The problem with helium and decompression has to do with its ability to difuse faster than N2. For this reason, a diver in decompression needs to take deeper stops and at more intervals to properly off gas the inert helium.
There is another phenomenon, know as isobaric counter diffusion. This can happen when a diver has not off gassed enough helium and switches to a heavy gas (i.e. Nitrox). This results in the slower diffusion of the N2 while the helium is off gassing at a rate 2.65 times as fast. This can result in the excess helium difusing through the skin causing blister and also doing the same kind of harm to the neural system as N2.
The problem in treating a helium DCS hit is keeping the helium diffusion under control and eliminating it without futher damage to the affected diver.
"Generally, for dives up to 80 to 120 minutes, Nitrox mixes require less decompression and swallow decompression stops than heliox through the transistion or "crossover point" depends on the depth of the dive and the decompression procedures used." (from "Extending the Envelope" by Dick Rutkowski).
Dick goes to to say that for deeper and longer dives (300 feet!) heliox gain the advantage. So, I guess the point is this: Recreational divers who like to dive beyound no DECO limits of heliox are creating another set of problems. In other words, Helium decompression is different and is govern by a different set of rules than our old friend nitrox.
There is another phenomenon, know as isobaric counter diffusion. This can happen when a diver has not off gassed enough helium and switches to a heavy gas (i.e. Nitrox). This results in the slower diffusion of the N2 while the helium is off gassing at a rate 2.65 times as fast. This can result in the excess helium difusing through the skin causing blister and also doing the same kind of harm to the neural system as N2.
The problem in treating a helium DCS hit is keeping the helium diffusion under control and eliminating it without futher damage to the affected diver.
"Generally, for dives up to 80 to 120 minutes, Nitrox mixes require less decompression and swallow decompression stops than heliox through the transistion or "crossover point" depends on the depth of the dive and the decompression procedures used." (from "Extending the Envelope" by Dick Rutkowski).
Dick goes to to say that for deeper and longer dives (300 feet!) heliox gain the advantage. So, I guess the point is this: Recreational divers who like to dive beyound no DECO limits of heliox are creating another set of problems. In other words, Helium decompression is different and is govern by a different set of rules than our old friend nitrox.