Mention a “deep dive” and watch the reactions. Novice divers want to know what it’s like.

More experienced divers who have been a bit deeper chat with excitement. Those qualified to venture to 40 meters/130 feet – the recommended farthest edge of recreational diving – also show enthusiasm, though somewhat tempered with respect for the challenge deep diving presents. There’s something a bit attractive, exciting and mysterious about “going deep.” As a new Open Water Diver, 18 meters/ 60 feet marks the depth limit to which you’re qualified to dive.

This limit isn’t arbitrary – it’s based on no decompression limits, nitrogen narcosis and air supply – but even if you’ve only made a few dives, you may be curious about deeper dives, perhaps simply to visit specific dive sites below 18 meters/60 feet. The Deep Adventure Dive will satisfy some of this curiosity and give you access to some of those dive sites by qualifying you to dive as deep as 30 meters/100 feet,in conditions as good as or better than those in which you have training and experience.


Deep Diving Activities and Objectives.
 
Have you ever wondered why a jetliner cruises at 10,000 meters/35,000 feet while a two-seater prop plane hums along at only 900 meters/3000 feet? A jetliner has to fly up where the air’s thin enough to reach the high speeds necessary for crossing long distances quickly. It doesn’t cruise up high “just to go up high.” Deep diving is similar. You don’t make a deep dive just to go deep, but as a means to an end. Deep diving gives you access to new dive sites that lie below 18 meters/60 feet, and allows you to extend some of the activities you enjoy to new depths. Through deep diving you can observe aquatic life that doesn’t live in shallower water, visit wrecks that rest in deeper water, as well as shoot photographs.

In some places, deep diving makes it possible to drift effortlessly past deep water reefs (for more information, see the Drift Diving section), and in other areas, you might collect or recover objects that were lost in greater depths. Those are just five examples of the many possibilities when making deep dives. In planning a deep dive, you must determine an appropriate objective. An appropriate deep dive objective will usually be singular because you have less no decompression time as you descent.

It’s a reasonable objective, too, such as participating in one of the activities listed above, and it’s based on your training and experience as well as dive conditions. An inappropriate deep diving objective is one that expects to accomplish too much in one dive, or for nothing more than the “thrill” of facing risk. It’s not unreasonable to deep for the challenges and expands your training and experience to greater depths – that’s what the Deep Adventure Dive and the Deep Diver courses are for – but to simply plunge into deep water without regard for appropriate procedures is neither reasonable nor prudent.

Definition and Limits:

Choosing a depth to define “deep” is a bit like picking an altitude to define “high.” Eighteen meters/60 feet may be “high” compared to standing on the ground, but compared to a satellite in orbit, it’s “low.” Clearly, both “deep” and “high” are subjective terms, though physiology and physics make defining “deep” for recreational diving a bit less subjective. In any case, you have to draw a line somewhere, if only to clearly discuss the subject. PADI and most of the recreational diving community define a “deep” dive as 18 meters/60 feet or below, but no deeper than 40 meters/130 feet.

Depths below 40 meters/130 feet lie beyond recreational diving. Given the limitations of recreational scuba equipment, the short no-stop dive times below 18 meters/60 feet and the scope and intent of recreational diver training, these depth limits serve well and have a solid track record supporting their appropriateness. Although 40 meters/130 feet has been set as the maximum, for general purposes, you probably want to treat 30 meters /100 feet as the optimal maximum limit, for four practical reasons: First, the short no decompression limits and rapid air use below 30 meters/100 feet make deeper dives incredibly short. Considering the time and effort to plan and make a deep dive, the activity and objective of a 30 meter/100 foot dive has to be very satisfying to be worth only ten minutes dive time.

