Nitrox – When to take the plunge…

A question that comes up quite regularly, but what is the right answer?

To give a proper thought, we must first look at the history and current events of Nitrox.

Used in a commercial setting for as long as there have been divers, nitrox didn’t come into mainstream use until the early 90’s and even then is was only really supported by “fringe” technical diving agencies such as TDI. In fact the British Sub Aqua Club (BSAC), the “governing body” of UK diving didn’t accept it’s use officially until 1994, after outright banning its use in 1992!*

Put simply, it’s the practice of using more oxygen in your breathing mix which in turn lowers the amount of nitrogen available to be absorbed into your bodies tissues while at depth. The result of this is longer no-decompression limits, shorter decompression times or the perceived safety factor if diving to air limits and a more energetic post-dive feeling. I say perceived, because when it comes to safety, it’s statistically null and as for the lack of lethargy, that’s subjective and difficult to measure. Mainly because if you dive enough to notice a difference, then it may be improved dive fitness rather than any benefit from the nitrox.

The downside of this higher oxygen, is far shallower depth limits than air and a requirement to track your cumulative dose of oxygen. For example: Air is 56m, Nitrox 32 is 32m and Nitrox 100 is 4, yes 4m!

Sounds simple, but is it…

Well, yes and no. While it is very simple to implement, it depends on your use as to how easy it is for the diver to manage.

If you are only diving on holiday with a guide, then it really is just a case of plugging the mix into your computer, then following the guide and any instruction from your computer during the dive.

Diving locally though is a different story. For one, you’ll likely be autonomous and not have a “higher being” watching your every move, leaving you free to make your own decisions about depth and time.

Diving on air, this isn’t such a problem as you are very unlikely to reach any of it’s physical limitations, due to your own decisions or not – tide for example.

On nitrox though, to get the benefit of using it, you need to have a mix that is as “strong” as possible for the maximum depth of the dive. This means that you have an absolute depth limit which lies inside recreational depths, that you must adhere to or face the risk of very nasty consequences.

A scenario that comes to mind, which has actually happened. You dive at Anfre post with north running tide. You pull up to a bobber and check the tide and notice a nice trickle. You know that because it’s half tide up, that the tide will continue in that direction. So you select a start depth of 20m, knowing that if you run north, the maximum depth will prove no more than 25m. After getting in the water, you notice that it’s getting slightly deeper, so you angle yourself into the tide slightly to make your way shallower, at this point you reach a steep slope and wooooosh – you’re in 40m!

On air, this isn’t a problem. You’ll either make your way up the line, or deploy your smb and head for the surface. Either way, provided you have the gas, there is no immediate danger.  On nitrox, you’ve just exceeded your depth limit by some margin! Alongside the danger of the nitrox itself, you now have an added danger of panic, due to knowing that you have exceeded this limit. Neither are good for your health, or an issue on air.

So straight away, we have 2 extra things that you need to think about before and during the dive. How deep am i going? (before) and How deep can i go?(during).

You’ll also need to need to make sure the mix in the tank is what you think it is, by religiously analysing it before every dive. Another step and thing to remember.

This is why nitrox was always considered a semi-advanced qualification, until it’s mainstream use got high enough to where the agencies could start to make money out of it without too much fear of it being dangerous. Now for example, you can use nitrox from pretty much day one, even on your Open Water course!

So to be a safe nitrox diver, you need to:

  • Have the knowledge of the dive sites to be able to know how deep they are, and once in the water be able to navigate a route that keeps you inside the limits
  • Have comfort around the methods of calculating the depth limits and tracking your cumulative exposure to the elevated  oxygen.
  • Have the confidence and skills to be able to control your environment and equipment while underwater. To make sure that you don’t get pushed around by the tide.
  • Finally, you’ll need to have a good comfort level whilst underwater, this will enable you to have a clear enough mind to make sure that you are thinking about these new limits.

So why use it at all?

For dives of 30-45 meters, you can nearly double your no-decompression time. That makes a big difference to your dive times, especially on multiple dives. Diving up the Platte scalloping in the summer would be almost impossible without nitrox, as by the 3rd dive of the day in nearly 40m the no-deco limits are just a few minutes.

Are you going to benefit?

Simply, if you are ending most dives because of low gas, then nitrox will be of little benefit. If however, you are frequently ending dives with plenty of gas left because you have hit a no-decompression limit, then absolutely nitrox is for you.

One final note, the nitrox courses offered by all agencies are “theory only” with dives being optional. I personally believe that this is a bad example of “bare-minimum” teaching, and will always make sure that my students get a dive in as part of the course. That way, we all go diving which is the whole point of learning, secondly, we can all make sure that we are happy with actually using nitrox. Also, be sure to pick an instructor that actually uses the stuff, the number of instructors teaching nitrox with no experience in using it is pretty scary!

As always, i’m keen to hear your thoughts on this. You can either comment below, send me a message or pop in for a chat.

Cheers and i hope to see you in the water soon! #nobullshitjustdiving


*from wikipedia, so probably wrong dates, but the gist is correct

Thrill Seekers, Finders Keepers, Losers Weepers…

It don’t need to be no deeper, it’s finders keepers – Mabel  – A great tune!

A few months ago, i posted this on facebook

“Went looking for something this morning on a secret mission. First run, lost my damn compass, which is embarrassing having labeled all the other recent “losers” as “tossers

Second dive went back and found it along with 2 more anchors! So not quite a member of the tossers‘ club just yet – well in that sense anyway…”

This post caused a bit of outrage, from people who really had no idea to what it referred to, seemingly because i was “being mean”. I’ve now since discovered that a couple of their mates had lost things this year and as such took offence and called me names. Which we’ve learnt from the modern political scene, is the first tactic of those that cannot debate someone with facts and knowledge. In fact, when this was pointed out, they deleted their comments which pretty much proves my point.

