Kerr joined the United States Public Health Service in 1944, first in the War Food Administration and later in the Industrial Hygiene Division.
While with the Industrial Hygiene Division he provided consultant services for labor unions which were then beginning to develop their own medical care programs.
[1] In October 1948 Kerr joined the newly formed Welfare and Retirement Fund of the United Mine Workers of America, simultaneously accepting an appointment as an area medical administrator in Morgantown, West Virginia.
[4] Coal workers' pneumonoconiosis (black lung disease) was one of Kerr's major concerns from the beginning of his employment by the UMWA and it became his primary responsibility after his appointment as director of the Department of Occupational Health.
[5] Along with Terence E. Carroll of the National Institute of Rehabilitation and Health Services, Kerr and his colleagues in the UMWA played a major role in gaining recognition of black lung as a disease entity and cause of disability.