Gradient Factors

*Clare Gledhill* · June 13th, 2006, 04:55 PM

Been having a chat about these with various people off board and thought it would make an interesting thread.

On our Tech 1 course we were taught to use Ratio Deco but were advised that checking stuff on computer is always a good move as more information and influences can be "a good thing". When using Decoplanner we were advised to start off with GF 30/90 as this would give the closest overall deco requirement compared to Ratio Deco and it was (I have since learned) a recommendation that Erik Baker gave (Erik was the guy who invented the Gradient Factor method)

Since my training, to be honest, I have merely used ratio deco for all the wreck dives I’m doing although I often play with DP to check my own thinking and various scenarios. As the dives start getting longer/deeper etc this becomes more of a factor and so I have started looking at it all a bit more closely. GF 5/90 gives a deep stop profile close to what I am comfortable with; a recent conversation suggests that 10/100 is commonly used as well - leading to a greater proportion of the deco done deep and less O2 time.

So - what do you use, what have you experimented with in the past, and what have you learned from it (Don't do it like this, you get bent is an acceptable response

)

Rob Andrews · June 13th, 2006, 05:56 PM

From my very limited understanding of gradient factors I would have thought that your 5/90 would have you doing the deco deeper and less o2 time then the 10/100 you mentioned?!?

I await to be corrected though.

Just found this post by Chasey shamelessly borrowed from YD, hope nobody minds.

Quote:

Gradient factors are a way of adapting Bhulman tables to incorporate deep stops and genital profiles or even modifying them to be even more aggressive than standard Bhulman models.

The shortest deco most aggressive deco is theoretically 100/100GF. This will get you shallow fast and will use the pressure imbalance of the expanding gas in your body to force the nitrogen out fast. If you follow the modern thinking this profile will have you bent as a 9 bob note in the water but will fix it on the shallow stops.

Some divers are running 100% + profiles like 50/120. Theoretically these profiles are imposable but the use of slow ascents and deeper stops allow for the very aggressive 120% Hi Gradient Factor. Well most of the time

The best way to think about Gradient Factors is two horizontal parallel lines. The top line is GF High 100%. The Bottom Line is GF low 0.

Below the bottom line you are on gassing so no decompression is taking place. Above the bottom line decompression is happening to some degree. Above the top line 100% GF High you theoretically get bent. The top and bottom lines are depths in relation to your decompression status.

So a 20/80 profile starts the decompression off 20% above the minimum off gassing level and finishes the decompression at 80% of the maximum decompression profile. The lower the Low decompression GF the deeper the deep stops will be. The Higher the High decompression figure the more shallow stops you will have to do.

limeyx · June 13th, 2006, 06:02 PM

Quote: (Originally Posted by Gledders)

Been having a chat about these with various people off board and thought it would make an interesting thread.

On our Tech 1 course we were taught to use Ratio Deco but were advised that checking stuff on computer is always a good move as more information and influences can be "a good thing". When using Decoplanner we were advised to start off with GF 30/90 as this would give the closest overall deco requirement compared to Ratio Deco and it was (I have since learned) a recommendation that Erik Baker gave (Erik was the guy who invented the Gradient Factor method)

Since my training, to be honest, I have merely used ratio deco for all the wreck dives I’m doing although I often play with DP to check my own thinking and various scenarios. As the dives start getting longer/deeper etc this becomes more of a factor and so I have started looking at it all a bit more closely. GF 5/90 gives a deep stop profile close to what I am comfortable with; a recent conversation suggests that 10/100 is commonly used as well - leading to a greater proportion of the deco done deep and less O2 time.

So - what do you use, what have you experimented with in the past, and what have you learned from it (Don't do it like this, you get bent is an acceptable response

)

Similar here, except we were told that the 30/90 (or 30/85) should (or "could") be replaced by 20/80 which would be closer to the VPM.

I think Jarrod posted that he recommends 30/90 but for long bottom times uses 10/100 ?

I've been using the ratio method exclusively, but do run stuff through deco planner also.

Would definitely be interested to hear other opinions.

rjack · June 13th, 2006, 06:34 PM

Deep stops 2 ATA above bottom depth has been mentioned as a better "rule of thumb" for dives less than 200+ ft. More like 40/XX in DP as far as I can tell.

5 or 10/XX is such slight off-gassing, I question the usefulness for less than very long exposures with slow compartments packed full of gas.

Richard

PBrown · June 13th, 2006, 06:38 PM

Quote: (Originally Posted by desertrat)

From my very limited understanding of gradient factors I would have thought that your 5/90 would have you doing the deco deeper and less o2 time then the 10/100 you mentioned?!?

