Finding the right mind set to prepare for a trimix dive to 100mts can take days, and we have to complete build up dives to reach our goal. Our day starts with another gallon of water consumed for breakfast..... hold the coffee for the week, it dehydrates you! The night before was spent drinking copious amounts of H2O and rest. Mind needs to be sharp as we are entering a realm of crush depth for the dive equipment we are using. Pee test in the morning, any signs of dehydration and the dive is off..... Clear pee... Alright, dive is a go! We have calculated out the ideal gas blend for that depth using our desktop decompression software (V-Planner). We need to eliminate the oxygen content as it starts to become toxic below 66mt / 218ft, (I know I can dive deeper on air and not be concerned about oxygen toxicity, but that's a different story all together). We need to replace the nitrogen as well, after hydrogen, helium is the second lightest and second most abundant element in the observable universe, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Whatever, put it our scuba tanks and call it Trimix, a mixture of helium, oxygen, and nitrogen. A shorten version, we are going to dive TMx 10/60, 10% oxygen, 60% helium, 29% nitrogen. I know right, 10% will not sustain life on surface, well done..... So, we need a travel gas that we can breathe on the surface and a deep deco gas. We calculate out that we will blend a TMx 18/15 as our travel gas, and not switch until we reach 1.4ata for the oxygen content, meaning our switch depth is 68mt / 223ft. With now 3 tanks on us we need decompression gases to accelerate our decompression, two most common deco gases 50/50 and 100% Oxygen. So, a total on this dive of 6 tanks that we will carry and safely switch to each regulator, because if not there's no coming home. An instant killer in technical diving, respect your gas switches!
On surface before starting the dive we perform a full gas shutdown drill and a modified out of air drill to keep our minds sharp. Its going to take roughly 5 minutes to reach bottom with one gas switch and the way down. We are descending into a dive site called "The gateway to hell" although it looks like a stairway to heaven.
On the descent we roll through the first thermocline at 70mts / 230ft, a deep dark cold feeling rushes over you. We continue on the descent, staring into a crack in the earth that has been there since the ice age. 30mt / 100ft still on the descent, we hit the second thermocline at 88mts / 290ft. The water temp is now reading 24c / 76f, I know it's cold to us, but still pretty warm at those depths. This is where time is now starting stand still, every breath were taking in 10 times that of the surface, the high amount of helium squeaks through the second stage. I am sitting at 100mts / 333ft, staring into the darkness and beauty of what the ocean has created in front of me. My mind is sharp analyzing all potential problems that could occur, however the high content of it is making me slightly light headed. A feeling one could not describe to a person that has never felt the deep like this.
One minute warning before the long ascent to the surface, focus.... Situational awareness has me checking time, gas supplies, depth and ascent rates to follow. Our bottom time is up, check and record pressures, within my rule of thirds we ascend. We are know in a critical zone as we ascend up the crack monitoring an above average ascent rate. Pass through the second thermocline and a rush of warm water warms us up, we reach our switch depth and safely switch to our deep decompression gas Tmx18/15. From now on we ascend no faster than 6mts/min. Whilst decompressing in the deep waters we constantly are monitoring each other and ourselves for any unusual behavior or symptoms, to much can wrong in this portion on the dive. @ runtime 29min of the dive we have a gas switch to 50/50 mix that will start to speed up the washout of nitrogen and helium, and @ runtime 41min of the dive we switch to 100% Oxygen for an even more accelerated gas tissue washout. At the completion of the dive 60min, we signal each other that we have completed our decompression schedules and we all feel that no DCS signs or symptoms. Before ascending we need to finish off the dive with a proper ascent to the surface. An additional 2min @ 5mt/15ft, 2min @ 3mt/10ft, and 1min @ 1.5mt/5ft. Once on surface we continue to breath down our Oxygen for a safety factor.
A look at the schedule that V-Planner has created for us to follow. However we still have our multi-gas dive computers, with back ups.
Dec to 220ft (3) Trimix 18/15 60ft/min descent.
Dec to 300ft (5) Trimix 10/60 60ft/min descent.
Dec to 333ft (5) Trimix 10/60 60ft/min descent.
Level 333ft (9) Trimix 10/60 1.11ppO2, 106ft ead, 113ft end
Asc to 240ft (11) Trimix 10/60 -40ft/min ascent.
Level 240ft (12) Trimix 10/60 0.83ppO2, 71ft ead, 76ft end
Asc to 220ft (12) Trimix 18/15 -40ft/min ascent.
