Quantifying the Exposure of Heavy-Equipment Operators to Respirable Crystalline Silica Dust.

* The inhalation of airborne crystalline silica has long been associated with lung disease.

* Chronic exposure to crystalline silica dusts can impair pulmonary removal of particulates, resulting in silicosis.

* Repeated acute exposures for periods of as little as two years can cause accelerated forms of silicosis.

* Individuals who have contracted silicosis are at increased risk for other pulmonary diseases, most notably tuberculosis.

* Respirable-dust sampling was performed for two months during the excavation of a large disposal pit at the Los Alamos National Laboratory.

* The excavation removed approximately 64,000 cubic meters of earth with scrapers, graders, backhoes, and dozers.

* Operators in pressurized cabs were exposed to lower respirable-dust concentrations than operators in enclosed, nonpressurized cabs and operators in open cabs.

* Dozer operators received higher exposures than operators of any other heavy equipment sampled because

-- all the dozers had open cabs,

-- dozers operated in the pit during the entire workday, and

-- ripping operations exposed dry earth unaffected by water applied as a control measure.

* There was, however, a downward trend in dust concentrations according to the amount of water applied to suppress dust.

* The results of this study suggest that excavation projects should apply the following control measures:

1. Use pressurized cabs when possible.

2. Use water sprays to suppress dust.

3. Regularly clean cab interiors to prevent drying and resuspension of dust tracked into the cab.

4. Rotate operators among equipment with different cab types.

5. Inform the operators of the hazards and the available precautions and monitor the operations to ensure that safety controls are used.

6. Ensure that doors and windows of nonpressurized cabs remain closed to minimize entrainment of dust