Archive for the ‘Tech / Advanced’ Category

How deep can you dive on SCUBA?

Wednesday, January 14th, 2009

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.

What is a Rebreather?

Tuesday, January 13th, 2009

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.