We all remember from our open water training that a stop at 10 to 20 feet for three to five minutes is recommended before surfacing from every dive. You may have read or heard about “deep stops” or Plyle stops”.
Read more ….
Things to consider before going tech!
by David Miner
Technical diving is a rapidly growing type of diving. Over the last 10 or so years, technical diving has become more mainstream, training agencies have implemented multiple technical certifications, and the diving community has accepted it as an important, safe, and fun type of diving. Today, equipment manufacturers, diving trade shows, and training agencies all promote technical diving.
There are many things to consider before jumping into technical diving. In this two-part article, we’ll be covering some of the most important things to consider before deciding if technical diving is for you.
What type of technical diving are you interested in?
The Diver vs. Murphy’s Law
by Jeff Petersen
Hogarthian diving is generally considered a specific “configuration style ” of back mount cave diving and there are numerous articles out there on the specifics of the Hogarthian configuration. Instead, this article is more about the psychological underpinnings and guiding principals of Hogarthian diving. The Hogarthian mindset and its concepts can be applied to the various forms of cave diving (and other types of diving).
With the plethora of articles expounding on proper hose lengths, regulator locations, and fittings, such a focus on the gear configurations isn’t necessarily a bad thing. Instruction on the specifics of gear configuration does allow the adopter to immediately leverage the “lessons learned” by so many others in the past. However, this focus on the mechanics of gear set-up can often be at the expense of not giving students a sense of the underlying motivation behind the configuration. A little appreciation of the Hogarthian psyche allows students to tailor their configuration according to their specific diving needs.
In a subsequent posting, I’ll put together a primer on the specifics of the back mount configuration for those unfamiliar to Hogarthian Style.
The Hogarthian emphasis on both safety and efficiency – with near equal importance – is why this method of gear placement does more than any other configuration “style” to generate synergies that minimize risk and maximize efficiency simultaneously.
The Hogarthian mindset is fundamentally about risk management. This mindset was borne from an exploration-intensive environment. And since exploration dives are intrinsically more risky, all other elements of the dive needed to be managed appropriately to minimize the risk.
The following summarizes the Hogarthian goals and strategies (rather than the specific gear configuration that results from the concepts). From the goal statements, the mindset evolves and then, in turn, this leads to the conceptual tools that the Hogarthian mind utilizes to realize the goals.
* Maximize your safety – For those without chemical imbalances, this is the number one goal – for the obvious reasons.
* Maximize your efficiency – While technically a secondary goal, this is a very close second. Since cave dives tend to be very goal-oriented (e.g. “we need to make it 3,000 feet into the tunnel to look for a side tunnel”), the ability to make it with the least risk and effort allows greater success and safety. More diver efficiency makes a dive safer; all things equal, the more efficient you can be, the less likely you are to create riskier situations. And if you do, the efficiency gives you more resources (e.g. lower air consumption) to manage a problem in the most expedient manner.
Mindset of a Hogarthian diver
* Treat all dives seriously – whether large or small, familiar or new cave, complacency can be a killer
* Constantly seek to refine – not re-invent – your gear
* Dive Team/buddy mental synchronicity – dive with like-minded divers
* Minimalism – less is better (up to a point)
– Idiot-proofing – making sure you can use the equipment as easily as possible under any conditions
– Bullet-proofing – elimination of unnecessary failure points
* Consistency of gear set-up (with a critical eye for constant re-assessment for improvement)
* Self-sufficiency – don’t be dependent on your dive team to save you; they should be an additional asset, not a crutch
The number one goal is safety, but we all know that we can’t engage in underwater activities with absolute safety. Since there will always be some degree of risk, the name of the game is risk management. In other words, what is (or what should be) your level of acceptable risk? Based on personal observations of divers, there is clearly a wide range of individual thresholds for acceptable risk. Unfortunately, many display an objectively high level of acceptable risk (based on their behavior), while their perception is quite to the contrary; they think they have a very low level of risk.
Dissecting risk… and your gear
Let’s break down the idea of risk into some manageable and more concrete categories to help illustrate how these concepts have to be addressed. Generally, risk increases with increased complexity. More gear equals more risks/failure points. Also a more complex item will invariably be harder to use properly in a stressful situation, thus increasing risk. These rules are bounded by the practical consideration that some increases to complexity introduces far more safety than the incremental risk introduced, such as adding an octopus (the back-up second stage) to your configuration. Generally, the increased safety it affords far out weighs the incremental risk of hazards such as free-flows and entanglement hazards. Of course these risks, in turn, need to be managed.