What the post actually related to is twofold…

First, there is a long-standing joke / banter between a few groups of active divers about losing shot-line anchors when wreck diving. The post above was related to this banter because i had actually found 2 anchors, which adds to my total of about 10 found this year while others have lost several. The anchors found were actually owned by a fisherman mate and have now been returned to him.

Secondly, there had been a recent spate of losses by some of the guys. The bloke i was diving with that morning had dropped a stage over the side while gearing up to dive the Bizon. Another had clipped a hang-tank with one of my regs attached to a lazy-shot on another wreck dive. Mistakenly he had clipped it to the wrong part of the line resulting in it working itself free during the dive and falling to its doom never to be seen again. There were several more this year, but you get the gist.

I believe that there is an important lesson here, which goes beyond just not losing your stuff…

There is a growing teaching method in the industry, that uses “absolute positive reinforcement” techniques. This is a teaching method, where all students are only ever given praise about the things that they are doing right, and never given negative feedback about things that they are doing wrong – yes i said it “wrong” it happens, we all make mistakes, especially when we are learning!

Now, this method might make you loved as an instructor by forming a circle of confirmation bias. By this i mean that you are a fantastic student / diver, so I must be a fantastic instructor. To say otherwise you might have to admit that you are not a very good student / diver and nobody wants to do that. There is nothing wrong with this, everyone feels warm and fuzzy inside, right?

The problem is that as divers, we are in constant battle with nature, while at the same time trying to harness physics to help with that battle. Your instructor and fellow divers might tell you that you are great, but nature won’t care about your super-made-up skills.

If you need to stop to adjust or fix something during a dive and the tide is running, it wont care and will continue to run.

If the gas pressure in your lungs is less than the water pressure outside, then the water will enter your lungs and you will drown.

Nature does not care and it will not feel emotion, it does what it does because of the laws of physics to which it abides. Period.

When it comes to equipment, sometimes shit happens, but most of the time it is a lack of something that causes the issue.

It could be a lack of knowledge in the equipment. Maybe it was bought over the internet, without the input of a suitably knowledgeable person and it’s not fit for purpose.  Or perhaps the kit is fine, but it’s been fitted or attached wrong.

Was the problem due to lack of maintenance or pre-dive inspection. I’m constantly amazed by the lengths people will go to just to save a few quid, remember, this stuff keeps you alive!

Are you properly trained or drilled in the kit. I’m definitely not saying that you need to do a course for absolutely everything, but have you tried it in the shallows in several different configurations before choosing what is best for you and have you consulted with your peers about that choice.

For an over the side drop, was it because the weather was too rough and you were falling about as the boat rolled, should you have been out there in the first place. Were you struggling on your own, because you’re stubborn, or are the rest of your team too selfish to help.

Was the kit that you were using suitable for the type of dive that you are doing. It’s all well and good taking 3 spares of everything, but sometime KISS is the best option. Are the bobbers on your line big enough to stay on the surface in the expected (or not expected) tide. Is your SMB visible, or is it one of those  (banned from my boat) yellow ones, or even worse stupid fucking 2 colour ones.

These are the sort of things that you need to be thinking about for every dive, regardless of what type it is. It’s obviously not exhaustive and i don’t think that you could ever document everything that might go wrong.

It’s all well and good giving someone nice words and a hug when things don’t go perfectly, but you are doing them a disservice. What you should be doing, is figuring out what went wrong, and how it can be avoided next time. Before there comes a time when there is no next time.

Everyone will be better divers in the end, and isn’t that the whole point?

Full-face Snorkel Masks – Thoughts

With popularity growing amongst users in the warmer oceans of the world, we’ve been hearing quite a lot about full-face snorkel masks (ffsm) this year.  Perhaps strangely, it’s the watersports retailers, rather than the dive shops selling these things. One of the largest diving manufacturers only makes them branded for their sports line, rather than their diving brand. Is it some big conspiracy, or something else.

Here’s what usually happens…

Someone will come into the bunker and ask if we have them, we will answer that we haven’t and go on to explain what we don’t like about them based on our experience. They then say that they’ve used one on holiday and that it was amazing. We agree to disagree and away they go, presumably to purchase one online.

A few days later, they come back in to ask about anti-fog. We say that there is a compound we use on a standard mask, but that we don’t think it works on the ffsm type from what we have seen / heard / experienced. They buy the anti-fog and away they go again.

A few days later, they return, admit that the ffsm is a heap of junk and buy a normal mask and snorkel. This has happened many times this year…

So, here is what we think…

The general rule with diving equipment, is that stuff that is designed to work with the water, works better than stuff that is designed to work against the water. Now i will admit that both a normal mask, and the ffsm are designed to work against the water, but a normal snorkel is designed to work with the water and that makes a difference.

With a standard mask, there are many, many variations in size and shape, with a ffsn, there only seems to be a couple – S,M, L – which isn’t enough. This makes good fit an issue, unless you have a perfect face for the ffsn.

A standard snorkel is just a tube with a mouthpiece, it is designed to allow water to flow in AND out very easily, meaning that with an easy technique, any water entering the snorkel can be easily blown out. Even if the diver fails to do this, it can be very quickly spat-out allowing the diver to breathe again as nature intended. This cannot be done so easily with a ffsm.