Second, nitrogen narcosis, the intoxicating effect of nitrogen as you go deeper, begins to have a noticeable effect on most divers below about 30 meter/100 foot. While susceptibility varies from person to person, this is an important consideration. Third, dives to depths beyond 30 meters/100 feet tend to be more associated with decompression sickness, particularly when making repetitive dives.  Using a single tank of air, it’s possible to overstay the no decompression limits when you’re that deep, and in any case, with short no-stop times dives tend to be closer to the limits. Finally, in many dive environments deeper than 30 meters/100 feet it becomes very dim, or completely dark due to light absorption. This means it’s not only difficult to see what’s around you, but difficult to read your gauges and use your equipment.

But they’re going Deeper…
 
The dive community accepts the 40 meter/130 foot limit for recreation divers virtually without exception, yet invariably, you’ll see or read about technical divers who descend well below 40 meters/130 feet. This doesn’t negate the limits for recreational divers, however. On close inspection, you’ll see that technical divers each wear significantly more equipment – often four to six cylinders, multiple regulators, etc. – and it is more elaborate. Diving to depths below 40 meters/130 feet often requires special helium breathing gases, and an hour or more making stage decompression stops. As you might imagine, this type of diving requires special training, and substantial experience in recreational diving before starting that training.

Even with the equipment, experience and training, technical diving by its nature entails significantly more risk than recreational diving. When you think about it, technical divers validate the 40 meter/130 foot recreational limit with all the extra hardware, special techniques and extensive training they require to manage the risk of going beyond. Technical diving isn’t for everyone, nor is it a necessary step in your progress as a diver even after thousands of dives. But, if this type of diving interests you, obtain the proper experience and training before attempting it.

Developing Your Personal Depth Limit.

While the dive community draws the general line for defining a “deep” dive at 18 metres/60 feet, you need to redraw that line based on the environment, your experience and your training. Nor can you overlook your buddy’s experience and training when deciding the depth limit. For example, 18 meters/60 feet may not seem deep and stressful at all when you and your buddy are properly trained, have been diving actively and you’re in warm, clear tropical water. The same dive without training after a ten-month pause in diving actively would certainly be more stressful and seem “deeper. Likewise a dive to less than 18 meters/60 feet in a cold, dark, poor-visibility lake could be considered deep even with training and experience.

Obviously, depth limits need to change to meet the circumstances. When setting your depth limit for a dive, take into account the dive site, yourself and your buddy. First, think about the environmental conditions. Based on them, what is a realistic depth limit? Maybe you need to plan a shallower dive and gradually extend the limit in the particular environment over a series of dives. Second, ask yourself whether you’re physically and psychologically fit for the dive. Are you in shape, do you have the training/experience and do you feel confident?
 
Third, consider the depth of any previous dives, the surface interval since the last dive and your pressure group. Check your dive computer if you use one. Repetitive dive have shorter no decompression limits that restrict how deep you can go (remember, you make your deeper dive first). Fourth, evaluate your location. If you have a problem, how long would it take to get a patient to emergency medical care? Fifth, review these factors as they apply to your buddy. The more conservative personal limits – yours or your buddy’s – should govern the dive.

Deep Diving Equipment.

Like most diving specialties, deep diving has its unique equipment requirements, which you can divide two groups: your personal equipment and specialized deep diving equipment. Additionally, deep diving calls for a support station and attention to using dive computers.
 
Personal Equipment.

Before making a deep dive, you need to evaluate your personal equipment’s suitability for deep diving. You may find that some of it needs service, and in some cases, replacement. Generally, you need to consider both equipment condition and appropriateness for use in deep water. Here are some guidelines:

Regulator:

The deeper you go, the denser the air your regulator delivers. A balanced regulator breathes consistently regardless of tank pressure. Virtually all modern regulator models perform adequately within recreational limits, though you want the best performance possible. Also, regardless of model your regulator needs to be in good working order through proper maintenance and service as recommended by the manufacturer (usually, that’s within the last year).

Submersible pressure gauge:

Have your submersible pressure gauge serviced annually (along with your regulator) and checked for accuracy. You (obviously) want an accurate SPG for all diving, but you don’t want to be at 30 meters/100 feet when you find out it reads 70 bar/1000 psi too high.