For the purposes of this discussion, I’m going to break gear risk down into three components: 1) Internal risk, 2) Accessibility risk, and 3) Environmental risk. Acknowledging that these components do, of course, have some interdependencies, let’s look at these forms of risk in greater detail. To help ground these seemingly academic distinctions, I will carry the analysis of our aforementioned second stage throughout the discussion.
This asks the question, “What is the probability the gear will work as it’s supposed to when it is needed.” How complex is the gear? How many internal components (i.e. how many possible failure points are there in the item)? Are the components electronics, mechanical, or some of both? The more internal components that are crucial to the function, the greater the risk of failure (i.e. more failure points). While risk describes a level of danger, a failure point represents a component whose individual failure renders the equipment inoperable.
Taking our octopus example, the selection of what secondary to put on the end of the hose is crucial. While most of your gear is quite literally your life support system, many people place an inordinate focus on the cost of the gear. This concern over cost must be weighed carefully against what risk are being managed (or exacerbated). Why would you want your secondary regulator to be of a lower quality than your primary? If you have to resort to it, you should expect the same level of performance that your primary affords you. This helps reduce physical and psychological stress and in turn, reduces the likelihood of greater gas consumption during its use. To draw conveniently from a couple handy clichés to make the point: Do you want to place your life in the hands of “the lowest bidder?” And: “How much is your life worth?”
A secondary risk is, given a functional failure, what is the reparability of the item. Can the gear be readily repaired underwater (i.e. immediately repaired)? For example, second stages with screw off covers are preferred over models where the diaphragm cannot be accessed without tools. This allows for re-setting the pop-it and flushing out foreign objects that may be causing a free-flow or other undesirable events.
This one is a little more obvious. Now that we have an octopus that should work as expected and, in the event of probable failures, can be fixed, we next ask: “Can the gear be deployed so that it can be used as intended?” In other words, can it be reached and deployed – regardless of the circumstances? With our new high performance and functioning octopus, we need to figure out the optimal location to store it. Since this is a back-up device, it has to be “stowed away” and may not be needed at all, but it must
always be readily available. One of the signature characteristics of Hogarthian configuration is the location of the octopus. It is worn like a necklace, resting just below the chin, held in place by a thin bungee tied around the mouthpiece. Ease of deployment is crucial. Given its location, some divers can retrieve it without using their hands by tilting their head down. For the less adept, it still takes only one free hand and a split second – even is zero visibility – to move the regulator into the mouth. If the necklace is too long the octopus will flop around and potentially get entangled with other equipment; it could also be more difficult to grasp in an emergency. If the necklace is to short, you can’t raise it to your mouth and keep it comfortable seated in your mouth for use. In the Hogarthian configuration, the octopus hose comes off of the regulator mounted over the left shoulder, laying behind the BC, and draped over the right shoulder. Hose length is selected to ensure that the second stage rests just below the chin and the hose doesn’t “hang” off the shoulder – another entanglement hazard.
Our last gear related risk asks the question, “What risk does the gear introduce that is unrelated to its function.” How will its presence – whether during use or “idle” – impact or be impacted by the environment? Is it an entanglement hazard with other gear? Does it hamper access to other gear or mobility? For example, will it impair the ability to use the power inflator or attach/deploy stage bottles? For our octopus example, one consideration is the overall size of the second stage. Larger stages create a larger profile extending off your chest. This can create a greater entanglement hazard in a very tight squeeze or even produce free-flows in tight all-rock restrictions. Are the exhaust vents and mouthpiece going to allow easy intrusion of sands, shells, etc? One solution to this is to place a section of window screen across the mouth so that when the rubber mouthpiece is attached, it holds the screen in place, taut across the opening.
While all of this may seem excessively academic and analytical, no one questions the value of having a back up second stage, but this illustrates just how focused the mindset of the true Hogarthian diver is on all the “little things” that could turn into big problems.
These attitudes can manifest themselves quite poignantly in dive site chatter. I have overheard countless divers describing their planned dive with boastful tones on how they were going to use multiple stage bottles and a scooter to reach the target penetration. To hear them talk, one would think they were getting points for each additional piece of equipment they could get into the cave with them. Conversely, a Hogarthian diver will pride himself on achieving the dive goal with as little additional gear as possible – while still remaining safe.
