Experts recommend extended safe times at PO₂ 1.3 bar.
New guidelines suggest divers can safely spend longer at PO₂ 1.3 atm than previously advised — up to four hours of work and four hours of decompression.
A panel of diving medicine experts has recommended revised exposure limits for central nervous system (CNS) oxygen toxicity when divers breathe an inspired partial pressure of oxygen (PO₂) of 1.3 atmospheres. The changes are based on recent research and field experience, aiming to bring guidelines in line with modern technical and scientific diving practice.
The issue
Breathing oxygen at elevated pressures carries risks, particularly seizures caused by CNS oxygen toxicity. Existing limits, published by NOAA in 1991, allowed divers 180 minutes at PO₂ 1.3 atm per dive and 210 minutes over 24 hours. These figures were not based on strong evidence and have often been exceeded by technical divers without apparent ill effect.
New findings
Recent Navy trials and community experience indicate that up to four hours of working dive time at PO₂ 1.3 atm, followed by up to four hours of resting decompression at the same level, carries a very low risk of seizures. This effectively doubles the allowable safe exposure compared to current NOAA limits.
Familiar names
The guideline was authored by an international group of researchers, including Neal Pollock, Simon Mitchell, and Michael Menduno, all of whom are well known to X-Ray Mag readers through their previous contributions to the magazine. Their involvement underlines the strong connection between current diving research and the wider technical diving community.
Why it matters
The revision reflects the reality of modern rebreather diving, where a PO₂ setpoint of 1.3 atm is commonly used. It provides a more realistic framework for long decompression dives while maintaining diver safety. The workshop consensus stressed that pulmonary oxygen toxicity remains a limiting factor for very long exposures but is generally reversible.
Importantly, NOAA has indicated that it plans to adopt these revised exposure limits in future editions of its Diving Manual, meaning they are likely to become standard guidance for both professional and technical divers.
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.
