Oxygen exposure and toxicity in recreational technical divers

Central nervous system oxygen toxicity is a recognised risk in recreational open-circuit scuba diving with the use of nitrox (oxygen-enriched air mixtures), but other forms of oxygen toxicity in other diving settings are poorly understood. However, divers using constant partial pressure of oxygen closed-circuit rebreathers (CCRs) for multi-day, multi-dive expeditions could potentially experience cumulative oxygen exposures above the current recommended limits.

We followed a number of technical recreational diving expeditions using CCRs and recorded the cumulative oxygen exposures of the individual divers. Lung function and visual acuity were recorded at intervals during the expeditions.

Over several 8- to 12-day expeditions, divers either approached or exceeded the recommended maximum repetition excursion oxygen exposure (REPEX) limits. Lung function did not show any significant decrement. Changes in visual acuity were reported in several divers but were difficult to quantify. Formal testing of one diver's visual acuity on return home demonstrated a myopic change that resolved over the subsequent eight weeks.

Recreational CCR divers conducting multi-dive expeditions of eight days or more may approach or exceed the REPEX oxygen limits. Despite this, there does not appear to be any significant decrement in lung function. Hyperoxic myopia occurs in some individuals. Changes in acuity appear to resolve spontaneously post exposure. Despite the lack of significant changes in respiratory function, divers should be cautious of such exposures as, should they require recompression therapy for decompression illness, this may result in significant pulmonary oxygen toxicity.