Disclaimer: this is meant as a thought exercise for technical divers only. Please do not apply any of these concepts to recreational dives or a dive <40m (~130ft). Stick to recommendations set forth by your training agency and computer.
My goal of this post is to:
1. Compile anecdotal information from people who regularly dive to >50m (~165ft)
2. Gather any scientific information/data/papers to help with what proper guidance should be for technical divers
3. Learn!! Is my math/logic even sound? Did I miss an important variable? Other factors? Etc.
I've been doing some searching and much of the data/papers are pretty old and inconclusive. However, the US Navy dive tables did change the ascent rate from 20m/min to 10m/min in 1993. In either case, the recommendation seems to be oversimplified and if followed at significant depths, would increase inert gas saturation (and thus deco times). The idea is that if one goes deep they'll want to get out "as fast as possible." But how do we quantify how fast? What is fast and what is safe?
There's a lot of tribal knowledge that ascending from depth the magical 10m/min barrier can be broken. The deeper one is, the faster they can ascend. The thought behind that is that the effect of depth/pressure to gas volume is logarithmic. The difference in volume (or the effect of pressure) is smaller the deeper one goes and so the probability of spontaneous bubble formation is reduced. I've created the following graph (blue line) to illustrate this. Note the linearity of the curve below 50m/165ft.
Here's the raw data:
The red line represents a calculated ascent rate based on the generic 10m/min (30ft/min) recommendation, relative to air volume. It's meant to be a ratio of air volume at different depths. The exact numbers, nor the intersection between recommendation and depth, isn't the important part here, as I don't expect people to follow this approach. The important thing to note is how quickly (mathematically) we may be able to ascend from depth. Even if we change the math to be a lot more conservative, it's obvious that the rate at which we can move through the water column at depth is incredibly high. This is important as it has a huge impact on further tissue loading and deco obligations.
It's also important to note that there are many variables not taken into account here. For example, I would think a deep dive on air (not recommended) couldn't follow the same logic. I'm making the assumption that this is a trimix dive with an equivalent narcotic depth (END) of a shallower recreational dive. Otherwise, even though the formulas above may "work" the nitrogen loading at depth and subsequently the formation of bubbles would present a great risk with fast pressure changes. We still don't know that 10m/min is a correct recommendation for every depth (rec level dive).
This is probably a lot to digest, thoughts, so far?
My goal of this post is to:
1. Compile anecdotal information from people who regularly dive to >50m (~165ft)
2. Gather any scientific information/data/papers to help with what proper guidance should be for technical divers
3. Learn!! Is my math/logic even sound? Did I miss an important variable? Other factors? Etc.
I've been doing some searching and much of the data/papers are pretty old and inconclusive. However, the US Navy dive tables did change the ascent rate from 20m/min to 10m/min in 1993. In either case, the recommendation seems to be oversimplified and if followed at significant depths, would increase inert gas saturation (and thus deco times). The idea is that if one goes deep they'll want to get out "as fast as possible." But how do we quantify how fast? What is fast and what is safe?
There's a lot of tribal knowledge that ascending from depth the magical 10m/min barrier can be broken. The deeper one is, the faster they can ascend. The thought behind that is that the effect of depth/pressure to gas volume is logarithmic. The difference in volume (or the effect of pressure) is smaller the deeper one goes and so the probability of spontaneous bubble formation is reduced. I've created the following graph (blue line) to illustrate this. Note the linearity of the curve below 50m/165ft.
Here's the raw data:
The red line represents a calculated ascent rate based on the generic 10m/min (30ft/min) recommendation, relative to air volume. It's meant to be a ratio of air volume at different depths. The exact numbers, nor the intersection between recommendation and depth, isn't the important part here, as I don't expect people to follow this approach. The important thing to note is how quickly (mathematically) we may be able to ascend from depth. Even if we change the math to be a lot more conservative, it's obvious that the rate at which we can move through the water column at depth is incredibly high. This is important as it has a huge impact on further tissue loading and deco obligations.
It's also important to note that there are many variables not taken into account here. For example, I would think a deep dive on air (not recommended) couldn't follow the same logic. I'm making the assumption that this is a trimix dive with an equivalent narcotic depth (END) of a shallower recreational dive. Otherwise, even though the formulas above may "work" the nitrogen loading at depth and subsequently the formation of bubbles would present a great risk with fast pressure changes. We still don't know that 10m/min is a correct recommendation for every depth (rec level dive).
This is probably a lot to digest, thoughts, so far?
