TDI Diver News


5 Best Wreck Dives in North Carolina’s Famous “Graveyard of the Atlantic”

by Thomas Powell:

Around the world, divers and dive professionals will tell you that different areas have some of the best diving available. The desire to find new and exciting places to dive often leads to the development of “best dive location” lists that get printed in various publications. Many of these lists often include dive sites off the coast of North Carolina.

The North Carolina coast is one laden with a rich maritime history beneath the waves. If you have ever had the pleasure of diving the North Carolina coast and its famous “Graveyard of the Atlantic,” you know that there are hundreds of wrecks that range from wooden-hulled sailing vessels to modern artificial wreck structures. The wrecks sit at depths from 60 foot recreational limits to depths beyond the reach of standard technical diving methods. Each one of these fascinating structures lay in blue waters with a feel and visual display much different from traditional tropical settings.

When divers ask North Carolina natives what the best dive sites are off their coast, very rarely is the same answer provided. For that reason, I have chosen to list five favorites that are only a small portion of what North Carolina waters have available.

1. The U-Boats (U-352, U-701, U-85)
North Carolina is lucky to have three scuba-accessible World War II era U-boats beneath her waters. Those vessels represent a unique era in American history. The U-352 is one of the most famous wrecks off the North Carolina coast and she sits in 110 feet of water. Various charter groups offer trips to dive her on a regular basis and crowds from all over the planet come to partake in this experience. In truth, the U-352 is the wreck that first draws many divers to the North Carolina coast. Conversely, the U-701 and the U-85 are more difficult to visit. Temperature changes, currents, and visibility also make these dives a bit more difficult. Despite an increased level of difficulty to visit, these wrecks have the benefit of experiencing fewer divers, making the sites less disturbed by human intervention, each year. Many divers seek to dive all three of these U-boats and over time many have achieved this accomplishment. Diving the North Carolina U-boats is a historical experience as well as an exciting experience.


USSAeolus” by US Navy – Transferred from en.wikipedia to Commons by User:Magnus Manske using CommonsHelper.. Licensed under Public Domain via Wikimedia Commons.

2. Aeolus
The Aeolus is a wreck that was sunk off the North Carolina coast for the sake of developing an artificial reef system. She is 400 feet long, sits in 110 feet of water, and is broken into three major pieces from the hurricanes that often hit the North Carolina coast. Once a cable repair ship, the Aeolus is now a wreck famous for it’s abundance of sand tiger sharks. Divers often experience them in large groups, and they are mostly found in and around the wreck. Any diver who ventures out to the Aeolus will always remember an incredible dive that can rival almost any “shark dive” out there today.

3. USS Indra
The USS Indra was once a landing craft repair ship that was sunk as an artificial reef. She is 338 feet long and is a common dive location visited by the various North Carolina charters. The site has little current, remains largely intact, and offers dive depths from 30 to 60 feet making the wreck a fantastic place for new divers or a place to complete training programs. Similarly, she is close to shore and easily accessible throughout the dive season. The USS Indra is one of the wrecks more commonly visited by divers off the North Carolina coast and is perfect for any type of diver to get a “first taste” of what North Carolina coastal diving is all about.

4. Proteus
The Proteus was once a luxury passenger liner that sank in a collision in 1918. This makes the vessel a true wreck sitting in roughly 120 feet of water. Though she is old and maintains a large debris field, she still has the appearance of a ship, and items that would be found aboard a luxury liner are still being recovered from this site. The water surrounding this site is often warm and clear due to Gulf Stream currents and the structure still provides enough coverage to allow reprieve in the event that a current is present. The Proteus is also a hot spot to encounter sand tiger sharks and various other types of marine life such as large sting rays. On some occasions, divers have even reported sand tiger shark numbers in the hundreds on this site. Diving the Proteus is an incredible experience that will leave any diver wanting to experience more of the blue Carolina waters.

5. Normannia
The Normannia is a pleasant wreck to dive and often described as “pretty.” She is 312 feet long and was once a passenger ship and freighter. She is easy to navigate with the bow, stern, and boilers somewhat intact; but time has caused the wreck to fall into itself to a large degree. The wreck sits in roughly 100 feet of water and the Gulf Stream currents often provide a warm and clear environment. Many of the normal North Carolina fish are found on the wreck of the Normannia, but again, Gulf Stream waters have had an effect and caused many fish species often found in southern tropical waters to take up residence on the wreck. The Normannia is a perfect blend of east coast experiences combing wildlife from southern waters with that of the central east coast.