Stop at 220ft 0:11 (13) Trimix 18/15 1.38ppO2, 182ft ead, 182ft end
Stop at 200ft 1:00 (14) Trimix 18/15 1.27ppO2, 165ft ead, 165ft end
Stop at 180ft 1:00 (15) Trimix 18/15 1.16ppO2, 148ft ead, 148ft end
Stop at 160ft 1:00 (16) Trimix 18/15 1.05ppO2, 131ft ead, 131ft end
Stop at 150ft 1:00 (17) Trimix 18/15 1.00ppO2, 122ft ead, 123ft end
Stop at 140ft 1:00 (18) Trimix 18/15 0.94ppO2, 114ft ead, 114ft end
Stop at 130ft 1:00 (19) Trimix 18/15 0.89ppO2, 105ft ead, 106ft end
Stop at 120ft 1:00 (20) Trimix 18/15 0.83ppO2, 97ft ead, 97ft end
Stop at 110ft 1:00 (21) Trimix 18/15 0.78ppO2, 88ft ead, 89ft end
Stop at 100ft 1:00 (22) Trimix 18/15 0.72ppO2, 80ft ead, 80ft end
Stop at 90ft 1:00 (23) Trimix 18/15 0.67ppO2, 71ft ead, 72ft end
Stop at 80ft 2:00 (25) Trimix 18/15 0.62ppO2, 63ft ead, 63ft end
Stop at 70ft 4:00 (29) Nitrox 50 1.56ppO2, 32ft ead
Stop at 60ft 1:00 (30) Nitrox 50 1.41ppO2, 26ft ead
Stop at 50ft 2:00 (32) Nitrox 50 1.26ppO2, 20ft ead
Stop at 40ft 4:00 (36) Nitrox 50 1.10ppO2, 13ft ead
Stop at 30ft 5:00 (41) Nitrox 50 0.95ppO2, 7ft ead
Stop at 20ft 3:00 (44) Oxygen 1.60ppO2, 0ft ead
Stop at 15ft 15:00 (59) Oxygen 1.45ppO2, 0ft ead
Surface (59) Oxygen -20ft/min ascent.
-- lost gas--> These tables are brought down as a back up for a lost gas situation, the diver would have to be alone to follow these tables, you learn more about this in the deep air courses.
OK 50 100 18/15
333 (9) (9) (9) (9)
240 (12) (12) (12) (12)
220 0 (13) 0 (13) 0 (13) 0 (13)
200 1 (14) 1 (14) 1 (14) 2 (15)
180 1 (15) 1 (15) 1 (15) 3 (18)
160 1 (16) 1 (16) 1 (16) 1 (19)
150 1 (17) 1 (17) 1 (17) 2 (21)
140 1 (18) 1 (18) 1 (18) 1 (22)
130 1 (19) 1 (19) 1 (19) 2 (24)
120 1 (20) 1 (20) 1 (20) 3 (27)
110 1 (21) 1 (21) 1 (21) 3 (30)
100 1 (22) 1 (22) 1 (22) 3 (33)
90 1 (23) 1 (23) 1 (23) 4 (37)
80 2 (25) 2 (25) 2 (25) 5 (42)
70 4 (29) 3 (28) 4 (29) 5 (47)
60 1 (30) 3 (31) 1 (30) 1 (48)
50 2 (32) 5 (36) 2 (32) 4 (52)
40 4 (36) 7 (43) 4 (36) 6 (58)
30 5 (41) 10 (53) 5 (41) 8 (66)
20 3 (44) 4 (57) 4 (45) 5 (71)
15 15 (59) 16 (73) 21 (66) 24 (95)
These are tables we need to take in case the dive went too deep or too long.
333, 9 333, 12 336, 9 336, 12
(9) (12) (9) (12)
(12) (15) (12) (15)
240 0 (16) 0 (16)
220 0 (13) 1 (17) 0 (13) 1 (17)
200 1 (14) 1 (18) 1 (14) 1 (18)
180 1 (15) 1 (19) 1 (15) 1 (19)
160 1 (16) 1 (20) 1 (16) 1 (20)
150 1 (17) 1 (21) 1 (17) 1 (21)
140 1 (18) 1 (22) 1 (18) 1 (22)
130 1 (19) 1 (23) 1 (19) 1 (23)
120 1 (20) 1 (24) 1 (20) 1 (24)
110 1 (21) 1 (25) 1 (21) 1 (25)
100 1 (22) 2 (27) 1 (22) 2 (27)
90 1 (23) 2 (29) 1 (23) 2 (29)
80 2 (25) 3 (32) 2 (25) 3 (32)
70 4 (29) 4 (36) 4 (29) 4 (36)
60 1 (30) 1 (37) 1 (30) 1 (37)
50 2 (32) 4 (41) 2 (32) 4 (41)
40 4 (36) 5 (46) 4 (36) 5 (46)
30 5 (41) 8 (54) 5 (41) 8 (54)
20 3 (44) 4 (58) 3 (44) 4 (58)
15 15 (59) 21 (79) 15 (59) 21 (79)
Respecting deep diving comes with experience and training, I tell my students "anyone can deep dive, that's the easy part, however it's the smart divers that come home alive". Diving deep on a single tank with no planning or redundancies is just down right dangerous, get the training and enjoy your deep dive career.
By: Richard Devanney
To a new diver, thoughts of narcosis can be very mixed. Some may find it to be a scary prospect, whilst let’s be honest others will relish the thought of getting a free thrill during a dive, which may tempt them to go deeper than their certification and/or level of competence should otherwise allow. This contrasts with a cautious, risk-averse diver. They know narcosis as something to become familiar with in a controlled environment, before taking active steps wherever possible to minimize its effects on all future dives. Now some of you may be thinking “that’s rubbish, who wants to be risk-averse!”. My response to this is that you dear reader are exactly the person that this article is aimed at.