To allow the ffsn to have the best chance of fitting, it needs to have a substantial strap that covers most of the back of the head. This strap needs to be pulled tight, to keep the heavy (out the water) and bouyant (in the water) ffsm in place. This means that if you do get water in it, or need to remove it quickly for another reason, it is difficult and could easily (in my experience as a diving instructor) lead to a panic situation. Not good in the middle of the sea.

I mentioned above about the fogging. This is caused by warm moist exhaled breath condensing due to temperature change on the lens, as a ffsm has a lens made from plastic, it will tend to fog more than a standard mask because it (unless it’s cheap rubbish) will use tempered glass. The other big factor is that a normal mask is only connected with exhaled breath when the diver breathes out through their nose, which should only be done for a specific task such as equalization or water clearance rather than each breath. This leads on to one of the biggest problems in snorkeling…

Snorkeling is very easy, and for the most part people pick it up very quickly without any real training. Historically, i believe that most people would have only tried snorkeling locally if they had an interest in other aspects of the sport or experience in the sea. Or maybe they were introduced by an experienced mate who showed them the ropes. Now though (and this is a good thing) snorkeling is readily available to more people and some of these may not be very comfortable in the water. If you are not comfortable in the water to start with, then you shouldn’t be having a go without proper instruction. Whether this is from an experienced mate or proper instructor makes no difference really, but you need to make sure that you know what to do and how to do it.

Anyone wanting to know more about the basics, can take a free online or app based course with SSI through us by clicking here.

The bad points of the ffsm don’t end there, there are also technical / physiological issues.

Breathing is the act of air being pulled into and pushed out of your lungs. On it’s journey, it needs to pass through your mouth and windpipe down into the capillary laden  air sacs in your lung tissue. These are where the gas exchange of oxygen (in) and carbon dioxide (out) takes place. Any area other than these air sacs is termed “dead air space” and has no respiratory benefit – other than filtration etc, but for the purpose of this that’s a bit too “deep”

Dead air spaces are important in diving, because we are adding to them with any breathing apparatus that we use. This means that a larger proportion of our breath is doing nothing in the way of bringing in oxygen or expelling carbon dioxide. There is no 2 ways about it, the ffsn makes this worse!

The problem with lack of oxygen and too much carbon dioxide, is that you can initially feel out of breath, often this leads to a more rapid but shallow breathing pattern, which in turn adds to the original problem. If left unchecked, it can lead to unconsciousness, and in water that normally means drowning. With a normal mask and snorkel, you can just spit the snorkel out and easily push the mask off your face, this is not so easy with a super-tight ffsm.

I’m not saying that these incidents are very common, with a little research i’ve found a death or 2 which cites a ffsm as a factor, but who knows the actual truth of the matter.

From usage point of view, the ffsm also fails. You’ll struggle to dive below the surface, which is the general progression as a snorkeler. Firstly, you’ll struggle to equalize your ears, which for most people means a maximum depth of 1.5 meters, unless you want to hurt your ears. Secondly, even if you can equalize your ears, there is the problem of volume of air in the ffsm itself. This needs to be equalized as you descend with air from your lungs. In a standard mask, this only equates to a few ml, but in a ffsm it’s a lot more.

So to sum up, the ffsm is: Uncomfortable, heavy, leaks, fogs, stops the diver from progressing and may even be downright dangerous.

The best way i believe, is to get a good quality standard mask and snorkel that fits and learn to use it properly. You’ll enjoy it far more in the long run, and you never know it might lead you into more advanced snorkeling / freediving or even SCUBA diving being a big passion in your life.

If anyone wants to learn more about this snorkeling (or diving), you can send us a message, or pop into the bunker for a chat. You can also sign up for the totally free, no strings attached online courses here – you’ll just need to register “Dive Guernsey” as your affiliated center, don’t worry we wont spam you!

Narcosis – Friend, Foe or Both…

Now, I know that this will get controversial, but that’s kinda the point isn’t it?

I’m talking narcosis, or as the textbook puts it Nitrogen Narcosis. Though if we were to be technical or even pedantic, we’d call it Inert Gas Narcosis. This is because it describes the narcotic effects of all gasses, especially the inert ones. Inert means a gas that has no chemical influence on the cellular chemical reactions that keep us alive. This excludes Helium though, which is an inert gas added to the mix to reduce narcosis – and lower the Oxygen level for very deep diving, but that’s for another day.

I’m going to split narcosis down into 2 contributory areas: Scientific / Chemical and Outside factors, which I believe almost have an equal responsibility for what we actually feel in the water. I’ll then talk about the things I have observed over the years.

Scientific / Chemical

As we all learnt in our first dive class, divers are subjected to far more pressure than normal. Over millions of years we have evolved in a pressure of roughly 1 atmosphere, which is approximately 1 bar or 14.7 psi. We also learned that as we descend, we encounter an extra 1 bar of pressure per 10m of water depth (in salt water, fresh is 10.3m). To put this into context, to gain 1 bar of pressure we only have to descend 10m or 33 feet. To lose 1 bar of pressure we must ascend (in air) to something called the Karman line, which is the place where our atmosphere essentially stops and the pressure becomes almost zero. Though this is actually not quite far enough, it’s close enough for our purpose today and it stands at a whopping 100 kilometers, which in old money is 62 miles or 330,000 feet!

I digress (but fascinating no?), back to the diving.

As the pressure increases, the molecules of the gas we breathe are squashed together, meaning that when the gas is delivered to you, it’s at ambient pressure. This is worked out using the simple formula: Depth / 10 + 1. So at 25m, the gas is being delivered to the diver at 3.5 bar. This means that you are getting a much higher concentration of the gas molecules at depth than you would at the surface, the factor is the same number as the pressure, so using the example above, you are breathing 3.5x the molecular quantity or total mass.

