Deep diving can be an emotive subject in the diving circles, to some the maximum depth a diver has attained is an overriding factor in a divers skill and competence. While the practice of ‘Bounce Diving’ (A very fast descent on an air mix to a target depth of 60 M+ then immediately ascending) is a known method of deep diving for the most part a divers skill is not proportional to the depth reached. Certainly a different way of gauging a divers skill would be a diver carrying out a pre-planned technical dive to a deep depth then carrying out exploration and other work while submerged. Of course diving is an adventurous sport and one way of achieving that adventure is to dive deep purely for the sake and challenge of going deeper than before. For others diving as much of the ocean as possible and penetrating deeply will explore a little more of the underwater realm.
Deep diving is accompanied by extra dangers and the desire for pushing the limits should be tempered by the need for caution.
It can be difficult to define a deep dive. For a beginner with only a few dives under his belt it may be 15 meters or so. For an experienced diver it may be 30 meters. In fact an unspoken rule in diving is that 30 meters is considered the benchmark for what may be considered a deep dive. In tropical and sub-tropical waters there is some leeway and complacency to deep diving and some of the difficulties are somewhat overstated, although most should be adhered to.
Risks of Deep Diving
Although diving is arguably considered a risky undertaking it should be made crystal clear that deep diving up to and beyond recreational limits brings with it increased risk and hazards.
The risk of decompression illness increases with the rapid decrease in permitted bottom time when the diver is deeper than 30 meters.
Poor light, often poorer visibility, increased cold, unfamiliarity with the surroundings are all factors that can contribute to the higher risk of the diver being affected by nitrogen narcosis.
Nitrogen Narcosis means that careful monitoring of depth, time and air consumption is made less certain just when more care is actually necessary.
For many divers there is a psychological fear of deepness and darkness. This problem can exacerbate nitrogen narcosis as well as contribute to other problems.
Air consumption is increased not only by depth but also by the cold, anxiety and by the heavier exertion of diving and breathing at depth.
Loss of buoyancy at depth can cause considerable problems divers. The use of buoyancy compensation devices such as drysuits, and buoyancy compensators, is essential on these dives. Diver rescue poses a problem at any time but the above factors compound a rescue from depth. In addition, the sheer physical distance to the surface complicates any rescue.
The limited availability of emergency services in the event of an in-water accident or a post-dive decompression problem complicates a potential deep-diving incident.
Having said all this divers choosing to expose themselves to these risk can benefit from discovering new dive sites, shipwrecks and certain marine life may only be found at certain depths. The adventure and enjoyment in doing this can be immense as well as that some divers thrive on the challenge and dangers faced.
Categories of Deep Diving
It is important to keep in mind that deep diving is not for anyone, no matter how long someone has been diving. A veteran diver of the shallow reefs should feel no shame in having not ventured deeper into the underwater depths. It is useful, however, to categorize deep dives by depth bands.
30 – 40 Meters
Increased care and experience is required for most dives. Nervous and unskilled divers should think carefully before committing to entering this region. Experienced divers should now become more aware, both of themselves and their buddy.
40 – 50 Meters
This is the kind of diving that should only be undertaken by divers experienced in deep diving and aware of the risks. Air consumption, narcosis and the chill factor all become heavily apparent now. These depths are for dive-fit divers with the appropriate back-ups and water conditions.
50 Meters +
Recreational divers should not undertake dives to these depths. Air consumption and narcosis loading are now at levels only technical divers should consider. Oxygen toxicity is now a distinct possibility and air / gas mixes are consumed at over treble the level than that at 10 meters. Diving in this region requires a very high level of competence, aptitude, equipment and experience. It is therefore considered the domain of the very few.
The above categories and comments apply mainly to temperate waters and in warmer waters / tropics some of the deeper diving constraints are reduced, thus allowing deeper depths to be reached.
Personal Equipment – Deep Diving
The deep diver must be thoroughly familiar with his personal equipment. He needs to be able to put his hand on his direct-feed inflator, for instance, without hesitation. Many problems on deep dives are casued by divers using unfamiliar equipment acquired just for the dive, thus causing problems with buoyancy and ill-fitting harnesses. Ideally all your diving equipment needs to be comfortable and unlikely to be an annoyance, as due to possible decompression requirements you will be wearing it a lot longer than normal. A prime example of this is the wearing of a thicker wetsuit than normal to combat heat loss to the wearing of a dry suit.