Tanks:

Because you use air faster in deeper water, use a 12 liter/71.2 cubic foot or larger capacity cylinder. Remember that you want maximum air supply to provide a reserve and ample air for your safety stop, not so that you can push or exceed the no decompression limits.

BCD:

Your BCD should be in good working condition. Check the BCD for leaks, either in the bladder or valves and have it serviced as necessary before deep diving with it.

Exposure suits:

The suit you use in shallow water may not be appropriate for deep diving. Deeper water tends to be colder; if you drop through a thermocline (the abrupt transition to cold water you learned about in your Open Water Diver course), the temperature can plunge. On top of this, the water pressure compresses neoprene wet suits, reducing their insulation at greater depths (this isn’t an issue with most dry suits). Choose your exposure suit based on the deep water temperatures.

Alternate air sources:

The standard place to wear your alternate air sources is clearly marked in the triangle formed by your chin and the lower corners of your rib cage. Here, either you or your buddy can easily find and control the alternate in the event of an air supply emergency. Besides an extra second stage alternate, you may want to go for a pony bottle alternate air source for deep diving. A pony bottle uses a totally independent regulator and an extra supply of air, making you more self-sufficient in the event of an emergency.

 


Gauges:

Deep diving requires carrying a complete set of instruments: a dive computer or depth gauge and timer, plus a compass. Have your gauges’ accuracy checked annually, or if they’re dropped or subjected to any abuse. Many divers carry backup timers and depth gauges while deep diving.

Surface Signaling Devices:

If you become separated from your group, you may want to gain the boat’s attention. An easy way to do this is to use an audible and/or surface signaling device. When deep diving, attach an audible and visual surface signaling device to your BCD. Audible devices like whistles or air horns (devices that attach to the low-pressure inflator of the BCD) can be easily heard at night or in limited visibility conditions and visual signaling devices like a signal mirror or surface marker buoy (safety sausage) can be easily seen in the daytime.

Special Equipment for Deep Diving.

Besides your personal gear, deep diving calls for some equipment that wouldn’t necessarily use for diving shallower. This equipment makes deep diving easier and in many environments, contributes significantly to safety.
 
Reference line:

If you’ve already made a Night Adventure Dive, you’re familiar with using a line to help maintain your orientation and control during ascents and descents. A reference line meets the same purposes in deep diving, and helps you maintain buddy contact and your safety stop at 5 meters/15 feet. Choose a size line you can hang on to easily for your reference line – typically 12mm/1/2 in. or larger – and suspend it from a separate float when shore diving to tow with you. When boat diving, you may also tow a float, but it’s common to use the anchor line as the reference line. This is acceptable, provided that the water is fairly calm, but in rougher water, the anchor line may snap up and down in the first 5 to 6 meters/15 to 20 feet as the boat pitches and rolls. If you try to hold the anchor line in such conditions, you can be injured if it jerks you up suddenly. Another problem with using the anchor line is that you may not be able to locate it for your ascent if the boat had to re anchor during during your dive.
 
Emergency breathing equipment:

Short no decompression limits and safety stops make a pause at the 5 meter/15 foot level inevitable on virtually all deep dives. It’s much easier to accidentally exceed no decompression limits on a deep dive, thus requiring emergency decompression. You should make safety stops on all deep to help avoid decompression sickness. Emergency breathing equipment at the safety stop level ensures that you have enough air to make a safety or emergency decompression stop. The most common emergency breathing system is simply a tank and regulator suspended from a line to hang at 5 meters/15 feet.  Some dive boats have second stages on 6 meter/20 foot hoses that reach down from the surface, eliminating the suspended tank.
 
Spare weights:

Although you usually account for air consumption when weighting yourself, it’s common to want just a bit more weight to help you stay at safety stop depth. Typically, you put spare weights with clips on the emergency breathing equipment, either clipped to it, in a mesh bag or similar container. If needed, clip a weight to your weight belt or BCD.

