Technically Speaking

By Bill Nadeau

It may come as a surprise to many divers that perhaps one of the greatest talents a technical diver can possess is managerial skills. As the complexity of a dive increases, so do its risks. Good sport and technical divers need to manage and reduce that risk by adjusting their dive plan accordingly. This involves managing the different aspects that encompass the successful execution of a dive. A good manager (diver) must understand what these different aspects are and what kind of approach they have to take to manage their dive. The final step involves putting it all together in a sequential checklist that helps us develop our dive plan.

We begin by determining our Dive Objectives . This part includes the where, who and why part of the dive. First you must determine where it is you are going to dive, with whom and why. The "where" part of a dive includes how deep and how long, as they represent some serious factors in pre-dive planning. They may also determine geographically where you need to go as well as who is going to go with you and why you even want to go in the first place. Once a site is selected you must determine if the site suits your abilities AND your buddy's. Never pressure another diver into making a dive at a site he is not comfortable with"trust-me" dives kill divers.

Next you need to Plan the Fundamentals by using good old Dalton and his law of partial pressures. On every dive we must calculate the best gas for the planned depth based on our personal physiological limits. Dalton's Law is the primary tool we use to begin managing our dive planning process. It is very important because it begins the "how" part of our dive plan. Planning the fundamentals starts by determining what your personal PO 2 limits areand that can only be done by you and no one else. From your training you learned that PO2 limits should be adjusted according to your personal level of physical fitness, age, present disposition, diving activity and the environment you are diving in. The same questions must also be applied to deco and travel gases as well. When diving rebreathers, depending on the make and application, divers need to consider a third dimension to Dalton's Law as their FO2s (not just what is in the supply cylinder but what FO 2 is inspired) are not necessarily fixed. In advanced dive practices, divers will adjust the maximum acceptable limits during various points in the dive to meet their particular needs.

Once the bottom gases and deco mixes have been selected a diver needs to determine how much bottom time is required to meet his objective and what method he will use to Determine the Decompression Profile (be it dive tables or decompression software). Just choosing the right table or program can take time and some serious research. This is what is referred to as managing your residual nitrogen and its on/off gassing rates into/out of your tissues.

A diver must consider how much oxygen is being consumed as oxygen is less forgiving than nitrogen when its levels exceed the recommended dosage. This is what is referred to as Managing the Oxygen and includes checking incidental exposures of PO2 levels over 1.6ATA as well as prolonged exposures to PO 2s exceeding 1.3ATA. For many, it may appear logical that the more oxygen and less nitrogen we use in a dive (assuming we stay within safe acceptable parameters), the less deco time will be required. This is not always the case. The example in the illustration shows that it was actually better to have a lower FO 2 (EAN75) in our deco gas allowing us to begin our decompression earlier and starting our off-gassing quicker. In this instance we reduced our decompression time by a minute, our clock by 1% and our Maximum PO 2 exposure to 1.48ATA. Also, in the event of an extreme bailout scenario this diver could breathe his deco gas deeper than a diver using 100%.

A quick review of the dive plan so far will reveal whether our plan is within our limits. A diver must continually evaluate through a dive plan and ascertain whether the dive plan exceeds the capabilities of any of the team members before carrying on with other aspects of management. If it does, then we must go back and adjust the dive plan accordingly.

Only after the decompression profile and mixes have been chosen may the diver begin to calculate how much gas he/she will need. This is what is referred to as Managing Your Gas Supply. Tallying the volume of gas you will need to complete a dive safely involves applying your respiratory rate to your depth, dive time and factoring in all of the contingencies.

In the next edition of Technically Speaking I will discuss some of the different approaches we can take to determine what our gas consumption rate is and choosing a Gas Management Rule that best suits a dive plan. I will also complete the discussion of dive management by reviewing other aspects including equipment, contingencies and the environment. Until then consider what dive management means to you by reflecting on what responsibilities a manager actually holds.