Staged decompression scuba diving provide the techniques for safe deeper and longer diving.
Koh Tao, Thailand
Big Blue Tech celebrates the graduation of Lin Wang from her TDI Decompression Procedures course conducted by TDI Instructor Ash Dunn over 3 days on Koh Tao Island off the coast of Thailand.
Dive history update: Snorkels are out, decompression stops are in. Four reasons:
We’ve learned that every dive is a decompression dive. You on-gas; you off-gas. Surface with too much of the former and not enough of the latter: You’re bent. Safety stops are a decompression stop. Slow ascents are a decompression technique. You’re a decompression diver, like it or not.
We like it. There’s no reason that with proper training, skills and equipment recreational divers can’t employ this legitimate technique for maximizing hard-earned diving dollars. Especially considering the next reason:
We’re wired. Virtually all of today’s dive computers provide the information you need to plan and execute simple forms of decompression diving. Some computers do it with graphic displays and flashing icons. Some talk us through it.
We’re stupid. Boiled down, decompression is a relatively simple procedure. You ascend to a given depth and hang out for a period of time prescribed by your computer, then go up another 10 feet and zone out again. Try not to fall asleep.
But don’t be fooled: At some point, a few curve balls will get tossed your way and the best laid plans take a turn south. That’s why the key to responsible decompression dives is planning and preparing for the things that can go wrong.
What’s Wrong With This Picture?
Most divers are never taught proper deco technique in traditional diving courses. And that’s fine since PADI, SDI, SSI, NAUI and others do not consider planned decompression as part of their charter. Safety stops receive strong mention, but little attention is paid to precision and accuracy. Consequently, watching many sport divers do safety stops is like trying to follow a yo-yo in action. You can get away with that kind of sloppy technique in safety stops because they aren’t required for the dive profile.
But with planned decompression, stops are factored into the overall dive profile. If you decide to take your 30- foot stop at 20 or 15 feet, the odds are you may get to experience the reality of decompression sickness firsthand.
Method #1: Use dive tables to predict a dive profile that includes required decompression stops. This allows advance planning for “bottom gas” (what you will need to breathe during the working portion of the dive) and “deco gas” (which you’ll need to complete the decompression). Given this scenario, the diver can easily compute a schedule that will allow him to carry enough gas supply for both portions of the dive and allow a contingency factor.
A diver breathing standard compressed air can use that gas for both phases of the dive. Indeed, most tables published for sport diving assume that any deco will be made on the same stuff that the diver was breathing while he was swimming about on the reef or around a wreck.
However, most divers planning decompression today look for an additional safety edge by using pure oxygen or a nitrox mix to increase the efficiency of off-gassing. These divers carry a smaller cylinder of “deco gas” to switch to, usually around the 20-foot stop, or they use one provided by the dive boat.
Method #2: Plan the dive and the decompression as it occurs. This is done with dive computers and allows a much greater window of flexibility to the dive plan since no rigid profile is set in advance. The governing factor in this type of plan is to allow enough gas to complete whatever decompression may be required. There are endless variations to gas volume management that can be calculated by the diver under water, including the classic cave diving “rule of thirds” (one-third of your gas for the descent and dive, one-third for the ascent and decompression, and one-third for reserve).
Method #3: Divers using secondary deco cylinders have an extra edge on the folks who want to decompress on the remaining air in their primary tanks. Not only will they benefit from the higher oxygen mix, they will also generally have from 20 to 50 cubic feet of additional gas to breathe during the hang.
Tips for Avoiding the Chamber
So you completed your dive and are ready to head up to begin the decompression indicated. Here are some basic do’s and dont’s.
- Know your computer. If you haven’t thoroughly familiarized yourself with your computer’s decompression functions, don’t even think about trying a deco dive just to see what happens. Some units will default if no-decompression profiles are exceeded. Others will scramble if you venture beyond a certain depth limit. Still others have deco models so conservative that you will spend more time at 10 feet than you spent in line at the DMV.
