Revised guideline for central nervous system oxygen toxicity exposure limits when using an inspired PO2 of 1.3 atmospheres

Technical and scientific divers breathing gases delivering hyperbaric pressures of inspired oxygen may be at risk of developing cerebral oxygen toxicity which can manifest as a seizure with little or no warning. The principle preventative strategy is adherence to time limits based on inspired PO₂ levels promulgated in 1991. These limits had their origins in US Navy studies of exposures to higher inspired PO₂s than are typically utilised by modern divers. Indeed, the duration limits for inspired PO₂s in the range typically utilised by technical divers (≤ 1.3-1.4 atm) have relatively little experimental provenance. Contemporary technical dives often involve decompression durations that result in breaches of these limits, and anecdotally, this common occurrence seems associated with a low risk of cerebral oxygen toxicity. A committee of experts recently sought experimental evidence that might support an adjustment to the recommended duration limits for typical technical dives. Such evidence exists only for an inspired PO₂ of 1.3 atm, which is a common default in use of constant PO₂ rebreather devices. The (1991) limit for a single exposure to an inspire PO₂ of 1.3 atm is 180 min with a 24-hour maximum of 210 min. Recent studies provide reassurance that dives with an inspired PO₂ of 1.3 atm consisting of up to 240 min of working dive activity followed by up to 240 min of resting decompression are associated with an acceptably low risk of cerebral oxygen toxicity. This recommendation was promulgated and endorsed at a recent workshop convened by the National Oceanographic and Atmospheric Administration (NOAA) involving technical and scientific divers.