Simon is the best-selling author of Scuba Confidential – An Insider’s Guide to Becoming a Better Diver and Scuba Professional – Insights into Scuba Diver Training & Operations. Both books are available now from Oceanic Ventures.

Understanding narcosis, being aware of its effects, and knowing how to manage it are important tools for divers.

When you dive deep, you often see people do strange things under the influence of narcosis. One diver will swim away from his buddy, lost in his own thoughts until he suddenly realizes he is alone in the ocean. Another will keep looking at his computer every few seconds, apparently not registering what it is telling him. A third will stop on a reef wall and stare fixedly at a branch of coral for a good five minutes. Later, he will tell you that he thought the coral was a moray eel and that he was waiting for it to move.

This sort of thing can be funny but there is a serious side to narcosis. The diver who heads off into the blue without his buddies loses the support of the team. The diver who cannot remember what his computer was showing just a few seconds after looking at it is suffering from short-term memory loss and this makes it difficult for him to follow a dive plan.

Narcosis is an integral part of scuba diving. The only way to avoid it is not to dive deep. If you want to dive to 100ft and beyond, then you are just going to have to get used to it!

What is Narcosis?

Air, even oxygen-enriched air like NITROX, is an intoxicating cocktail. Many people will tell you they enjoy the “buzz” of going deep. This “buzz” is mainly due to “anesthetic potential”, something all gases have. In the right quantity, any gas can knock you out. Nitrogen, the major constituent gas in air, has substantial anesthetic potential and, as you dive deeper, the partial pressure of the nitrogen increases, and the depressant effect on your central nervous system becomes greater.

The effects are similar to alcohol and, just as with alcohol, they are dose-related. Narcosis is progressive and increases with time and depth. At 100ft a diver will experience mild symptoms such as euphoria and slow reactions but at 150ft the diver may not be able to function intellectually at all.

There is a widespread misunderstanding of what narcosis is. Many divers claim that they do not suffer from narcosis because they feel more relaxed, comfortable, confident, and capable at depth.  However, these are actually the most common symptoms, and, although it might sound like a good thing to feel like that, in fact, this state of mind will lead a diver to take more risks, forget or throw out the dive plan, react to an emergency more slowly and lose track of time.

Managing Narcosis

The good news is that narcosis can be managed.

The first steps are to recognize that it is there and understand what it is doing to you. Then you must train yourself to focus on important issues such as time, depth, and the dive plan and not allow yourself to get distracted.

Exercise mental control over everything you do. Move slowly and deliberately when carrying out a task at depth. You are more likely to get it right if you do something in a sequence of short steps, rather than try and do it quickly.

You can also use memory cues. Technical divers wear wrist slates to remind them of complex dive plans and experienced instructors carry checklists for training dives. They also make debriefing notes as they go because they know that later they will not be able to depend on their memory for the things that happened while they were at depth.

Probably the best defense against narcosis is to rehearse team rescue and self-rescue drills and skills until they become instinctive. Then, in an emergency, you will automatically choose the correct response without thinking about it.

Contributory Factors

A number of factors can aggravate narcosis. These include fatigue, alcohol, stress, cold, and dark water. Anticipating the effect of these additional factors is the key to dealing with them. For instance, use a drysuit in cold water, minimize alcohol intake, and get a good night’s sleep before a deep diving day.

Final Word

Narcosis is something to be understood and managed, rather than feared. There is no law against diving under the influence but proceed towards deep diving gradually. Don’t just go off the deep end straight away!

Originally from the UK, Simon has lived in the Asia-Pacific region for almost 40 years and has been involved at the sharp end of the scuba diving industry since the early 1990s, pioneering mixed-gas deep diving in the region, first in Hong Kong and later through Professional Sports Divers, his dive centre in Guam, Micronesia. He then moved to the United Kingdom to run a major technical diver training agency and work with cutting edge dive equipment manufacturers VR Technology. Today, he is one of the most prolific and well-known scuba diving and travel authors around. As well as his many books and guides, Simon writes regular columns for a variety of magazines and, under the pen name S.J. Pridmore, has recently published a highly-acclaimed first novel May the People Know I’m Here? After a decade in Indonesia, then a couple of years back in Hong Kong, these days Simon and his wife Sofie live in the south of Taiwan, still on the move as always, trying, but so far failing, to find a cure for their itchy feet.