Narcosis is caused by the gas being absorbed into the divers tissues and slowing down nerve transmissions. Essentially meaning that the electrical impulses within your brain are delayed to or even missed on the receptors. It’s thought that it happens throughout all your other tissues too, but this is only conjecture and of little importance. With the pressures encountered at normal diving depths, this is only really enough to slow down your thought processes and make you feel a bit “tipsy” but at very high pressures it’s believed to act like a powerful anesthetic and could knock you out.

So when we bring these 2 bits of info together, we have a formula to “explain” narcosis. We take the percentage of the gas we are looking at and multiply it by the depth to reach a “narcotic factor”. For example, if we use air – 21% Oxygen (02) / 79% Nitrogen (N2) – and look at just the 79% N2 at a depth of 30m we end up with .79* x 4 = 3.16 which we’ll call the narcotic factor, though those that have knowledge of nitrox will know that it’s actually partial pressure.

We can also do the same for other depths: 10m (1.58) 20m (2.37) 30m (3.16) 40m (3.95) 50m (4.74) 60m (5.53) & 100m (8.69)

*As we are working with a percentage, we express this number as a decimal, it’s not absolutely necessary but makes for simpler numbers.

From this we can then say that most people will be fine with a factor of 3.5 (34m), and that some people will be fine to up to a factor of 5. This is where the personal preference comes in. Out of interest, the maximum air record is 145m set in 1993 by Bret Gilliam** which would give a “factor” of 12.25!!

** There was apparently a dive to 155m in 1994, but this was very controversial and led to Guinness stopping the SCUBA air depth record.

So if you are happy to dive air to 40m, then you are happy with a narcotic factor of 4 (0.79 x 5). Which is the general gist taught by all the agencies, though they may not explicitly say so as it’s built into the recreational depth limits.

So far, we have just looked at air, so what about other gasses. Well, if we exclude Oxygen for a minute we can say that all gasses give a narcotic value in relation to their atomic weight or mass (there are other factors, but mass is the main one). So for example, if we ignore everything but the narcotic value, then we can say that the most narcotic is Radon with a mass of 122, and the least is Hydrogen with a mass of 1. So from this, as Nitrogen has a mass of 14, we can say that Radon is 8.7x more narcotic and Hydrogen is 14x less. Whilst Radon is definitely not used in diving, Hydrogen can and has been in the past, though it’s felt to be a bit unstable with it’s willingness to blow up – see Hindenburg! A gas that is commonly used is Helium with a mass of 4, so that does work out to be the best choice as it’s 3.5x less narcotic than Nitrogen.

With Oxygen, although it is actually more narcotic than Nitrogen with a mass of 15, it’s thought not to have much affect due to the different storage, transportation and use in the body over the inert gasses.

 Outside Factors

I believe that when it comes to narcosis, the mathematical ” narcosis factor” plays only some part to it. In researching this, I came across a Wikipedia article that stated “no diver will every build up tolerance to narcosis”                                     I think that this is total rubbish, as when I was scalloping full time and diving 50m every day, I felt great doing it. Now that i’m not doing it so much, the narcosis is definitely more evident.

When I think back to my deepest local dives, some of the best ones have been 58m on air. When I say best, i’m scoring by: clarity, fluidity, ease of sending the shot up, tying knots, wreck navigation, finding the shot, focus on plan & time, gas management, problem solving and everything else about the dive.

At the same time my worst ever dive for narcosis was at 45m on trimix. It should have felt like being at about 28m, but I was off my tits! I put this down to several factors in descending importance:

Rushing to get in the water. We were on a boat with about 8 other tech divers and I was team of 3 others. So after running about helping 8 others to get in the water, I was left trying to manage all my own stuff alone. At the time it was twin 10’s and 2 deco gasses. Also, the boatman had told my team to get in the water and i could see them struggling in screaming tide at the surface so i was trying to get in asap.

Speed of descent. I think that this plays a massive role in onset of narcosis, and although it’s related to the “narcosis factor” it’s not often talked about.

Light & Visability There is no doubt in my mind that narcosis effects are stronger when in low light and visibility conditions. It’s one of the reasons many warm-water divers get a shock when they dive locally.

C02 & Workrate One factor that is coming into common knowledge and teaching is that excessive amounts of C02 will worsen the narcosis. It’s thought that C02 is a catalyst for many of the diving nasties, though not much is known about the exact mechanics of it as so little research is being done. C02 levels are lifted due to either excessive workrate and poor breathing through technique or poorly maintained equipment – and rebreathers, but that’s beyond the scope of this.


With this section i’m hoping that some other people will write and add their personal experiences as they may be different to mine. Below is  written as my own feelings and what I have witnessed in others.

Personally, i’m quite happy diving to normoxic depth limits on air. In other words 57m ish. Having done these sort of depths literally hundreds of times, i’m saying this with the experience to back it up. Though we don’t really get the opportunity locally to go deeper than that easily, I think that it’s the limit for me. That said, on one dive in Jordan, I switched from Trimix to air on ascent at 66m and that was fine too.

For me narcosis used to be fun and enjoyable, i’d find myself in a heightened mood in the deep as i went about my business. These days a lot of the time i don’t really feel it,  on the worst days it just tends to add a slight fuzziness that I need to concentrate a bit harder to overcome. I honestly cannot say that it ever feels anywhere near dangerous to me on a good day – more on this later.

