Diluent selection and the great alpinist v siege debate

mempilot · 15th June 2007, 14:46

Quote: (Originally Posted by Drmike)

FWIW once at depth 72m I had to bail to the only breathable gas I had which due to a series of cock ups was pure O2!

(dont ask but blame vidar

)

Ouch! You actually took a breath of O2 at 72m?????? How the f*&$k does that happen?

Glad to hear you made it through that!

Mark Chase · 15th June 2007, 14:50

Quote: (Originally Posted by mempilot)

Mark,

Did you ever experience any adverse effects right after a spiked bailout to 2.0? Just curious. I've talked to OC divers that have had problems with vision going from low PO2 bottom mix on the ascent to 1.6PO2 at their first gas switch.

Some text that I've read seems to indicate the spike is the problem. I don't always believe everything I read, since PADI says PO2 above 1.4 will kill you, but a jump from say a 1.2 setpoint to 2.0 seems like a drastic jump??

Just curious what the effects were? -vision, alertness, etc...

Eric

I cant say i noticed anything at all. I took four or five hits on the way back to the shot all spiked to 2.5. I have hit 1.7-1.8 going down the shot too fast as well, on both the KISS and the Hammer Head.

OC I always gas switched on to 1.6. Even my 21/35 gas switch was 66m on 1.6. Again I never noticed a problem. I feel there is more of an issue with the nitrogen spike than the 02 spike. The visual problems could have been a wave of narcosis? Only guessing and I am sure this had occured to them too.

I did 60-70m dives on 17/60 and then gas switched to 32% at 40m so I went from an END of 4.5m to a ND of 40m in one go which was always a bit of a head rush. In thos days no one thaught to dive 30/30 for deco.

ATB

Mark Chase

gathan · 15th June 2007, 15:25

Quote: (Originally Posted by mempilot)

Did you ever experience any adverse effects right after a spiked bailout to 2.0? Just curious. I've talked to OC divers that have had problems with vision going from low PO2 bottom mix on the ascent to 1.6PO2 at their first gas switch.Eric

I remember doing fairly long in-water O2 stops at a PO2 of 2.5 (15msw) while using the USN SSD helium partial pressure tables in the 80s. I never experienced nor heard of any of my peers experiencing such symptoms then. The development of the Canadian Forces SSD heliox tables saw the O2 stop move up to 9msw (same depth for the CUMA rebreather tables).

Andre

mempilot · 15th June 2007, 15:31

Thanks Andre. Interesting point. I think Mark may have hit the nail on the head with the N2 spike being the culprit. Going from trimix with a .22 FN2 to nitrox with a .50 FN2 would be a fairly significant spike in N2 and could cause the effects noted.

Quote: (Originally Posted by gathan)

I remember doing fairly long in-water O2 stops at a PO2 of 2.5 (15msw) while using the USN SSD helium partial pressure tables in the 80s. I never experienced nor heard of any of my peers experiencing such symptoms then. The development of the Canadian Forces SSD heliox tables saw the O2 stop move up to 9msw (same depth for the CUMA rebreather tables).

Andre

Gilles · 15th June 2007, 15:47

Quote: (Originally Posted by Dave Sutton)

Steve,

Why don;t you reverse this and carry the sphere with air and feed your wings/suit/BOV from that and then carry trimix offboard *when needed*? This allows the rig t be dived "naked" as a nitrox rig in shallow water and then you can simply snap the "trimix du jour" onto the rign as appropriate for the depth and run offboard dil while keeping the sphere with air for wings feed etc.? Thsi reverses the "typical" gas distibution but has worked a charm. Makes the core-rig *always the same* and trimix is then handled as a "module added as required".

Dave

Have to say this config works great, even on a rig that doesn't use spheres.

Thank you DS.

