 Genetic studies DNA will be done from peripheral blood samples 20 ml to study differences in Heme oxygenase 1 HO-1 gene sequencing between participants with evidences of clinically definite silicosis according to American Thoracic SocietyEuropean Respiratory Society ATSERS guidelines and participants without evidences of clinically definite silicosis.DNA samples will be obtained and coded in the same day of a participant visit and after collecting reasonable amount of samples examination of genes of interest will be done.Analysis of data will be done after the completion of data collection and laboratory tests. 