Anyone that has been to 30m+ will have experienced some level of narcosis, many though will say that they haven’t. They did, they just didn’t know about it because for most people it’s no big deal. It’s often that you’ll hear people draw parallels between narcosis and alcohol, which is a good way to explain it. In small quantities, it makes most people happy and allows them to get more enjoyment out of whatever they may be doing. Of course, in large quantities it can lead you to do stupid things and lose your mind. There has to be a personal limit.

One thing that i have heard a few times over the years as i travel, is the resort instructor telling students to not go below 30m or they’ll “get narked”                  I can never sit back and listen to this so will argue the point. It’s not that i want everyone to dive deep (for one they’d be in my way), but at the same time I don’t like the idea that people are scared of an imaginary line and that if they ever venture to 30.1m they’ll get knocked out as if they have just been caught by a McGregor left hook.

The other story that gets told often is that a diver suffering from narcosis will try and give their regulator 2nd stage to a fish. Now, i’ve not witnessed this myself, but I have heard it from people i trust. I think that if this does indeed happen, I don’t think that the diver thinks the fish needs the reg, I think that the diver does it for a joke, and as they are “narked” it tends to go wrong, or at least be taken the wrong way.

One person that I used to dive a lot with used to get an experience that he called “nitrogen psychosis” Essentially, when at depths over 40m he used to think that everything was out to get him and was going to go wrong – air was going to run out, reg was going to stop working, shark was going to eat him, he was going to get the bends, that sort of thing. Obviously, he stopped diving deep once he decided that it wasn’t a one-off as that’s not a good state to be in underwater!

Another that I used to dive with a lot, got such a high from the narcosis, that he would be in an amazingly good mood for the whole dive and even afterwards – he would often be seen with a big grin on his safety stop singing along to a tune in his head started on the bottom!

Where narcosis does get dangerous, is when it distracts from the important things like the monitoring of gas and deco obligations. Which is why it’s a good idea to push yourself under the supervision of an instructor or buddy that is far more experienced than you in diving those depths and more likely to be actually paying attention to you, rather than being too busy with their own stuff. It’s silly to think that an instructor can dive in Havelet a couple of times a month and then be on point in the deep! One time I was with a student on a 40m dive. We came across a lost parlour pot and I had a quick look in through the mesh (nothing inside) and then “stepped” back to allow the student to do the same. He then spent the next 5 mins looking into the pot from every possible angle multiple times, as if there was something really interesting in there. I was convinced that he was narked and to prove my point, I allowed it as long as I could and then called for him to follow me. By this time we were at the end of our bottom time and were ready to ascend. I don’t know how long he would have stayed looking without the intervention, but from a decompression and gas perspective it could have led to an issue if it had been another 5 mins. Once back on the boat, I asked him about it and he was adamant that he’d had 1 quick look and then carried on!

As I think about all the divers that I know, there is quite a varied “tolerance” to narcosis, I know some people that don’t like to dive below 40 without Trimix, and that’s perfectly fine. It’s all about personal choice, provided that they remember that Helium only reduces narcosis, it doesn’t effect or enhance any other skill. As Mark Ellyatt quotes on his website “Helium provides only sobriety, not experience or buoyancy skills!”

So… Please absorb your inert gasses responsibly…

To Boldly Go… A bit deeper than the time before

Never Ever, Have I Ever…

Heard a student start a course saying that they want to dive deep. There are exceptions to this rule of course, but the majority start off with “I only want to go 10-15m, that’s enough for me”

That limit sticks, right up to the point that they go to whatever their target depth. where they decide that it was great and not really any different from a couple of meters, they also see there there is no “magic” line at 18m – which incidentally is only there because the pioneers chose 60″ as the entry level depth, had they been of the modern world, chances are 20m / 66″ would have been the limit.

So then it starts, the lure of the DEEP…

Anyone that’s sensible will progress their depth, with plenty of shallower dives in between. That way they bring up their comfort and skill level to the maximum depth hit previously before planning another PB dive. Most will also be progressing through the core courses at the same time, allowing each aspect of their diving to be complimentary – please don’t think as some do, that doing course after course after course is the best way. You have to get experience in there somewhere. If i had to put a number, then 15 dives as a buffer to early PB dives and 30 between courses. There is of course a limit to how deep people will go, this is a very personal thing and nobody should ever pressure, or feel pressured to break that personal limit. From experience, i would say that 100% of properly experienced divers will do 30m, this drops to about 50% for 40m, 10% for 50m and 2% 50m+ this rule will change slightly thought if you factor in helium use in either trimix or helitrox.

So, why go deep at all?

Well, locally speaking the diving is just… Better… I’m not saying that all shallow diving is rubbish, far from it, but there are many benefits to heading deeper. The main one is that as you go below 18-22 meters (depending on time of year) then you will lose most of the seaweed, which in the shallows, is hiding all the topography and life. As you pass this invisible line (actually to do with light penetration) you’ll start to see far more interesting life, soft corals, gorgonia, sponges and the incredibly pretty swathes of jewel anemones.

One thing that is almost always better in the deep, is the visibility. I think of vis in 2 ways, the actual distance that you can see and the clarity of the water. For me clarity is way more important than actual distance. You can bet that 99 times out of 100, clarity in the deep will be better than the shallow, especially in the summer months with the “bloom” in the water. One thing that does dwindle with depth though, is the light. But luckily there is a new-fangled device for fighting this – it’s called a torch.

