The Phreatic Zone

Scuba diving and in particular, technical diving is a sport where the choice and configuration of equipment provokes considerable interest and debate. Spend a day on any charter boat and you will see so called “technical” divers sporting an infinite array of equipment and gadgetry all configured differently and much of it, unnecessary and unsuited to the intended mission. The “more is better” mentality prevails. 

Leading technical divers discovered long ago that a delayed response to an emergency situation in the water poses an unacceptable risk and that the risk can be managed by minimising, standardising, streamlining and simplifying the basic equipment configuration. 

The Basic System

The DIR diver is immediately recognisable by his equipment configuration. The basic system shown utilises a stainless steel backplate, rigged with a one-piece harness and a back mounted buoyancy compensator, or ‘wing’ sandwiched between the backplate and a pair of steel cylinders. The backup regulator is mounted on a short hose and hangs around the neck for easy access. The primary regulator is mounted on a 2m hose which runs down, behind the wing on the right side, under the hip mounted primary light canister, across the chest, around the neck and into the mouth from the right side. This is the regulator donated to a buddy in an gas-share

The Backplate & Harness

The DIR harness is made from one continuous length of webbing woven through the backplate to form the shoulder loops and waist straps. The waist straps are fastened using a high quality, stainless steel weight belt buckle. There are no quick releases or other potential failure points. The crotch strap has a loop in the front, through which the waist strap passes.It is immediately noticeable that the DIR harness is not adorned with multiple d-rings to hang “gear” from. There are just 3 d-rings on the harness and two on the crotch strap. The two chest-mounted d-rings carry the backup lights, held close to the harness with small sections of bicycle inner tube placing them in a protected position under the arms where they go virtually unnoticed until required. The right chest d-ring carries the light head, when not in use and the primary regulator, when not being breathed. The left chest d-ring, together with the left hip d-ring carries stage cylinders. There is a single submersible pressure gauge clipped off to the left hip d-ring. The front crotch strap d-ring is redundant unless a diver propulsion vehicle (DPV) is used so it is kept out of the way by passing the loop through the d-ring before securing the harness. The remaining crotch strap d-ring (or ‘butt’ ring) is used to carry additional equipment such as reels and/or spools. 

The DIR harness follows the contours of the body with no protrusions or encumbrances and leaves the entire chest area clear and unobstructed. No weight belt is worn. Positive buoyancy is offset by the weight of the backplate (approx. 2.5kg) with any additional weight carried between the cylinders and the backplate in the form of a V-weight, the position of which can be adjusted along the length of the cylinders to achieve perfect in-water trim. By eliminating the weight belt, DIR divers eliminate a potential source of danger in the form of accidental release. 

Good Trim

With all this heavy equipment, some divers believe they must use large buoyancy wings with as much as 100 pounds of lift, or even dual bladder wings for “redundancy”.

In truth, most divers are either over-weighted, have difficulty “getting down” and/or have difficulty in maintaining neutral buoyancy in the last 10m or so of their ascent to the surface. Poor technique and poor equipment selection often cause these problems but they can be overcome by understanding how to ‘balance’ the rig. There are two criteria that must be met for a rig to be considered ‘balanced’. First, the diver must be weighted so that he can swim up from depth with full cylinders and without the use of the wing for buoyancy. Second, with near empty cylinders the diver must be able to comfortably maintain neutral buoyancy at a depth of 3m with little or no gas in the wing. The DIR diver understands the concept of a balanced rig and carefully selects cylinders, exposure protection and buoyancy compensator according to the prevailing conditions. The DIR diver makes use of a simple set of wings with generally no more than 55 pounds of lift. The wings are not restrained by elastic cords and are free to wrap around the cylinders providing the buoyancy where it is need without trapping gas. This system facilitates a streamlined posture and the all-important horizontal ‘trim’. The DIR diver maintains this horizontal ‘trim’ with the feet up during descent, ascent, throughout the dive and particularly during decompression. Good ‘trim’ and a refined finning technique is paramount during all dives. Poor ‘trim’ combined with poor finning technique is inefficient and leads to disturbance of sediment resulting in reduced visibility. 

The wing inflator hose is routed along the corrugated hose to the inflator fitting and held tight to the corrugated hose with small sections of bicycle inner tube, minimising the risk of entanglement and keeping the rig clean and streamlined. Both the dry suit feed and the wing inflator hose share the same type of fitting so that, in the event of a failure, the wing can be inflated with the dry suit 

Gas Shutdown

The use of an isolation manifold is essential when diving with twin cylinders since it enables a faulty regulator to be isolated whilst still maintaining access to all the gas in both cylinders.

The manifold uses redundant barrel type o-rings as opposed to facing seals. This gives a more positive seal and is more tolerant to impact. The nuts normally used to tighten the centre section are left loose allowing the isolator to rotate slightly in the event of an impact. In true DIR tradition, as many potential underwater failure points as possible are eliminated. Soft rubber knobs are used on all cylinder valves which are kept fully open at all times. 

One of the essential skills practised and refined by DIR divers is the gas shutdown. The isolation or shutting down of a cylinder must be an intuitive reaction to an emergency situation. Correct choice of exposure protection and undergarments must permit easy access to all cylinder valves. 

