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Diving the Dahab Blue Hole on Trimix

Saturday, April 23rd, 2016

I’d been diving at the Dahab Blue Hole a few times, but with the intention of diving the arch, I decided to enroll in a TDI Trimix course with Team Blue Immersion in Dahab. First, though, let’s explain, in simple terms, why trimix is a good idea for this dive. A term familiar to all tec-trained divers is Maximum Operating Depth (MOD), which means the maximum depth at which a gas mix can safely be used. Any deeper and the partial pressure of oxygen (or pO2) exceeds a safe limit, which simply means that by exceeding the given MOD of a gas mix, a diver risks acute oxygen toxicity. The standard gas mix for scuba divers, which we call air, contains approximately 21 percent oxygen, and has a MOD of 184 feet (56 m). Nitrogen narcosis is also a problem, caused by the increased concentration of nitrogen in our tissues the deeper we go. A dive to the arch, deeper than 184 feet, is therefore beyond the limits of a standard oxygen mix.

So, how does trimix make diving deeper possible? As you may have guessed, “trimix” means three mixes, which is to say three breathable gases in your tank. Along with the standard nitrogen and oxygen, helium is added to the blend to create trimix. The mixture contains lower oxygen and nitrogen percentages, thereby reducing narcotic effects and increasing MOD. Helium makes a good breathing gas because it’s less narcotic than nitrogen due to its low density, which also makes it easier to breathe. And, as an inert gas, it doesn’t interact with any other chemicals. On the downside, it can reduce body temperature.

So, in order to enjoy the beauty of the famous arch at 197 feet (60 m), I needed to take a trimix course. The TDI course has the following prerequisites:

  • Minimum age 18
  • Minimum certification of TDI Advanced Nitrox and Decompression Procedures Diver, or equivalent
  • Proof of 100 logged dives


As anyone who has completed a well-taught tec course will know, the beginning of the course is always a mixture of in-the-water drills, repeated until perfect, and dry-land theory, which includes a lot of math. Don’t let that discourage you, however, as it’s fairly simple. During the course, students refresh their tec knowledge and learn a few new things as well. The course covers the following, among other topics:

  • Gas planning based on equivalent narcotic depths
  • Nitrogen and helium absorption and elimination, CNS and OUT limits, isobaric counter diffusion.
  • Decompression gas choices
  • Emergency and contingency planning (equipment failure, omitted decompression, etc.)
  • Decompression diving procedures
  • Proper trim, buoyancy and finning techniques
  • Management of multiple decompression/stage cylinders
  • Emergency procedures (equipment failures, catastrophic gas loss, omitted decompression, navigational errors, injured/unconscious diver, etc.)
  • Equipment considerations, cylinder labeling, analyzing trimix nitrox and mixes, and gas-blending procedures

The average day during the five-day course meant skills and drills in the morning, theory and diving planning in the afternoon, a beer over dinner, and early to bed. Many people find the rescue-diver course tiring as it’s quite physical at times, but the trimix course added mental challenges to the mix as well.

The training leads up to the final dive of the course, a 197-foot (60 m) trimix dive through the arch at the Blue Hole. With the excitement building, the evening before was dedicated to planning out the dive, writing up the plan on our slates and wet-notes, analyzing the gas blends, labeling tanks, and preparing equipment for our early-morning dive. The 20-minute drive to the site gave us the opportunity to go over our dive plan and mentally prepare. Earlier is better when it comes to the Blue Hole, as there are fewer snorkelers and other divers, and the light gives the arch an eerie, deep-blue color as it comes into view. Our dive plan gave us three minutes to reach 197 feet from the signal to descend, and what an amazing three minutes it was, spent in the trim position, free-falling through the water as the arch came into view and we started to slow the descent rate. Coming to a stop and holding position at 197 feet, we entered the arch. With our plan allowing for 14 minutes of bottom time, we could complete a swim-through of the arch and take a good look around, catching some larger fish silhouetted in our torch beams. As the last minute approached, we prepared ourselves for the ascent and the start of our decompression. As I still had one vacation day left, we dove the arch again the next day from another entry point outside the Blue Hole, but this time I was a fully qualified TDI Trimix diver.

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Triton Artificial Gills Project Reimburses, Then Relaunches

Monday, April 18th, 2016

Back in 2014, a piece of equipment called the Triton artificial gills got a lot of media attention for claiming to be able to filter oxygen from water in the same manner seen in fish gills. While the idea of a highly-compact breathing unit was fascinating, it received much criticism as to its plausibility.

Since then, the project has leapt from the design schematics and onto crowdfunding site Indiegogo, where its creator ran a highly successful campaign. Setting a goal of collecting $50,000, the project quickly reached that and beyond, ending at around $900,000, but not without a lot of controversy. However, the Stockholm-based company that ran the campaign has refused to share any of the technical details of the product, citing “legal reasons,” but without going into detail as to what those legal reasons are.

