What is Tec Diving and Why Should You Care?

What is Tec Diving and Why Should I Care? (Continued)
by Jerry Otte

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Contents
What technical diving is and is not
Why you should care
Technical Diving Equipment
Being a Smart Diver and a Smart Consumer
Technical Dive Training
PADI/DSAT Technical Diving Course Prerequisites

Technical Diving Equipment

Technical diving makes use of very different equipment than recreational scuba. In many ways, it is the equipment in technical diving that sets it apart from recreational diving. Unlike recreational scuba, technical diving equipment is based on redundancy. Redundancy means that should a piece of equipment fail, there is a backup that the diver can switch to in order to complete the dive.

In recreational scuba, if our tank or regulator fails, we depend on our buddy to bring us to the surface. Because we always have direct access to the surface and are not required to make decompression stops, an emergency ascent directly to the surface should always be possible. Not so in technical diving. In technical diving, required stops and overhead compartments may prevent the diver from ascending directly to the surface for minutes or even hours. Therefore, technical divers need to be able to switch to backup equipment in order to safely complete a dive following an equipment failure.

Keeping in mind the principle of redundancy, here is a list of the equipment typically found in the technical diving kit:

Technical Diving Kit

High capacity cylinder with H or Y valve or doubles with manifold and isolator valve
Two regulators, one with a 7 foot hose
Harness
Redundant inflation (either dry suit or additional backup inflator and bladder on wings)
Stage or decompression cylinder and regulator
Multigas dive computer
Backup timer and depth gauge (ideally a backup multigas computer)
Wreck reel
Lift bag

Cylinders

The primary gas a technical diver uses is called back gas. As the name suggests, this is the gas carried in the cylinder or cylinders on the diver’s back Because of the extended bottom times, technical diving usually involves bringing significantly more breathing gas on a dive. To do this technical divers use single high capacity cylinders with H or Y valves or double cylinders with a manifold and isolator valve.

The preference in technical diving is always doubles with a manifold and isolator valve. The reason for this is that even a blown burst disk or O-ring in the cylinder neck can be overcome with this system. The diver simply shuts down the isolator valve and switches to the regulator on the post that is still functioning properly. Only a portion of the gas is lost, and if the diver has calculated his air consumption properly and used the rule of thirds, there should be sufficient gas to abort the dive and surface safely.

Regulators

Following the principle of redundancy, technical divers always have two regulators attached to their primary cylinder(s). One regulator is used as the primary and the other is used as both a backup and alternate air source. In the typical configuration, the primary regulator has a 7 foot hose that loops down around the diver’s wreck reel and then around the diver’s neck. When sharing air, the diver passes this regulator to the out-of-air diver and shifts to the backup. The seven foot hose makes it easier for the out-of-air diver to swim behind when exiting a cave or wreck. The primary regulator also has a low pressure inflator hose that attaches to the primary inflator.

The backup regulator is on a short hose and attaches to a necklace around the diver’s neck. In an emergency, the diver can easily replace the primary with the backup. The SPG is also typically attached to the backup regulator, as is the backup inflator hose. If the diver is using a dry suit, the backup inflator hose attaches to the dry suit. If the diver is using a wetsuit, the inflator attaches to the backup inflator and bladder.

Harness and Wings

Instead of the recreational BCD, technical divers use a harness and wings system that allows for more flexible configuration of the kit. The harness is either a steel or aluminum back plate with appropriate webbing or a soft pack like the Dive Rite Transpac®. In either case, the harness consists of adjustable shoulder straps and waist strap and metal D-rings that equipment like stage tanks can be attached to. In addition, there are holes or grommets in the back plate or pack that are used to bolt the harness to the cylinders. Some harnesses can be configured for use with a single tank; others cannot.

Wings consist of the inflator and bladder used for buoyancy control under water and/or supporting the diver on the surface. Depending on the number of cylinders being used on the dive, the technical diver selects a set of wings with the appropriate amount of lift to support the equipment. Some wings provide more than 80 pounds of lift. In addition, some wings come with a backup inflator and bladder. If the technical diver does not intend to use a dry suit, the backup inflator and bladder are considered necessary.

Stage Bottle

Stage or Decompression Cylinders

Stage or decompression cylinders (sometimes called “sling” tanks) can range in size. Typically a 30 cubic foot to 80 cubic foot aluminum cylinder is selected as a stage or decompression bottle. These cylinders are normally configured with clips that allow them to be attached to the D-rings on the diver’s harness.

Stage or decompression bottles have three primary purposes in technical diving. First, they can contain enriched air to accelerate decompression. By removing some of the nitrogen from the diver’s breathing mix, decompression stop times can be reduced significantly. This reduces the amount of gas required for the dive and reduces the risk of hypothermia. Unfortunately, performing gas switches on a technical dive is one of the most dangerous aspects to technical diving. If a technical diver switches to the wrong gas at depth, he could convulse and drown.

The second reason for using stage or decompression cylinders is to increase the gas supply. On very deep or very long technical dives, it may not be possible to carry enough gas for the entire dive on the diver’s back alone. By carrying one or more additional cylinders, technical divers can dramatically increase their time at depth and reduce the risk of running low or out of air.

The final reason for using a stage or decompression cylinder occurs in specialized trimix dives. Trimix is a gas mixture of nitrogen, oxygen, and helium used to reduce nitrogen narcosis on very deep dives. Trimix blends are divided into two categories by technical divers: normoxic blends and hypoxic blends. A normoxic blend is any combination of nitrogen, oxygen, and helium with 21 percent oxygen. This is the normal percentage of oxygen in air.

A hypoxic blend, however, is a combination of nitrogen, oxygen, and helium where the oxygen percentage is something less than 21 percent. When diving below 185 feet, the partial pressure of oxygen begins to rise to potentially toxic levels. As a result, dives below 185 feet require that the percentage of oxygen in the diver’s back gas be reduced. In cases where the oxygen percentage is too low to be breathed at the surface without the risk of losing consciousness, the technical diver must use a travel gas. The travel gas is a cylinder (usually a decompression mix) that the diver uses to “travel” to the depth at which the back gas is safe to breathe.

Dive Computers

In recreational diving, dive computers are helpful tools used to extend bottom times and simplify dive planning. In technical diving, dive computers are required. A good multigas computer allows the technical diver to make all necessary stops based on the exact dive profile he has dived. A multigas computer allows the diver to switch gases and still continue to track nitrogen absorption and oxygen exposure.

Although written tables generated using a PC are always used in planning a technical dive and calculating gas requirements, they are only used for backup on the dive. Technical divers follow

Multigas Computer

their dive computer and either back up the computer with another computer or a timer, depth gauge and the tables generated by the PC dive planning software.

Wreck Reel and Lift Bag

Like recreational divers, technical divers carry wreck reels for penetrating wrecks and caves. But they also carry a wreck reel (along with a lift bag) for redundancy. In the event that a technical diver cannot relocate a descent line and must make an ascent without a line, the technical diver attaches a lift bag to the wreck reel and inflates the bag. Once the bag is at the surface, the technical diver then follows the line up, using it for reference at each decompression stop.

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