Each of these wreck sites offers a wonderful and exciting experience to a diver visiting the North Carolina coast, but a diver who is interested in the “Graveyard of the Atlantic” dive sites should contact the coastal charters and go diving. Diving the various available wrecks is the only way to decide for yourself what site is really “the best.” Having been diving around the world, I believe the North Carolina coast and her “Graveyard of the Atlantic” is truly a wonderful diving experience that is different from most places people venture. The only way to understand why it is different is to test the waters and give it a try.

– Dr. Thomas Powell
Owner/Instructor Trainer – Air Hogs Scuba, Garner, NC


Why You Should Invest in Visual Inspection Training

by Don Kinney:
high pressure cylinder
There are many reasons to invest in formal visual inspection training. The best reason is safety; to keep everyone out of harm’s way from a cylinder failing while under pressure, or a compressor failing to work properly. There are also other reasons, even financial reasons, to invest in such training.

A properly trained individual will understand the allowable damage on a specific style of cylinder, the workings and proper operation of a compressor, and they can help develop safe filling procedures for a facility. There are a great number of people who have been around for a long time and have experience in these areas, but when was the last time they had a refresher course, listened to new ideas or developed new techniques? Taking a formal inspection training course can help a novice understand the nuances and dangers involved and can also give new ideas and techniques to the seasoned veteran.

Here are but a few reasons to take a formal training program:

Protect your investment in your equipment (cylinders, valves and compressors)

A company or person has invested hundreds, thousands or even millions of dollars in the cylinders they use recreationally or for business. These cylinders are quality pieces of equipment that can withstand specific uses and/or environments. There are times that the uses or environments exceed the design of the cylinder. The cylinder can then be exposed to factors that may weaken it due to corrosion and stress.

Many of these conditions can be reduced or eliminated as long as the cylinder is properly maintained.
An example of such a circumstance is a steel storage cylinder sitting on concrete with no barrier. The bottom of the cylinder is in direct contact with an environment where it is exposed to moisture. If this condition goes unchecked, it could lead to damage which may render the cylinder useless due to the level of corrosion. With proper training a person charged with the maintenance of the cylinder may prevent such an occurrence and keep that cylinder in service for its intended service life.

When a cylinder becomes damaged it must be determined if the damage exceeds an allowable limit. Simply having damage does not render a cylinder unsafe to use. Most cylinders are designed with a certain amount of damage expected and are designed to withstand that damage. The person maintaining the cylinder must know the allowable limits and understand how to gauge the amount of damage. When looking inside a cylinder and corrosion is detected, how can the inspector measure the damage and make an assessment? Proper training will give the inspector hands on knowledge with a trained professional.

The same principle holds true for the valve on the cylinder. The valve has moving parts and components designed to retain high pressure gases. Constant use, as well as infrequent use, can have an affect. Over-use or over-tightening the valve can affect the high pressure seating material. No use, with the addition of contaminates, may cause the valve to seize or not work as designed. With proper maintenance and care, a cylinder valve should have a long serviceable life. Proper training can cover common issues and proper maintenance tips to ensure a long service life.

If a person or organization has invested in a compressor, it is likely one of the most expensive pieces of equipment in their high pressure arsenal. The compressor is a complicated piece of machinery with numerous moving parts that must work in unison to achieve its rated service pressure. Small particles, not enough oil, too much oil or wearing seals can cause very expensive, unexpected repair bills. The compressor must be maintained, parts replaced and it should be on a scheduled, budgeted maintenance procedure. It is when the compressor is neglected or ignored that the maintenance costs become problematic. Proper training can help the staff develop a maintenance schedule and keep the compressor running as intended.

With a compressor working properly the compressed gas needs to be filled into a storage cylinder. How can this be accomplished safely? The compressor will likely handle pressure well above 207 BAR/3000 PSI. Even much lower levels of pressure, in the hundreds, is enough to go through skin and cause life threatening injuries. The person operating a high pressure fill station must understand these risks. The person filling a cylinder is also the most likely person to notice a safety issue with a storage cylinder and prevent a problem by not using a specific cylinder until it is properly inspected and found safe to use. The fill station can be one of the most dangerous assignments, and that person needs proper training to keep themselves and the facility safe.

Keep yourself safe – hazards from noise to explosions

Working around cylinders and compressors exposes a person to noise and other dangers such as air embolisms and possible failures of the valves or ruptures of cylinders. Care and maintenance of the cylinders and machinery is one step in preventing these issues. But a more critical step is training the person or employees to be safe around the hazards. Simple training tips, such as wearing hearing protection, how to properly move the cylinder, or how not to handle a valve, can go a long way in protecting a person and property. A formal training program will help an organization develop a proper and useful training program.