If your into scalloping, then there is no doubt that the scallops are more dense in the deeper water, mostly as less people go that deep. There is a fine balance though, as the deeper depths mean much shorter dive times which in turn means that you catch less. Many people over the years have thought that depth would improve their catches, most soon discover that the execution of the dive also becomes more important as you go deeper. When it comes to scalloping, most stick to the mid range of 20-40m, anywhere outside of this range is likely to be hit and miss and we can’t have that in such a fierce competition…

Some say that competition has no place in diving, i couldn’t disagree more. Whether it be on number of scallops, size of fish, max depth, dive-time or gas remaining. There is absolutely nothing wrong with a bit of healthy competition between mates and even with yourself. Competition is in human nature, it’s what drives us as individuals and as a race to be better than we were yesterday. If it weren’t for this drive, we would most likely still be living in caves! Of course, the competition needs to be healthy, and it needs to be last on the long list of dive requirements – with safety being first. Maybe with our divers the battle is more in the open as we shout “SCORE” after every dive, but trust me it happens all over the world. Where you don’t see it, it just means that there is probably less to compete over – why do you think dive guides in the warmer climes have such low breathing rates?! Those that don’t want to compete in diving, probably can’t…

Another reason is “lust for rust”, anyone that likes to wreck dive will eventually decide to go that bit deeper. This is because whilst there are many wrecks in the shallows, most resemble a pile of “stuff” with seaweed growing out of it. For me, i like to be able to recognise what the wreck was in it’s previous life.

For wrecks less than 20m, you’re really limited to just the Forth. If you go up to 30 ish, then you can add the Cement wreck (30m) and the Ammo wreck (32m). A diver that pushes to the next step will gain access to a heap more: Mary Toovey (42), Figaro (45), Stella (46), Brighton (50), Niko (50), Duanna (50) Cairnside (52), M483* (52). Those that really show a passion and aptitude for the deep and go on to Trimix will open up the really special ones: Edirne (55), Bizon (58), Rouen (58), Jeanne Marie (58), St Malo (69) and many others.

*Arguably the best wreck dive in the channel islands – for more info and links to video, see the main website

In listing all these reasons, i’ve missed out one very important one – diving deep is immense fun. This is largely due to narcosis (more on this in a later blog). Well at least it is to some people, now i’m not saying that everyone needs to dive deep, people should do what they want. But if you like pushing yourself and you’re willing to accept the increased risk, why not go for it.

One last point i’d like to make, is that just because you can dive deep, you don’t have to. I know that it gets said of me that I only dive deep and yes, if i have the choice, then mostly i will pick deep over shallow. Of course, if i’m diving with someone, then i will dive to their limits and I do enjoy the occasional shore dive. If i didn’t then i wouldn’t do it especially not on my own (which i have been known to do in desperate dry times). Only last week I went into Havelet to dive with someone because they needed a buddy, instead of going scalloping and earning money.

What the naysayers miss though is that if you can dive deep, then you can dive shallow. A skill that doesn’t work the other way. Think of it this way, can a racing driver drive a normal car slowly, the answer is of course yes, but does being able to drive a normal car make you able to drive a racing car fast…

So go forth and embrace the narcosis!

Rebreathers, first impressions from a buddy…

Now that there are a couple of new rebreather divers in Guernsey, it’s more than likely that you’ll hear some rebreather-speak this coming year. So I thought that i’d write a post about what they are, and what my first impressions are of being a buddy to someone diving with one.

Firstly, my only experience diving with one is a try-dive a few years ago with Mark Ellyatt in the south of England, whilst over there doing some SDI / TDI Instructor training. This consisted of a 10 min chat and then jumping into the shallows of a bay to swim about for an hour.

For those that don’t know, what we refer to as a “rebreather” is more accurately called a “Closed Circuit Rebreather”  or CCR for short. All CCR’s will have 6 common components, an Oxygen (02) cylinder, Diluent cylinder, scrubber, a head with various electronic monitoring systems, some counter lungs and a breathing loop.

The 02 cylinder is just that, a cylinder filled with oxygen.

The Diluent cylinder is filled with a gas compatible with the maximum depth of the dive. This would typically be air (21%) down to about 40m and trimix for depths beyond that.

The scrubber is essentially a canister filled with soda-lime, a chemical that reacts with C02, changing it chemically and effectively trapping it within the soda-lime itself.

The head comes in many different configurations, but all will contain a number of 02 cells like you get in a nitrox analyser. These cells will then be read by a CPU and the information displayed on a screen for the diver to see. Many units also have a built in controller that runs the unit based on that information.

The counter lungs offer storage capacity for gas before and after exhalation, they are flexible and somewhat collapse when you breathe in and inflate when you breathe out.

The breathing loop is a set of hoses that run from the scrubber, to the mouthpiece via the counterlungs.

So, how does it work…

The diver breathes in, taking in gas from the 02 rich inhale counterlung, 02 is transferred in the divers’ lungs to the blood stream. In turn the body gives out C02 and water vapour. This low 02 / high C02 mix is then exhaled into the  exhale counterlung, prevented from going anywhere else by 1-way valves in the breathing loop. On the next breath, this gas with then be pushed into the scrubber. As it passes through the scrubber the C02, water vapour and soda-lime cause a chemical reaction which traps the C02. The gas that reaches the top of the scrubber will then hopefully be low 02 and no C02.

This low 02 gas will then pass over the 02 analyser cells, this information will be sent to the diver and controller. The diver or controller will then make a decision as to whether the 02 level is sufficient. If it’s not then either the controller will open a solenoid valve or the diver will press a button to allow more 02 in to the system to bring it back up to the correct level. The gas then continues it’s path back into the inhale counterlung and on to the divers’ lungs again.

Where does the Diluent come in?

