Exposure to soda-lime dust in closed and semi-closed diving apparatus

Background: Chronic exposure to hyperbaric hyperoxia and venous gas microem bolism have been shown to contribute to the long term health effects of div ing, especially diver's lung function. Factors related to special diving eq uipment may add to these effects. This study was conducted to evaluate poss ible additional hazards for respiratory function of divers employing closed and semi-closed diving apparatus. Methods: We analyzed soda-lime dust foun d in the air-intake loop of a closed-circuit oxygen rebreathing diving appa ratus which had passed through the filter screen of the diving apparatus's soda-lime cartridge. The geometrical characteristics were evaluated by scan ning electron microscopy. The amount of dust that passed through the screen during a normal dive profile was measured by an artificial airflow through a filter membrane. After dives by subjects using these devices, the pH-val ue of water condensate in the air-intake hose was measured. Results:There w as a relevant amount of residual soda-lime dust found in the air-intake loo p. The dust particles showed diameters down to 1 mum and a rounded structur e. The total amount of dust averaged 9.6 mg . m(-3) of breathing mixture. D uring diving, the mean pH-value of condensate in the hose is estimated at 8 .87 (+/- 0.12). Conclusion: There is a relevant exposure to soda-lime dust in divers using closed-circuit rebreathing apparatus. This occupational exp osure may contribute to chronic airway inflammation and subsequent developm ent of small airway disease in divers.