The benefits of diving nitrox have long been know, which is why today it is the breathing gas of choice for most divers. During all nitrox courses one of the biggest topics is elevated PO2 and why not to exceed the single and 24 hour exposure limits. When discussing PO2 limits for divers, it is common knowledge that a 1.6 is the maximum and divers should reduce the PO2 based on environmental conditions, repetitive dives, workload of dive and decompression obligations. But what is not commonly discussed is what to do in the unfortunate situation of a diving incident when a diver has been using nitrox.
Diving incidents are something that no one wants to deal with but, just like anything else, the more you do it the more likely you are to be involved in an incident. When incidents happen, there is a lot to think of and to deal with when it comes to divers using nitrox. There is an added piece of information that is needed: their PO2 exposure. For the sake of ease we will break this down into two types of diving:
- Multiple days of single tank nitrox diving or the use of semi-closed circuit rebreathers (SCR)
- Technical diving involving decompression or the use of closed circuit rebreathers (CCR).
Before we get into that, a reminder of the two types of oxygen toxicity is important. The type that affects recreational (sport and technical) divers the most is Central Nervous System (CNS) Oxygen Toxicity. This is generally caused by a high dose (high PO2) with short term exposure. The second type, which is general only seen in commercial diving or medical treatment, is Pulmonary Oxygen Toxicity; this is low dose (low PO2), long term exposure.
For divers doing multiple days of single tank nitrox diving or using an SCR, they generally do not come close to the single exposure limits, mostly because of air consumption rates, but they can be right on the edge of the 24 hour limits. It can be very difficult to ascertain exactly what their long term exposure has been unless they have programmed all mixes into their dive computer, or have logged all their dives, including the mixes they used, in their log books.
For divers conducting decompression or CCR dives, the tracking of dives becomes a little easier because it is either one or two dives per day or, in the case of a CCR, they operate on a fixed PO2. In both situations, the information is usually right at hand, as either the cylinders are labeled, th decompression schedule has been written down as a back-up, a multi gas computer has been used or the CCR’s built in dive computer has stored all the information (if using a eCCR).
No accident is exempt from the confusion that surrounds it but it is very important to collect the information regarding PO2 exposure and send it along with the diver if their treatment is going to involve a recompression chamber, which most diving incidents do. Medical treatments generally start with a PO2 of 2.8 and go up from there, so it is easy to see why hyperbaric doctors would want to know the oxygen levels in a diver prior to starting a treatment. Prior oxygen exposures aside, chamber operators will run whatever the appropriate schedule is, it is just best to provide as much information as possible to them. The best way to handle this is: send the diver’s computer along with them, send their logbook or send their decompression schedules, but – if time permits – get copies of all of this information. When items start changing hands, they have a tendency to get lost and as any diver knows, you need a backup plan. At minimum, the diver’s dive computer should be downloaded and their dive profiles can be quickly hand written or scanned.
The best time management technique to accomplish all necessary tasks is to assign a person for each task and collect all the information as soon as time permits. Fingers crossed you will never have to deal with a diving incident, but if you do find yourself in such a situation, be prepared and everything will go as smooth as possible.
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