- Monitor ascent rate. Your ascent is part of your total decompression profile. If it’s supposed to take you two minutes to come up to your first stop, don’t do it in 30 seconds. Likewise, don’t come up unreasonably slow as this will only increase nitrogen gas loading during the deeper part of the ascent. Your computer should remind you if you ascend too quickly for its deco model by either flashing a warning on its display or beeping at you with an audible signal.
- Control your buoyancy. Stay in control by dumping excess air during the ascent, and stop completely at least 10 feet below the first stop to ensure you can hover comfortably. Dive with extra weight to counteract the positive buoyancy of tanks as they are empty.
- Stay static. Preferably, your first experiences should include some type of static support like an anchor line or deco bar. This also gives you a firm handhold if current is present or if the dive boat is swinging on its mooring.
- Keep it simple. Initially, no decompression should be planned with more than one stop until you are completely comfortable with your ability to maintain depth, predict breathing rate, and manage your gauges.
- Do it all. Never cut a decompression stop short. Spend all the time required at the depth prescribed. It’s OK to extend the last stop. You can consider that part of your “safety stop.”
- Assume the position. If you’re in a vertical position at your stop, measure the designated stop depth at the chest area. Ideally, try to maintain a horizontal position during the stops as this will subject the body equally to the surrounding pressure.
- Chill. Decompression should be a period of relaxation. Mild exercise is fine and benefits outgassing, but activities should be limited to easy swimming while maintaining depth. Arm windmills or bicycling the legs while holding onto a line or bar also can improve circulation.
- Don’t chill. On long hangs, even warm tropical water can edge you toward hypothermia. You’ll often need to be more warmly dressed as a decompression diver.
Technical Training Agencies
IANTD (International Association of Nitrox and Technical Divers) reorganized in 1992 to expand from basic nitrox training. Offers full curriculum of tech courses, instructor programs and insurance. Contact: 9628 N.E. 2nd Ave., Suite D, Miami Shores, FL 33138-2767. Tel: (305) 751-4873.
PSA (Professional Scuba Association) was founded by Hal Watts and provides a wide variety of tech diving training at Forty Fathom Grotto near Ocala, Fla. Contact: 9487 N.W. 115th Ave., Ocala, FL 34482-1007. Tel: (352) 368-7974.
TDI (Technical Diving International) was founded in 1994 and is currently the largest tech agency in the world with over 5,000 member instructors. Offers full curriculum of tech courses, instructor programs and insurance. Contact: 18 Elm St., Topsham, ME 04086. Tel: (207) 729-4201.
Deco Diving–The Real Risks
Over the years, the mainstream diving community has shunned stage-decompression diving by sport divers, resulting in a significant stigma surrounding the practice. The fact is: Many, if not most, shop owners and instructors do not have an adequate understanding of stage-decompression diving and its risks. The risk of DCS for a diver properly executing a stage-decompression dive is probably about the same, if not less, than it is for a diver making a no-stop dive because of more efficient off-gassing, thus minimizing “silent” bubbles formed during ascent.
The Real Risks
Less risk of DCS, however, does not mean that the stage-decompression diver does not face other significant risks. Stage-decompression divers are forced to stay below a virtual ceiling or face a high risk of DCS. Therefore, they must carry additional equipment that allows them to solve problems at depth, because surfacing is not an acceptable option.
Risk — Dealing with this gear on a dive boat results in a higher risk of physical injury.
Risk — The extra gear results in a larger profile while diving, creating an increased risk of overexertion due to swimming resistance.
Risk — The additional equipment creates a greater number of potential failure points in the gas delivery system, increasing the potential of a failure.
Risk — Because stage-decompression divers cannot rise above the decompression ceiling, should they miss the ascent/descent line, their risk of being carried away from the boat in a current is greater.
Risk — Stage-decompression diving also tends to result in longer in-water exposure times, greatly increasing the chance of hypothermia.
Risk — The extended exposure time also equates to increasing the odds of experiencing a problem while under water.