All divers have been taught the basics of what narcosis is
All divers have been taught the basics of what narcosis is, along with what they should do to reduce its effects during a dive. At open water level narcosis isn’t really of great concern, as it’s not usually noticeable by diver nor observant buddy up to the 18m (60ft) maximum depth range. For advanced divers going to 30m (100ft), it’s your new imaginary friend, sitting on your shoulders with its feet in the stirrups, poised and ready to take over the reins. But many will hardly notice its effects. Those that do should be able to cope fairly easily- there are always exceptions to this of course. But what about going deeper than 30m- how does it affect you then? Can you maintain control? At what point will it start to control you? These are kind of important considerations, so let’s delve a little deeper to find out more.
What’s in a name I hear you ask- It’s ok, I can’t really hear you. But seeing as you probably would have asked anyway, the nomenclature originates from the Greek word narke, and loosely translates to “numb”. But it has collected a few other familiar names over the years; “the martini effect” (ridiculous), “rapture of the deep” (I was hoping that when the rapture does come I can just go for a dive and let it pass me by) I’m sure there are more names but they will be equally silly. Most people call it Nitrogen (N2) narcosis because there’s more of it in your cylinder of air than oxygen. Yet there are some people- mainly technical divers, that call it inert gas narcosis, because you know, nitrogen is inert and they crave accuracy and order. Some even more anal tech divers go further and call it gas narcosis, because they want to outdo other tech divers in the accuracy and order stakes, and also because carbon dioxide and oxygen are also narcotic (though it’s unclear as to how narcotic one is relative to the other). But for the sake of concision, I’ll call it narcosis for the rest of the article because, a- I’m a lazy typist, and b- any excuse to wind up the online dive police.
As you go deeper during a dive, narcosis will increasingly affect you in numerous ways. If you continue descending beyond both your maximum depth and better judgment (whichever comes first!), it will eventually induce an anesthetic effect on you, and there hasn’t been an alarm clock invented that will wake you up from that slumber. Thankfully, deep air diving is not in vogue anymore so there aren’t as many stories of divers descending to oblivion as there used to be.
The exact mechanism of how narcosis works is not universally agreed upon, but the theory that most diving physicians agree on is the so-called Meyer-Overton hypothesis. This states that the narcotic effect of a gas relates to its solubility in the lipid (fat) phase of body tissues. The higher the solubility of body tissues, the more readily nitrogen (and other narcotic gases) will dissolve into them (as per Henry’s law). In this case, those body tissues are the nerve membranes of the brain. It’s believed that once enough nitrogen is dissolved into the lipid membranes, it will mechanically interfere with the transmission of signals between nerve cells.
The narcotic effect of gases on humans has been quantified in terms of their so-called Relative Narcotic Potency (RNP). Of the gases used in diving, helium has the least narcotic effect when breathed. At the other end of the scale, argon has the greatest effect, which is precisely the reason it is not breathed (along with it having a high gas density). Here’s the full list of diving-related gases, ranging from the breathable to the breathable but only under certain circumstances, to the “I would love to breathe that but it’s too expensive”, and ending with the “Superman can freedive indefinitely anyway so why is it even on the list?”:
- Helium (least narcotic)
- Xenon- (most narcotic)
Helium is not narcotic at diving depths (though it affects the nervous system beyond the 100(ish) meter range due to the rate of compression- this is known as High-Pressure Nervous (or neurological) Syndrome- or HPNS. It affects the central nervous system and symptoms include myoclonic jerking and somnolence- basically, you uncontrollably shake and then fall asleep- almost the opposite of when your dog runs in its sleep).
Not being narcotic is one of the numerous reasons why helium is a good gas for deeper diving- if you can afford it.
Hydrox- a mixture of hydrogen and oxygen has been used experimentally on very deep commercial diving projects by French company Comex, and when I say deep I mean humans standing on the sea bed at 500 meters deep (1,640ft). Theos Mavrostomos went to 701m (2,299 ft) in a chamber, just because he could.
However, because of its tendency to create large, messy, and often inconvenient explosions, hydrogen can only be used with 4-5% oxygen in the mixture, and therefore requires specialized equipment not to mention extensive training before it could be used- all at considerable cost. Neox- a mixture of neon and oxygen is a good alternative to helium as a deep breathing gas, as it is both not very narcotic and it doesn’t distort the voice unlike helium, but it’s very expensive to use (You can see a pattern forming here can’t you), and apparently if you do get DCS when using it, symptoms can be severe. Argon is only used to put in drysuits instead of air, and thankfully the regulator attached to the cylinder supplying it will not have a 2nd stage regulator attached, just in case you or your buddy are seeking out a Darwin award- it’s anoxic.