Dive light:

Because some deep environments can be relative dim due to light absorption by water, you may find a compact light useful for deep diving when you want to look in holes or cracks, or to read gauges. In some environments with low visibility, a dive below 18 meters/60 feet can be completely dark without a light. Be sure the light has been rated to 40 meters/130 feet. For more information on dive lights, refer to the Night Diving section.
 
First aid and emergency oxygen:

It’s recommended to have these available for all diving activities, but they can be extra important for rendering aid when deep diving, and in remote locations. You’ll learn more about handling diver emergencies when you complete the PADI Emergency First Response program and the PADI Rescue Diver course.

Surface Support Station.

The easiest way to deploy deep dive equipment is by using a surface support station, which combines your reference line, emergency breathing equipment and spare weights into a single unit. A surface support station is simply a float with an anchored line and a weighted 5 meter/15 foot line for suspending your emergency breathing equipment and spare weights. The anchored line doubles as your descent/ascent reference line and keeps your surface support station in place. When boat diving, the boat replaces the float.

Deep Diving with Computers.

Dive computers have become almost standard equipment in many environments, and it’s easy to see why. Computers combine time and depth gauges (and air supply, in some models) and calculate your theoretical nitrogen uptake and release throughout a day of diving. They can extend your no decompression time on multilevel dives by giving you credit for slower nitrogen absorption as you ascend to shallow depths (like The Wheel does). Various models provide a range of information that may include ascent rates, temperature, emergency decompression and more. When diving with a computer, there are six basic guidelines to follow, along with the instructions in the computer’s instruction manual. First, use the computer as a no decompression device. Stay away from required decompression stops – they greatly complicate the training and equipment requirements.

Second, you and your buddy should have individual computers. Never attempt to share one between two or more divers. Third, always follow the computer with the more conservative readout, yours or your buddy’s. Fourth, if your computer fails, follow the manufacturer’s instructions. If there are none, make a normal ascent at 18 metres/60 feet per minute (or the computer’s rate, whichever is slower) and a safety stop, perhaps as long as your air supply permits if you think you’re close to the no decompression limits. Consult the manufacturer’s instructions to determine when you may dive again; you may have to wait 12 hours or more. Fifth, whenever feasible, back up your computer by calculating your profiles with tables. This gives you a way to keep diving if your computer fails, plus it can help give you some idea of how much no stop time you’ll have when planning repetitive dives. You’ll find that The Wheel, with its multilevel ability, is the best choice for this.

Sixth, when diving in a group in which most divers don’t have computers (not unusual in a few areas), be sure the divemaster knows you and your buddy do have computers and may have more no decompression dive time available than the rest of the group. For more information on dive computer use and multilevel diving, see the Multilevel/Computer section. Check out the PADI Multilevel Diver course for more about diving with computers.

Enriched Air Diving and Deep Diving.

You may already be familiar with enriched air nitrox (a.k.a. “nitrox,” “EAN,” “EANx”), which is simply air with extra oxygen blended in so that you have a greater proportion of oxygen than found in air. Air is (for practical purposes) 21 percent oxygen, 79 percent nitrogen, whereas popular enriched air blends have, for example, 32 percent oxygen, 68 percent nitrogen (EANx32) and 36 percent oxygen, 64 percent nitrogen (EANx36). The purpose of enriched air is to extend your no decompression time by reducing the amount of nitrogen in your breathing gas. This is particularly advantageous for dives between 18 meters/60 feet and 30 meters/100 feet. For instance, using EANx36, your no stop time at 28 meters/90 feet is 40 minutes compared to 25 minutes with air.