As the diver descends 2 things occur. The volume of the gas in the system will decrease as the water pressure (depth) increases, meaning that there wouldn’t be enough to breathe. Secondly, the pressure (quantity) of 02 will increase. If 02 was added to the loop to make up for the lost volume, the pressure of 02 would quickly reach dangerous levels. So to stop this happening, a low 02 mix must be added to make up the volume. In the case of gas loss from the loop, adding diluent may drop the 02 pressure, in which case the diver or controller will add more 02 to maintain the mix to the required level.

As the diver ascends, the opposite happens. The volume in the loop increases and the pressure of 02 drops. To counteract this, the diver has to “lose” some gas from the loop via a valve, or exhale through their nose so that the gas escapes. The diver or controller will simultaneously be adding 02 to maintain the mix to the required level.

In short, the 02 cylinder raises the pressure (quantity) of 02 in the loop, whilst the Diluent lowers the pressure (quantity) of 02 and raises the volume of gas in the loop.


As a buddy, you need to have a fair understanding of all this stuff in case you need to help a CCR diver. You also need to make sure that you keep a close eye on them both figuratively and literally. Because with no bubbles there is less to see, especially on descent / ascent, and no noise either.

As a non CCR diver, you’ll likely always be the person to end the dive as the CCR has several hours of endurance per fill. Also, due to the constant pressure (quantity) of 02 provided, they’ll have a longer NDL or less decompression than you will on normal scuba gear.

You may be reading this and think “What’s the downside” well, there are a few.

Firstly, you have the expense of the unit originally, plus high service and maintenance costs. This can be offset somewhat if you are saving on Helium costs by doing lots of deep diving, but it does have to be a lot of diving!

Secondly, the CCR diver has to pay attention, like ALL the time. It’s not something you can check every now and again. If you don’t check it enough, it’s very likely that it’s going to ruin your day! This also applies to pre-dive checks, post-dive maintenance and everything else to do with the CCR, if you scrimp on either time, focus or cash it’s not going to end well.

For me, this actually detracted from the enjoyment of diving somewhat, having to pay so much attention to the CCR and less to the fishes.

But, when all is said and done, CCR?   YES, sign me up…



Drysuit? Pah, just use some bin-sacks and sticky tape…

There’s no doubt that if you want to be a “serious” or year-round diver in Guernsey you have 2 options. Either you grow a massive pair of balls (or the female equivalent) and dive in a wetsuit, or you get a drysuit.

I should point out that by “serious” i mean someone that does multiple dives on one day, or someone that does long or deep dives.

Now, for those that don’t know, there are 4 main types of what is called Exposure protection.

The first is a reef suit or rash vest, this is a very thin garment that protects the user from scrapes, and offers some protection against sunburn. Typically these are worn in very warm places and offer little or no thermal protection.

Next is the bog-standard wetsuit. These are made from neoprene which is gas bubbles in a rubberish material. Wetsuits work by trapping a little water which  allows your body to heat it. Once the water has warmed the water it is effectively trapped and works as part of the insulation. Neoprene varies in thickness from 0.5mm to 7mm. A typical suit used in Guernsey would be a 2 piece 7mm suit resulting in 14mm of insulation on the torso.

Third, we have the Semi-dry. These are basically a wetsuit with much better seals and typically a dry zip. This means that water infiltration is minimal and very little gets in. We’ve seen this type of suit come in and go out of fashion over the last 25 years, currently they are in fashion so much that production of the standard 7mm wetsuit is non-existent. Personally i’m not convinced that the semi-dry is any better than a wetsuit. What i do know though is that they are more expensive to buy, require more care and are more likely to get damaged and need expensive repair.

Last, but by no means least is the drysuit. These come in many different styles and options, with the main one being the material, which is either neoprene or membrane. Neoprene suits are normally worn with minimal under clothes, with the suit itself providing good insulation. A membrane suit offers practically no insulation, so you need to wear an undersuit. One of the big benefits to using a membrane suit is that you can vary the type and thickness of the undersuit throughout the year according to the insulation needed.

A drysuit works by keeping all the water out with seals on the neck and wrists, with the boots usually fitted to the suit. The seals are made from either latex, neoprene or silicone – which has only been around for a short while. Because of these seals, the suit becomes an air-space which means that you need to equalize the pressure by adding air on the way down, and removing it on the way up. This is done with 2 valves, an inlet on the chest that feeds air from your cylinder to the suit and a dump valve on your left shoulder to allow excess air to escape. The modern dump valve is variable which allows the diver to set the pressure at which it opens. Back in the time when Noah had hull inspections, there was a type of dump called a cuff dump. A cuff dump is a very cheap valve that sits around the wrist, when you raise your arm and the sleeve fills with air, it dumps – great for waving on the surface.

That’s it, it’s really no more difficult than that!

Or maybe it is more difficult, what with all the courses available and the horror stories that you hear…

Fact, I’ve never issued any certification relating to drysuit use, there is just no need. Providing that the “student” has more dives than they can count on their fingers, then it’s never a problem. Like most things, some take to it quicker than others, but the difference is generally between 5 and 30 minutes!

So why all the horror stories?

Well, I think in the vast, vast majority of cases it comes down to one of 2 things. Either the person has not been told how to use the suit, or it’s the wrong suit for that person. In other words, they’ve borrowed a suit from a mate, or bought something 2nd hand on the cheap. They then get into the water and soon discover that it’s not as easy as it looks!

To follow this theory, lets have a look at the things that can go wrong with either type of suit.

With a wetsuit, very little. If you can get it on and breathe, then you’re good to go.  The suit will loosen slightly as it gets wet and compressed by the water pressure. The only real danger with a wetsuit is if the neck is really too tight it can compress the arteries in your neck, which fools your brain into slowing your heart which can lead to unconsciousness. If it’s too loose, then you get colder quicker and if it leaks it doesn’t matter because that’s what it’s supposed to do.