So what happens when we get narced? Do we take our regulators out to give to the fish? Generally, things are a little more subtle than that. If you descend to 30-40m (100-130ft) you may feel euphoric, lightheaded, or a little bit tingly. You may find that your ability to concentrate has reduced, and your ability to care has fallen commensurately with it. Other symptoms include perceptual narrowing (tunnel vision), altered perception of time, anxiety or paranoia, memory loss, and even a feeling of numbness. Many divers will insist that they feel nothing and think they are absolutely fine. If you ever find yourself diving on trimix between 30 and 60m (100-196ft), you will most likely have observed that, whilst you have a very clear head because you are breathing in less N2, anyone diving with you on air is noticeably slower when it comes to, well everything- communication, physical dexterity, and general coordination. Their situational awareness is almost non-existent. When watching them try to achieve a simple task, it’s all the more amusing to know that they won’t even remember how badly they were doing it- when they get back on the boat they will think that they were fine and that all their tasks were completed properly and efficiently- ignorance is bliss and relativity is difficult to gauge when everyone is riding on the same beam of light.
So how badly do these symptoms affect how in control you are during a dive?
Well, it depends on your susceptibility on the day and how deep you are; your sensitivity will change every dive; there are many factors that will influence how narced you feel on a given day. The lines are blurred as to how much of an influence each factor has on you. Tiredness, dehydration, alcohol or drugs (prescription and recreational), cold water (affects you much more than warm water), higher work of breathing, bad visibility, turbidity (particles in the water), seasickness, fear, vertigo, task loading, current, descent rate. That’s a big list of influences.
A build-up of carbon dioxide can also increase narcosis. Swimming against a current will make your breath harder, and breathing harder underwater is not very good for you because gas densities under elevated pressures are such that it is more difficult to move those gases in and out of the lungs. It’s bad enough when a regulator is forcing the air into your lungs; when you are on a rebreather you are doing the work so it’s even worse. The bigger the atom, the harder it is for you to move it. So it’s harder to expel CO2 from the lungs and consequently the body, which allows it to build up. CO2 is more narcotic than N2, but its effect on narcosis is not simply an effect of higher partial pressures of CO2. In the blood CO2 is a dissolved gas in a non-compressible fluid, so partial pressure is not the only factor at play. If it was then we would not be able to go diving because levels would quickly prove fatal as we descend. In addition to narcosis, CO2 acidifies the blood and has anesthetic properties, so hypercapnia (or excess carbon dioxide) is not very good for you. CO2 is also a vasodilator so it has an influence on CNS oxygen toxicity risk. Basically, CO2 is bad.
Staying in control
The thing about narcosis is, that it’s very easy to get complacent about it. There is such a thing called normalization of deviance. It’s not a diving thing, it’s a human thing, so divers do it because they are usually human. It’s basically becoming accustomed to bad/unsafe behavior because it’s done so much without any negative consequences that it’s not considered bad/unsafe anymore; it’s considered the norm. A great example is a professional videographer filming open water groups in between solo diving to get the shots they need, but without the qualification, training, and redundant gas source. Another example is not doing a full or thorough buddy check before diving. There are countless other examples. People continue bad behaviors because 99 times out of 100 nothing will go wrong. But something only needs to go wrong once.
With narcosis, you may feel anxious during a 30m dive, or just so spaced out that you hardly check your air and don’t keep track of your buddy. These are not good things, but you made it back to the boat so it must have been ok- you’ll just continue to deal with it. But what if something does go wrong, what if your buddy gets very low on gas and you need to share? Will you be able to act on this quickly and safely when you already have a head full of anxiety or are feeling mentally slow, or have poor motor skills- or all three? We know that most accidents occur because of numerous factors rather than one single thing. If something goes wrong, isn’t dealt with and it leads to another thing going wrong, then the odds may be stacked high against a safe outcome because there’s just too much going on in a critically short window of time. Call it the domino effect or the incident pit or whatever you want.
Now just so you know I’m not trying to be dramatic, I know that the chances are that for most people in the 30m (100ft) range and even the 40m (130ft) range, a low on air diver or BC malfunction etc will usually be dealt with to provide a safe outcome. They may be messy but hey, you’re narced. Remember by the time you’re back on board the boat you’ll think you did a great job of it anyway! This is just an article to hopefully make you ponder some things in your diving that you maybe don’t think about too much.
So how about at between 40m and 55m (130-180ft)?
I shouldn’t really have to mention that going beyond 55m on air is not a good idea, with narcosis being one reason why. You will be on another planet mentally and as you continue to descend you will find yourself completely incapacitated before the inevitable unconsciousness arrives. Some people don’t think you should really be going beyond 30m on air (yes I’m one of them, but I also know that trimix is prohibitively expensive). Yet at these kinds of depths, you really do have to exercise very conservative judgment about your ability to deal with things going right, along with your ability to cope and solve problems if things go wrong, not simply whether you will manage to do the dive with no issues. If you have any inkling whatsoever that you may not be able to handle yourself or your team mate being out of gas or tangled up, it’s probably time to get your trimix qualification. The helium in trimix offsets some of the nitrogen so you feel more clear-headed. The problem with doing these dives without trimix is that you are impaired remember, so you don’t have good judgment in the first place! You won’t really know until it all goes wrong. Sure, you can practice going to 50m and do some drills to see if you get better/faster/more efficient at them, but remember the trimix divers watching the air divers? Don’t kid yourself. A big part of risk management involves being honest with yourself.