Compliance with some countries hazmat laws

Because the person or facility is dealing with compressors and cylinders and there is a risk of rupture and damage, most areas and countries have rules in place to keep persons and property safe. Even if an area does not have a governing body, it should be the operator or owner’s responsibility to develop rules that keep themselves and everyone safe. Governing bodies may dictate what training is required or how frequently that training must be administered. However, if no rules exist for proper training, it is important for the organization or person to develop common sense training to keep persons and equipment safe. Taking a formal training course will help to make a person or organization compliant with local rules and regulations, or give the organization proper training if no governing body exists.

There can be no guarantee that if a person takes formal training and follows all the rules, that an issue wont develop. However, if steps are taken to train persons in allowable damage, the repair of valves, the workings of a compressor and the dangers involved when dealing with high pressure gases, there is a greater chance to reduce the threat. A formal training program goes a long way in keeping personal safety as well as a facility safe and preventing damage to the expensive equipment it has purchased and wants to maintain for a long service life.

Interested in International Training Visual Inspection Course?
Get more info here >

About the author: Don Kinney is the owner of Cylinder Training Services ( Don started formally working with and filling cylinders in 1991. With his background in public safety he continued to gain knowledge in the field of high pressure cylinders and began to develop training programs. He has developed programs for PSI/PCI including; Eddy Current testing (2003), SCBA, Fire Department (2004) and their Fire Safety Seminar program (2004). He went on to develop his own visual inspection program covering cylinders, valves, cleaning and compressors in 2011. At this time he realized that inspectors needed a source for affordable and high quality inspection tools. His tools are designed for the high pressure cylinder industry, and to assist them in determining damage and ensuring cylinders remain safe. In 2014 he developed an inspection program for International Training (SDI/TDI/ERDI) where he published a manual and developed an on-line training program. Don continues to dedicate himself to safety in the high pressure cylinder industries. He prides himself on understanding the client and their needs and coming up with a safe and useful training program designed to keep them safe and save them thousands of dollars.


A Guide to Keeping Your Ears Safe and Healthy While Diving

ear diagramEar injuries are one of the most common ailments associated with scuba diving. Pressure differences between the middle and outer ear and the environment can cause a painful squeezing sensation commonly known as “ear squeeze.” Not only can this condition result in shortened dive time, it may cause more serious issues such as hearing loss, dizziness, ringing in the ears and other pressure-related injuries.

General ear care and preventative maintenance

There are several preventative measures that divers can take to ensure that the ear stays safe and healthy while diving.
Use either a commercial product designed to remove water from the ear canal ,or a mixture of half white vinegar and half rubbing alcohol after a diving excursion to gently clean and dry the ear canal. This can also help to prevent swimmer’s ear.

Breathe fresh, clean air before descending into the water. Since the eustachian tube connects the eardrum to the throat, and ultimately the respiratory system, avoiding irritants such as boat fumes and cigarette smoke will help divers avoid inflammation and pain.
Drink lots of water to thin mucus so that it doesn’t clump and block the eustachian tube.

It is recommended to avoid dairy products for two days before a dive as it can contribute to thick mucus.
Don’t dive with congestion or a cold when there is already a buildup of fluid in the throat and eardrums. Congestion causes a shrinking in the tubes, which makes it harder to force in air and equalize pressure.

Use a nasal rinse or oral decongestant to help thin the mucosal lining and flush out irritants that can block nasal passages. Check with your physician before taking any medication, even over the counter, before using the medication while diving

Ear pain while diving

If scuba divers experience ear pain during, or after a dive, there are a few safety measures they can take. The most common method of relieving ear pressure while diving is to stop descending (or even ascend a couple feet), and then close the mouth, pinch the nose and gently blow air into the mouth and nose. This aids in alleviating built-up pressure in the ears. Do not blow too hard as this can cause permanent ear damage.

Sometimes it is best to let the pressure build a little bit before trying to equalize, but not to the point pain is felt. Pushing air through too often can stretch the eardrum and damage the eustachian tube, causing pain as well as making it even harder to equalize with each dive. A general rule of thumb is to equalize every five feet of water depth.

Diving feet first is another ear safety technique that can prove helpful to divers. When diving head first, gravity naturally pulls all of the fluid into the head where it accumulates in the eustachian tubes and swells. If a diver descends feet first, the fluid is pulled toward the feet and away from the head.

Another method to try when equalizing your ears becomes difficult is, to tilt the head to the side. The tilting action can help to stretch out the tubes and allow them to open: you may also try to swallow. Finally, if the ears cannot be cleared, divers should ascend to the surface before permanent damage occurs.

