<prompt> Minimum duration of developing coal miners pneumoconiosis is -2-4 years4-6 years8-10 yearsMore than 10 years  <response>: - The coal miners pneumoconiosis has two phases; first phase is simple pneumoconiosis which is associated with little ventilatory impairment. - this phase may require about 12 years of work exposure for its development. - second phase is characterized by progressive massive fibrosis Reference: Parks textbook of preventive and social medicine, 23rd edition, pg no:806 p 