So what can you do about it? As with most things technical diving, risk management begins on land before you even start day dreaming about how great you look in a wetsuit. You’ll need to think about:
- What’s your dive plan- how deep do you want to dive?
- What do you want to achieve on the dive, what are your objectives, are they complex/simple?
- What’s the weather like? Will it get choppy? Will there be a current? Could the weather change during the dive?
- How cold is the water? Will there be a thermocline? Wetsuit or drysuit- heated vest?
- Visibility good or bad, turbidity?
- What’s the competence of your dive team? Is there a big difference in competence?
- How many people are you diving with? Who is doing what?
- Could you use gases other than air (helitrox or trimix)?
- Will you free descend or use a shot, can you do a slow, staged descent?
- Is it a decompression dive?
- How good is your regulator, is it appropriate for the depth you want to dive in terms of ease of breathing, i.e. balanced?
If you think about it, none of the above are new things to think about.
You should be considering them in some form or another on every dive. But you could also ponder your water entry, will you have to swim hard against a surface current to get to a descent line? Can you have a rest before descending? You shouldn’t be out of breath during a dive so being out of breath immediately before is a little bit silly. Can you descend in a slow and controlled way? Staging your descent and descending slowly can help reduce task loading with ear equalization, equipment comfort and settling into the dive. It will also provide a gradual increase in nitrogen exposure to the brain in terms of PPN2. This is extremely anecdotal but I personally don’t want to drop like a stone and find myself suddenly hit by a wall of fuzziness- but that’s just me.
Whether it’s a decompression dive or not is markedly different to a no-stop dive. The usual advice on narcosis is that if you don’t like the feeling then ascend and it will disappear. Whilst that’s true, for a deco dive the missing component of that is “in how long”. I have done many a deco dive where I know I am narced, and as I ascend and switch to 50% Oxygen…. Yep, still narced.. time to move up to 12m now, yep, still narced. There is a noticeable delay, even after breathing a gas with less N2 before the effects start to disappear. If you have to navigate back to a specific point during your ascent and the vis is not great, maybe take that into account.
Another consideration about decompression dives is the complexity of your plan.
Technical divers plan dives, they also plan contingencies. Some plan contingencies of contingencies. Then they are all written on slates or wet notes to view during the dive. The main plan, over depth/over time, over both, one lost gas, another lost gas, multiple lost gases, minimum gas, ascent pressure, turn pressure. Many variations of these.
Dive planning is important, as is contingency planning.
So what am I getting at? Well having 3 or 4 plans written down is all well and good, but what about when you’re narced, and you find that you have to actually use one of the backup plans? It’s stressful and can be complicated depending on how narced you might feel. Yes, practice practice practice I hear you say, but it’s the instructors saying that and it’s easy for them to say- it’s their job to dive every day. They will find these things easier, otherwise, why are you going to them? It’s a bit harder for people that do it as a hobby to get in anywhere near as much practice as they would like.
So here’s the real question, aimed at hobby divers. Who out there will tell me that they will immediately refer to their back up plan and utilize it correctly if a real emergency occurs at depth? It’s more likely a case of deal with the immediate problem, start heading up, and then at the first available opportunity take stock and think about how much you deviated from everything because there were more pressing things going on than referring to back up plans. By then all your plans could be completely irrelevant. So let’s get down to brass tacks and be realistic- how complicated is your plan? Can you simplify it anymore to make it easier to read/use when needed? This might be the way it’s written down, the way you compare total runtime to your bottom timer, it may even be as simple as ensuring that you have a dive computer with a stopwatch function (yes please in dive mode as well as gauge mode shearwater, hint hint). Why do you think you might go over depth or over time? Can you actually do the dive with a simple plan and back up plan in your head? Again, just things to ponder.
One of the biggest things to factor in is who you are diving with.
You may be lucky enough to have friends that you regularly dive with, who are sensible and you dive well together. That’s great. The alternative is when you dive with people you don’t know. Of course there will always be people with different levels of experience and competence and after all, diving can be a great way to meet new people and learn new things. I’m not talking about deep decompression dives either, just regular dives to 30-40m. I’m talking about a specific type of person. Basically, don’t dive with the person at the beginning of this article who’s aim is to get as narced as possible. They are rule-breakers, and in my opinion, potential life-takers. There are plenty of real-world stories of this kind of person ignoring a dive briefing and taking someone equally unskilled, inexperienced and unqualified inside a wreck or cave, to find themselves trapped, or find their way out but the buddy doesn’t. Swap wreck for depth and the outcome may be the same. Diving is not a competitive sport (Though I sometimes wonder that when browsing certain Facebook groups), and the laws of physics apply to everyone.
Like most things, diving procedures, equipment considerations and the like are not rocket science once learned properly, but there are numerous things to consider. One that is often neglected is risk management, and certainly risk management as it relates to narcosis. We often just get on with it and assume everything will be ok. But as I’ve said a few times you only need things to go wrong once. So be prepared, know your limits and set them accordingly not just based on yourself, but also based on who you are diving with, when, and where.
Maybe it’s time to see what the fuss is about with trimix.
