First a disclaimer: This is a general discussion. Most of the people I dive with feel that doing anything I say will get you bent and urge you not to actually try any of this at home.
And, some ground rules. I want to try to keep this away from too technical of a discussion of slow compartments, fast compartments and other model related stuff. The decompression models are a great foundation to start with, but they don't actually answer any real world questions. Plus, while I have had the fortune to discuss this kind of thing with some of our real current pioneers, I am not qualified to accurate describe what they have told me.
This is aimed at recreational open water dives. But, keep in mind that all dives are "decompression dives." However, on recreational dives, it is safe to perform the decompression at 1 atmosphere (the surface) rather than at depth. (To avoid exceeding the maximum M-values of the models. There, I broke the rule, hopefully it is out of my system now.) So, follow along with the technical decompression stuff, I am going somewhere that applies to "no-deco" dives.
Background (AKA, even the stuff DAN gets right). Everyone has been taught to make a safety stop at 15' for 3-5 minutes. This does reduce the risk of decompression sickness. However, the common misconception places too much emphasis on this being like a safety "decompression" stop where you are getting some great benefit of offgassing by breathing air for 3 minutes at 15 feet. You probably aren't. In all likelihood, the primary benefit to your average open water diver is it forces them to halt their trident missle like ascent to the surface and induces a slower ascent.
Some Theory (unavoidable, I hate it too). In theory there is some super slow, moving at 1 micro meter per minute ascent rate that would give you the pefrect decompression from a 500' dive. However, this would vary at each depth and would require ridiculous decompression tables, so the models use 10' increments. Once it is safe to move up 10', you move up to the next level. (Historical digression, the old Orca computers used to give the actual depth ceiling. It was hilarious to watch people finish "deco" in 2' of water with their valves breaching the surface.)
The "new" safety stop. Open water divers are starting to pick up the "deep stop" theories that technical divers have been using for years. There are numerous iterations of this, 2 atm off of the bottom, some percentage of your bottom atm, etc. However, like the safety stop, this has often been simplified to 1/2 your max depth for a few minutes. Once again, this helps by slowing the ascent even more. But, 1/2 max isn't really optimum for any square profile dive.
Deep stops work best on deep helium dives. They miraculously allow you to greatly shorten shallower stops. This is because helium ongasses and offgasses so much more quickly. So, you can start off-gassing more efficiently with a lower gradient (Tehcnical term again, the difference between the partial pressure of the inert gas (anything non-oxygen) dissovled in your skull and the pressure of the inert gas you are breathing.) These deeper stops help prevent any "pre-dcs" problems on the shallower portions of deco and making this deco more efficient. This is because, while you can generally "successfully" decompress without these deep stops by staying longer at shallower depths, you body has some pre-symptomatic dcs that slows down the process and makes it take longer. Plus, it does do a little more damage this way. If you can prevent this pre-symptomatic stuff, the time spent on shallower stops can be reduced.
Now, for the recreational diver using nitrox (stop using air once you have decen bouyancy skills) the bad news is that, helium is a much easier gas to decompress off of so you get less benefit from "deep" stops. However, you do get a benefit. Remember, in theory, a super slow ascent is the safest way to dive. This, is what deep stops and safety stops are really trying to get you to do.
So, how can you improve your dive safety. I can't help there remember, listening to me will get you bent. (The following assumes dives 100' or shallower, so the "in generals" get even less accurate on deeper dives. After 100', I would encourage using helium for the safety in the reduction of narcosis and decompression risk.) In general, and that is a big in general, you can come 20-30 feet off of your max bottom depth at 30 feet per minute. A great way to help do this is to make 20 second stops every 10 feet. Once you have come off the bottom your 20-40 feet, you want to start moving at 10' per minute. Making, a 1 minute stop every 10' to help control this. Once you get somewhere in the 40-10' range, depending on your dive, you may want to start making slightly longer stops. On most recreational dives, I will do a few minutes slowly going from 20-10'. A nice slow ascent from 10' is also beneficial if conditions permit. Here, you just have to do it slow. Using the 1 minute stop thing at 0' won't help much.
This can be made much simpler by just planning and diving multi-level dives. Not maxing your time at 100' and planning to spend a portion of your dive at 70', then at 50' obviates the need for some of the steps discussed above. This is best learned by feel. Once you start getting it right, you will feel much better after dives.
Soapbox. I hope the discussion doesn't focus on this. My big problems with computers being "ridden" up is people don't focus on the slow gradual ascent that can be achieved by a multi-level dive or the focused slow ascent procedures discussed above. There is more of a, "oh crap, two minutes from deco, let's bolt up 30' to add more time mentality that is actually counterproductive to a safer ascent. There is nothing wrong with using a computer if you follow the procedures discussed above since its ndl will, in general, be very conservative with the proper diving practices. For this topic though, UP just posted several old threads that cover it in massive detail and there is no need to rehash it.