5/90 would indeed start deeper, as it only allows you to go 5% into the deco zone when deep before it calls for a stop, but it will give you more time on O2 as it's only allowing you to go 90% into the deco zone when shallow (compared to 10/100).

Simon & I tend to use 20/100, although I'm trying to ween him onto 10/100.

cheers,
Paul

*Clare Gledhill* · June 13th, 2006, 06:55 PM

Quote: (Originally Posted by PBrown)

Simon & I tend to use 20/100, although I'm trying to ween him onto 10/100.

Now that's funny....

Guess who suggested it to me

rjack · June 13th, 2006, 08:09 PM

Quote: (Originally Posted by PBrown)

5/90 would indeed start deeper, as it only allows you to go 5% into the deco zone when deep before it calls for a stop, but it will give you more time on O2 as it's only allowing you to go 90% into the deco zone when shallow (compared to 10/100).

Simon & I tend to use 20/100, although I'm trying to ween him onto 10/100.

cheers,
Paul

Not sure what kind of profiles your doing...

But how much more shallow time? Is that 10% difference really meaningful? Do you feel different?

Richard

Mark Chase · June 14th, 2006, 12:06 AM

10/100 is a very aggressive profile for well prepared physical fit divers in warm conditions. I have little doubt that a big dive on 10/100 would bend me.

I have had niggles on big dives diving 30/90. This is a much less aggressive profile. 20/100 would be a slightly better than 10/100 and 5/100 is really pushing it.

Starting the stops that deep will mean your still on gassing and any off gassing will be PP02 based rather than bubble based. As a result you need to be on a high PP on the deep stops to make it work properly.

Doing 5/100 10/100 deco without a basic understanding of the mechanics of off gassing is mad. Doing to many deep stops too deep on low PP02 back gas is worse than a waste of time, its just increasing your risk of a hit. I would strongly advise anyone who's thinking of doing these sort of profiles to do a bit of reading first and to step outside their training to do so.

Short exposure diving can lull you into a false sense of security. Short bottom times and shallow diving you can push it and get away with a lot but your saving 10-20mins of deco so what's the point?

Doing 10mins at 80m and saying you did it on 10/100 isnt going to impress me. You save a whole 3mins of deco over doing a 20/80GF profile. If you can do 40mins at 80m and get out clean on 10/100 I will be amazed. You would have 42mins less deco than me.

I find its good to punch in some numbers for a reality check now and then.

At Tec1 level with 50% for deco 18/45 back gas Running thirds on 12s and using an Al80 for deco your not going to do much more than 30mins on the bottom.

50m for 30mins 10/100GF = 37mins of deco TTS

50m for 30mins 20/80 = 49mins of deco TTS

50m for 30mins 30/90 = 41mins deco TTS

So you save 12mins of deco and in doing so push your body to its limits and risk DCI over my 20/80 granddad profile. For what? 12mins of staying in the water?

I cant see the sense of it.

However the big danger is not here its when you start thinking you can run this sort of deco on big dives with much greater in water exposure resulting in dehydration and heat loss.

The harder you push it the smaler the margins become

ATB

Mark Chase

rjack · June 14th, 2006, 01:25 AM

Thanks for the examples Mark.

Although all of your examples are too aggressive for me at the Tech1 level with only 1 deco gas anyway. The thought of decoing out on backgas for an hour and a half+ makes me shudder.

Richard

**neilh** · June 14th, 2006, 09:44 AM

Quote: (Originally Posted by Mark Chase)

I would strongly advise anyone who's thinking of doing these sort of profiles to do a bit of reading first and to step outside their training to do so.

I'll admit that while I find these threads interesting, most of the content goes way over my head because deco theory, gradient factors, etc are all a mystery to me!

Your point about reading and research is a good one - any suggestions for some good places to start?

June 13th, 2006, 04:55 PM	#1 (permalink)
Clare Gledhill (Online) GUE Instructor Site Admin Join Date: Nov 2005 Location: UK Posts: 1,540	Gradient Factors Been having a chat about these with various people off board and thought it would make an interesting thread. On our Tech 1 course we were taught to use Ratio Deco but were advised that checking stuff on computer is always a good move as more information and influences can be "a good thing". When using Decoplanner we were advised to start off with GF 30/90 as this would give the closest overall deco requirement compared to Ratio Deco and it was (I have since learned) a recommendation that Erik Baker gave (Erik was the guy who invented the Gradient Factor method) Since my training, to be honest, I have merely used ratio deco for all the wreck dives I’m doing although I often play with DP to check my own thinking and various scenarios. As the dives start getting longer/deeper etc this becomes more of a factor and so I have started looking at it all a bit more closely. GF 5/90 gives a deep stop profile close to what I am comfortable with; a recent conversation suggests that 10/100 is commonly used as well - leading to a greater proportion of the deco done deep and less O2 time. So - what do you use, what have you experimented with in the past, and what have you learned from it (Don't do it like this, you get bent is an acceptable response ) __________________ Clare . "Keep away from people who try to belittle your ambitions....Small people always do that, but the really great make you feel that you too can become great." Interested in DIR dive training? Always happy to chat/answer questions so get in touch via PM or visit www.dirdiver.co.uk

