A disturbing PADI rumor

[SubMariner]

You'r wrong. I am an SSI instructor, and I have no knowledge of such things (and I am in costant conection with HQ).

As another poster pointed out, it was SDI, not SSI that has switched from tables to PCs.

Finger must have slipped while I was typing.

Apologies for any confusion.

~SubMariner~

 

[JustAddWater]

Talk about collateral damage. A few times, and not just on this board, I've heard mistaken references to SSI when the intentions were toward SDI. Regarding the rumor, I haven't heard of it outside of this thread.

 

[MikeS]

DD,

Hopefully you will not take this as a personal attack and it is not meant to be rude or disrespectful, but… This is a great example of an illogical argument against dive computers.

You say that “Batteries in Computers can go dead” and this is certainly true. But is this not an example of the lack of correct maintenance? I have only played with four different models of computers but all of them have a battery indicator that gives you an early warning before the battery goes dead. Additionally I think that every diver using a computer should have a spare battery in his or her save-a-dive kit, I certainly do.

The moral of the story is not computers are bad because the batteries go dead, but rather, lack of proper maintenance and poor planning can result in difficulties. And from what you say no one was placed in danger as a result.

If the same computer/battery logic you mention were applied to tanks/air you would only use surface supplied air. If indeed a diver does not properly maintain his or her tanks, by refilling them with air, and then chooses to ignore the pressure reading, he will run out of air. The same concept is applicable to boat motor/fuel, boat motor/oil, camera/film, valves/O-rings, etc., etc.

Just my thoughts, any and all opposing thoughts are welcome.

Mike

 

[padiscubapro]

Originally posted by Walter
Cindy,

SSI teaches tables. SDI does not.

padiscubapro,

"Padi did back off the limits on compared to the Navy tables"

No, they did not. The NDL's were arrived at independently. As a result most are less than the US Navy NDL's, but the NDL for 130 ft is identical. Tables which were backed off are less than the US Navy NDL's at all depths. DCIEM also arrived at their limits independently, but their NDL's are all less than the US Navy's and less than the RDP for all depths except 40 ft.

"eliminted one of the very long tissue groups from their calculations (whick really only comes into play on very long shallow dives)"

They eliminated all compartments (tissue group is a misnomer) with half times over 60 minutes. You are incorrect about the longer compartments only coming into play on long shallow dives. The longer compartments' are obvious on long shallow dives, but they also play an important role in repetitive dives.

"Shorter surface intervals don't always decrease safety"

Face it, no tables are safe. You can get bent following any table. Some are safer than others. If you plan the same two dives with a short surface interval or a long surface interval you will have less of a chance of getting DCS with the longer surface interval. A shorter surface interval is less safe.

"The recreational dive planner also gives padi's program a safety standard they can defend"

They can defend the standard, possibly even successfully. It would be easier to successfully defend if the plantif didn't have a readily available table that was more conservative for the jury to compare with the RDP.

"Law suits in the US are just to easy to file."

I certainly agree with that.

I should have chosen my words more carefully..

From what I have seen most of the newer tables used the Navy ables as a starting point (no reason starting with longer limits where people were know to have taken hits), they just didn't lower the numbers.. All of dsats compartments have different max mvalues than NAVY and other haldaneon models.. If I remember correctly DSAT used dopler measurements on the divers.. to help determine mvalues for their tables. Each of the table desuigners used different criteria, DCIEM tables do have shorter limits but they also were designed to allow decompression diving, where the RDP does not.. ANy model that is designed to work with deco diving will have much shorter NDL limits... look at most haldane models the 100ft limit is somewhere between 16 and 18 minutes where RDP allows 20.... A side not one can not just look at the raw numbers it important to take into account the definition each table uses as bottom time and when it starts and ends..
A perfect example is the Tables ANDI uses they say the no stop time for 100 ft is 23 minutes, you might say wow thats an extra 3 minutes , but wait, ANDI's defination of BT is: BT starts after decending past 5ft and ends when the diver reaches the first pause at 30 ft.. so ANDI takes into account almost 3 minutes for ascent.. I don't feel like getting into the who ANDI decent/ascent procedures..

The long half time compartments (I used the word tissues because most people are familiar with that term) really don't get loaded to saturation Remember it takes about 6 half times to saturate/desaturate compartments.. so a 2 hour compartment would take 12 hours to saturate (obviously the first 4 hours of ding would do the most tissue loading), surely that would be extremely difficult to accomplish on OC scuba even if you were able to get enough gas other factors would get you first cold, dehydration ect..

Most divers would be hard pressed to log 5 hours a day on scuba, even on a live aboard thats about the most you can get.. When Im on my CCR the best I can usually do is about 6 hours dive time, and that includes at least 1 very long dive..


MY comment about shorter surface intervals has to be taken in context, if I am doing repetive deco dives with some type of gradient factor tied in, by the time I surface I'm well below the critical limits.. I'm definately using a High o2 mix so my slow tissues aren't getting loaded and the loaded tissues are rapidly offgassing..

If you don't want to take the risk of getting bent go play golf..(not a personal attack on you) Decompression is hardly an exact science more like educated "I think this works". Statistically tables have very low accident rates but the risk can never be zero.

