Dive Table Question

[olstykke]

Hey guys, thanks for the encouragement.

But to the science...

And I do agree... daily living is problably more dangerous. Driving. mowing the lawn.



What are the differences in the dive algorythms?

And what is suunto rfering too with cumulative nitrogen loading? The way i was understanding it, they weren't just refering to Repitiive Diving...

But lifetime nitrogen loading causing ill effects on the soft tissues.



And for decon diving. How does one get into it? I'm not planning to do it, but maybe you all have some resources I might investigate into this question.



This topic may need to be reposted in another forum I'm not aware of.

 

[Diver0001]

But is diving safe.

It depends on what you compare it to. Relatively speaking, fewer people drown scuba diving than swmming, for example.....but swimming doesn't have the image of being risky.

Risk is also about (a) the chance of something happening and (b) the consequences if it does occur. In terms of comparison, the *chance* of an accident are very small, smaller than virtually every other sporting activity. However, the consequences should an accident occur can be more severe.

IN terms of the typical types of accidents you can probably classify them in

- barotrauma to the ears and lungs
- marine life injuries
- physical injuries due to things like slipping and falling or dropping a weight on your foot or getting hit by a boat
- drowning
- DCS
- Hypothermia
- Accidents resulting from existing medical conditions like heart attacks etc.

I probably missed a couple. In terms of risk management you have a couple of relevant techniques

- risk reduction
- risk avoidance
- risk acceptance

If you train well and work on your skills then you are working on risk reduction and you can ruduce the risk very significantly like that. If you never pratice your AAS drills, for example, then you are engaged in risk acceptance. If you never touch the marine life then you are engaged in risk avoidance. Another type of risk reduction and avoidance is to never go over the NDL's or never go out of your comfort zone. Get the picture?

You'll notice a lot of discussion about accidents and risks on these internet forums but if you look behind the stories what you'll see is a lot of good information being passed back and forth over risk reduction. Maybe that will help you interpret what you're seeing a bit better.

It may be better if someone can give some comparisions of risk. For instance, is diving riskier behavior than driving?

Statisically speaking your risk of injury on dive day is much higher driving to and from the dive site than it is while you're under water.

What are the chances of one suffering a DCI?

If you follow the proper dive planning and ascent procedures then your chances of getting a DCS are very small. I dont remember the number out of my head but even divers who habitually push the limits or engage in decompression diving have small rates of DCS. It's like 1 in 10,000 IIRC. Further if you apply "risk reduction" I just mentioned to your DCS risk you'll realise that there are many measures you can take to reduce your chances of gettting a DCS very significantly.

It would be good for you to post a question on the Dr. Deco forum about how to reduce your DCS risk and you'll get a lot of useful information. Maybe even some things you weren't taught or never thought about.

R..

 

[trevinkorea]

I think there is no need to fear injuries from diving provided you and you buddy are mentally, physically and emotionally prepared to dive, have planned the dive, have all required equipment in good condition and dive within your training, recreational limits and comfort zone.

Regarding your question about safety, I just looked in the PADI rescue manual and there are some stats. (This is most likely biased in favaour of diving but seems reasonable.)

A survey of 10,000 perticipants prepared by the U.S. Natiohnal Safety Council Accident Facts.

American football - 2.17%
BAseball - 2.09%
Basketball - 1.86%
Soccer - .91%
Volleyball - .37%
waterskiing - .20%
Raquetball - .17%
Tennis - .12%
Swimming - .09%
Bowling - .04%
Scuba - .04%

I believe running would be very high on this list as well.

To give you a personal example.

In ten years of diving I have only suffered two minor pressure related complications and in my first month of driving in SE Asia I had three accidents one which whiped off the entire side of my car. And, as a university instructor I have suffered more injuries in the past year than in ten years of diving.

Diving like driving requires that people take steps to reduce risk. When we drive we maintain our cars, wear seatbelts and receive training. Diving is the same take care of your gear, take along the necessary safety equipment and stick to your training.

