Setting: Two urea fertilizer producing factories in Saudi Arabia.
Objective: To determine the prevalence of respiratory symptoms and diseases in employees exposed to ammonia gas.
Design: A cross-sectional study involving 161 exposed subjects and 355 controls. All completed a respiratory symptoms questionnaire, with additional questions on present and past occupations. Ammonia concentrations were measured in the different sections of the factories.
Results: The ammonia levels in factory B were well below the threshold limit value (TLV) (range 0.02-7.0 mg/m3 of air). In factory A the range was 2.0-130.4 mg/m3. The control and exposed groups were comparable with respect to their smoking habits. The exposed subjects in factory A had significantly higher relative risks (RR) for all respiratory symptoms; the same was true for haemoptysis (RR: 4.1, 95% confidence interval: 1.63-10.28). Bronchial asthma, chronic bronchitis, and a combined diagnosis were significantly higher among those exposed to high cumulative ammonia levels. However, in the logistic regression analysis ammonia concentration was significantly related to cough, phlegm, shortness of breath with wheezing and bronchial asthma.
Conclusion: Exposure to ammonia gas in the workplace is significantly associated with increase in respiratory symptoms and bronchial asthma. Re-engineering measures to lower the levels of ammonia in factory A are strongly recommended. The affected employees should be removed from further exposure and followed up.