In the Hogarthian world, you don’t bring something unless you truly need it. True need here is the operative phrase and the more contentious consideration. We all realize that if a specific set of events occurs, our hypothetical item will be needed. In the end, these “what if” exercises boil down to gut-level probability analysis of the genuine likelihood of need, the items true value, and the risks it introduces during all of its “downtime.” Then – after all of that mental math – if you decide to bring it, make sure it works.
We discussed how the first macro risk is gear and that all of it will fail – eventually. The next macro failure point is you – your brain and your body movements. To minimize your risk of failure, you need to practice and configure yourself so that everything can become second nature, like learned instincts. Then, under stress, you don’t have to consciously manage your actions; instead, unconscious reactions suffice. One of the keys to the success of this concept is to always configure your gear the same way. Whether you are in a large or small cave, deep or shallow, everything needs to be in the same place. That way, your body and mind get trained where to reach for the octopus, the pressure gauge, the power inflator, without fumbling around or requiring thought.
On the brain side, stress itself is a huge risk factor. Since stress can lead to bad decisions and ultimately panic, the near elimination of stress is crucial for safety. Managing your gear – knowing where it is instinctively and using it with ease – will avoid additional stress.
A term that has gained significant popularity as a community and market segment is “Tech Diving.” Unfortunately, the “tech” in Tech Diving means technical and technical translates into gear – more and more gear. For the Hogarthian diver, “tech” is about technique. Technique can always be counted on – you always have it with you.
Another consideration as a failure point is the rest of the divers in your dive team or other divers diving in the system during your dive – or even previous to your dive. Can you trust your life on a stranger’s placement of a line arrow pointing the way out?
While this topic warrants a separate posting to do it justice, for now, the key take away is that your dive buddies should have the same mentality and gear configuration. With the same configuration, each diver is better poised to help each other out. This can be crucial in low visibility and stressful situations where your next action may make the situation safer or much more deadly. You know where everything is on your buddy when he’s having a problem, because it’s in the same place on you – the gear placement that has become second nature for you from consistent placement and practice.
Some people think of the Hogarthian style as rigid and stagnant. The Hogarthian configuration does continue to evolve, although its evolution now is in incremental refinements rather than massive redesigns. Changes to the configuration are based on more of a “scientific method.” A change is proposed, analyzed and evaluated by peers, tested, and then if the test results bear out, adopted. Of course, there is no “Hogarthian Institute” that reviews and ratifies revisions to the doctrine, but there is a strong word-of-mouth-community where new refinements are vetted and either adopted or abandoned based on experience.
Ultimately, understanding and embracing the Hogarthian mindset ensures that when you tailor your configuration, it is a genuine enhancement appropriate to the specific peculiarities of your diving needs. While the Hogarthian goals of safety (risk reduction) and efficiency (getting the most out of your dive) are grounded in cave exploration, the Hogarthian mentality can serve any diver well – be it 30 foot reef divers, nitrox or mixed gas divers, deep wreck divers, or spearfishermen. No matter what kind of dive you’re doing, there’s always a fair amount of effort that goes into making it happen, so you want to get the most for your effort and money. And regarding safety, we’ve all heard the admonition “it only takes a few inches of water to drown.”
A deep look at new species!
by Richard L. Pyle
I awoke in my London hotel room sticky with sweat; the mid-July heat mitigated only by an oscillating fan. I pushed aside the mosquito netting that surrounded my bed and glanced outside the window to get a sense for the weather. We had been up late the night before, futzing with our equipment and discussing alternatives for the day’s plan. If conditions were right, we would head for Poland. If the wind was too strong, however, we’d only go as far as Paris. As I watched the treetops sway gently in the light morning breeze against a sunny blue sky, the prospects for Poland seemed good.
But typical of the first day of any expedition of this sort, the last-minute tweaks to our equipment dragged on throughout the morning, delaying our departure significantly. It was after lunchtime before Poland appeared on the horizon, and the afternoon brought with it strengthening winds. We could have pushed it, but it’s never wise to push things this early on in an expedition. So we settled for a spot closer to Paris instead. The entire journey from London to Paris took only 45 minutes. Not bad, really – for an outrigger canoe.
