Editing Nitrox (section)

===Oxygen toxicity===
{{Main|Oxygen toxicity}}
Diving with and handling nitrox raise a number of potentially fatal dangers due to the high [[partial pressure]] of oxygen (ppO<sub>2</sub>).<ref name=noaa/><ref name=dan/> Nitrox is not a deep-diving gas mixture owing to the increased proportion of oxygen, which becomes [[oxygen toxicity|toxic]] when breathed at high pressure. For example, the maximum operating depth of nitrox with 36% oxygen, a popular [[recreational diving]] mix, is {{convert|29|m|ft}} to ensure a maximum ppO<sub>2</sub> of no more than {{convert|1.4|bar|abbr=on}}. The exact value of the maximum allowed ppO<sub>2</sub> and [[maximum operating depth]] varies depending on factors such as the training agency, the type of dive, the breathing equipment and the level of surface support, with [[professional diving|professional divers]] sometimes being allowed to breathe higher ppO<sub>2</sub> than those recommended to [[recreational diving|recreational divers]].

To dive safely with nitrox, the diver must learn good [[buoyancy]] control, a vital part of scuba diving in its own right, and a disciplined approach to preparing, planning and executing a dive to ensure that the ppO<sub>2</sub> is known, and the maximum operating depth is not exceeded. Many dive shops, dive operators, and gas blenders (individuals trained to [[Gas blending for scuba diving|blend gases]]) require the diver to present a nitrox certification card before selling nitrox to divers.<ref name="scubadiving.com" />Additionally, it is strongly encouraged for divers to confirm the percentage of oxygen in their tank before every dive, regardless of the specified amount on their tank.<ref name="Scuba doctor" /> This is done by expelling a small amount of air from the diver's tank into an [[oxygen sensor#Diving applications|oxygen analyzer]]. This is to further limit the possibility of oxygen toxicity due to errors in previous testing.<ref name="Lippman and Mitchell 2005" />

Some training agencies, such as PADI and [[Technical Diving International]], teach the use of two depth limits to protect against oxygen toxicity. The shallower depth is called the "maximum operating depth" and is reached when the partial pressure of oxygen in the breathing gas reaches {{convert|1.4|bar|abbr=on}}.  The deeper depth, called the "contingency depth", is reached when the partial pressure reaches {{convert|1.6|bar|abbr=on}}.<ref name="scubadiving.com"/> Diving at or beyond this level exposes the diver to a greater risk of central nervous system (CNS) oxygen toxicity. This can be extremely dangerous since its onset is often without warning and can lead to drowning, as the regulator may be spat out during convulsions, which occur in conjunction with sudden unconsciousness (general seizure induced by oxygen toxicity).

Divers trained to use nitrox may memorise the [[acronym]] VENTID-C or sometimes ConVENTID, (which stands for '''V'''ision (blurriness), '''E'''ars (ringing sound), '''N'''ausea, '''T'''witching, '''I'''rritability, '''D'''izziness, and '''C'''onvulsions). However, evidence from non-fatal oxygen convulsions indicates that most convulsions are not preceded by any warning symptoms at all.<ref name="bennett2003-375" /> Further, many of the suggested warning signs are also symptoms of nitrogen narcosis, and so may lead to misdiagnosis by a diver. A solution to either is to ascend to a shallower depth.