Bottom Line — Stage-decompression diving requires training and experience beyond the norm. The only way to truly learn to properly execute stage-decompression dives is to seek out a quality training program from an experienced, knowledgeable instructor. While there are increased risks involved, done properly the risks of stage-decompression diving are manageable within an acceptable level.
Narcosis, decompression, oxygen, nitrox and addrenaline a tech diver make!
Koh Tao, Thailand
Big Blue Tech celebrates the successful completion of a TDI Extended Range diver course for Ian Jordan and David Tipping by TDI Instructor James Thornton-Allan conducted over 4 days on Koh Tao Island off the coast of Thailand.
Considered by many to be the one of the most challenging experiences for the recreational technical diver, the TDI Extended Range course provides the training and experience required to competently utilise air and Nitrox for dives up to 55msw that require staged decompression.
Extending your range doesn’t necessarily mean diving “deep”, it can simply mean diving for a longer duration. Example: Performing a dive on a wreck in 30msw with a 60 minute bottom time.
This course builds on the fundamental knowledge base developed throughout the Advanced Nitrox and Decompression Procedures courses. You will perform decompression dives that require accelerated staged decompression utilising air, Nitrox and Oxygen mixtures.
One of more divisive subjects in technical diving concerns using compressed air as a breathing gas on dives below 130 feet (40 m).While mainstream training agencies still promote and teach such courses (TDI,IANTD and DSAT/PADI), a minority (NAUI Tec, GUE, UTD) argue that diving deeper on air is unacceptably risky, saying that helium mixes should be used for dives beyond a certain limit (100–130 feet (30–40 m), depending upon agency). Such courses used to be referred to as “deep air” courses, but are now commonly called “extended range” courses.
Deep air proponents base the proper depth limit of air diving upon the risk of oxygen toxicity. Accordingly, they view the limit as being the depth at which partial pressure of oxygen reaches 1.4 ATA, which occurs at about 186 feet (57 m). Helitrox/triox proponents argue that the defining risk should be nitrogen narcosis, and suggest that when the partial pressure of nitrogen reaches approximately 4.0 ATA, which occurs at about 130 feet (40 m), helium is necessary to offset the effects of the narcosis. Both sides of the community tend to present self-supporting data. Divers trained and experienced in deep air diving report less problems with narcosis than those trained and experienced in mixed gas diving trimix/heliox, although scientific evidence does not show that a diver can train to overcome any measure of narcosis at a given depth, or become tolerant of it.
Trimix/Helitrox is a popular course here at Big Blue Tech but for our students the cost of helium back home (Australia and England) made the cost of the divers far greater than the benefit. The choice to dive deep air is personal but also financial as some regions in the world have heavy tax on helium and it can also be very difficult to obtain.
The Divers Alert Network does not formally reject deep air diving per se, but indicates the additional risks involved in an article by John Lippmann, DAN. “How deep is too deep?”. http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=29.
The course covered varied degrees of difficulty from strong current, zero visibility and 4m waves. Koh Tao can be very hospitable at 18m but deeper then 30m a seemingly “cocktail” dive can become quite a challenge for even the most experienced diver.
Approximately a year ago, Technical Diving International added an additional step to the line up of courses available to Closed-Circuit Rebreather (CCR) divers and blended the traditional Advanced Nitrox course into the first level of CCR training.
This resulted in four progressive steps in TDI CCR program:
* Air-Diluent to 30 metres/100 feet with no decompression
* Air-Diluent to 45 meters/150 feet with full decompression
* Mixed Gas-Diluent (trimix) to 60 metres/200 feet
* Advanced Mixed Gas-Diluent to 100 metres/330 feet
Breaking out the “entry-level” progression for CCR divers meant that there was time to include all the information contained in the old stand-alone advanced nitrox course. We feel his translates into a smoother transition for students and it seems popular with them because they neither have to “suffer through” the stand-alone course, nor do they have to pay for it!
