Browsing Tag dive skills
The 5 main trends in decompression
Decompression theory has a reputation of being complicated and hard to learn.
In my experience, it doesn’t have to be!
We can reduce the complexity if we just keep in mind these 5 main trends of decompression theory.
*Note: this article isn’t meant to be a thorough understanding of decompression theory. The main goal is to simplify decompression theory in layman’s terms.
Trend 1 – The deeper you go, the more nitrogen you take up because of the higher pressure of the gas you breathe.
Whenever you scuba dive, you are breathing gas at ambient pressure.
This means that you are breathing more molecules of nitrogen for every breath that you take when deeper than sea level.
The deeper you go, the more molecules of gas you take in, even though the volume of gas in each breath doesn’t change.
This extra nitrogen is absorbed into your body and eventually, will need to be released when you ascend to the surface.
Trend 2 – The longer you stay, the more nitrogen will get absorbed into your tissues.
If you spend longer in the water at depth, then the more breaths you will take and more nitrogen will be absorbed into the body.
Trend 3 – If the gas you use has a lower nitrogen content, then there will be less nitrogen available to be absorbed into your tissues.
Let’s compare two gases, one with a lower nitrogen fraction than the other.
Which gas will cause more nitrogen absorption into the body given that all else is the same (number of breaths taken, depth and duration of dive)?
I think the answer would be fairly obvious.
This basic idea is the reason why Enriched Air Nitrox (EAN) gas mixes exist.
A commonly available EAN mix is 32% oxygen and 68% nitrogen.
This provides an 11% reduction in nitrogen content as compared to normal air.
Choosing an Enriched Air Nitrox mix is always a good idea for reducing your decompression obligation.
Trend 4 – The slower you ascend, the more excess nitrogen will leave your body.
A less commonly known trend would be how fast you surface from each dive.
By ascending slower, you’re allowing time for the nitrogen in your tissues to leave your body.
A faster ascent rate also causes any gas bubbles in your body to expand.
It will also cause the release of excess nitrogen as bubbles instead of being transferred back to the lungs for exhalation.
By slowing down our ascent rate, we can control the size of these bubbles and at the same time allow nitrogen to work its way out of our tissues.
Trend 5 – The longer the surface interval, the less nitrogen you will have before your next dive.
Once on the surface immediately after a dive, there will always be some excess nitrogen in your tissues. This is the concept of residual nitrogen.
The more residual nitrogen you have in your system, the more conservative you should be on your subsequent dive.
Thus, the longer you stay on the surface before your next dive, the more time the excess nitrogen has to leave your body.
The less nitrogen in your system, the better it is for your decompression obligation on your next dive.
Putting it all together
So what does this mean for divers?
How can we navigate the complexities of decompression while staying safe?
The 5 main trends in decompression
General rules
Once you understand these trends, then how do we put everything together?
I consider these 5 trends as adjustable variables in my overall decompression obligation.
I can tweak or adjust one or more while leaving the others in place, allowing me to ‘adjust’ my decompression obligation based on the dives I’m planning to do.
Planning a day of diving
Keep the number of dives per day to 3 (roughly 9 am, 1 pm, 4 pm, with a break for lunch).
You can add on a dawn dive and a night dive as these would extend the beginning and end of your diving day.
Let’s look at how this relates to a decompression table.
Let’s look at a PADI RDP table and trace a line that follows a surface interval of 1 hour and 2 hours.
The PADI RDP table showing a 1 hour and 2 hour surface interval line
We can notice that we end up with a pressure group of J and C respectively if we have a starting pressure group of Z.
With a more realistic pressure group of between G and M, you would end up with a pressure group between A to E after a 1 or 2-hour surface interval respectively.
With a 2-hour surface interval between each dive, 3-day dives are all that you have time for anyway.
What about if you happen to miss a safety stop?
If you do happen to miss a safety stop, then change up one of the other parameters on your next dive.
You could do a longer surface interval, do a slower ascent, stay shallower, or dive for a shorter time.
You can still change the depth and length of your dive if you are on a fixed dive schedule.
Always ascend slowly
For ascents, I would always take my time to ascend, limited by the gas that you have remaining.
However, I only do this after I’m shallower than 6m. Any deeper than that and you would still be taking on nitrogen into your system.
If there’s a nice shallow reef with things to look at while you are at your safety stop, and you also have plenty of gas left, then why not stay and enjoy the view?
Personally, I would ascend slowly (9 m per min) to half of my depth, then move at 3 m per min up to 6m.
Once at 6m, provided the team has gas, I’d take my time and enjoy the sights until everyone’s computers have cleared or we get bored!
We’ve been known to hang around at 6 m for 15 to 20 mins!
And always dive Nitrox!
As for gas choice, if you ask me, there’s no reason to dive air if there’s nitrox available.
If I can reduce my decompression obligation just by changing the gas I dive with, it’s a no-brainer.
There’s so much benefit in diving nitrox, and these days it doesn’t cost much either.
There you have it!
Some simple and easy to remember rules for planning a day of diving while keeping yourself safe.
Now, get out there and know your decompression obligation!
Why does my finger get cut on bolt snaps?
