Go deep, stay long

The final question everyone asks.   Unfortunately, there is no short answer to this question, and the usual response is: it all depends.  After the strange looks, I start to explain some physics and physiology, and lose most people after a few sentences.

Let’s start out by changing the question.  Why do you get out of the water?  Without getting too deep into the physics / physiology and finances, we have one of several reasons:
1)   Limited ability to withstand the temperature drain of water immersion
2)   Limits on the amount of gas we have
3)   Large fish with teeth

Normally, 1 and 2 are the major limiting factors.  When the original question is posed, it is usually referring to our gas limits, so let’s look closer at the factors affecting it.

Without getting too deep into the explanation, lets just use a couple of generalizations.
1)  The deeper you go, the less time you have.
2)   The harder you work (underwater) the less time you have.
3)   Different people consume air at different rates.
4)   The bigger you are, the less time you will have.
5)   New divers will have less time than experienced divers.

Numbers 1 and 2 are immutable facts.  Numbers 3 - 5 are generalizations that vary greatly based on the individual, their physical fitness, and level of skill and comfort in the water.

Just to throw a wrench into the works, we must also consider the size of the tank.   As discussed before, different tanks carry different amounts of gas, and can allow us to stay longer.

Let’s consider an average dive (not working hard), by an average diver at an average depth (60 ft) with the average tank (Aluminum 80).  In general this diver should have gas to dive for about an  hour.

This is a another common question along with:  How do you learn to dive?  How long does it take?

There are several Internationally recognized SCUBA training agencies.  There are some differences in the classes, but they all have a similar elements.

Classroom:  Learning ranges from books, to multimedia, to Internet training, but each contains a degree of classroom participation.  Here an instructor can answer any questions, and emphasize safety points.  Often they will stress procedures that me more common in the local diving area.  Yes, there is a test.

Pool:  The first dive experience is in “confined water”, usually a pool. Here we learn to perform certain skills in a safe, controlled environment.  Once mastered we move on to Open Water.

Open Water:   This is usually a lake or quarry.  Here we practice the skills again, and get to swim around and enjoy the dives.   The final dives may be on a boat, depending on the local diving.

I like to think of the class as covering two general areas:  First, how to plan and execute your dive, and second, how to safely handle any problems that may occur during a dive.

The Basic SCUBA class roughly takes 14 hours of classroom, 10 hours of pool, and 5 open water dives.

Once completed, it’s recommended that new divers stay shallow (less than 60 ft) until they feel comfortable with the skills they have learned.  Then they can take additional training to learn the skills necessary to go deeper.

When people first hear about SCUBA diving, many ask this question.   My standard response is “to the bottom”.   While I am joking a bit, unless you’re doing a wall dive, this is usually the case.

Part of the answer depends on the location of the dive: off the coast of New Jersey, the bottom slopes gently for the first 30-50 miles.   Shortly after this we hit the Continental shelf, commonly called the Canyon.   Here the depth drops sharply to several thousand feet.   Obviously our diving is on the gently sloping bottom.

About 3 miles off the beach, the depth averages about 60ft.  After 20-30 miles, there are some great wrecks in 130 ft.   The bottom slope does vary from place to place.   There is narrow trough cut by the Hudson river commonly called the Mud Hole.  It is deeper than the surrounding area, but the outflow of the river makes the conditions more challenging.

The rest of the answer depends on the diver’s experience and training:

Novice divers should stay shallower than 60ft, until they develop the skills and comfort in the water necessary to go deeper.

Advanced divers go between 60 and 130 ft.  At this point they carry additional safety equipment necessary to perform these dives.

Technical divers go beyond the 130 ft range down, sometimes in excess of 300 ft. These divers have spent years training and practicing for these dives.  They carry redundant gear and practice techniques to survive equipment failures.   Many famous shipwrecks are in this range: the Andrea Doria, the U-869, the Black Sunday wrecks including the S.S. Carolina.  These all fall in this range of technical dives.

How deep do I personally go?  Well, I teach Technical Divers.  While I enjoy spearfishing and photography in the 50-130 range, we can often be found diving in the 180-250 range.

Many people see my dive gear, and ask “What newfangled contraptions is that”? Ok, maybe they don’t use the word “newfangled”, but you get the point. I dive a Closed Circuit Rebreather (aka CCR). While people think of these as “new”, they actually predate the gear we consider standard SCUBA (also called Open Circuit or OC).

History: Early rebreathers were used not for diving, but for escape. Mines and Submarines both presented situations where a compact breathing device was needed to allow crews to escape to safety. Theses were developed back in the early 1900, and produced in quantity by 1910. Open Circuit SCUBA was not commercially available until the mid 1940s.

How do they work: Let’s start with a quick review of metabolism. Our cells take in food and Oxygen (O2). These are combined to produce energy, but have a toxic byproduct of Carbon Dioxide (CO2). Our Cardiopulmonary system takes some of the O2 from the air we breath, and distributes it to our cells. At the same time it takes the CO2 generated by our cells, and releases it into the air that we exhale. The O2 and CO2 exchanged by our lungs is actually a small percentage of the volume of gas that we breath (about 3%-5%).

On Open Circuit, when a diver inhales, the regulator provides the diver with gas (usually air) at same pressure as the surrounding water. When we exhale, the gas is vented out into the water producing the column of bubbles associated with diving.

When a CCR diver exhales, the gas is vented into a flexible chamber called a counter lung. Within the Rebreather, O2 is added back into the gas, and it is passed through a “scrubber” which removes the CO2. We then inhale the same gas which again contains the proper O2 percentage.

With OC 95% of the gas we exhale has not been affected by our respiration. It is not used. It is wasted. On CCR, this 95% is recycled, cleaned of CO2, enriched with O2, and breathed again. This allows us to make use of smaller tanks, as our O2 consumption does not change with depth.