Skeptics pointed out that the technology required to create the James Bond-looking device simply isn’t available. In order to filter and store enough oxygen from seawater to sustain a human being, the item would need to be much, much larger, and the pressure needed for this to happen would require the user to swim at record-shattering speeds.

Following criticism from several sources, including scientific experts, as well as inquiries from Indiegogo backers, the campaign managers somewhat suddenly decided to refund all $900,000 for having mislead Indiegogo users.

However, they almost immediately re-launched the Indiegogo campaign, with a slightly altered pitch, now claiming that the unit doesn’t simply filter oxygen out of water, but instead contains liquid oxygen, which, in combination with the artificial gills mentioned in the original campaign, allows users to breathe underwater for up 45 minutes. In spite of their previous claims having been debunked, and their original campaign shut down, users are still flocking around the product, which, at time of writing, has gathered a little more than $327,000 in backing.

Buyer beware, however, as the technology they’re describing — whether it’s the liquid-oxygen technology or the micro-porous filters — simply doesn’t exist in the form they’re referring to, experts say. So it’s highly unlikely that this version of the product will hit the market any more than the last one.

Because Indiegogo doesn’t require companies to have a working prototype of their products, it is sometimes very difficult to determine the credibility of the claims in campaigns. But, as the saying goes, extraordinary claims require extraordinary proof, and with a claim like this one, which would turn everything we know about underwater-breathing technology on its head, the proof should indeed be extraordinary.

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First Impressions: The Shearwater Perdix Dive Computer

Saturday, April 2nd, 2016

Dominated by the large, square color screen — though it was also available in monochrome — the original Shearwater Predator looked less like a dive watch and more like a somewhat clunky iPhone that you’d strap to your arm. Followed by the Petrel and the Petrel 2, these computers have, in part, set a new standard for the legibility and richness of data that you can expect from a modern dive computer.


One of the main advantages of the larger screen is that all important information is always available without the user having to cycle through various screen modes, as is common in dive computers with smaller screens. The original Shearwater computer was targeted largely at the technical market, and could be used for open-circuits, closed-circuits, trimix, nitrox and air. Without sacrificing the Predator’s technical aspects, the company produced the Petrel and the Petrel 2, aimed squarely at the recreational-dive market, and suitable for anything from easy, shallow reef dives to extended, technical wreck dives on closed-circuit rebreathers.

The Shearwater Perdix

Now, with the Shearwater Perdix, the company is making its range of dive computers even more attractive. Boasting the same versatile features as the Petrel, and allowing for recreational diving, tec diving and rebreather diving using a range of gas mixes, the Perdix is smaller and lighter, has a slimmer profile, and a longer battery life.

The 2.2-inch widescreen display is in only available in full color and is as easily legible as its predecessors, which allows the diver to get an overview of all relevant information in a single glance. It features the adaptive safety stops that the Petrel is known for, wherein every dive is treated as a deco dive, and number, depth, and duration of stops is adjusted to your dive time, depth and history. By providing a “Time to Surface,” the diver always knows how long they should expect to spend on their ascent, all safety and deco stops included.


The computer features four settings: OC Recreational, which allows the use of up to three oxygen/nitrogen gases (either surface air or nitrox), OC Technical, which allows for the use of up to five trimix gases, CC INT, for closed-circuit rebreather diving, and a gauge mode. All modes are user customizable in terms of what they show and where. Everything is controlled by two buttons, one on each side.

The Perdix is 30 percent smaller in profile than the Petrel, and features a contoured design that allows it to sit closer and more streamlined on the diver’s arm. Powered by two AA batteries, the Perdix gets up to 30 percent longer life out of a set of batteries as well, compared to the Petrel 2. The batteries are, of course, user interchangeable, and don’t require specialized tools. It is advisable, however, to purchase two sets of high-quality rechargeable batteries, as the bright, large, colorful screen does take some oomph to power up, and you risk spending a lot of money on disposable batteries (not to mention creating a lot of battery garbage).

My overall first impression of the Perdix is that this could very well represent a popular breakthrough when it comes to high-res dive computers. While the Predator was definitely meant for tec diving, the Petrel and Petrel 2 garnered many die-hard fans, particularly among more advanced divers who did both recreational and technical diving. The Perdix, depending on its retail price, may be the choice of divers who do primarily or exclusively recreational diving, but still want the advantages of a full-screen dive computer.

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Scuba Diving and Exercise Timing

Thursday, March 31st, 2016

Most, if not all, scuba-diving manuals urge divers to stay physically fit as part of their readiness for diving. Being a fit diver helps reduce your gas consumption during a dive, helps you fight against a current, lets you dive longer with less physical strain, and reduces your risk of decompression illness (DCI).