15th June 2007, 14:46	#131 (permalink)
mempilot What is this..terrafirma? Current Rebreather/s: Megalodon Other Rebreather/s: Megalodon Join Date: Aug 2006 Location: Ft. Lauderdale Posts: 1,269	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by Drmike) FWIW once at depth 72m I had to bail to the only breathable gas I had which due to a series of cock ups was pure O2! (dont ask but blame vidar ) Ouch! You actually took a breath of O2 at 72m?????? How the f&$k does that happen? Glad to hear you made it through that! __________________ MEM "Da Pilot" Black holes are where God divided by zero.* "If at first you don't succeed, don't dive silent." "Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins "Donkey's kill more people annually than plane crashes."
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15th June 2007, 14:50	#132 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,539	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by mempilot) Mark, Did you ever experience any adverse effects right after a spiked bailout to 2.0? Just curious. I've talked to OC divers that have had problems with vision going from low PO2 bottom mix on the ascent to 1.6PO2 at their first gas switch. Some text that I've read seems to indicate the spike is the problem. I don't always believe everything I read, since PADI says PO2 above 1.4 will kill you, but a jump from say a 1.2 setpoint to 2.0 seems like a drastic jump?? Just curious what the effects were? -vision, alertness, etc... Eric I cant say i noticed anything at all. I took four or five hits on the way back to the shot all spiked to 2.5. I have hit 1.7-1.8 going down the shot too fast as well, on both the KISS and the Hammer Head. OC I always gas switched on to 1.6. Even my 21/35 gas switch was 66m on 1.6. Again I never noticed a problem. I feel there is more of an issue with the nitrogen spike than the 02 spike. The visual problems could have been a wave of narcosis? Only guessing and I am sure this had occured to them too. I did 60-70m dives on 17/60 and then gas switched to 32% at 40m so I went from an END of 4.5m to a ND of 40m in one go which was always a bit of a head rush. In thos days no one thaught to dive 30/30 for deco. ATB Mark Chase __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System
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15th June 2007, 15:25	#133 (permalink)
gathan MixedGas Current Rebreather/s: Classic Kiss Other SCR Other Rebreather/s: Other SCR Join Date: Sep 2005 Location: Tottenham, Ontario, Canada Posts: 202	Re: ad_ward9 slamming everyone elses gear Quote: (Originally Posted by mempilot) Did you ever experience any adverse effects right after a spiked bailout to 2.0? Just curious. I've talked to OC divers that have had problems with vision going from low PO2 bottom mix on the ascent to 1.6PO2 at their first gas switch.Eric I remember doing fairly long in-water O2 stops at a PO2 of 2.5 (15msw) while using the USN SSD helium partial pressure tables in the 80s. I never experienced nor heard of any of my peers experiencing such symptoms then. The development of the Canadian Forces SSD heliox tables saw the O2 stop move up to 9msw (same depth for the CUMA rebreather tables). Andre
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15th June 2007, 15:31	#134 (permalink)
mempilot What is this..terrafirma? Current Rebreather/s: Megalodon Other Rebreather/s: Megalodon Join Date: Aug 2006 Location: Ft. Lauderdale Posts: 1,269	Re: ad_ward9 slamming everyone elses gear Thanks Andre. Interesting point. I think Mark may have hit the nail on the head with the N2 spike being the culprit. Going from trimix with a .22 FN2 to nitrox with a .50 FN2 would be a fairly significant spike in N2 and could cause the effects noted. Quote: (Originally Posted by gathan) I remember doing fairly long in-water O2 stops at a PO2 of 2.5 (15msw) while using the USN SSD helium partial pressure tables in the 80s. I never experienced nor heard of any of my peers experiencing such symptoms then. The development of the Canadian Forces SSD heliox tables saw the O2 stop move up to 9msw (same depth for the CUMA rebreather tables). Andre __________________ MEM "Da Pilot" Black holes are where God divided by zero. "If at first you don't succeed, don't dive silent." "Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins "Donkey's kill more people annually than plane crashes."
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15th June 2007, 15:47	#135 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 762	Re: Diluent selection and the great alpinist v siege debate Quote: (Originally Posted by Dave Sutton) Steve, Why don;t you reverse this and carry the sphere with air and feed your wings/suit/BOV from that and then carry trimix offboard when needed? This allows the rig t be dived "naked" as a nitrox rig in shallow water and then you can simply snap the "trimix du jour" onto the rign as appropriate for the depth and run offboard dil while keeping the sphere with air for wings feed etc.? Thsi reverses the "typical" gas distibution but has worked a charm. Makes the core-rig always the same and trimix is then handled as a "module added as required". Dave Have to say this config works great, even on a rig that doesn't use spheres. Thank you DS. __________________ Gilles http://www.dirrebreather.com
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