Captain James Cook was far from his home in England on Christmas Eve, 1777, when he encountered a barren island in the central Pacific a few miles north of the Equator. Cook named it Christmas Island, and apparently found it to be a somewhat desolate place, without strong prospects as a commercial port. He had no way of knowing at the time that he had stumbled on the world’s largest coral Atoll (in terms of land area). Over the next two centuries, the island was occupied by various westerners, during which time the four main villages received their names: “London,” “Paris,” “Poland,” and…”Banana.” The island now bears the name “Kiritimati,” and is overseen by the Kiribati government (based in the Gilbert Islands).
I was only thirteen when I first visited Christmas Island – dragged along by my bird-watching parents as part of the inaugural effort to promote eco-tourism. There were no scuba diving facilities back then, but just by snorkeling and wandering around the tide pools in front of the hotel, I immediately fell in love with the place. It had every attribute of a stereotypical tropical island paradise: pristine blue waters, spectacularly colorful tropical fish, acres of coconut trees, mild breezes, and miles and miles of white sand beaches unblemished by human footprints.
In the years that followed, I returned to Christmas Island many times – helping the Waikiki Aquarium capture baby black-tip sharks for display in public Aquariums throughout the world, and also with friends to challenge the unexplored outer reefs on our own. The last of this series of trips was in 1989. By that time, my fascination for discovering new species of fishes on deep coral reefs had led me into deeper waters. On one particularly memorable dive that trip, I descended rapidly down the outer reef slope towards my usual maximum depth of 200 feet. But when I got there, the slope kept on going downward. And so did I.
My corpse may very well have remained there to this day, had a trigger deep within my reptilian brain not issued a survival-mode command: “Enough.” When I stopped to look at my depth gauge, it was literally pegged at 300 feet. As I contemplated the implications of this, the debilitating effects of nitrogen narcosis caught up with my rapid descent. Through an inebriated fog, I could see about fifty feet further down where the slope gave way to a precipitous drop-off, falling vertically into the inky black unknown. Along its crest was a veritable forest of large sea fans and clouds of fish – an ichthyologists’ wet dream. One fish in particular caught my eye – a small pale tilefish with a dark tail that I didn’t recognize. Was it a new species, or was I suffering from narcosis-induced hallucinations? Should I swim down and try to catch it?
“Not today,” came another command from the reptilian brain. “I’ll be back,” was my conscious brain’s reply, and I reluctantly headed up. It was another 20–30 vertical feet of ascending before the needle on my depth gauge finally retreated from its 300-foot peg. After several hours of decompression, I emerged through the surf back onto the beach, wondering if I had really seen a new species of tilefish, and vowing to return some day to find out.
Sixteen years later, that day finally came.
Floating in the outrigger canoe off Paris, waiting for the highly improvised rusty old porthole that served as the boat’s anchor to snag the reef, we prepared for our first dive of the expedition. Sponsored by the Association for Marine Exploration, a non-profit organization created specifically to support this kind of research, the trip was supported by funds from General Electric in connection with Esquire magazine’s “Best and Brightest” issue of 2004. Our deep diving team consisted of John Earle, Brian Greene, and myself. John, a retired commercial airline captain who has been scuba diving since the 1950’s, epitomizes the notion of a “renaissance man.” Poet (Princeton, with honors), veteran (pilot for the military during Vietnam), naturalist (both land and sea), scientist (his knowledge of reef fishes would put most Ph.D. ichthyologists to shame), surfer, explorer, philosopher – his intellectual breadth and depth can only be described as humbling. Several years beyond the FAA mandatory retirement age for commercial pilots, John is more active and in better physical shape than most guys one-third his age. Brian grew up at Kwajalein Atoll in the Marshall Islands, and is now finishing his undergraduate studies at the University of Hawai‘i. When he swims side by side with sharks (not an altogether rare occurrence), the sharks are the ones that seem out of their element by comparison. Brian has lived more during his twenty-five years than most people do throughout their entire lifetimes.
For my part, the reckless deep-air diving days are well behind me. At the time of my previous trip to Christmas Island, I had only just begun to look into ways of making these deep exploratory dives less hazardous. Starting in the mid- to late-1980’s, several groups of intrepid divers around the world independently began borrowing techniques from the military and commercial divers – incorporating helium and different ratios of oxygen into our breathing mixtures to eliminate narcosis and reduce decompression times, using multiple large-capacity cylinders and other high-tech gear – to develop a new set of protocols for extending the limits of self-contained diving while simultaneously reducing the risks. From our efforts to share experiences, successes, and failures with each other emerged a new revolution in the recreational diving community, which later came to be known as “Technical Diving.”