When choosing fins, always remember that with an efficient fin, there will be a direct correlation between how much oxygen and energy you use and how much air you use. This is particularly important for novice divers who will no doubt need to conserve air more than an experienced diver who is relaxed in the water and already has sound air consumption.
There is a vast array of fins on the market and you will need to consider your level of experience, kicking style and ability, leg power and type of diving you will be doing in order to determine which type of fin will best suit you. Diving fins should neither be too short (snorkelling fins), or too long (like free diving fins). As a general rule, the stronger the leg, the longer and stiffer the fin should be. However, fins with rigid sides and a flexible middle made up of different materials will generally provide more thrust power with less effort. Many top end fins will incorporate a number of materials in the blade and foot pocket including carbon fibre, graphite and polymers to maximise the amount of energy transfer from the leg to the fin. Believe it or not, there is a great deal of science that has gone into the manufacture of fins!
Closed Heel or Open Heel?
Full foot fins are usually cheaper than open heal fins, easy to don and less bulky, however, if they are not a perfect fit for you will cause lots of friction issues and blisters. Never compromise, always go for fit when selecting full foot fins. Do not be talked into buying wet suit socks to ensure a proper fit for full fit fins or be tempted to purchase full foot fins where your toes feel cramped because they are on sale! If your fins stay on at your heel, they will not fall off in the water. Quite simply put, if full foot fins do not fit perfectly do not purchase, you are wasting your money and will live to regret your decision.
The downside of a full foot fin is that is the water is cold, they do not offer any thermal protection for your feet. Another negative is, if you are shore diving, you will need to consider where you will be walking as, without boots, your feet will be vulnerable over rock pools and similarly on hot dive decks.
As a result of the restrictions on full foot fins, most divers tend to go for an open heel fin type where a neoprene dive boot or dry suit boot is required to be worn underneath. Open heel fins are more adjustable, comfortable and versatile than full foot fins and provide cushioning and chafing protection, but tend to be bulkier, more expensive and can have complex strap adjustment mechanisms. An open heel fin worn with a dive boot will offer thermal protection in colder water and given that water is a much better conductor of heat than air is. Versatility is key with an open heel fin, the same fin being able to be worn with a pre-fitted dry suit boot or even a pair of trainers, eliminating the need for multiple fins being required in different conditions. Open heel fins also have the added advantage of providing additional stability and maximum propulsion. Whilst fit will vary between style and manufacturer, most manufacturers will provide a shoe size range as a guide for each fin size to make fitting a little easier.
Split Fin vs Paddle Blade?
Ask any experienced diver or dive professional this question and it will undoubtedly provoke a lively discussion! Whilst paddle blade fins have been around for many years, split fin technology is a relatively recent addition to diving.
The whole idea of a split fin is that the blade causes a vortex in the water as you swim along. Also, on the divers upward fin stroke, where minimal propulsion is achieved in any fin, the split blade opens up and allows water to easily pass through. These features essentially provide excellent propulsion for less effort and ensure that a split fin is more efficient than a paddle fin. In essence, split fins are easy to use and as a result, many divers find that they can conserve up to 40% more air with a split fin over a more traditional paddle blade. People who suffer from cramping, are injured or have weak knees, ankles or back problems will benefit from using split fins because they are so easy to use.
Well, whilst split fins may be more efficient than paddle blades, they are not as powerful. What this means is that whilst split fins may be easy to use when the conditions are good, when the conditions turn, you simply will not have the power that a paddle blade fin can offer. In any sort of current, give me my paddle blade fins any day over splits! Because of the extra grunt that a paddle blade will offer, they tend to be the preferred option for most dive professionals when power is key for chasing students, conducting rescues and so on.
In summary, you really need to assess the type of diving that you intend on doing most of. If this involves cruising around on easy sites with little current, or you are prone to cramping or nursing an old injury, then splits are probably the answer for you. If however, you want to go on and do more technically demanding diving in conditions that are less than perfect, go for a paddle.
Article written by Author J9 on http://divebuzz.com
Many divers I talk to or over hear in conversation often think that Nitrox is used for deep diving, this in fact is the biggest misconception scuba diving. In fact the deeper you dive the less oxygen is needed in the cylinders, to maintain a safe partial pressure of 1.4ATA on bottom.
The first evidence of a dive using enriched air in 1879 by Henry Fleuss, who was a master diver for Siebe, Gorman & Co. of London. He was breathing a mixture of 50 to 60 % oxygen enriched air in a large fresh water tank, a week later he logged a dive in open water with the same mix and equipment. Siebe continued his research into Nitrox mixes and between the two World Wars he introduced the technique of using different concentrations of oxygen mixed with nitrogen. This was used to great effect by British commandos during World War Two who used oxygen-enriched air rebreathers. Their rebreathers used a mix of 45 to 60% oxygen which had a greater maximum operating depth than their opponents who used pure oxygen rebreathers were limited to 6mt / 20ft.
If we breathe Nitrox during our dive we gain significant bottom time before we reach our no-stop time. The exact amount of extra bottom time will depend on the depth that we are diving to and the Nitrox mix that we are breathing.