June 13th, 2006, 05:56 PM	#2 (permalink)
Rob Andrews (Online) New Member Join Date: Nov 2005 Location: Wombourne, West Mids, UK Posts: 131	From my very limited understanding of gradient factors I would have thought that your 5/90 would have you doing the deco deeper and less o2 time then the 10/100 you mentioned?!? I await to be corrected though. Just found this post by Chasey shamelessly borrowed from YD, hope nobody minds. Quote: Gradient factors are a way of adapting Bhulman tables to incorporate deep stops and genital profiles or even modifying them to be even more aggressive than standard Bhulman models. The shortest deco most aggressive deco is theoretically 100/100GF. This will get you shallow fast and will use the pressure imbalance of the expanding gas in your body to force the nitrogen out fast. If you follow the modern thinking this profile will have you bent as a 9 bob note in the water but will fix it on the shallow stops. Some divers are running 100% + profiles like 50/120. Theoretically these profiles are imposable but the use of slow ascents and deeper stops allow for the very aggressive 120% Hi Gradient Factor. Well most of the time The best way to think about Gradient Factors is two horizontal parallel lines. The top line is GF High 100%. The Bottom Line is GF low 0. Below the bottom line you are on gassing so no decompression is taking place. Above the bottom line decompression is happening to some degree. Above the top line 100% GF High you theoretically get bent. The top and bottom lines are depths in relation to your decompression status. So a 20/80 profile starts the decompression off 20% above the minimum off gassing level and finishes the decompression at 80% of the maximum decompression profile. The lower the Low decompression GF the deeper the deep stops will be. The Higher the High decompression figure the more shallow stops you will have to do. Last edited by Rob Andrews; June 13th, 2006 at 06:03 PM. Reason: found chaseys post on gradient factors

June 13th, 2006, 06:55 PM	#6 (permalink)
Clare Gledhill (Online) GUE Instructor Site Admin Join Date: Nov 2005 Location: UK Posts: 1,540	Quote: (Originally Posted by PBrown) Simon & I tend to use 20/100, although I'm trying to ween him onto 10/100. Now that's funny.... Guess who suggested it to me __________________ Clare . "Keep away from people who try to belittle your ambitions....Small people always do that, but the really great make you feel that you too can become great." Interested in DIR dive training? Always happy to chat/answer questions so get in touch via PM or visit www.dirdiver.co.uk

June 14th, 2006, 12:06 AM	#8 (permalink)
Mark Chase(Offline) New Member Join Date: Nov 2005 Location: Kent England Posts: 905	10/100 is a very aggressive profile for well prepared physical fit divers in warm conditions. I have little doubt that a big dive on 10/100 would bend me. I have had niggles on big dives diving 30/90. This is a much less aggressive profile. 20/100 would be a slightly better than 10/100 and 5/100 is really pushing it. Starting the stops that deep will mean your still on gassing and any off gassing will be PP02 based rather than bubble based. As a result you need to be on a high PP on the deep stops to make it work properly. Doing 5/100 10/100 deco without a basic understanding of the mechanics of off gassing is mad. Doing to many deep stops too deep on low PP02 back gas is worse than a waste of time, its just increasing your risk of a hit. I would strongly advise anyone who's thinking of doing these sort of profiles to do a bit of reading first and to step outside their training to do so. Short exposure diving can lull you into a false sense of security. Short bottom times and shallow diving you can push it and get away with a lot but your saving 10-20mins of deco so what's the point? Doing 10mins at 80m and saying you did it on 10/100 isnt going to impress me. You save a whole 3mins of deco over doing a 20/80GF profile. If you can do 40mins at 80m and get out clean on 10/100 I will be amazed. You would have 42mins less deco than me. I find its good to punch in some numbers for a reality check now and then. At Tec1 level with 50% for deco 18/45 back gas Running thirds on 12s and using an Al80 for deco your not going to do much more than 30mins on the bottom. 50m for 30mins 10/100GF = 37mins of deco TTS 50m for 30mins 20/80 = 49mins of deco TTS 50m for 30mins 30/90 = 41mins deco TTS So you save 12mins of deco and in doing so push your body to its limits and risk DCI over my 20/80 granddad profile. For what? 12mins of staying in the water? I cant see the sense of it. However the big danger is not here its when you start thinking you can run this sort of deco on big dives with much greater in water exposure resulting in dehydration and heat loss. The harder you push it the smaler the margins become ATB Mark Chase __________________ The only DIR Inspiration diver in the village