However, enriched air brings with it concerns of oxygen toxicity, caused by breathing elevated oxygen under pressure if you exceed the maximum depth for a particular blend. For example, the maximum depth for EANx36 is 27 metres/90 feet – descending deeper presents a significant risk of losing consciousness and drowning due to oxygen toxicity. Enriched air also has concerns regarding using equipment with elevated oxygen. For these reasons, don’t use enriched air unless you’re properly trained and certified in its use. When you’re properly trained and certified, you know how to avoid and minimize the risks listed above, making enriched air an excellent and useful way to extend your no decompression time. Click here for the PADI Enriched Air Diver course.

Deep Diving Techniques.

Once you’re properly equipped, deep diving becomes a matter of reapplying the diving techniques you already know to the deep water environment. You already know how to use the buddy system, how to check your buoyancy, how to make ascents and descents, how to handle out-of-air emergencies and other diving techniques, now you’re going to learn to apply the same skills when diving below 18 meters/60 feet.

Maintaining Buddy Contact.

In your Open Water Diver course, you learned to keep contact with your buddy so you can assist each other in watching time and depth, or help each other if a problem arises. You also learned to reunite with your buddy on the surface, and then to resume your dive, if you become separated. The buddy system plays the same roles when you deep dive, but it’s more important that you maintain buddy contact because if you’re separated and forced to surface to reunite, the dive ends. You seldom have the air and no decompression time available to re-descend into deep water. To maintain contact on deep dives, watch each other during descents and ascents. Stay within touching distance and swim side-by-side just above the bottom. In poor visibility you might want to use a short “buddy-line” to maintain contact. Frequently monitor each other’s depth and air supply.

Neutral Buoyancy at Depth.

Maintaining neutral buoyancy on a deep dive differs little from a shallower dive, but keeps a few points in mind. First, begin the dive properly weighted – so you float at eye level with an empty BCD and holding a normal breath. (If you check with a full cylinder, add about two kgs/five pounds to compensate for the air you use during the dive.)

Second, during descents and ascents, adjust your buoyancy frequently – don’t wait until you’re rising or sinking rapidly. Finally, with proper weight your BCD (or dry suit if you using one – see the Dry Suit Diving section for more about buoyancy control with dry suits) should be all you need to maintain neutral buoyancy. You shouldn’t need to remove any weights at depth. See the Peak Performance Buoyancy section about protecting sensitive bottom environments by refining your buoyancy skills.

Descents and Ascents.

Descents and ascents on deep dives require more attention to maintaining control because you travel through more water. A few techniques and a reference line, however, make it easy to govern your ascents/descents. This can be especially important with lower visibility since you don’t have as many visual clues to keep you oriented.
 
Head-up descents.

It’s usually best to descent into deep water so that you keep your feet below head level. This position makes it easier to control your buoyancy, equalize your air spaces and remain oriented. The position also helps if you need to readjust equipment during the descent. When descending, keep your right hand on the reference line and use the left to operate your BCD and equalize your ears. When beginning your descent, don’t forget to set your bezel or timer if necessary.

Controlling descents and ascents.

It’s important to control your descents and ascents to reduce the risk of squeezes or DCI. The first step in controlling your descents and ascents is to maintain buoyancy control. If you regulate your buoyancy frequently, you eliminate the vast majority of out-of-control ascents or descents. If you need to, you can stop or slow an ascent or descent with a reference line, even with your hands occupied. The first way is to lock the line with your elbow. This is the fastest way to stop or slow on the line, but most people find the second method, wrapping your leg around the line, less tiring. This isn’t as quick, but you can stay there easily if you want to hold the position for more than a few moments.

Descents and ascents without reference.

It’s best to descent into, and ascent from, deep water with a reference such a line, sloping bottom or reef wall. If you can’t, make these four techniques part of the descent/ascent: First, descend/ascend in a head-up position so you remain oriented. Second, face your buddy and stay close, maintaining eye contact during the descent/ascent. Third, use your computer (or depth gauge and timer) so your ascent rate doesn’t exceed 18 meters/60 feet per minute. Fourth, adjust your buoyancy frequently to remain neutral and prevent a runaway ascent/descent. During an ascent, make a safety stop at 5 meters/15 feet and listen for boats and other overhead noises. Wait for any noises to pass before ascending with one hand overhead for protection.