A totally adequate air supply is essential for deep diving. The majority of incidents are caused by an inadequate supply of air, often resulting in too rapid ascents. It is an excellent idea to plan to end the dive with a reserve of about one third of your air remaining. This air can also be useful on the surface when there is a swell.
It would be unwise to recommend cylinder capacities for deep diving as air consumption varies for each individual and is also dependent on the underwater activity pursued.
The quality and reliability of the regulator is also extremely important. An unbalanced regulator with poor inhalation and exhalation resistance will result in an increase in air consumption. A regulator, which is of good quality and is reliable, as well as being a balanced one will give considerable confidence and performance to the diver. Some diver use a form of breathing control to regulate their air consumption even further.
Although running out of air on a deep dive is a rare occurrence, it can be a most frightening experience. Some though must be given to alternative air supplies. These could be an independent pony cylinder with a separate regulator system right through to full twin set with independent regulators mounted on each cylinder. The drawback to the latter is that each cylinder must be ‘breathed down’ evenly otherwise the weight imbalance may be a troublesome distraction.
Most deep diving incorporates decompression stops to ensure safe off-gassing of nitrogen from the body tissues. Many divers who dive deep use a high blend oxygen blend of nitrox as a decompression gas. This is because of the reduced amount of nitrogen in the mix, which ensures a more enhanced decompression than using air. Some divers carry 100% O2 cylinders for maximum decompression effects although only fully qualified tech divers are normally allowed to do this.
The nitrox is normally carried by each diver throughout the dive and it is advisable to have a spare cylinder of decompression gas suspended from the shot line at the 6 – 9 meter mark in case of emergency. Note that when it comes to carrying decompression gas the line between normal recreational diving and technical diving starts to blur, consider further training in tech diving when it comes to this.
Buoyancy loss need not be a problem with the use of direct-feed inflators. However, it is important that divers are aware of buoyancy loss and compensate during their descent rather than waiting until the target depth and being at maximum buoyancy loss. The total buoyancy loss at 30 meters can be up to 10 kilos when wearing a wetsuit.
When wearing a wetsuit, buoyancy adjustment should be carried out using the BCD’s direct feed inflator. Oral inflation by removing the demand valve at depth presents too great a risk of dropping or fumbling the demand valve particularly when compounded by the effects of nitrogen narcosis.
Deep divers should also know the correct method of controlled buoyant ascent. This involves slowly venting air on ascent to achieve a normal rate of ascent, and not dumping all the air at depth, which will result in negative buoyancy.
A drysuit gives much better and safer control over buoyancy at depth than a wetsuit. All modern drysuits are fitted with direct-feed inflators. To prevent the suit squeezing, it is necessary to bleed air into the suit as the diver descend, so the question of negative buoyancy does not really arise. Of course, the full buoyancy of the BC is still available should an emergency arise. For this reason, plus its greater insulation properties at depth, the drysuit finds favour amongst most divers who regularly dive deep.
Instruments and Accessories
It is vital that depth and time are accurately recorded on every dive. On deep dives the inaccurate recording of times and depths has led to many decompression and other incidents. Consequently, instruments must be regularly checked for accuracy and have bold, luminous faces. At depth, with the problems of narcosis and poor light conditions, they must be clearly readably.
The use of a bottom timer, which automatically switches on and records bottom time (provided you initially set it), and a depth gauge with a maximum depth recording needle has much to commend it. Further developments in decompression computer technology have made these computers, smaller more streamlined and the ultimate solution to deep diving instrumentation.
A powerful and reliable torch can transform and uneasy dive in poor visibility to one in which the objective may be seen, explored, enjoyed in relative ease. It also provides the buddy divers with a means of location and identification in the gloom.
A decompression table slate is essential on these types of dives for reference during the dive, although they should not be used for dive planning during the dive. Do not try to memorize dive times for different depths. Instead, write out the figures of the planned dive on a separate slate.