June 13th, 2006, 06:02 PM	#3 (permalink)
limeyx(Offline) New Member Join Date: Nov 2005 Location: Los Angeles, CA Posts: 707	Quote: (Originally Posted by Gledders) Been having a chat about these with various people off board and thought it would make an interesting thread. On our Tech 1 course we were taught to use Ratio Deco but were advised that checking stuff on computer is always a good move as more information and influences can be "a good thing". When using Decoplanner we were advised to start off with GF 30/90 as this would give the closest overall deco requirement compared to Ratio Deco and it was (I have since learned) a recommendation that Erik Baker gave (Erik was the guy who invented the Gradient Factor method) Since my training, to be honest, I have merely used ratio deco for all the wreck dives I’m doing although I often play with DP to check my own thinking and various scenarios. As the dives start getting longer/deeper etc this becomes more of a factor and so I have started looking at it all a bit more closely. GF 5/90 gives a deep stop profile close to what I am comfortable with; a recent conversation suggests that 10/100 is commonly used as well - leading to a greater proportion of the deco done deep and less O2 time. So - what do you use, what have you experimented with in the past, and what have you learned from it (Don't do it like this, you get bent is an acceptable response ) Similar here, except we were told that the 30/90 (or 30/85) should (or "could") be replaced by 20/80 which would be closer to the VPM. I think Jarrod posted that he recommends 30/90 but for long bottom times uses 10/100 ? I've been using the ratio method exclusively, but do run stuff through deco planner also. Would definitely be interested to hear other opinions.

June 13th, 2006, 06:34 PM	#4 (permalink)
rjack(Offline) wet behind the ears Join Date: Nov 2005 Location: Seattle, WA Posts: 860	Deep stops 2 ATA above bottom depth has been mentioned as a better "rule of thumb" for dives less than 200+ ft. More like 40/XX in DP as far as I can tell. 5 or 10/XX is such slight off-gassing, I question the usefulness for less than very long exposures with slow compartments packed full of gas. Richard

June 13th, 2006, 06:38 PM	#5 (permalink)
PBrown (Online) New Member Join Date: Nov 2005 Location: Wiltshire Posts: 198	Quote: (Originally Posted by desertrat) From my very limited understanding of gradient factors I would have thought that your 5/90 would have you doing the deco deeper and less o2 time then the 10/100 you mentioned?!? 5/90 would indeed start deeper, as it only allows you to go 5% into the deco zone when deep before it calls for a stop, but it will give you more time on O2 as it's only allowing you to go 90% into the deco zone when shallow (compared to 10/100). Simon & I tend to use 20/100, although I'm trying to ween him onto 10/100. cheers, Paul

June 13th, 2006, 08:09 PM	#7 (permalink)
rjack(Offline) wet behind the ears Join Date: Nov 2005 Location: Seattle, WA Posts: 860	Quote: (Originally Posted by PBrown) 5/90 would indeed start deeper, as it only allows you to go 5% into the deco zone when deep before it calls for a stop, but it will give you more time on O2 as it's only allowing you to go 90% into the deco zone when shallow (compared to 10/100). Simon & I tend to use 20/100, although I'm trying to ween him onto 10/100. cheers, Paul Not sure what kind of profiles your doing... But how much more shallow time? Is that 10% difference really meaningful? Do you feel different? Richard

June 14th, 2006, 01:25 AM	#9 (permalink)
rjack(Offline) wet behind the ears Join Date: Nov 2005 Location: Seattle, WA Posts: 860	Thanks for the examples Mark. Although all of your examples are too aggressive for me at the Tech1 level with only 1 deco gas anyway. The thought of decoing out on backgas for an hour and a half+ makes me shudder. Richard

June 14th, 2006, 09:44 AM	#10 (permalink)
neilh(Offline) Haemoglobin on the bus... Join Date: Nov 2005 Location: Barnsley, UK Posts: 1,900	Quote: (Originally Posted by Mark Chase) I would strongly advise anyone who's thinking of doing these sort of profiles to do a bit of reading first and to step outside their training to do so. I'll admit that while I find these threads interesting, most of the content goes way over my head because deco theory, gradient factors, etc are all a mystery to me! Your point about reading and research is a good one - any suggestions for some good places to start?