And, some ground rules. I want to try to keep this away from too technical of a discussion of slow compartments, fast compartments and other model related stuff. The decompression models are a great foundation to start with, but they don't actually answer any real world questions. Plus, while I have had the fortune to discuss this kind of thing with some of our real current pioneers, I am not qualified to accurate describe what they have told me.
This is aimed at recreational open water dives. But, keep in mind that all dives are "decompression dives." However, on recreational dives, it is safe to perform the decompression at 1 atmosphere (the surface) rather than at depth. (To avoid exceeding the maximum M-values of the models. There, I broke the rule, hopefully it is out of my system now.) So, follow along with the technical decompression stuff, I am going somewhere that applies to "no-deco" dives.
Background (AKA, even the stuff DAN gets right). Everyone has been taught to make a safety stop at 15' for 3-5 minutes. This does reduce the risk of decompression sickness. However, the common misconception places too much emphasis on this being like a safety "decompression" stop where you are getting some great benefit of offgassing by breathing air for 3 minutes at 15 feet. You probably aren't. In all likelihood, the primary benefit to your average open water diver is it forces them to halt their trident missle like ascent to the surface and induces a slower ascent.
Some Theory (unavoidable, I hate it too). In theory there is some super slow, moving at 1 micro meter per minute ascent rate that would give you the pefrect decompression from a 500' dive. However, this would vary at each depth and would require ridiculous decompression tables, so the models use 10' increments. Once it is safe to move up 10', you move up to the next level. (Historical digression, the old Orca computers used to give the actual depth ceiling. It was hilarious to watch people finish "deco" in 2' of water with their valves breaching the surface.)
The "new" safety stop. Open water divers are starting to pick up the "deep stop" theories that technical divers have been using for years. There are numerous iterations of this, 2 atm off of the bottom, some percentage of your bottom atm, etc. However, like the safety stop, this has often been simplified to 1/2 your max depth for a few minutes. Once again, this helps by slowing the ascent even more. But, 1/2 max isn't really optimum for any square profile dive.
Deep stops work best on deep helium dives. They miraculously allow you to greatly shorten shallower stops. This is because helium ongasses and offgasses so much more quickly. So, you can start off-gassing more efficiently with a lower gradient (Tehcnical term again, the difference between the partial pressure of the inert gas (anything non-oxygen) dissovled in your skull and the pressure of the inert gas you are breathing.) These deeper stops help prevent any "pre-dcs" problems on the shallower portions of deco and making this deco more efficient. This is because, while you can generally "successfully" decompress without these deep stops by staying longer at shallower depths, you body has some pre-symptomatic dcs that slows down the process and makes it take longer. Plus, it does do a little more damage this way. If you can prevent this pre-symptomatic stuff, the time spent on shallower stops can be reduced.
Now, for the recreational diver using nitrox (stop using air once you have decen bouyancy skills) the bad news is that, helium is a much easier gas to decompress off of so you get less benefit from "deep" stops. However, you do get a benefit. Remember, in theory, a super slow ascent is the safest way to dive. This, is what deep stops and safety stops are really trying to get you to do.
So, how can you improve your dive safety. I can't help there remember, listening to me will get you bent. (The following assumes dives 100' or shallower, so the "in generals" get even less accurate on deeper dives. After 100', I would encourage using helium for the safety in the reduction of narcosis and decompression risk.) In general, and that is a big in general, you can come 20-30 feet off of your max bottom depth at 30 feet per minute. A great way to help do this is to make 20 second stops every 10 feet. Once you have come off the bottom your 20-40 feet, you want to start moving at 10' per minute. Making, a 1 minute stop every 10' to help control this. Once you get somewhere in the 40-10' range, depending on your dive, you may want to start making slightly longer stops. On most recreational dives, I will do a few minutes slowly going from 20-10'. A nice slow ascent from 10' is also beneficial if conditions permit. Here, you just have to do it slow. Using the 1 minute stop thing at 0' won't help much.
This can be made much simpler by just planning and diving multi-level dives. Not maxing your time at 100' and planning to spend a portion of your dive at 70', then at 50' obviates the need for some of the steps discussed above. This is best learned by feel. Once you start getting it right, you will feel much better after dives.
Soapbox. I hope the discussion doesn't focus on this. My big problems with computers being "ridden" up is people don't focus on the slow gradual ascent that can be achieved by a multi-level dive or the focused slow ascent procedures discussed above. There is more of a, "oh crap, two minutes from deco, let's bolt up 30' to add more time mentality that is actually counterproductive to a safer ascent. There is nothing wrong with using a computer if you follow the procedures discussed above since its ndl will, in general, be very conservative with the proper diving practices. For this topic though, UP just posted several old threads that cover it in massive detail and there is no need to rehash it.
