Case study: 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.

Source: Electronic Library of Construction Occupational Health and Safety