In short diving is a very safe sport as long as you do it reasonably.

Regarding the expereince with the computer manuals. I think it is a liability thing. IF they don't tell you in point blank terms about the dangers regardless of how insignificant the probability of occurence, they are leaving the company open to being sued.

Regarding the instructor. Some instructors overstate the dangers to make a point. They want to make sure thier students understand the dangers (liability) and don't take unnecessary risks (safety). Some instructors also do this to discourage people who are not really ready to dive. I sometimes use this technique if my classes are very large. For the first week I try to scare some of the students off to get rid of the ones who just want an easy grade. It's not always the best technique but, sometimes there are people who simply should not be taking a class. It's always a good idea to try and think like your instructor and seperate the true content from the performance. Teaching is like acting. It is not so much the content as the delivery. The instructor in question may have been over stressing the dangers as an attention grabber.

After my Open Water I was terrified to even swim in the ocean becuase of all the "dangers". I think a good scuba instructor should be able to introduce the risks without terrifying the studnets. Perhaps is you are overly worried you may want to consider taking a course from another instructor who can teach you how to mitigate the risks as opposed to simply trying to scare you.

 

[Diver0001]

....snip....

One of my instructors at the shop said "It's not a question as to if you'll have a DCI, but when"

As an aside to this post, if this comment was meant to be taken at face value then I would personally give this instructor a wide berth and look for someone more willing to address reducing the risks with proper training.

A risk of DCI isn't something you just accept and suggesting to a new diver that this is normal is unmitigated nonsense, IMO and I would have serious reservations about the quality of instruction I was getting from someone who feels they need to say these kinds of things.

R..

 

[Diver0001]

And for decon diving. How does one get into it?

Once you have enough experience it is just a matter of finding a *good* instructor and taking a course.

The name of the transitional course varies from agency to agency but most of them call it something like "advanced nitrox and deco procedures" or something along that line.

You can look on the website from IANTD for a typical example.

R..

 

[Dive-aholic]

...What are the differences in the dive algorythms?

And what is suunto rfering too with cumulative nitrogen loading? The way i was understanding it, they weren't just refering to Repitiive Diving...

But lifetime nitrogen loading causing ill effects on the soft tissues.

Suunto uses a very conservative algorithm, possibly the most conservative on the market. Does it need to be that conservative? No. On a recent dive trip a friend was diving with the Suunto Cobra and I was diving with a Sherwood Wisdom. We had pretty similar profiles (actually I think his was more conservative). What I mean by that is our dive times were almost identical and our depths were pretty close. I tended to stay a little deeper most of the time and for longer periods of time. By the 3rd dive of the day, the Cobra had locked him out. The Sherwood said I could still dive. Neither of us was bent.

It may just be a marketing gimick or Suunto may have something there, but I haven't seen numbers showing that the extra conservativism is necessary.

Oh, and I did check the wheel and we were still okay.

I'm not knocking Suunto. They make good computers. I was even considering a Vytec before this last trip. I just thinks it's a little too conservative and would rather dive the wheel than have it tell me I've gone past my limits when I haven't.

And for decon diving. How does one get into it? I'm not planning to do it, but maybe you all have some resources I might investigate into this question...

Enroll in a course. There are lots of them out there offered by different agencies - DSAT, IANTD, TDI, etc.

You can also browse the tec forum.

 

[MikeFerrara]

Living is dangerous and is, in fact, always fatal.

Other than that...diving can be real dangerous if you aren't any good at it or if you think that you're better than you are. At least though you have some control unlike being on the highway with all the nuts.

On the subject of DCI...study decompression theory and apply what you learn along with a little common sense.

Oh...and disregard those stats that compare the injury rate of diving to activities like bowling. Only an idiot would make such a comparison given the drastic difference in the types of injuries possible. I read about MANY more scuba deaths than bowling deaths. In fact I've never heard of a bowling death. I have seen diving accidents and near misses but I've never witnessed a bowling accident. Well...maybe I've seen one or two folks fall on their faces after too many trips to the bar...does that count?