Donating the Primary Regulator

Primary and backup regulators
The backup regulator is instantly accessible as it hangs around the neck on an elastic necklace. This is YOUR backup and is breathed if you need to gas-share. The backup regulator feeds from the left post and, with practice can be deployed hands-free. 

The primary regulator is the one donated to a buddy in an gas-share scenario and is mounted on the long hose. Deployment of the primary regulator and long hose is simplicity itself. The regulator is removed from the mouth and passed up and forward whilst ducking the head slightly. In the event that the primary regulator is grabbed spontaneously (a common scenario in a ‘real’ out-of-gas situation) simply ducking your head allows the long hose to deploy freely, while placing your mouth in immediate proximity to the backup regulator. 

Donating the regulator in your mouth to an out-of-gas diver is one of the cornerstones of the DIR configuration.

Donating the primary regulator guarantees that the out-of-gas diver receives a working, high performance regulator immediately. Divers need not swim side-by-side whilst sharing gas. The long hose allows divers to swim in single file to negotiate narrow passages in caves or while penetrating a wreck. 

Positioning of the primary and backup regulators on the manifold outlets is of paramount importance. The primary regulator must feed from the right post. When diving in an overhead environment (wreck or cave) it is the left post which will roll shut on contact with the overhead. The right post will roll open. Imagine the scenario where two divers are exiting a wreck or cave whilst gas sharing. The out-of-gas diver leads with the donor behind. If the donor has his primary regulator on the left post and makes contact with the roof of the cave or wreck and rolls the valve shut, the out-of-gas diver is suddenly out-of-gas again! However, if the donor has the primary regulator on the right post and the backup on the left post, the donor will probably notice his valve make contact with the ceiling and simply reach back with the left hand and turn the valve back on. 

All second stage regulators are left finger tight on their hoses so that they can be quickly and easily swapped in the event of failure. The locking pins are removed so that the faceplate can be removed underwater to clear debris. 

Light Cannister Placement

The primary light is a vital piece of equipment to the DIR diver. It is used for signalling, maintaining buddy contact and in keeping with the DIR philosophy of “less is best” performs multiple functions. The canister aids routing of the long hose and provides a source of ditchable weight. These days, primary lights tend to use HID (High Intensity Discharge) technology providing a burn time of up to four-and-a-half hours from a 6 amp, 12 volt battery. 

The canister is mounted on the right side of the waist belt, as far back towards the backplate as possible and is held in place with a separate weight-belt buckle which retains the canister when de-kitting on the surface prior to entering a RIB for example. 

The light cord is just long enough to reach from the canister to a functional position in the left hand. The light head is mounted on the back of the hand leaving the fingers free to manipulate reels or other equipment and the light can be focused to achieve a penetrating tight beam used for communication. 

Backup lights are simple three “C” cell, twist-on lights. There is no external switch and only a single O-ring sealing the unit. These lights use a 4.5 volt bulb and are ultra reliable. When a backup light deployed, it must work. The last thing you need is a blown bulb. The lights are attached to the chest D-rings by stainless steel bolt snaps. A backup light is deployed by first removing it from its rubber retaining ring and then turning it on, only then is it unclipped from the d-ring, meaning that if it is dropped, at least it can be seen. 

Instrumentation
In keeping with the DIR principles of streamlining and eliminating possible failure points, the DIR diver rejects bulky consoles, in favour of a single submersible pressure gauge. The 24″ high-pressure hose is run straight down from the left post. A stainless steel bolt-snap is tied to the pressure gauge fitting with cave line and clipped off to the left hip d-ring. 

All remaining instrumentation is wrist mounted. A bottom timer sits on the right wrist where it can be easily illuminated by the light in the left hand. A backup timer sits on the left wrist and has its strap removed and replaced with two elastic cords thereby eliminating another potential failure point. 

Other equipment details
The concept of minimalism, streamlining and the elimination of all possible failure points extends to even the most basic items of dive gear. Stiff rubber jet-fins have their straps discarded and replaced with stainless steel spring straps with no quick-release catches to break or otherwise get snagged. A small knife with a serrated edge is carried on the waist strap where it can be reached easily with either hand. DIR divers do not strap knives to the leg or arm. 

Additional equipment is carried in a large cargo pocket on the left thigh. Depending on the dive, the pocket carries items such as a spare mask, safety spools, surface markers, line arrows, spare bolt-snaps and a whistle. All these items are clipped off to small loops of elastic cord in the pocket. To locate an item, simply pull all the equipment from the pocket, whilst still attached to the elastic cord, locate the item required, unclip it and stow the remaining items. 

DIR divers choose the traditional stainless steel bolt-snap as the preferred method of attachment for all equipment. Any attachment which has the potential to trap line is rejected. Bolt-snaps are tied on using cave line. There is nothing attached to the diver which cannot be cut free with the knife. 

How can I find out more about DIR diving?

Global Underwater Explorers (GUE) provides formal training for DIR technical, cave and rebreather diving. GUE provides an intense diver training programme, with an emphasis on diver awareness, problem solving, stress management and conservation. GUE’s web-site provides detailed information about DIR diving, exploration, training and equipment configuration. Visit www.gue.com for details. 

Thanks to Bob Cooper for writing this article (Apr 2001)