One of the most serious long-term health problems associated with underground mining is Coal Workers' Pneumoconiosis (CWP), more commonly known as Black Lung Disease. It occurs in some coal workers, normally after 15 or more years of exposure to coal mine dust, and leads to a variety of respiratory problems. Two types of pneumoconiosis are recognized-simple CWP, which has been estimated to affect 6.9 percent of miners and is a condition that does not impair the miner's ability to work nor reduce life expectancy; and a more severe form of black lung (called progressive massive fibrosis) that occurs in about one percent of the cases and results in severe lung damage. Although the relationship between coal dust and CWP has long been recognized, detailed knowledge of the relationship is insufficient for setting up authoritative guidelines to reduce the health risks for those employed in dusty underground environments. CWP is not only a health problem for workers that causes considerable distress, it is also a very expensive problem-the total annual costs associated with CWP approach two billion dollars. As part of its efforts to combat CWP, the U.s. Bureau of Mines in 1983 established a Generic Mineral Technology Center to carry out basic research into all aspects of respirable coal dust: 1) control of dust generation; 2) the behavior of dust in the mine; 3) characterization of dust particles; 4) interaction of dust and lung; and 5) the relationships among dust generation and mobility and the mine environment, geology, and seam characteristics. Penn State, West Virginia University, the University of Minnesota, and the Massachusetts Institute of Technology are involved in this research, which is administered from the Department of Mineral Engineering at Penn State. Our work is one of the seven projects to be conducted at Penn State. We are concerned particularly with the characterization of dust and its relationships with the mine environment, and our main goal is to establish standard procedures for describing and measuring these variables.