With all the advantages of physical exercise, many divers do seek to boost their physical fitness levels through training. However, while it is important that you do exercise, when you exercise in relation to your diving may be equally important. If diving is your priority, you’ll want to schedule your fitness routine to accommodate your scuba diving, especially if you’re planning an active vacation, where you’ll be participating in other physical activities as well, such as hiking, biking or kayaking.

For the purpose of this article, “exercise” is defined as a physical activity that exceeds the exerciser’s current capacity, in order to trigger a response in the body that improves physical fitness. This is what is known as progressive overload. While scuba diving may require a diver to undertake some physical strain, such as carrying tanks to a boat, it’s typically not intense enough workout, nor a long enough workout to trigger progressive overload.

Performing strenuous exercise right before scuba diving, however, may result in dehydration and muscle fatigue, which can be problematic when you’re underwater. As for the increased risk of DCI posed by exercise before scuba diving, the picture is a bit muddled. Some studies have shown a potential increase in risk of DCI, especially if the exercise is quite challenging and includes a lot of muscular activity, as found in strength training, or impacts heavily on the joints, such as running and other cardio. Other studies seem to indicate that exercise right around 24 hours before scuba diving might have some preventative effect on the risk of DCI. However, this effect is largely unproven. In any case, it is wisest to avoid strenuous exercise 24 hours before diving, and this is also what the Divers Alert Network (DAN)  recommends.

As for exercise after diving, the statistics are a little more clear-cut. Studies have shown an increase in the presence of microbubbles in test subjects’ bloodstreams after intense exercise, which are indicators, though no guarantee, for risk of DCI. We already know that a diver who is physically fatigued during a dive is at an increased risk of DCI; hence the dive-table recommendation for calculating the dive as being longer and more challenging than it actually is. It’s only natural to assume that this same calculation, to some extent, also comes into play after diving, and so follows the recommendation to avoid physical strain after a deep dive.

In short, while there haven’t been any reported cases of DCI that have, without a doubt, been caused by exercise after diving, the general recommendation is to avoid hard exercise for 24 hours before to 24 hours after scuba diving, especially when doing long, deep, or repetitive dives. For the vacation diver, this is usually possible, and is a perfect excuse for a siesta. For the occasional diver, this is hardly a huge issue, either, as a workout schedule can easily be made to accommodate weekend diving. Dive professionals, however, will want to be careful — physical fitness is important, but tailoring your workout around your diving is important, too.


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Sipadan Employs Underwater Police Force

Thursday, March 24th, 2016


Ever wanted to spend your workday scuba diving and protecting coral reefs? Does the title of “underwater cop” sound appealing? In Sipadan, Malaysia, an underwater police force has become reality. The island is famous for its vast variety of coral and marine life, and is a legendary dive destination.

But, as with so many popular dive spots, Sipadan is suffering under its own popularity. The influx of divers has caused severe damage to corals, by divers who were either too careless or too inexperienced to avoid damaging the delicate animals. The local government, knowing full well that the health of the corals is key to the economically important dive-tourism industry, has now taken steps to ensure the protection of the dive site.

As part of a pilot program, four rangers will patrol the area in scuba gear, particularly near the most popular of the island’s dive sites. They will be tasked with intervening if divers are damaging corals. In time, the Malaysian government intends to train more dive marshals to join the task force.

Patrolling marine reserves has always been a challenge. In most places around the world, monitoring is done via boat, typically by park rangers or the nation’s coast guard. These vessels are able to spot illegal boat traffic, fishing and dive boats anchored in places where diving isn’t allowed. It is much harder for them to patrol other damaging behavior, though, such as improper anchoring (seeing as it’s hard to see from the surface if an anchor is on corals or not), or damaging behavior by divers who are in an approved spot.

In spite of the fact that all major dive organizations include training in environmental awareness and urge divers to help protect the marine environment, authorities and dive professionals around the world frequently report diver behavior that cripples corals, harms animals, or damages wrecks. Videos of this sort of behavior also find their way to social media from time to time. While it is a small minority of divers who can’t seem to act responsibly, the damage they do is significant, both to the marine environment and to the reputation of the sport.

However, dive professionals have limited sanctioning options. They can ban an individual from diving with them again if they observe unwanted behavior, but there’s nothing stopping that individual from going to a different dive operator the same day. And rarely does going to the authorities have much effect.

Malaysia’s new step, while it may seem extreme, may make a difference. With authorities routinely present in the area, divers might think twice before snapping off a piece of coral for a souvenir, or become more mindful about where they place their hands and fins as they stop to take a photo. It’s a sad statement that it’s necessary to take such a step, but positive nonetheless that the Malaysian government is willing to address it.

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