New book on scrubber canisters by John Clarke

[Para Goon]

The book is now available on Amazon again...my #1 dive buddy just ordered it for me

 

[mr_v]

Just bought it. Looking forward to geeking out.

 

[mr_v]

A few pages in, and I am sold. Well-written and easy to read. If you hope to see only a few pages of tech information, you'll be disappointed. The book is rather thick with plenty of graphs and supporting information. In other words, it is for tech divers.

 

[mr_v]

Finished the book. Pretty thoughtful stuff. While I never pushed scrubber, the Dr. Clarke's writing wants me to be even more conservative. A few quick points.

• Too many environmental, design, and physiological variables influence scrubber duration. No two dives are alike and it is hard to predict scrubber breakthrough. The book supports the hypothesis with simulation and field test outcomes.
• Temperature and CO2 sensors may help alerting divers when CO2 levels become too dangerous.
• There is a trade-off between what we call WOB and scrubber efficiency. Deep divers may benefit from larger sorb grains, like 408. (Don't blindly follow this point - read the book first)
• CCR manufacturers do not always publish useful statistics. E.g., if you follow the average scrubber duration as a guide, you have a 50% chance getting a nasty surprise.

Of course, there is much more to the book. Read it and follow the formulas. If you know some stats and physics, you'll enjoy the read.

 

[Big-swede]

[QUOTE="mr_v, post: 9846836,
[*]CCR manufacturers do not always publish useful statistics. E.g., if you follow the average scrubber duration as a guide, you have a 50% chance getting a nasty surprise.
[/LIST]
[/QUOTE]

I dont have the book, can you explain what you meant with this?

I have never met someone whos run out of scrubber within the manufacturing recommendation so to say that 50 % is in for a nasty surprise seems... well a bit overexaggerated.

 

[mr_v]

[QUOTE="mr_v, post: 9846836,
[*]CCR manufacturers do not always publish useful statistics. E.g., if you follow the average scrubber duration as a guide, you have a 50% chance getting a nasty surprise.
[/LIST]

I dont have the book, can you explain what you meant with this?

I have never met someone whos run out of scrubber within the manufacturing recommendation so to say that 50 % is in for a nasty surprise seems... well a bit overexaggerated.
[/QUOTE]

You're right, it is hard to run out of scrubber if you following manufacturer recommendation because such recommendations are very conservative. Note, I explicitly stated "average" as opposed to "recommended." However, the author makes a point that manufacturers do not always reveal how they arrive to specific numbers and the devil lies in details.

Here is an example of how a dive can fail if you plan based only on average duration.

Suppose you believe that a scrubber canister lasts 100 minutes "on average" in the same conditions that you'll experience on the next dive. The next question is: What does 100 average run time really mean?

Unless you tracked every dive and have enough data to establish a breakthrough point, you'll probably perform sampling. By looking at multiple data samples, you'll determine that 100 mins is the average or the mean of means. In that case, it is likely that 50% of scrubber canisters will last longer than 100 minutes and 50% will last shorter. What's the absolute shortest duration for the scrubber canister? For that, you'll need to know the standard deviation and confidence intervals.

Suppose the standard deviation is 10 min. If so, then there is a 95% chance that the average scrubber duration is between 80.40 and 119.6 minutes (average +- 1.96 x 10). You can look at it this example from another angle - there is 2.5% chance that the scrubber will last shorter than 80.40 mins. Do you feel lucky?

If you don't feel lucky and the 95% confidence interval is not good for you. You want to be 99% confident. Using the same principles, you'll find out that there is a 99% chance that the scrubber will last longer than 74 minutes. In other words, if you want to be 99% sure that your scrubber will last, you'll plan your dive for no more than 74 minutes or 25% shorter than the observed average.

So what about the "nasty" surprise? If you did not bother thinking in terms of the confidence intervals and went on a 100 minute dive using "average" as your guide, the probability of scrubber breakthrough would be 50%. It is highly likely that manufactures pad their recommended numbers, but without full access to data, it is hard to say what they really are... So don't push the sorb, stay conservative, and stay safe.

 

[TuckerIdaho]

Didn't CE standards in some cases address that? IE: some scrubbers have a "real" potential life of 5-6 hours yet due to CE, they're restricted far below that.

 

[mr_v]

Didn't CE standards in some cases address that? IE: some scrubbers have a "real" potential life of 5-6 hours yet due to CE, they're restricted far below that.

I suppose. I am not an expert of scrubber design / manufacture. Simply raising a few interesting points mentioned in the book... Found it to be good food for thought.

 

[grantctobin]

Didn't CE standards in some cases address that? IE: some scrubbers have a "real" potential life of 5-6 hours yet due to CE, they're restricted far below that.

Here’s an example of a manufacturer that estimates different conditions:

not available - InnerSpace Systems Corporation

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www.megccr.com

 

[rsingler]

Just gave my wife the link to Amazon for a Christmas present for her favorite husband.
She looked at me and said, "This is a book? On rebreather scrubber canisters? Is this your porn?"