Factors affecting deep scuba diving
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Perhaps I missed it, but the OBP (Over Bottom Pressure) required at these depths is a significant problem for gas planning. 1200' is 534 PSIG (0.445 PSI/FSW). Add 500 PSI+ (or about 100 PSI if using a larger hose like commercial divers) for the optimum demand regulator performance required at that depth and suddenly a lot of the deep mix on your back is inaccessible. Also, you can't use the same RMV that keeps your lungs adequately ventilated at 200' at 1200'.
Edit: Most commercial diving operations use an RMV of 1.5 CFM to calculate gas requirements. My best guess is that no less than 0.75 CFM at that depth on Trimix would be required and probably closer to 1.0.
To make matters worse, you need a much richer O2 mix on ascent to optimize decompression so there is even more deep mix that is unusable. This won't help deep Scuba divers but here is a related technique that saturation divers use:
To be honest, we also overfilled as standard procedure.
There are, but not the kind that recreational divers are familiar with.
BandMask 18 | Kirby Morgan
Lightweight fiberglass and stainless steel hats have almost totally replaced the use of masks in commercial diving due to better head protection and communications (dry ears). Most divers also find them more comfortable on long dives as long as they don/t have to pop their heads out of the water much.
Keeping the regulator in your mouth is a small part of the problem. Keeping lips sealed around the regulator is the show-stopper in a seizure or diminished or lost consciousness event.
Dead air space is significantly higher in a FFM, or lightweight hat used in commercial diving, than a mouthpiece. It is the price we pay for hardwire communications that is necessary for safety and performing the work. Commercial divers are trained to breathe deeply and as rapidly as they want to manage CO2 buildup under high gas densities and workloads. However, they have unlimited gas supplies from a large number of sources, most of which are switched for us at the surface and in the bell.
The divers are only responsible for one gas switch, to their bailout bottle.
Edit: Most commercial diving operations use an RMV of 1.5 CFM to calculate gas requirements. My best guess is that no less than 0.75 CFM at that depth on Trimix would be required and probably closer to 1.0.
To make matters worse, you need a much richer O2 mix on ascent to optimize decompression so there is even more deep mix that is unusable. This won't help deep Scuba divers but here is a related technique that saturation divers use:
To be honest, we also overfilled as standard procedure.
There are, but not the kind that recreational divers are familiar with.
BandMask 18 | Kirby Morgan
Lightweight fiberglass and stainless steel hats have almost totally replaced the use of masks in commercial diving due to better head protection and communications (dry ears). Most divers also find them more comfortable on long dives as long as they don/t have to pop their heads out of the water much.
Keeping the regulator in your mouth is a small part of the problem. Keeping lips sealed around the regulator is the show-stopper in a seizure or diminished or lost consciousness event.
Dead air space is significantly higher in a FFM, or lightweight hat used in commercial diving, than a mouthpiece. It is the price we pay for hardwire communications that is necessary for safety and performing the work. Commercial divers are trained to breathe deeply and as rapidly as they want to manage CO2 buildup under high gas densities and workloads. However, they have unlimited gas supplies from a large number of sources, most of which are switched for us at the surface and in the bell.
The divers are only responsible for one gas switch, to their bailout bottle.
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markmud
Self Reliant Diver--On All Dives.
Thanks to Doppler and Akimbo!
It never ceases to amaze me how the technical diving community can obsess over the smallest little detail of safety equipment and procedures while ignoring that 800 Lb gorilla staring them the face -- getting bent. Very few make any practical provisions for treating DCS, let alone a forced omitted decompression.
Commercial and military divers almost always require a treatment chamber onboard when decompression is required, thought they also use it extensively for Sur-D-O2 (Surface Decompression using Oxygen). I have seen dozens of cases of DCS in my career and all were successfully treated, beginning within minutes of reported symptoms. I have no doubt that most, if not all, would have resulted in serious long term injury or death if treatment were delayed for hours of days.
I'm the first to support people making their own risk-reward calculations in life as long as they accept the results when things go bad. But I also have to ask what the hell are you thinking? The vast majority of technical diving is performed for entertainment, which of course is recreation. Short bottom times are followed by terminally boring and risk-filled decompression that exceeds their bottom times by several times. They also get to spend big bucks on equipment and breathing gas. Unless there is a reason to dive deep, like a wreck or worksite, why go? This is fun?
Know where your nearest treatment chamber is, that it is manned and ready to take emergencies, how you can get there in an emergency, and how long it will take after you make "the call". Expedition dives that are many hours or days from a chamber should be fully trained and equipped for IWR (In-Water Recompression), which sucks compared to a chamber but beats laying on deck waiting to die. OK, rant over. It is safe for children to come out now.
Commercial and military divers almost always require a treatment chamber onboard when decompression is required, thought they also use it extensively for Sur-D-O2 (Surface Decompression using Oxygen). I have seen dozens of cases of DCS in my career and all were successfully treated, beginning within minutes of reported symptoms. I have no doubt that most, if not all, would have resulted in serious long term injury or death if treatment were delayed for hours of days.
I'm the first to support people making their own risk-reward calculations in life as long as they accept the results when things go bad. But I also have to ask what the hell are you thinking? The vast majority of technical diving is performed for entertainment, which of course is recreation. Short bottom times are followed by terminally boring and risk-filled decompression that exceeds their bottom times by several times. They also get to spend big bucks on equipment and breathing gas. Unless there is a reason to dive deep, like a wreck or worksite, why go? This is fun?
Know where your nearest treatment chamber is, that it is manned and ready to take emergencies, how you can get there in an emergency, and how long it will take after you make "the call". Expedition dives that are many hours or days from a chamber should be fully trained and equipped for IWR (In-Water Recompression), which sucks compared to a chamber but beats laying on deck waiting to die. OK, rant over. It is safe for children to come out now.
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OP
I recall that the press time to my deepsest saturation dive strorage depth was a little over 4 hours. I further recall the compression arthralgia I experienced to be quite painful, but lessened considerably ( but not completely ) over the 29 days we were stored at 22ata.
I had the benefits of a climate-controlled living space, 24 hour room service from a dedicated topside crew, enormous gas blend reserves, hot water suit comfort, a flush toilet, interesting / challenging work to perform AND...a whopping nice paycheck after de-saturation!
Why anyone would attempt to yo-yo another 500' or so beyond the aforementioned depth of 22ata, on open circuit, leaves me gobsmackedly baffled.
Cheers,
DSD
I had the benefits of a climate-controlled living space, 24 hour room service from a dedicated topside crew, enormous gas blend reserves, hot water suit comfort, a flush toilet, interesting / challenging work to perform AND...a whopping nice paycheck after de-saturation!
Why anyone would attempt to yo-yo another 500' or so beyond the aforementioned depth of 22ata, on open circuit, leaves me gobsmackedly baffled.
Cheers,
DSD
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