Estimating proper ascent rate.

As you know well by now, the maximum ascent rate with the Recreational Dive Planner is 18 meters/60 feet per minute. Slower is acceptable, and many dive computers expect you to go slower. It’s easy to determine your rate when using a computer and many electronic depth gauges because they either have ascent rate “speedometers”, or they have indicators that warn you when you exceed their prescribed rate by bleeping, blinking or honking. If you’re diving without a computer, use an analog depth gauge and timer to time your rate so that it takes four seconds or longer to ascend one meter, or ten seconds or longer to ascend ten feet. When ascending from any depth, be a S.A.F.E. diver. Slowly Ascend From Every dive and make a three minute safety stop at 5 metres/15 feet.

More Deep Diving Techniques.

Deep Diving Breathing Techniques.

Even with your regulator in top condition, you can over breathe it during stress or stress or strenuous activity in deep water. This happens when you demand air faster than the regulator can deliver it. This causes you to feel like you can’t get enough air, or that you’re suffocating – a frightening experience if you don’t know what’s happening. The deeper you are, the more easily you can cause this because each breath requires a greater air mass than when you’re shallower. This is why you need to avoid working hard and also avoid physical demands that cause you to breathe heavily.

Even on a shallow dive it’s crucial to avoid overexertion while diving, but particularly while deep diving. Always breathe consistently, slowly and deeply. Don’t let yourself get out of breath. If you relax and move slowly, you’ll conserve air and avoid getting out of breath. If you ever feel like you can’t get enough air while deep diving (or shallow), stop all activity and rest. If conditions are such that you can’t continue the dive without undue exertion after catching your breath, terminate the dive and ascend properly.
 
Air Supply Control.

From day one as a beginning diver, you learned to monitor your SPG (submersible pressure gauge) to prevent running low or out of air. In deep diving, you and your buddy need to watch your SPGs more frequently because you use your air much more quickly. For example, you use your air about twice as fast at 30 meters/100 feet as you do at 10 meters/33 feet. Logically, you should be watching your SPG at least twice as often.

Besides constantly monitoring you SPG, you can avoid air supply problems by conserving your air. Avoid overexertion, exercise or any strenuous activities, such as long swims. Deep dives should be relaxing. End the dive with an ample reserve, based on the dive specifics, so that you can return to your ascent point, ascend, make a safety stop and surface with enough air to handle the unexpected. Finally, you can calculate your air consumption to help you plan your air supply requirements for a deep dive.
 
Anti-Silting Techniques.

When you reach the bottom on a deep dive (or any other, for that matter), you want to avoid kicking up silt because doing so ruins the visibility and can make it difficult or impossible to see. On a deep dive you don’t typically go as far, so causing a silt out when you hit bottom can mess up visibility over the entire area you’re going to explore. And, careless bottom contact can destroy corals or other fragile aquatic life, as can a silt cloud settling on top of it. To prevent silting out the dive, slow your descent as your near, but before you reach the bottom, and stop kicking.

Establish neutral buoyancy, and when swimming, stay well off the bottom. If you must stop and maintain contact with bottom, find a spot away from the reference line (so other divers won’t descend on top of you) and free of aquatic life and sharp objects. Exhale momentarily to become slightly negatively buoyant, and then allow yourself to gradually settle, inhaling as you land gently on your knees. See? Almost no silt.

Making Safety or Emergency Decompression Stops.

In your Open Water Diver course, you learned that when using the Recreational Dive Planner, or any table or computer for that matter, it’s wise to make a safety stop at the end of any dive. Also, you learned that some dives with the RDP require a safety stop, and that if you accidentally exceed any limit on the Recreational Dive Planner, you need to make an emergency decompression stop. It’s no sweat to make either a safety or emergency decompression stop with a reference line, and you may have done it already: Ascend no faster than 18 meters/60 feet per minute (or whatever your computer likes, if you’re using one) until your depth gauge/computer shows 5 meters/15 feet.

