Scuba police

[theduckguru]

I would be interested in knowing if the same resorts that forbid diving when you are going to fly in less than 24 hours also don't sell alcohol to divers for the same reasoning.

 

[InTheDrink]

It's relatively simple no? Guided diving has become a commercial operation and in the vast majority of cases they will want the following:

1. Maximum money for least time/effort spent
2. Minimised exposure to being sued
3. Minimised risk to equipment (e.g. charging for bottles on less than 30 bar)

Poor basic training standards actually add validity to this stance. Standards appear to have slipped so much that many divers are not safe to be left alone underwater. Sad but true. But that would explain many of the added safety margins. However clearly many are not based on logic nor guidelines - I remember too on two occasions not being allowed to dive after arriving to my location on the grounds that you shouldn't dive 24 hours before or after flying. However, we have created a situation in recreational diving where reason/sense and safety don't appear to be closely related.

J

 

[fisheater]

No diving AFTER flying? Not seeing the logic in that one.

 

[captain]

The University of Rhode Island performs numerous scuba-related studies. One of their studies performed back in the 1970s was done to see if water could enter a scuba cylinder. The took scuba gear down to 10 feet in a swimming pool and breathed the tanks down to zero. Then the depressed the purge button on the 2nd stage regulator 10 times. Later, when they took off the valve, they found cylinder was flooded with pool water.

Cichy, Francis, Hilbert Schenk, and John J. McAniff. Corrosion of Steel and Aluminum Scuba Tanks, University of Rhode Island Technical Report 62, 1978.

Frankly I am sceptical and could not access the report, but in any event who breathes their tank empty then presses the purge button 10 times.

 

[InTheDrink]

No diving AFTER flying? Not seeing the logic in that one.

That's the point - zero logic applied. But in the melange of mish mash quasi regulations who knows where logic starts and stops.

J

 

[redacted]

Frankly I am sceptical and could not access the report, but in any event who breathes their tank empty then presses the purge button 10 times.

You would also have to raise the 2nd stage and get gravity to help move the water to the 1st stage and tank. It would take some work beyond simply emptying and purging to move water into the tank. Probably easier (or more fun) to install a blown tank neck o-ring, add a little water and demand a full refund from the shop.

 

[Doc Harry]

Frankly I am sceptical and could not access the report, but in any event who breathes their tank empty then presses the purge button 10 times.

No one does that. But if a cylinder is nearly drained at depth and someone presses the purge button in an attempt to clear the reg, then water can enter the cylinder. Ask any dive shop, it does happen.

But you've got to place that old University of Rhode Island study in the larger context.

You have remember that back in the 1960s and 1970s, no one was inspecting scuba cylinders. No one even really knew much about cylinder corrosion. Then the U.S. Navy discovered widespread severe cylinder corrosion at a facility in Maryland in the 1960s. They consulted the Battelle Memorial Institute, who performed the first ever scientific studies of scuba cylinder corrosion and it's effects on cylinder strength. The Battelle Memorial Institute also made numerous corrective recommendations to the U.S. Navy, one of which is what we know today as the "annual visual inspection."

Following the Battelle study, numerous other scuba studies were performed in the ensuing decade, many of which were done at the University of Rhode Island. It was clear that water was entering scuba cylinders, but no one knew how. The study that I quoted above was done to see if water could, in fact, get through the second and first stage regulators and into the cylinder. (Remember, too, people were using J-valves back then I am sure a lot of people got pretty low on air.) A lot of people argued that water could not get through the second and first stages into the cylinder, and the corrosion was occuring for other reasons.

In Myth Buster fashion, the 1978 University of Rhode Island study demonstrated that water can get into the cylinder through the second and first stages.

You would also have to raise the 2nd stage and get gravity to help move the water to the 1st stage and tank. It would take some work beyond simply emptying and purging to move water into the tank. Probably easier (or more fun) to install a blown tank neck o-ring, add a little water and demand a full refund from the shop.

Gravity has nothing to do with it. It's pure hydrostatic force.

 

[velovp]

A perspective from a relatively new diver, but also from one who is familiar with teaching a sport with challenging technical aspects accompanied by risks (that being a flight instructor).
I think that recreational diving is a growing and evolving sport. Many of those who have responded to the blog spot are clearly long time and experienced divers that are accustomed to the relaxed, self reliant and regulating aspects of the sport. Times change. I think that InTheDrink has it correct in his statement, “Poor basic training standards actually add validity to this stance. Standards appear to have slipped so much that many divers are not safe to be left alone underwater. Sad but true. But that would explain many of the added safety margins”.
Those who are well trained and experienced might view the actions of some dive resorts and instructors to “protect us from ourselves” as an intrusion, however I cannot help but think that such policies have been brought on (for the most part) to deal with those who are OW certified (on paper), but who are wholly unqualified to make safe, independent judgments because of (fill in the blank): lack of experience; forgotten training; inadequate basic training; getting over a drunken stupor; arrogance; or just plain ignorance and stupidity. Many (perhaps more than what we might expect) fall into one category or another.
As a new diver I respect when a dive master tactfully ask questions about my experience and qualifications in order to plan their dive support to ensure a safe dive. In fairness, I have yet to encounter rigid “Scuba Police” type rules – but then, I have realistic expectations of what and what not to expect. I enter every dive situation looking for insight and guidance from dive masters who have “been there, done that” and who are sincerely looking after my safety.
My 2-cents.
Velovp

 

[redacted]

No one does that. But if a cylinder is nearly drained at depth and someone presses the purge button in an attempt to clear the reg, then water can enter the cylinder. Ask any dive shop, it does happen.

But you've got to place that old University of Rhode Island study in the larger context.

You have remember that back in the 1960s and 1970s, no one was inspecting scuba cylinders. No one even really knew much about cylinder corrosion. Then the U.S. Navy discovered widespread severe cylinder corrosion at a facility in Maryland in the 1960s. They consulted the Battelle Memorial Institute, who performed the first ever scientific studies of scuba cylinder corrosion and it's effects on cylinder strength. The Battelle Memorial Institute also made numerous corrective recommendations to the U.S. Navy, one of which is what we know today as the "annual visual inspection."

Following the Battelle study, numerous other scuba studies were performed in the ensuing decade, many of which were done at the University of Rhode Island. It was clear that water was entering scuba cylinders, but no one knew how. The study that I quoted above was done to see if water could, in fact, get through the second and first stage regulators and into the cylinder. (Remember, too, people were using J-valves back then I am sure a lot of people got pretty low on air.) A lot of people argued that water could not get through the second and first stages into the cylinder, and the corrosion was occuring for other reasons.

In Myth Buster fashion, the 1978 University of Rhode Island study demonstrated that water can get into the cylinder through the second and first stages.


Gravity has nothing to do with it. It's pure hydrostatic force.

I do understand hydrostatic force. But am interested in your explanation of how that would move water up a hose if the pressure in the tank is the same as ambient pressure.

 

[Doc Harry]

I do understand hydrostatic force. But am interested in your explanation of how that would move water up a hose if the pressure in the tank is the same as ambient pressure.

Simple. It's not.

Ambient water pressure must exceed internal cylinder pressure for water to flow into the tank.

The only way to get ambient pressure to equal cylinder pressure is to either remove the valve or hold the purge button long enough for equalization to occur.