The contrast between our high-tech rebreathers and the very low-tech outrigger canoe was stark, to say the least. We were joined in the spacious canoe by Matt Craig, a post-doctoral researcher at the Hawai‘i Institute of Marine Biology who was on a scouting trip for a future expedition, and our guide Danny Donegan, a former high-powered accountant who had turned in his business suit and tie for a wetsuit and a thick album of scuba instructor certifications, and was in Christmas Island to train local divers how not to kill themselves. Matt and Danny constituted our surface-support, ably assisted by two Gilbertese boat handlers.
“When should we expect to see you back?” asked Matt – a standard sort of question in this situation. “About three hours,” I figured, watching the sun creeping towards the western sky. “Since this is our first dive of the trip, we’ll try to keep it simple and easy. We may not even find deep water.” Detailed bathymetry charts of this part of Christmas Island are non-existent, and the only depth-reading device on the vessel was the keen eye of our boat driver looking over the side of the boat through polarized sunglasses.
A few minor technical glitches solved, John and Brian rolled off the boat and headed for the rendezvous point on the bottom, fifty feet below. I was the last over the side, and as I righted myself underwater and the curtain of bubbles lifted, I noticed something flapping just to the left of my peripheral vision. A loose line? A clump of my own hair? No. It was a huge centipede, and it was very clearly (and understandably) pissed off. If there is one thing on this planet that can reduce me instantly to a whimpering child, it is a centipede. And as this one scampered across my breathing hose and up my facemask, a whimpering child I became. John and Brian were waiting for me below, so I allowed myself only a moment to regain composure before descending to join them – all the while thankful that no one can tell when you wet your pants underwater.
We picked a bearing seaward, and the three of us set off swimming to find a drop-off. A few minutes later we were heading down a steep sandy slope, dividing our attention between our rebreathers and the insanely large numbers of fishes that surrounded us. I heard Brian trying to get my attention. Through the somewhat muffled but surprisingly intelligible underwater verbal communication that seasoned rebreather divers are capable of, Brian explained to me that a small Grey Reef Shark had inexplicably bumped him from behind, then took off like a terrified puppy. Moments later, muffled shouts from John alerted us to an adult Marlin swimming overhead. We were only ten minutes into the first dive, and things were already getting exciting.
But the highlight of the dive came a few minutes later, as we approached a depth of 300 feet. Hovering above their burrows in the sand were several small pale tilefish with dark tails. With helium replacing the mind-muddling nitrogen in my breathing gas, I saw the fish with sober eyes for the first time – and it was, unquestionably, a species new to science. It wasn’t to be our only discovery of the dive. Ten minutes later and sixty feet deeper, we encountered about a dozen triggerfish with bright orange tails that none of us had ever seen before; indeed, no human had ever seen before – yet another brand new species! So magnificent was our dive, that we stayed longer than we originally planned. We finally surfaced four and a half hours later – 90 minutes after Matt began looking for our surface floats, but just in time to watch a beautiful Paris sunset.
Over the past fifteen years, we have dragged our rebreathers and large cylinders of compressed helium all over the Pacific – from the Cook Islands to Papua New Guinea, from Palau to Fiji and American Samoa. Our mission is always the same: explore the habitat below tropical coral reefs in search of new scientific discoveries. Whereas conventional scuba is rarely used by scientists below 150 feet, and almost never below 200 feet, the rich and complex coral-reef environment with their associated diverse communities of life extend down to at least 500 feet in places. Most deep-sea submersibles, designed to withstand thousands of feet of pressure, come with a hefty price tag (upwards of $20-30,000 per day, or more), and have consequently been used almost entirely for exploration at depths much greater than 500 feet. Thus, the deep coral reefs between 200 and 500 feet throughout the world’s tropical seas – an area sometimes referred to as t
he coral-reef “twilight zone” – remains almost completely unexplored.
If modern studies of biodiversity have taught us anything, it is that going to a place where no one has ever been before will almost certainly result in the discovery of organisms that no one has ever seen before. Though we weren’t surprised to find new species on the deep coral reefs, we were wholly unprepared for how many were down there. The first clues came during an early deep diving trip to Rarotonga, where a few very short dives revealed more than a dozen highly conspicuous new species. Some of them were quite spectacular: one later sold in the Japanese aquarium trade for about $15,000 each.