Almost everyone who’s had any experience doing a course where drills and bolt snaps are involved ends up with fingers and thumbs cut up like in the photo above.
Why does this happen, and how can we prevent it?
Rushing is never a good thing
Bolt snaps, while great for attaching to dive gear, is terrible on fingers when used incorrectly.
The skin on our fingers gets softer when diving for a while.
This delicate skin is easily scratched and torn when rubbed on a sharp surface.
A badly torn up thumb from using a bolt snap incorrectly.
Be careful where you put those fingers!
Gloves aren’t really the answer, as always, I’m more in favor of dealing with the cause of the problem, rather than fixing a symptom.
The proper method for managing bolt snaps then is to place the side of your finger on the trigger, and not press your flesh into the sharp edges of the slot.
The proper way to hold a bolt snap open.
The sharp bit of a bolt snap is the slot that holds the spring of the trigger, not the trigger itself.
By placing your finger further out, you’ll reduce the risk of the two sharp edges slicing your skin.
Slow is smooth, smooth is fast
Get a good finger position on the trigger, then position the gate next to the D-ring before applying pressure. The bolt snap should slip right into the D-ring at this point.
Too often, I see divers trying to ‘catch’ the D-ring with the gate while holding it open.
Or they would apply too much pressure on the trigger because they are stressed out and trying to get the drill done quickly.
As with anything in life, rushing is never a good thing.
Slow is smooth, smooth is fast!
The two diving skill sets every passionate diver should consider
This post about skill sets is for serious divers who are truly passionate about diving all that this world has to offer, every ocean, every lake, every river. If that’s not you, then read no further!
The world is your oyster!
To me, any body of water is diveable given the right skills and logistics, it’s just a matter of whether it’s worth your time or curiosity.
My endless curiosity has always made me wonder what’s just a little deeper, just around the corner, underneath the surface.
Over time, I’ve built up a set of skills that I think truly allows me to look at any body of water on earth and think seriously about diving it.
All the time in the world
The first limitation in diving is one of time.
No decompression time limits and gas volumes limit most divers to about an hour on each recreational dive.
However, with technical diving, these limitations are made irrelevant with the appropriate logistics and skills.
In a technical diving course, you’ll learn how to manage different gas mixes, allowing for deeper dives and extensions of bottom time.
You would also learn how to calculate the decompression time and gas necessary to accomplish this.
Once you have the ability to dive with multiple tanks, then gas volumes also become irrelevant.
It just comes down to how many tanks you can carry or stage during your dive. It becomes a question of logistics.
Technical diving isn’t only about depth, but rather about decompression.
This can be calculated for a 2-hour dive at 25m, or a 1-hour dive at 75m.
Either way, doing a technical diving course allows you to go past recreational depths and time limits, whilst ensuring that you have the knowledge to plan enough bottom gas and deco gas to complete the dive.
It’s only cold in space
After getting technical diving skills, the next limitation most people face is the temperature.
Extended duration dives tend to suck the warmth from you, even in 28C water.
Warm water diving is actually limited to only a few degrees of latitude north and south of the Equator, and only tens of meters below the surface.
Once past the Tropic of Cancer and Capricorn, and you’re definitely in cold water country.
This leaves large areas of water that you’ll definitely need a drysuit to dive in.
Why limit yourself to Earth’s wonders that are only in warmer locales?
What about diving between continental plates in Iceland, or the wrecks of the North Sea?
So, the next most important skill set is learning how to dive with a drysuit.
This does take some time to get used to, as managing thick undergarments is no walk in the park.
But once you do, then all the wonders of the northern and southern latitudes will open themselves up to you, as well as longer dives in warmer waters.
Get wet anywhere!
With these two skillsets, I truly believe it enables divers to dive anywhere in the world you might want to.
Overcoming depth, time and temperature limits are not easy and will take some time to accomplish.
But just imagine knowing you can dive anywhere in the world. What a rush!
Bonus skill – getting in over your head
As a bonus, here’s the third set of skills that I think a true explorer should learn – cave diving, the last frontier.
I personally learned cave diving not because of the caves, but rather for the skills and knowledge of how to do dives in overhead environments.
These skills come in very handy when diving in wrecks, sea caves, or any kind of environment where you don’t have a direct ascent to the surface.
The true skill here is in learning how to better plan and manage your gas supply to guarantee that you and your teammates can safely ascend to the surface.
Another important skill set that cave diving teaches you is line management.
This is very useful in any survey or mapping exercise and keeps you on your toes as far as navigation is concerned.
Now, get out there and dive!
And there you have it, my three picks for the skill sets that you should consider to be a limitless diver!
The Path to Conservation
Speech on Reef Building projects by Livingseas at the ADEX 2017 Scuba360 Business Forum
A speech was given by Leon Boey to attendees of the Scuba360 Business Forum organized by the Blue Ocean Network at ADEX 2017 (7th April 2017).
He talks about the reef building projects Livingseas Asia has done previously.
He also highlights the current state of dive education and how it relates to marine conservation, finishing off with the things that dive operators and instructors can do to improve.
*Some images from the internet used without permission! Sorry about that!