The progression to level two (air-dil full deco) is gained with 30 hours of experience on the unit and six months diving it. This seems to be a popular change and was decided upon originally after meetings between TDI training staff and our senior ITs and CCR instructors.
But in the change, consideration was made for experienced OC decompression divers. They can if they wish move directly into level two course if they can show training and experience executing open-circuit staged decompression dives.
Some divers, moving into CCR diving for the first time, opt to take level one training regardless of their previous experience, and we accept that decision completely.
British sub aqua club technical diving course completed in South East Asia
Koh Tao, Thailand
Big Blue Tech celebrates the successful graduation of Daniel Mabellis from his BSAC Extended Range course conducted over 4 days on Koh Tao Island off the coast of Thailand by BSAC Extended Range Instructor Ash Dunn and assisted by Mark Slinn and Duncan Tyler.
The BSAC Extended Range Diver [ERD] course is a full technical diving qualification, enabling you to make deep decompression dives using high percent oxygen nitrox mixes [up to 100% O2] to accelerate your decompression stops during ascent.
The course includes theory, shallow water skill development and executing open water dives to a maximum depth of 50 metres.
In the practical sessions, Daniel make a series of dives, working progressively deeper to a maximum depth of 50 metres.
Daniel practiced and mastered many skills such as safety checks and visualization techniques, dealing with out of air situations and gas switching.
Daniel also practiced fitting and removing stage cylinders underwater, deploying a delayed SMB from depth, ascent procedures and proper position for decompression stops.
Gas management and use of run time slates was important, plus utilizing lazy shots and decompression trapezes. Daniel worked on underwater navigation at depth, deploying and using distance lines on the bottom, use of jon lines and emergency stage cylinders.
Daniel was also involved in briefing support divers and helping to arrange a deco station and emergency equipment, plus much more.
This is a full-on course, which is very challenging. But once you qualify as a BSAC Extended Range Diver the possibilities are endless – get ready for exploration and adventure!
The course was completed with 2 dives on the Unicorn Wreck off the coast of Thailand, Daniel continues his training with a Trimix course in Singapore on the HMS Repulse wreck.
British Sub Aqua Club Thailand provides technical diving certification with a edge.
Koh Tao, Thailand
Big Blue Tech celebrates the graduation of Etienne De Beer from his BSAC Extended Range Course conducted over 4 days by BSAC Extended Range Instructor Trainer Ash Dunn on Koh Tao Island off the coast of Thailand.
The Extended Range Diver [ERD] course is a full technical diving qualification, enabling you to make deep decompression dives using high percent oxygen nitrox mixes [up to 100% O2] to accelerate your decompression stops during ascent.
During the course the divers explored deep rock pinnacles, a shipwreck and shallow areas for skill practice creating a variety of conditions and experiences from limited visibility to crystal clear conditions.
Technical Diving International (TDI) instructor cross-over completed for a certified technical instructor.
Koh Tao, Thailand
Big Blue Tech celebrates the graduation of Alex Leeming from her TDI Advanced Nitrox and Decompression Procedures Instructor cross-over course conducted by TDI Instructor Trainer Ben Reymenants during a 8 day workshop on Koh Tao Island off the coast of Thailand.
Alex had been a PADI TecRec – DSAT Tec Deep Instructor for over a year and primarily working in Khao Lak on the west coast of Thailand. Now that Khao Lak is closed for the end of the season Alex found a job working in Vanuatu as a technical instructor but required her to be a TDI Technical Instructor which is what is the most sought certification in that region.
With her new job offer in hand Alex joined Big Blue Tech to complete her cross-over and work towards the upgrade to TDI Extended Range Instructor.
Alex followed an 8 day intense program at Big Blue Tech, doing multiple decompression dives per day followed by physiology and decompression profile seminars. A total of 300minutes of confined in-water skill fine-tuned her demonstration abilities. Alex commented after the course ; ‘this is one of the best and most intense diving courses I ever followed and I am looking forward to my Extended Range instructor upgrade’.During the 8 days workshop, Alex did incentives into wreck diving and CCR Diving
We wish Alex good luck in Vanuatu and look forward to diving with her again soon.