 

[CheeseWhiz]

I'm referring to things like "never re-enter the water if DCI is suspected". I take that as an opinion statement against in-water recompression. Not that in-water recompression is something that should be taught, but in certain circumstances it could be the difference between life and death and "Never" is a dangerous word.

In my opinion, it's more than an opinion. Basic treatment in a recompression chamber starts with the patient in for 6 hours (if memory serves) and involves a gradual pressure reduction, a treatment which is frequently accompanied by IV fluids, oxygen therapy and drug therapy. This is mighty tough to do at 20 feet with an aluminum 80 on your back. Not to mention keeping your body temperature up in the normal range for that length of time.

Skip the in-water treatment and head straight for the nearest chamber. You'll be much better off for it. In my opinion.

 

[scuba_adventurer]

PADI has 2 versions of the Recreational Dive Planner, the traditional table version, and the way the RDP was meant to be, the Wheel.

Why put instructions for both in the manual when the crewpack only comes with one or the other? If you buy a table, it comes with the instructions for it's use. If you buy the Wheel, it comes with instructions for its use. The ability to throw the instructions in the logbook is also a secondary benefit.

 

[otter-cat]

To those who would argue that computers are an "inevitable" progression, and that resistance to their complete substitution for tables is merely a knee-jerk reactionary opinion, I have a few thoughts that may be relevant. The speedometer/RPM gear analogy used hit home for me today because although I use a speedometer in all my vehicles, I ALSO use my tachometer, and pay attention to what gear I'm in. Their functions overlap somewhat, but are not the same. Having both allows me to monitor and control what my engine and vehicle are doing far better than either alone would. This afternoon while I was riding my motorcycle, my speedometer unexpectedly failed (despite proper maintenance & inspections.) I was glad I still had a working tachometer by which I could estimate my speed.

Working tables in training and in diving also helps people learn and retain a better idea of NDLs and appropriate bottom times. If they never use a table, it is easy to only look at the color of their graph, and would have no idea if their computer was malfunctioning and giving them way too much bottom time before NDL.

Taking care of your computer is important, as is regularly replacing the battery, BUT, there is always the possibility of the unexpected (defective battery, computer hits a rock and cracks & floods, defective computer's low-battery warning malfuctions, poor servicing technician, etc. etc.) A table, though not a guarantee against DCI (nothing is) will not malfunction. If you have it, and know how to use it, you can use it, no matter what happens to your computer.

Understanding tables involves some (albeit minimal) understanding of nitrogen loading and DCS. Using a computer does not necessitate this. Tables are an excellent learning tool, and a fantastic backup to your computer. Like a computer, they can be misunderstood, or misused, but tables should be here to stay. Most other safety critical technologies that rely on computers also have manual shut-offs or backups in case of computer malfunction. The table will do the same, and should always be looked at as a reference to compare to your computer. Using a computer is fine in most instances, but the tables are integral to being able to safely use your computer.

These are my thoughts anyway. I welcome any posts with alternate views.

otter-cat

 

[Scuba446]

Hmm, could we be talking about the same place that had these courses? hmmm....

 

[Drew Sailbum]

Originally posted by MikeS
For whatever reason there appears to be a totally illogical resistance to computers by people that learned and relied on the tables. I have not heard a single well stated logical argument against using computers. The typically story is “my cousin knew a guy who’s friend heard about someone who’s computer failed.”

Batteries going dead are certainly a real problem, but I have recently seen two divers with computer problems that would prove more troubling.

One diver had his computer get "stuck" in dive mode. The computer failed to recognize that his dive had ended, and it would not provide data for a repetitive dive. Had to ship the computer back to the factory, and continue diving using tables.

The other diver had a computer fail but contunue providing obviously incorrect data. It was obvious only because the calculated no-deco times were massively different from table values. (Computer listed 1 hour 24 minutes no deco time at 100ft) A diver not trained in table use might fail to recognize such a computer failure and take unsafe actions based upon the faulty data.

For now, I prefer that computer users have an understanding of tables and how a dive computer calculates data.

 

[MikeS]

Jeff,

I apologies for side tracking your thread, but I think this is an important issue.

Otter-cat

I disagree that using a table necessarily involves any understanding of nitrogen loading. I could teach any math capable person to use the table without any knowledge of what they are using it for. Tables and computers are both simply tools. After downloading the data from my computer I can see the theoretical nitrogen loading throughout the dive. In fact it even shows the level of tissue saturation for various types of tissue, fast saturating versus slow saturating. I can see what the effect of my safety stop on the different types of tissue. I’m not going to get that from any tables I’ve seen. What if the same amount of time spent in training on tables were spent on how to properly use a computer?

Drew

The problems you describe can happen to a SPG, depth meter, or bottom timer also, what’s the difference? In most of the books I’ve read, the Cave Divers is the latest; they are filled with examples of equipment failures such as SPGs (none of which were computers by the way).

It seems to me, whether using a computer or tables, SPG, depth meter, bottom timer combination there are some simple rules you should follow to stay out of trouble.

1. Your buddy’s equipment is your backup, follow the more conservative.
2. If you have an equipment failure, surface safely using your buddy’s equipment and end the dive.
3. If you dive in a situation where you can’t end the dive quickly you should carry redundant equipment.

In both cases you mentioned following these simple rules would have kept the divers you mention out of trouble.

Everybody,

Thanks for the dialog.

Mike