"Riding your Computer Up" vs. "Lite Deco"

[Bennno]

Do you seriously believe that a pre-dive briefing will tell you how they'll react if the crap hits the fan?

The crap did not hit the fan, the guy in the example didn't know the profile. It's also pretty standard not to do deco and deep dive with unknown people.
That's the reason dive shops do check dives and don't take people deep diving for their first dive with them.

 

[redacted]

Do you seriously believe that a pre-dive briefing will tell you how they'll react if the crap hits the fan (or if they think that the crap is hitting the fan)?

A pre-dive briefing at least insures that your insta-buddy has the opportunity to know what is on your mind. With any luck, it can become a discussion that results in mutual understanding and agreement. Doesn't prevent all problems but sure produces an opportunity to avoid some.

 

[Storker]

A pre-dive briefing at least insures that your insta-buddy has the opportunity to know what is on your mind.

Totally agree. And I make sure to have that pre-dive conversation with an instabuddy, too.

It doesn't tell you much about how the person will react if they believe that they're in over their depth, though (pun not intended)

 

[Bennno]

Doesn't prevent all problems but sure produces an opportunity to avoid some.

Yes, I agree, it doesn't prevent all problems but it really helps. It also helps when you ask people whether they have done deco before and what their deepest dive has been at that point.

People do get nervous when they hit deco for the first time or just dive deeper than they have before, that's normal.

 

[Bennno]

It doesn't tell you much about how the person will react if they believe that they're in over their depth, though (pun not intended)

You wouldn't know, but experienced divers and instructors can learn a lot from interacting with people before the dive.

Eitherway, just do a 60' dive instead of a 120' dive, when you never dove with the person, at least that gives you a change to see how they look in the water. It's safer, IMO.

 

[Edward3c]

The discussion regarding BSAC training and the BSAC 88 tables has been very interesting. It appeared to me that the BSAC table decompression times were considerably shorter than I was used to seeing, so I did a little research.

As a simple example, I looked at a single, clean dive to 100 ft (30 m/98ft) on EAN32. It is not perfectly easy to directly compare Buhlmann 100/100 to the BSAC 88 table, but the following is reasonably close. The Buhlmann NDL is 25 minutes and for BSAC it is 28 min. For a bottom time of 50 minutes, the Buhlmann deco obligation is 12 minutes @10 ft. For a dive time of up to 53 minutes, including ascent up to 6m/20 ft, the BSAC deco obligation is 6 minutes @6m/20 ft.

BSAC 88 has been used for many dives over many years and has proven safe. This is another good example of decompression algorithms with different profiles falling within the general bounds of safety. I don't think all the specific details regarding the derivation of the BSAC tables have ever been available, however, the model is significantly different than the majority of decompression algorithms we are familiar with.

I would certainly appreciate comments from @Edward3c @KenGordon or others very familiar with BSAC 88

For copyright reasons there should not be any BSAC Tables available on the Internet. Any found must be treated with suspicion and cannot be relied on for accuracy or dive planning. [Note: BSAC does not own the copyright]

Be aware that 'bottom time' for the 88 Tables is defined from leaving the surface to the first stop or 6m if no stops are required. Time spent on deco stops are additional to the bottom time.

 

[scubadada]

For copyright reasons there should not be any BSAC Tables available on the Internet. Any found must be treated with suspicion and cannot be relied on for accuracy or dive planning. [Note: BSAC does not own the copyright]

Be aware that 'bottom time' for the 88 Tables is defined from leaving the surface to the first stop or 6m if no stops are required. Time spent on deco stops are additional to the bottom time.

I had difficulty finding any BSAC tables. I found Table A for EAN32 in a BSAC student instructional booklet, it appears authentic. I believe I interpreted the BSAC bottom time correctly, including the ascent to 6m

 

[Bob DBF]

History of decompression research and development - Wikipedia

A little bit of background information about the BSAC 88 tables, worth the few moments to read.


Bob

 

[scubadada]

History of decompression research and development - Wikipedia

A little bit of background information about the BSAC 88 tables, worth the few moments to read.


Bob

Thanks @Bob DBF , I had read that.

There is also a nice section in Powell's Deco for Divers, pp 160-162 of the second edition. The aggressiveness of the decompression profile is discussed

There is also a rather extensive discussion of the BSAC 88 tables in Lippmann and Mitchell's, Deeper into Diving, pp 261-281 of the second edition. The aggressive nature of the deco stops is again discussed. The entire set of BSAC 88 air tables is reproduced in the book.

 

[scubadada]

Hi DD,

The current Sports Diver syllabus requires for SO3 the instructor to teach diving with planned deco stops. Last Saturday I took a student through the gas planning requirements for a 38m dive of 28 min bottom time. We then did the runtime, including stops, at a much shallower depth. What I was looking for was getting to the stops on time and maintaining buoyancy during the stops.

So @Edward3c I redid the analysis of the simulated deco dive

For BSAC the dive rounds up to 39m and 29 min and yields 1 min of deco at 9m and 6min of deco at 6m

For Buhlmann ZH-L16C the dive is to 38m/125 ft with a bottom time of 25 min (subtracting the 3 minute ascent to 9m in the BSAC example). For GFs 100/100 the deco profile is 3 min at 20 ft and 10 min at 10 ft. Any lower GFs have a longer deco profile. For example 45/95 gives 1 min at 50 ft, 1 min at 40 ft, 2 min at 30 ft, 5 min at 20 ft, and 11 min at 10 ft.

This is what made me think the BSAC deco profiles are significantly more aggressive than what I was used to seeing.