Technical divers explore shipwreck off the coast of Thailand
Khao Lak, Thailand
Continuing the expedition James Foleher and James Thornton-Allan arrived in Khao Lak to commence technical wreck diving on the Mv Sea Chart 1 Wreck wreck located close of the famous Similan Islands off Tab Lamu pier south of Khao Lak.
The Mv Sea Chart 1 Wreck lies in 45m of salt water on it’s starboard side. The 85m long shipwreck sank from rough seas in August of 2009.
Diving from a wooden “longtail” boat provides quick and easy access to the ship wreck. Arriving at the site which has a permanent government mooring line on it you can see the outline of the wreck from the surface which is typical for the conditions in this region which is typically 30-40 meter visibility.
The divers completed 2 accelerated decompression dives with the first one being a orientation dive followed by a small penetration dive.
The next few days will be focused on penetration of the wreck and exploring further into the structure, rooms and cabins in an attempt to reach the engine room. With skills gathered from technical diving and training in overhead environments both the TDI Advanced Wreck and TDI Cave Diver levels the wreck will proove to be a perfect environment to gain experience.
This will be the third time Big Blue Tech has conducted technical diving on this wreck and it is already evident from the last time that divers have been heavily removing items from the wreck. It is quite common for divers to take souvenirs from wrecks however it take away from future divers a chance to see it undisturbed. Many great wrecks in the world have gone from exciting and interesting to boring metal skeleton shells from divers “recovering” items from wrecks. With that the divers will be following it’s philosophy about wreck diving and will not be removing anything from the dive site.
Technical divers discover decompression diving methods in Thailand.
Koh Tao, Thailand
Big Blue Tech celebrates the graduation of Dave Mitchell and Martin Edvardsson from their TDI Decompression Procedures Diver Course conducted over 3 days in on Koh Tao Island in the Gulf of Thailand.
The TDI Decompression Procedures course certifies Dave and Martin to conduct staged decompression dives to a depth of 45m using enriched air nitrox up to pure oxygen.
The students conducted their training on two dive sites that have wrecks in enhance the interactive learning experience by training in a environment that technical diving is best suited for.
This is the second (2nd) stage of training in the series of TDI’s tech diver development program.This Course examines theory, methods and procedures of planned stage decompression diving. The objective of the course is to train divers how to plan and conduct standard staged decompression dives not exceeding a maximum depth of 150 fsw / 45 msw.
During the course the students looked at the most common equipment requirements, gear set-ups, decompression techniques and dive planning.
High mixes of oxygen used to cheat decompression in Thailand
Koh Tao, Thailand
Big Blue Tech celebrates the graduation of Thomas Lanik from his TDI Advanced Nitrox course which concluded over 4 dives and 3 days on Koh Tao Island in Thailand.
The Advanced Nitrox Course teaches the student the skills required to use high mixes of oxygen combined with technical diving equipment to avoid decompression and extend their diving limits for much longer no-decompression dives.
Thomas learned how to handle the high mixes of oxygen and the proper procedures for switching to gas at depth and handling stage cylinders at depth. Thomas also learned about gas management, advanced dive planning and task loading associated with complex technical dives.
Thomas will remain with Big Blue Tech and continue to gain experience in preparation for his Decompression Procedures course in the future. He’s already signed up to our wreck trip on Friday to give him exposure to the benefits of technical diving.
Technical divers return to shore after 4 days at sea
Khao Lak, Thailand – The Valentines Tech Expedition contingent of Big Blue Tech return to Khao Lak today after coming ashore from the Mv Pawara after the completion of a 4 night technical diving liveaboard on the Similan and Surin islands.
The liveaboard was the base of our diving while completing a TDI Extended Range course which trained the divers to conduct accelerated decompression dives to depths of 55 meters / 180 ft using 3 mixes of gas with air, nitrox and oxygen over 4 cylinders worn simultaneously.