So for an air dive to 30mt / 100ft the partial pressure of nitrogen during the dive is
4 x 0.79 = 3.16bar. If we are breathing Nitrox with a 32% oxygen content (and 68% nitrogen) then the partial pressure of nitrogen is 4 x 0.68 = 2.72 bar.
So as the inspired partial pressure is lower when breathing EAN32, the tissues will on-gas slower at any point the same tissue will contain less nitrogen than if the diver had been breathing air. Oh one other thing, it makes you look COOL!!!
What will you learn in your Nitrox theory?
History of Enriched Air Nitrox (EAN)
Forty percent oxygen content and less
Above 40 percent oxygen content
Equivalent air depth (EAD) introduction of concept only for demonstration
Switching mixes on repetitive dives
Oxygen (O2) integrated
Advantages and Disadvantages of EAN
Use as air for physiological advantage with air tables or computers
Use to extend no-decompression bottom times or shorten surface intervals
Oxygen toxicity hazards and depth limits
Discussion of myths and facts regarding EAN mixtures
Use and theory of oxygen analyzer
Gas analysis and logging
Common Mixing Procedures
Partial pressure blending
Membrane separation system
Why use Nitrox on Roatan?
Why you ask? Take advantage of staying 33min on the shipwreck "El Aguila" instead of 16min on air, air supply permitting of course.
Travel out to the other shipwreck further up the coast "Odyssey" and explore the triple decker super structure on Nitrox. Again spend up to 35 min or so enjoying the large wreck without being pushed by no-deco limits of air.
Or take advantage of diving a divesite on the south west tip of the island known as "Texas" , once you swim into the large barrel sponge area it has a depth of 18 to 21mts 60 to 70ft, whilst diving Nitrox you will be able to enjoy your time on bottom and not be limited to your no-deco limits on air.
The PADI Enriched Air Course will approximately take the student a day of classroom theory, dont worry though we have an air-conditioned classroom to kick back and relax in.
I’ll start this by declaring I am deeply fascinated by octopuses. My first encounter happened while in Indonesia. I had 7 dives logged and was on my last dive in AOW. Octopuses are Houdini level experts at hiding and are rarely seen during the day as they are nocturnal feeders. Still, I held onto hope and it happened. Casually as could be, the instructor and I saw a small octopus rapidly changing colour, strolling across the sandy ocean floor. I was immediately fascinated and have held onto that novel experience since.
Of all the invertebrates that lack a backbone, octopuses are the most like humans. Partly how they maintain eye contact. Now, I don’t know about you but the minute I’m below - I’m looking for a fish connection. I am constantly creating scenarios in my head of swimming by Margaret, the porcupine fish who, no matter what the current brings in, is ALWAYS playing with a smile. Or I’ll swim by the ALWAYS grumpy goby, and start a dialogue... “Seriously Gerald, could that bottom lip stick out any further? I think you’ve perfected the Robert De Niro impression. She had a sex change 19 years ago….MOVE ON GERALD!”
Reef fish only really make eye contact for 5 seconds while swimming away from you, constantly looking over their tail fins, waiting for the ultimate attack. A girl can only take so much rejection before she swims off to stress out another fish you know? But octopuses are different. In a staring contest, they’ll most likely win. It’s impossible not to sense the intelligence behind their eyes. Their many other attributes speak across the human experience. Their dexterity could make any acrobatic jealous, any chef would be envious of their hundreds of taste sensitive suckers and any magician should only dream of being as capable of escaping a seemingly foolproof container. This distinguishes them from other intelligent mammals like dolphins, which for all their smarts are limited by their anatomy and can’t (easily) unscrew anything.
On the other hand, octopuses may be one of the most extra-terrestrial creatures in the ocean (have you seen their comparison in Arrival? They have 3 hearts and blue blood. As defense mechanism, they have evolved to eject ink while making a getaway. They have no bones. Their only inflexible body part is their beak and a nub of cartilage around their (amazing) brains. As a result they can move through any gap, hole or crack larger than these unyielding body parts.
Just as humans are mammals, Octopuses are cephalopods, which is Greek for “head-foot”. Literally, their anatomy is this weird. They have arms attached directly to one side of their head and their torso (a bag like sac) attached to the other side of their head. If you didn’t know, cephalopods is a category that captures snails, clams, slugs and oysters amongst others and they were the first predatory animal to hunt in the ancient seas. This category evolved over 500 million years ago from a small animal with a shell like a witch’s hat.
If that isn’t enough, if at this point you still need convincing that octopuses are worthy of your further attention, the nervous system of the octopus sets it apart from any other creature (as a result it is a constant topic of debate amongst concerned professionals whether the octopus is a conscious creature)
Octopuses have 500 million neurons. Honeybees and cockroaches, which after cephalopods, have a claim to the Earth’s most neuronally rich invertebrates, only have one million. (Humans have 86 000 million neurons)
Evaluating the intelligence of other animals more often than not tell us more about our own intelligence, and I am constantly playing with this idea during every dive, while trying to find my next fish connection. Experiences and interests, such as the one with the common octopus, creates further motivation to preserve the lives of other organisms so they can continue to adapt and grow, just as humans do, in an ever changing environment.