As our techniques have improved, so too has our ability to find new species. It wasn’t long before we abandoned simply recording how many we had found (over a hundred and counting), and started measuring the rate of new species per hour of exploration time. We’re now up to eleven new species per hour on average, and on some dives the number is closer to thirty. That’s a new species of fish for every two minutes spent on the bottom. Conservative estimates put the total number of undiscovered deep-reef fishes at around 2,000 to 2,500. Pretty impressive, considering that the world total for all known coral-reef fishes is about 6,000 species.
One of the pitfalls of going where no man has ever gone before is that sometimes when you get there, there’s nothing particularly interesting. As Brian and I continued our 30-minute swim across a barren sandy underwater dessert one day later in the expedition, my optimism for exciting discoveries began to attenuate. Just as we were about to give up, the promise of a deep drop-off appeared at the edge of the suboptimal visibility. Quickening my pace downward ahead of Brian, the bottom started sloping at an ever-increasing incline, and I suddenly descended into air-clear water. Though dimmed to a twilight indigo by the murky layers of water above, I could see hundreds of feet in either direction as magnificent rock buttresses protruded seaward, their crests lined with forests of massive sea fans, atop a seemingly bottomless cliff plunging into black abyssal depths. The hairs on the back of my neck stood erect – not only because of the flashback to my dive sixteen years before, but for another reason as well, as captured by the microphone on my running video camera:
“It’s f—ing cold down here…”
“What’s down there?,” Brian can be heard asking in the background.
“Lots of cold water,” was my snappy reply.
As is often the case, an abrupt transition from murky to clear water is accompanied by an equally abrupt thermocline – a sharp demarcation between two bodies of water of substantially different temperatures. The warmer water is less dense, and floats above the cooler water. I have occasionally experienced thermoclines of 10-15 degrees Fahrenheit over a few feet. But this time, the balmy 85-degree shallow water, in which my t-shirt and swim trunks were ample thermal protection, gave way to water that was in the low- to mid-50s.
Once, while watching a program on the Discovery Channel about mountain climbers ascending some alpine peak, I asked a friend why it was that, in order to be considered an “adventurer,” you had to go some place really cold. I guess I finally earned my adventurer’s stripes on that dive.
But as trite as it may sound, I can honestly say it’s not the “adventure” we’re after in our pursuit of new critters on the deep reefs. The real excitement comes not from fending off the occasional shark, gawking at a passing Marlin, or even the awe-inspiring and never-before-seen undersea vistas. These things can surely get the adrenaline flowing – but they represent only one dimension embodied by the spirit of exploration. The real intellectual excitement comes from observing, for the very first time, a new kind of organism that no human has ever encountered before. One more piece in the almost incomprehensible global biodiversity puzzle. Two hundred and fifty years of careful documentation by generations of scientists has yielded fewer than two million species of living things. Even the most conservative estimates put the total count at several tens of millions. We have barely begun to understand the rich diversity of kin we share this planet with, and the species we know about already are, almost by definition, the easiest to find. We still have a long way to go to document the full extent of Earth’s most precious resource, and we are racing against the clock as global warming and more direct forms of over-exploitation threaten to extinguish what there is before we even get a chance to know it ever existed.
Things to consider before going tech!
by David Miner
The last article discussed the different types of technical diving, the training involved, and the benefits of technical dive training. This month, we’re going to talk about the types of equipment needed for technical diving, some of the costs associated with technical diving, and the risks involved with technical diving.
Equipment required for technical diving
Technical diving requires much more gear than standard open water diving gear. If you’re a gear head, you won’t be disappointed if you get into technical diving.
Technical diving takes you to places where special gear is required to safely execute the dive. Technical is not about attaching everything in a dive shop to you and going diving, but it is about taking and using the right gear for the type of technical diving you are doing. Cave diving and penetrating deep into a wreck requires special reels with guideline so that you can find your way out of the overhead environment. Double tanks with a manifold for two complete regulators are also typically used in cave diving and deep wreck diving. Other equipment that is used are backplates and harnesses, HID lights, backup lights, wing type BCs, dry suits, stage bottles with a separate regulator, decompression bottles with a separate regulator, oxygen bottle with a special regulator, etc.