January 2005, Issue 174

Microcontroller-Based Nitrox Analyer

DIVE SCIENCE

In general, the deeper you dive, the less time you can stay down. One tool you can use to increase your dive time is Nitrox, which decreases the amount of nitrogen in the gas you breath. Because the percentage of nitrogen decreases, the percentage of oxygen increases to maintain the same overall volume and pressure. This can introduce complications. Oxygen can become toxic to the central nervous system (CNS) if it’s breathed at too high a pressure and concentration.  CNS oxygen toxicity can result in convulsions and loss of consciousness, which can lead to death when you’re submerged under water. Because the pressure of the gas breathed increases with depth, the maximum dive depth must be limited to prevent the pressure of the oxygen from nearing toxic levels. The higher the percentage of oxygen in the Nitrox blend, the shallower the maximum allowable dive depth. For these reasons, it’s important for you to know the percentage of oxygen in the mixture that you’ll be breathing so you can plan a safe dive. 

When you purchase a tank of Nitrox, you must follow the specific procedures set by the major dive certification agencies to minimize the chances of accidents. Typically, when a technician creates a certain mixture of Nitrox and fills a tank with it, he checks the percentage of oxygen with a commercial analyzer. When you’re ready to take possession of the tank, it’s your responsibility to verify the percentage of oxygen in the Nitrox. Typically, you’ll use the same analyzer that the technician used to make this measurement. 

After you know the percentage of oxygen, the maximum allowable dive depth then can be determined from a set of Nitrox dive tables. Next, the percentage of oxygen, maximum dive depth, date, and your name are recorded in a Nitrox fill logbook as well as on a sticker that is placed on the tank. As you can see, the extra checking decreases the likelihood of an error. However, if you and the technician were to use different analyzers, an additional margin of safety would be added. Now that the background and disclaimers are out of the way, let’s move on to the device itself.