Color me surprised! In doing a little research, I found the NOAA Dive Table for EANx 32 -- 32% O2 Nitrox -- and the table goes to 130 feet, or a ppO2 of 1.6 ATM. For comparison, the NOAA Dive Table for air shows a maximum NDL bottom time at 130 feet of 10 minutes, while the EANx 32 Table shows a maximum NDL bottom time at 130 feet of 20 minutes. So, at least under the NOAA table (from the recently revised 4th Edition of the NOAA Diving Manual), comparatively short exposure to ppO2 of up to 1.6 ATM is low in risk. The Dive Manual itself recommends a max ppO2 of 1.4 ATM, with limited increases to as much as 1.6 ATM acceptable.
However, a recent article in Alert Diver (the DAN publication) notes that CNS Oxygen Toxicity events, including siezures, have been documented at a ppO2 of 1.3 ATM in divers with heavy exertion, while divers who are resting and relaxed can tolerate ppO2 of 1.6 for more than an hour. The same DAN article notes that there are two different manifestations of Oxygen toxicity -- pulmonary Oxygen toxicity, which usually manifests only after several hours (it has been observed at ppO2 levels as low as .45 ATM with 30 hours of continuous exposure), and Central Nervous System or CNS Oxygen toxicity, which requires a higher ppO2 but can manifest much more quickly. Certain medications and CO2 load can increase a diver's susceptibility to Oxygen toxicity.
Personally, I like a wide margin of safety, so I think I stick with my rule of thumb not to exceed a ppO2 of 1.2 ATM, knowing that I can exceed that limit for short periods without a substantial risk.