It’s not critical, but try to grasp the line so stop depth lies about mid-chest level if you’re vertical. Maintain neutral or slightly negative buoyancy and watch your depth and time. Or, you can watch depth while your buddy watches time. Fine-tune your buoyancy as necessary. When making a safety stop, it’s a good practice to review the RDP time and depth limits you planned to be certain you didn’t exceed them and require an emergency decompression stop – if you find you do, calculate your emergency decompression time and extend your stop to cover it.

Although it’s easiest to make a safety stop on a reference line or on shallow bottom, you can make a safety/emergency decompression stop mid-water if you need to. Make a proper ascent, slowing as you reach 5 meters/15 feet, and establish neutral buoyancy. Maintain a feet-down, head-up position while staying side-by-side with your buddy – this makes it easy to kick and/or release air from your BCD to maintain your depth. Monitor your depth and time. If there’s a mild current, you may swim slowly against it, but avoid overexertion. Some divers carry small inflatable buoys/signal tubes and small reels that they can deploy from 5-6 metres/15-20 feet, which provides a reference for a stop, and provides a visual reference for a dive master, boat captain or others at the surface.

If you miss an emergency decompression stop.

Should you find that you accidentally omitted an emergency decompression stop, remain calm and stay out of the water – do not make any more dives. Tell your buddies and other supervisory personnel that you missed the stop. Breathe 100 percent oxygen if available, and try to relax while monitoring yourself closely for any decompression illness symptoms. If any abnormalities develop, seek medical assistance immediately and stay on 100 percent oxygen. Make a habit of stopping on all dives and you greatly reduce the probability of missing an emergency decompression stop.

Also, US Navy procedures for handling an omitted decompression stop by re-entering the water require extensive surface support and are not normally considered appropriate for recreational divers. If you miss an emergency decompression stop, do not re-enter the water.
 
Deep Diving Along Walls.

One of the most popular places to make deep dives is along walls – near-vertical drop-offs into deep water. Because there’s no bottom next to many walls (well, of course there is a bottom, but practically speaking a bottom at 600 meters/2000 feet is “no bottom”), there are three special techniques to apply when deep diving along one. First, remember that many walls are found in warm, tropical climates with extremely clear water where it’s easy to be deeper than you realize.

Except for your computer or depth gauge, it may not feel much different at 30 meters/100 feet than at 22 meters/70 feet, so watch your depth closely. Second, you’ll probably use the wall as your reference, so stay close to keep your orientation. Hanging away from the wall in mid-water is exhilarating, but it’s easier to lose your orientation and end up deeper than you planned. Third, stay close to the wall, but not to close. Watch for delicate aquatic life, and avoid touching anything fragile or sensitive, just as you would on any dive.

Nitrogen Narcosis.

Your Open Water Diver course introduced you to nitrogen narcosis, which is the intoxicating effect nitrogen produces when you breathe it under pressure. Although the exact cause of nitrogen narcosis still eludes physiologists, most theories link it to nitrogen dissolving into a fatty material that covers nerve cells, interfering with the transmission of nerve impulses. The Deep Adventure Dive may take you deep enough to feel the first mild effects of nitrogen narcosis, so let’s review and look at narcosis. Although some divers feel “narked” at relatively shallow depths and others seem immune even at 40 metres/130 feet, the majority find narcosis first noticeable between 24 metres/80 feet and 30 metres/100 feet.

The symptoms (what you feel) and signs (what you see in your body) may be varied, depending on the individual.

Symptoms include:

• rigid, inflexible thinking
• poor judgement and short-term memory loss
• a false sense of security
• no concern for safety or a particular task
• euphoria and elation
• sleepiness, drowsiness or complacency
• undue anxiety

Signs include:

• inappropriate behaviour