Spirometry at 6 and 12 months was performed with the PC Portable Microlyser (P&A Medical Limited, Blackrod, UK) according to ATS/ERS Guidelines [Miller, et al. 2005], including proper calibration and a minimum of 3 acceptable spirograms. Due to logistical issues pre-employment spirometry was performed on only 23 of the workers and at an alternate facility. The largest FVC and FEV1 from all acceptable curves were chosen and compared to predicted values and lower limit of normal (LLN), and airflow obstruction was defined as FEV1/FVC < LLN, as recommended by the ATS/ERS [Pellegrino, et al. 2005]. Excessive longitudinal decline in FEV1 over the follow-up period was identified using a threshold of 15% decline from baseline, as recommended by ATS and ACOEM [Pellegrino, et al. 2005, Townsend, et al. 2011].