What is the maximum time we could be underwater when we dive with Nitrox? How is it different to normal air?
There are many advantages of diving with Nitrox like an increased bottom time for recreational dives. However, there is one main disadvantage, which is the oxygen toxicity that can occur due to increased levels of oxygen in the gas mix. Any gas that has any percentage of oxygen, can cause toxicity at a certain pressure. A diver using air, for instance, would have to go over 60 meters (198 feet) deep to experience acute oxygen toxicity (anyway fun diving doesn’t allow to go so deep, we're just showing you the difference). The danger of Nitrox is that this is a possibility with recreational diving/fun diving depths!
Consequently, there are two elements that divers using Nitrox have to take into account to avoid oxygen toxicity (1) the amount and (2) the length of exposure. Those two elements together are called the oxygen limit.
The amount of exposure is calculated using partial pressures, found by multiplying the percentage of oxygen in the mix by the atmospheric pressure at the planned dive depth. For instance, a diver breathing air (21 percent oxygen) at 40 meters (132 feet) (5 atm) is breathing a partial pressure of oxygen (PPO2) of 1.05 (0.21 x 5). The recreational scuba community generally recommends a maximum oxygen partial pressure of 1.4 ATA. That means that the maximum operating depth for EAN32 is 34 meters (112 feet) and EAN36 - 28 meters (95 feet).
Consequently, Nitrox doesn’t allow you to go deeper.