July 1st, 2013
Dive Rite introduced oxygen tracking on a dive computer in 1992 with the launch of the Bridge, the first user programmable computer from 21% to 50%. It has since become the standard for any Nitrox computer. Oxygen tracking was developed by Randy Bohrer and the late Dr. Bill Hamilton for SEIKO EPSON. SEIKO EPSON went on to patent the technology of graphing oxygen tracking on dive computers, but decided it was too important not to be on all dive computers to enforce the patent. This led to the birth of the OLI (oxygen limits index), which was based on hyperbaric treatment studies. See this article for more information: A PROVISIONAL METHOD OF OXYGEN EXPOSURE MANAGEMENT FOR A RECREATIONAL DIVE COMPUTER
In the oxygen tracking algorithm, we don’t track OTUs at all. Hamilton’s OTU approach was used to manage long exposures, such as saturation type dives. For the dive computers, we track one value – the oxygen limit index. This index accounts for both CNS and chronic/whole body oxygen toxicity (or oxygen tolerance). The 90 minute half time for recovery is very conservative for CNS toxicity, since we know that it is possible to breathe oxygen at high partial pressures if a short air break is taken periodically. It is adequate for chronic/whole body toxicity, since it allows for full recovery in an amount of time that is sometimes used in respiratory therapy.
The Nitek Q has nine bars for tracking oxygen and nitrogen. At 80% of calculated maximum oxygen exposure the bar graph will start to flash once the 8th bar starts to fill up. The Nitek Q will assume oxygen loading for one hour after the dive. This is our conservative approach to oxygen tracking. With a 90 minute half life, the 8 bars lit will drop to 4 in 90 minutes, then drop to 2 bars in another 90 minutes, and to 1 bar in another 90 minutes. If your oxygen loading exceeds 100% the graph will flash until it is back into range.
Remember, tracking is only as good as the information supplied. Properly analyzing and entering the correct gas mixture is a good start.
Pictured: Dive Rite technical computers starting with the Bridge II through Nitek Q