into disposable protective clothes at the worksite.
   
   
4. Shower and change into clean clothes before leaving the worksite to prevent contamination of other work areas, cars, and homes.
   
   
5. Do not eat, drink, use tobacco products, or apply cosmetics in dusty areas.
   
   
6. Wash hands and face before eating, drinking, or smoking outside dusty areas.
   
   
7. Do not park cars where they can be contaminated with silica or other pollutants.
   
   

   The personal hygiene habits mentioned above are important because workers may take home silica and other harmful substances on their clothes, skin, hair, and automobiles. Exposure to these substances may make other household members sick.

   Question 10. What additional information is available about preventing silicosis?

   Additional information about preventing silicosis is available in the publications on the following Suggested Reading List and from the Other Useful Resources listed at the end of this document. Note that the NIOSH documents on this list are available at the Web site printed at the end of each reference. Single copies of NIOSH documents are also available free from NIOSH at

   Telephone: 1–800–35–NIOSH (1–800–356–4674)
   Fax: 513–533–8573
   E-mail: pubstaft@cdc.gov

SUGGESTED READING

Cherniak M [1986]. The Hawk's Nest incident: America's worst industrial disaster. New Haven, CT: Yale University Press.

CPWR [1999]. Silica in sandblasting and rock drilling: hazard alert. Washington, DC: The Center to Protect Workers' Rights.

DiNardi SR, ed. [1997]. The occupational environment—its evaluation and control. Fairfax, VA: American Industrial Hygiene Association.

NIOSH [1987]. NIOSH guide to industrial respiratory protection. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 87–116 (full text of document is available at www.cdc.gov/niosh/87–116.html).

NIOSH [1992]. NIOSH Alert: request for assistance in preventing silicosis and deaths from sandblasting. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 92–102 (full text of document is available at www.cdc.gov/niosh/92–102.html).

NIOSH [1996]. NIOSH Alert: request for assistance in preventing silicosis and deaths in construction workers. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 96–112 (full text of document is available at www.cdc.gov/niosh/consilic.html).

NIOSH [1997]. Construction workers: it's not just dust! Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 97–101 (full text of document is available at www.cdc.gov/niosh/1997–101.html).

NIOSH [1997]. NIOSH pocket guide to chemical hazards. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 97–140 (full text of document is available at www.cdc.gov/niosh/npg/npg.html).

NSC [1996]. Fundamentals of industrial hygiene. 4th ed. Chicago, IL: National Safety Council.

Parkes WR [1994]. Occupational lung disorders. 3rd ed. Oxford, England: Butterworth-Heinemann, Ltd.

 

OTHER USEFUL RESOURCES

 

The Center to Protect Workers' Rights (CPWR)
Telephone: 1-301-578-8500
Web site: www.cpwr.com

Mine Safety and Health Administration (MSHA)
Toll-free telephone: 1–800–746–1553
Other telephone: 1–703–235–1452
Web site: www.msha.gov

National Institute for Occupational Safety and Health (NIOSH)
Toll-free telephone: 1–800–35 NIOSH (1–800–356–4674)
Web site: www.cdc.gov/niosh/homepage.html

Occupational Safety and Health Administration (OSHA)
Toll-free telephone: 1–800–321–OSHA (1–800–321–6742)
Web site: www.osha.gov