Statistics is useless unless the right question is asked and the data gathered and manipulated to answer that question. The question that was asked in gathering the scuba vs bowling numbers was "How can we prove to the consumer that diving is as safe as anything else they can do and get them to spent their descretionary funds with us?" ishonest people then use those numbers to asnswer your quations about how safe diving is for you and your family. A very different question and even if your 10 year old might slip and pull a muscle while bowling the chance of them spitting their lungs out while bowling is ZERO.

 

[DA Aquamaster]

What are the differences in the dive algorythms?

A quick and dirty history of deco...

Many tables are derivatives of Haldane's models used as the basis for the original Royal Navy and US Navy dive tables around 1910. The original model had some serious flaws but these have been largely corrected over time based on a large accumulation of operational data. The Navy has also developed new tables based on statistical rates of DCI based on the experiences of US Navy divers. The potential problem with these tables and some of the tables derived from them is that they were not really designed for repetitive multiday diving and the way they are used operationally by the US Navy differs from how sport divers would normally use them.

The University of Wisconsin developed the Huggins tables in the mid 80's based on doppler ultra sound research that indicated small asymptomatic bubble formed well within the NDL's on US Navy tables. The resulting table followed the basic USN format but with shorter no deco limits to keep divers bubble free.

Professor Albert Buehlmann developed tables beginning in the 1960's using the same basic idea but with more mathematical tissue compartments (12) including some with much longer half times. He has also developed tables for altitude diving and his ZHL-16 model is widely used in many computers. His tables are generally much more conservative than US Navy tables.

These tables have more recently been modified by by others using bubble Gradient Factors and incorporating slower ascents and deep stops which makes them more conservative. This adaptation is used in some software applications including GUE's DecoPlanner and DPlan.

The RGBM (Reduced Gradient Bubble Model) is a similar approach but using a Haldane model embedded with gradient factors and other limits on reverse profiles, and repetitive multi-day diving. RGBM is used in GAP deco planning software and recreationally adapted RGBM applications are used in several dive computers. The downside of the computer based models is that it is not very permissive on multi-day dive trips, but it is conservative. And if you read the fine print on many non RGBM dive computers, you will usually find a disclaimer indicating they are not intended for repetitive dives over multiple days. So RGBM computers are perhaps overly conservative, but they are at least designed for the average rec diver doing week long tropical dive trips.

Since about 1980 there has been research and continuing development of the Variable Permeability Model which like the GF and the RGBM approachs, produces profiles with slower ascent rates, and deep and short deco stops combined with shorter shallow stops compared to a Haldane/US Navy profile.

The basic idea behind GF, RGBM and VPM models is that off gassing occurs faster before bubbles form so that the use of shorter deeper stops is more effective in eliminating nitrogen than the "bend and treat" Haldane appproach of doing longer and shorter stops after bubble formation has occured in the tissues.

In the last 10-15 years, the use of accellerated deco as become very common. In this approach decompression gases with comparatively high percentages of oxygen (50%, 80% and 100% are common deco mixes) are used to increase the rate of inert gas elimination. The result is shorter and cleaner decompresison. Both gradient and VPM tables and software allow for this option.

Personally, I feel a lot better after doing deco on a Gradient Factor or VPM profile than I ever did on any Haldane table.

And for decon diving. How does one get into it? I'm not planning to do it, but maybe you all have some resources I might investigate into this question.

Technically oriented training agencies (TDI, IANTD, GUE, etc) offer decompression procedures courses. I think advanced nitrox and deco procedures courses are worth taking even if you never do deco diving as you will learn a lot about deco theory. Similarly, playing around with some of the deco software out there can give you a feel for how the theories work and can give you an intuitive sense of how to improve and add a safety margin to your nitorgen elimination even on recreational dives within the NDL's.