For a drysuit, there are a great many things that can go wrong.

If it’s too tight on the body it wont allow for the movement that you need and it could restrict your breathing. If it’s too loose, then it will hold too much air, this will mean that you need more lead to sink. That extra air can move about far too much and upset your trim and balance in the water. If all that excess air ends up in the feet then it can “blow” off your fins and make righting impossible which will lead to the inability to remove excess air and result in an uncontrolled ascent to the surface.

If the neck seal is too tight, it can compress your arteries and lead to unconsciousness. If it’s too loose, then it will leak. This results in massive loss of thermal insulation, buoyancy and in a bad case can make it impossible to exit the water in the normal way due to the weight, especially if the suit is too big.

If the wrist seals are too tight, they can affect the dexterity of your hands which will make tasks more difficult. If they are too loose, they will leak leading to the difficulties mentioned above.

If the boots are too tight, you can suffer cramps in your foot and calf, this can make it difficult to swim which in turn can render the diver helpless. If the boots are too big, then your fins can easily come off. When this happens, chances are you are heading, uncontrolled, to the surface. Maybe this leads to nothing more than a bit of embarrassment, or maybe you damage your ears and sinuses. Or perhaps it’s a very bad day and the fast ascent leads to a lung over-expansion injury, omitted decompression and “the bends”.

In the good old days, this sort of thing was very rare. This was because people would buy a drysuit and the training would be thrown in. There was no need to teach someone how to use a drysuit that wasn’t right for them because nobody was trying to get their “Drysuit badge” (watch out for blog on this later). Of course, there are some places that can have “school” drysuits, but these are only the very biggest of dive centers with 100’s of students in very cold places where drysuit is the only choice all year round. Remember, the suit needs to fit properly, with appropriate insulation, correct boot size and have seals of the right size. So the idea that somewhere can have a couple of school suits to “suit” everyone is just stupid!

So, the bottom line…

Unless you are happy to make a suit out of bin sacks and sticky tape, get a decent one. Not only will it be a joy to dive in, it will last for many years. The best in our opinion is Otter, they are the only make we use and actively supply.

Students – Get some experience first in a wetsuit to be sure that local diving is for you, then get a suit that fits and is right for the job. Next get someone that knows what they are doing – someone that actually uses one on a regular basis – to show you how to use it.

Instructors – Just stop it, you should know better, or maybe that’s the problem…


To Float, or Not To Float…

The neutral buoyancy debate

Recently, on a near daily basis I’ve been reading articles about how student divers should never kneel on the bottom. The authors say that this is to prepare them for “real” diving.

I want to share my thoughts…

First, let’s look at why the authors are writing these articles in the first place. Now unless they are small scale meant for their own students and divers then they WILL be doing it to try and get noticed. Usually this is an effort to become a well-known national or international instructor and travel for work. Or it’s because they are looking to become published in magazines ect. Obviously the more shocking the material the more likely they are to be noticed.

To the topic in hand. What is being said in all these writings, is that student divers should never be taught to kneel on the bottom. They then usually show a picture of a “typical” dive class with students kneeling on the bottom waiting to perform their skills, this is then backed up with another picture of some divers trashing a coral reef or silting up a cave – both bad things as every diver should know, but not really the same thing. Just because you have knelt on some sand or a pool bottom, it doesn’t mean you’re going to kick the hell out of the reef.

The thing is though, whilst it’s a great ideal to have every student perfectly floating neutrally buoyant. The fact is though, that it’s just not realistic in a Open water class. For us that dive in poor vis, there is no way that an instructor could maintain a safe level of control if all the students were off the bottom. ‘Cos lets face it, they are students and therefore learning!
Good buoyancy control is motor skill, a feeling if you will. Some people do pick it up easier than others, but for the vast majority it takes a little while. I would say, that in nearly 15 years of teaching only a handful of students have had good buoyancy right off the bat. Most do take around 10-15 dives to really get the hang of it.

The problem I think, is that there are too many instructors teaching the absolute bare minimum courses. Yes they are doing everything required, but what is actually required in the course syllabus isn’t that much. For instance every pool dive has “fun and skills practice”, while every open water dive has a “underwater tour” portion of the dive. Now these are quite vague, does 30 seconds count? I don’t think so, and will always give students 5-10 minutes “play time” at the beginning and end of every pool session and end each sea dive only when a comfort or air limit is reached, this usually means at least 45 mins dive time after skills have been performed.
Also, it’s become very common for instructors to push course after course after course, with absolutely no normal dives in-between. In fact, there are even some instructors with almost zero real dive experience.
One example, is people taking the Peak Performance Buoyancy Course (PPB). Now there are times when this would be valuable, for instance when taking on a new student that wasn’t taught properly in the first place. I think that there is absolutely no reason for people to immediately take the PPB course with the same instructor. The fact is that all agency standards state that buoyancy must be “mastered” before Open Water (or equivalent) certification. So in essence, the instructor is saying “I didn’t do my job properly, your buoyancy control needs work, so pay me more money to do something I should have done in the course that you have just paid me to teach you” – this is not on!!

Personally I always try and get a few extra dives in, either during or after the course, to make sure that the student has got to the proper level. Let’s be honest, nobody expects an amazing diver after the Open Water course, BUT an Open water diver should be competent and comfortable in the planning, execution and navigation as part of a similarly qualified buddy team in conditions similar to those in which they trained. In other words, 2 divers finish the course in the morning, they should be capable of going for an easy shore or boat dive in the afternoon…