RESUMEN
Natural background radiation to which humans are continuously exposed to come from the primordial radionuclides on the surface of the Earth. Industrial activities which concentrate natural radionuclides usually in residues and waste materials may enhance natural radioactivity on the ground via airborne contamination. In this study, ambient gamma dose rates were measured inside and outside two industrial facilities in Leyte, Philippines, to assess possible contribution of NORM materials in enhancement of natural radiation background in these areas. Ambient gamma dose rates measured at selected sites from Tacloban City to Isabel, Leyte and in nearby areas of Kananga and Ormoc City, Leyte were within the range of the background ambient gamma dose rates measured in the Philippines, ranging from 21 to 124 nSv/h. The workers in the phosphate rock storage and phosphogypsum pond areas in the phosphate fertiliser production plant received the highest annual effective external dose of 0.76 mSv.