This course was delivered by James Thornton-Allan and Andy Cavell for students Yvonne Fries, Helen Artal, Duncan Tyler and Thomas Hallstrom.
This would be the second technical diving trip in the similan islands for Big Blue Tech this season and again it proved to be a holiday setting with challenging and interesting dives. While the diving conditions are described below it was the extra touches of relaxing watching movies, sun tanning on the roof and trips in the dinghy to the beaches, which really made this trip relaxing and enjoying as a holiday.
Technical diving is saturated with bravado and peer pressure which have lead to serious diving accidents around the globe, we’re more about having fun on the surface and focusing as a team underwater which allows each diver to relax and progress at their own pace. In addition to our relaxed atmosphere we also encourage a alcohol free environment and no smoking during the diving day which has contributed to our perfect record of no diving related injuries.
The Similan Islands is located off the west coast of the west side of Thailand just north of Phuket from a town called Khao Lak. There are several ways to reach the similans by speed boat, long tail or liveaboard and is listed as one of the best diving destinations in the world. The Similan and Surin Islands are protected marine parks managed by the Thai government to prevent fishing and destruction to help the marine environment sustain for generations to come. Divers must pay a park fee to enter the marine park which is enforced by roaming park police boats. It seems the greatest enforcement in the area is getting the money from the dive tour operators rather than protecting the environment from fishing or negative effects like litter or pollution but it’s a better system than nothing at all.
The dive sites we visited on our trip was East Of Eden, Boulder City, West of Eden, Elephant Head Pinnacle, Christmas Tree Point, Koh Bon, Koh Tachai, Richelieu Rock, Richelieu Rock(sunset), Koh Bon Pinnacle, Boonson Wreck.
Over these sites we found ourselves at the mercy of very strong currents pushing us in all directions with changing temperature. On a dive a Elephant Head Pinnacle at 55m a freezing cold wall of cloudy water washed over us making the visibility very limited and giving all of us instant brain freeze that took your breath away. While we were struggling to adjust to the temperature we were being pushed all over the place at a very fast rate, so strong that you couldn’t kick against it to keep in place, our only option was to hide behind rocks and do strategic zig zag movements through the dive site back up to recreational diving depths where is was warm and clear again but it was an experience that taught everyone how to handle vicious currents and how to stay together as a team.
On a dive to Koh Bon we finally saw Manta Rays, thankfully our instructor dropped his mask off the back of the boat, as he went do to get it just below the surface we noticed two large manta rays circling us about 10m below us. This would be a first for some of the divers who have had plenty of chances but never actually seen one. The Giant Manta Ray or “Manta Birostris” is mostly black with a white underbelly, long triangular wings and a tail without stinger. It also has a pair of movable flaps just in front of its mouth. They can grow up to 3-4 meters wide and are recorded as up to 22ft or 670 cm in diameter or “disc” size making these very exciting animals to be witness to. These gentle giants are also one of the few rays that don’t sting so you can get quite close without worry of harm. We spent in total about half an hour with these majestic animals, while other divers were restricted by their single cylinder and no decompression limits we spent over an hour at depth without any concern for air or decompression since the dive was planned well in advance.
As the final night rolled around many started falling asleep after dinner showing clear signs of fatigue from the days diving. It was decided as a group that we would skip the last 2 dives and sleep in, we would come back with the speed boat to visit Koh Bon Pinnacle at a later date. It was also the 11th of February which is Andy Cavell’s 27th birthday. We all knew that coming back from the trip and it being Andy’s birthday that we would be well into a few drinks so it’s good to rest up for such vigorous Olympic style consumption.
Returning to shore we unloaded the boat into our taxi and headed off to our hotel for a nap, shower and relaxed for the next few days until the 13th when we would head off to the big shipwreck off the coast called the Sea Chart 1 which is 85m long in 40m of water.
Special thanks to the staff of Big Blue Khao Lak and Mv Pawara for taking such good care of us and bending over backwards to accommodate our trip.