Very rarely do us Dive Masters get a snow day, but that is exactly what happened one morning last week. Let me start with; diving during a rainstorm is a treat. You are going to get wet no matter what, so why let precipitation deter you from a good time? To be completely unaffected by any elements, submerged, 10, 20, 40 feet under water, floating on your back, looking up as drops disrupt the surface in a static, white noise sort of manner, is a calming, novel experience. There are dangers associated with diving during a storm, though very few actually influence behaviour underwater. Instead it is the entry and exit from the boat during a storm where most accidents happen.
On this day, last week, the water and wind were consequently too rough to even consider a boat dive from any side of the island, so the morning boat was cancelled, leaving 8 dive masters and 4 instructors puttering around the shop. A movie on skills (sans popcorn) was turned on for review and all dive masters settled in. Not 35 minutes later, the instructors interrupt the movie and being yelling about a missing diver. We all quickly recognize the interruption as a drill and even quicker scatter like cockroaches being chased by a flame. The next 40 minutes evolved into what can only be described as mildly controlled chaos. The missing diver was eventually located but was unable to be resuscitated as her bottom time was well over 20 minutes. The supervising instructors were disappointed, but as we were all reminded by our newest DM from Switzerland, drills like the one we just bombed, are the reason we all become better, as individuals and as a team. Rather than thash out every error we made, I’m going to isolate and highlight the correct response to an emergency which is an important refresher for all divers of any level.
Missing Diver/Search + Rescue
1. Assess the Situation
a. Before anyone moves in any direction, assign a lead. No matter what the conditions, you will be working as a team, but it is far less confusing and much more efficient to know who is delegating tasks and who should be aware of all information passing through.
b. Collect all information. Who is missing, Where were they last seen, When were they last seen, What are they wearing, How much air did they have left, Why did they go missing?
2. Create a Plan
a. The DM’s were informed of the missing diver in a classroom where we were watching a movie. We had a white board, multiple maps, a spine board, emergency oxygen, first aid, and various other useful tools, which you can be sure none of us took advantage of, because in the excitement we all just bolted for our equipment. What we should have done was draw the search area/dive site on the white board, and assign teams and search patterns.
b. Assign roles to your team. There were 8 of us. Perfect for one snorkel team of two, two scuba teams of two and one team of two to stay on land. Discuss search patterns, recall signals if a team finds the diver, assign gear, compasses and have the land team put emergency services on standby while checking the missing diver’s hotel on the off chance they have surfaced and gone home.
a. After this crucial first and second step, MOVE! Time is crucial for increased survival rates. Get your gear and get to the water. Have one more meeting before entering the water to ensure everyone is clear on the plan, or to accommodate any changes.
b. Communicate! When you create a plan stick to it. The easiest mistake to make is to become an independent member and abandon your team with dreams of becoming a hero.
c. Depending on the diver’s condition when found, the recovery standards will differ. The most experienced EFR trainee should work on the patient until EMS arrives.
At the end of the day, we all learned that you cannot succeed without the cooperation and help of your team. We became stronger as a group and will definitely be carrying this lesson into many other experiences.
Here are some photographs of just some of the variety of fish we have here in Roatan, Honduras. The location of these shots are mostly taken in dive sites ranging from Pablo's to Spooky Channel. How many can you identify? If you haven't done so already, ask to do a fish identification dive and one of the instructors will go through with you, the best techniques for finding and learning as many fish as possible.
All photographs are taking by the talented Alex Harper-Graham find more photos by clicking the link www.alexandrahbphotography.com
Some of these fish can be spotted swimming amongst the beautiful mesoamerican reef, and the others are more shy and hide in the coral and take cover from predators.
As the staff are busy looking for exotic features and creatures for you, safety is still our first concern with our customers making sure we do air checks when needed and not to worry if you run low on air, we always have a divemaster intern that will assist your safety stop and buddy with you back to the ladder.
Be sure to follow us next week on an adventure, we haven't been able to promote funday friday lately because of weather issues. Next week will be worth waiting for, make sure to follow along....... happy bubbles from CTD
The hawksbill sea turtle (Eretmochelys imbricata) is a critically endangered sea turtle belonging to the family Cheloniidae. It is the only extant species in the genus Eretmochelys. The species has a worldwide distribution, with Atlantic and Indo-Pacific subspecies.
The hawksbill's appearance is similar to that of other marine turtles. In general, it has a flattened body shape, a protective carapace, and flipper-like limbs, adapted for swimming in the open ocean. E. imbricata is easily distinguished from other sea turtles by its sharp, curving beak with prominent tomium, and the saw-like appearance of its shell margins. Hawksbill shells slightly change colors, depending on water temperature.
While this turtle lives part of its life in the open ocean, it spends more time in shallow lagoons and coral reefs. The World Conservation Union, primarily as a result of Human fishing practices, classifies E. imbricata as critically endangered. Hawksbill shells were the primary source of tortoiseshell material used for decorative purposes. The Convention on International Trade in Endangered Species outlaws the capture and trade of hawksbill sea turtles and products derived from them.