Material and Method: Fifty-two sandstone workers with an ILO classification chest radiographs profusion CAG ≤1/1, FEV1 and forced vital capacity (FVC) that decline as measured using follow-up FVC maneuver spirometry testing were interviewed. Work exposure, personal protective equipment, and symptoms (if any) obtained through questionnaire was also included.

Results: The 52 participants mostly were female, average age 48±8.9 years, and mostly non-smokers. Mean of FEV1 decline at one-year follow-up was 105.4±131.7 mL (95% CI 68.7, 142.0) with increasing of FEV1 decline among high exposure, smokers and exposed for 10 years or more. The mean FEV1 decline among workers with all those factors was 272.0±155.5 mL. Subgroup analysis with independent t-test and multiple linear regression models revealed only FEV1 decline was found in high exposure group. FVC decline trended similar to FEV1 decline. Mean of FVC loss was 119.4±181.1 mL (95% CI 69.0, 169.9), while mean FVC loss among those classified as high exposure smoking workers with 10 years or more of exposure was 376.0±216.2 mL. However, the FEV1 and FVC declined among sandstone workers were at least three times greater than Thai physiological decline.

Conclusion: Although ILO chest radiographs were normal or near normal, the FEV1 and FVC declined among silica dust exposed workers. Therefore, FEV1 deterioration should be monitored in order to comply with the UK RCS Dust Exposed Surveillance Guideline, especially among high exposure.

Keywords: Spirometry, FEV1, FVC, Silica dust, Occupational, Medical surveillance, ILO chest radiograph