Hey there,
There is a lot going on in these deep dives. Often the show a small amount of descent, some of the bottom time and small amount of the decompression.
First the Amazon expedition was a bit strange and they did break have an accident but underplayed it.
The diver ran out of oxygen (I believe) on ascent and you can hear the inspiration rebreather beeping on the ascent. This is the rebreather warning the diver that the system is having problems and he must address them for his own safety. First problem was the vis was so bad they could hardly read their displays and second he was ascending with a large video camera and trying to manage his rebreather problems. We as viewers are never told if he bailout out to open circuit or just rode the loop to the surface. With any breathing loop as you ascend your oxygen partial pressure rate drops and then you could be breathing a hypoxic mix near the surface (fancy language for breathing something that does not have enough oxygen to maintain life functions.) You see the diver breathing O2 on the boat; from this I would surmise that his ascent rate was too fast and they were being carefully to assure he was not getting any type of DCS problems. Again proper details were not provided.
I have not seen the Pacific series outside of a few clips. From what I have seen it has been Richard Pyle's group of Hawaii. They do research on collecting fish in the twilight zone about 300 to 400 ft. This is covered on Richards website and also the museum website. Richard's group uses CIS-Lunar units that were developed by Bill Stone out of his caving needs and ability to do exploration. These units are now starting to show their age however they are servable by an outfit on the east coast. Richard and his group have been using this unit for ages and adapted it sometime ago. His website shows a number of concerns for using rebreather at extreme depth. For fun look up the movie "diving terrets syndrome." This shows the changes of light and water temp exposure as they descent to over 400ft. One of my favorite movies.
The funny thing is the camera crew (that I saw briefly) is running MK15.5 units that were from the Bio-marine area that are really old. Bio Marine was a spinoff of the General Electric engineers that developed the rebreather for the space program. The layout of this system is incredible and still very desirable even in today's standards.
These units have probably had all the electronics and controls updated by one of a few businesses that offer such products. However the MK15.5 have been pretty much bullet proof units in the past and with proper service and TLC they seem to run for forever.
It should be noted that Howard Hall and his crew also runs a MK15.5 unit and he has all custom boards and electronics for his unit. I had the pleasure if meeting Mr. Hall and discussing the options of the Diverite Optima rebreather a few years ago. A truly amazing gentleman.
It should be noted that these dives are technical in nature. The units require vigilance of not only the correct oxygen content, but also the proper flushing of the system for trimix, decompression and monitoring of life support systems. The clear benefit is the total reduction of gas requirements, linear decompression, and breathing nice warm gas. So for divers that are making 300ft dives the systems pay for themselves in gas costs but they represent an invest of a different kind of life support system.
There is a rebreather group here on scuba board. I would recommend Rebretherworld.com and have a look around.
In the metroplex there is an assortment of rebreather divers.
Andrew