Nothing can ruin a good day of diving faster than ear problems. Following a few simple preventative steps and implementing an equalizing routine will go a long way in eliminating pain to the ear while scuba diving.


Best Advice for Diving Dry in the Summer

by Dr. Thomas Powell:
dry suit diver
Comfort is one of the most important factors that can influence how often a scuba diver gets wet. In the middle of winter, the warmth and protection provided by dry suits are often the only reasons that many divers are willing to accept cold temperatures. Conversely, the summer is a time when more layers come off and divers look forward to warmer temperatures. Despite the change in the weather, many divers choose to use one exposure protection suit for every type of diving and wear a dry suit year round. If a person chooses to wear a dry suit throughout the year, some considerations must be made, and certain factors must be recognized. These factors may include temperature, comfort, general maintenance, and basic physiology.

The first thing to remember is that a dry suit is designed to encapsulate certain parts of a diver. The diver must then choose what thermal layers are worn underneath, unless the suit being used is neoprene. Despite thermal needs, any type of encapsulating material with no breathability can cause a person to perspire in the summer heat. For this reason, a diver must monitor the temperature outside and his or her own core temperature to ensure that he or she does not overheat preparing for a dive or waiting on a dive buddy. One suggestion would be to don the dry suit halfway and then finish prepping any other dive gear. Then, do not finish donning the suit until the time to gear up and get wet arrives. The goal is to stay relaxed and to prevent overheating.

Summer heat and perspiration go hand in hand. If a person is wearing a dry suit, that person must remember to take in fluids and calories. Even floating on the surface of the water on a lazy sunny day can cause a person to grow warm and sweaty. Over time, fluid loss and excessive caloric burn can cause many issues that everyone learns about during basic open water training. To prevent this problem, during surface intervals, a diver should drink water and consume a snack. Time on the surface can also equal a period during which the dry suit seal can be opened and the diver can cool off by removing the top portion of the suit as needed.

General Maintenance
One factor divers seem to have a habit of forgetting is basic equipment care. In the winter, divers often protect their dry suits because it is the only thing letting them get wet. In the summer, some think it is an asset to leave drying on the hood of the car, but a wet suit can be used if needed. The problem is however, the hot summer sun can damage seals just as severly as freezing dampness. Similarly, certain wax types can melt in the hot sun leaving a zipper unlubricated. The reality is that being lazy with equipment is always a bad idea. Dry suits need to be hung properly out of the hot summer sun in a manner that allows the suit to ventilate, dry, and remain protected.

Finally, diving dry in the summer must be a comfortable adventure for any diver. Sometimes, cooler waters do require undergarments of heavier thicknesses, but the diver must remember to stay cool on the surface. The process of diving should be fun. Sweating to death on the surface, but then racing to the water to cool off, and finally using the dive to properly acclimate is not fun. Dry diving in the summer is something that should planned out, and the diver should take the time to stay comfortable.

Diving dry during the summer can also allow a diver to remain well-practiced (on dry suit technique) and comfortable. Similarly, it eliminates the need for multiple wetsuits for various water temperatures. No matter what a diver chooses to do, comfort is key and the proper amounts of time and effort must be put into maintaining equipment, staying safe, and having fun.

– Dr. Thomas Powell
Owner/Instructor Trainer – Air Hogs Scuba, Garner, NC


TDI Cave Diving in Thailand

by Ben Reymenants:
cave diving thailand
Thailand will always be seen as the exotic country fringed by white sandy beaches, with honeymooners drinking from a coconut while petting a baby elephant. Tourists are drawn to the turquoise waters rather than the idea of jumping into a black hole in the ground. Thais translate the word “diving” as, “Dam Narm,” literally meaning “black water,” ironically as they point to the clear, blue ocean water.

The term “cave diving” itself draws wide eyes. Most rural farmers firmly believe dragons and ghosts live in those bottomless pits deep in the jungle, and jumping into one of them resembles suicide rather than stimulation to the explorer’s mind.

It’s no wonder Thailand isn’t synonymous with cave diving like Mexico and Florida seem to be. Few explorers over the last two decades have ventured into the jungle at their own expense to lay lines and teach cave diving. Unfortunately, very little information was shared and when the next generation of cave divers came along, and caves had to be rediscovered all over again. Luckily some GPS data was passed on, and cave instructors have driven days through the jungle to locate one of the hundreds of caves. Even today, we still come across old brown lines in passages we had believed to be previously untouched.

laying lines in thailand cavesHaving dived over a decade in Thai caves, we are still finding new caves and passages, some deep, dark and murky, others shallow and crystal clear. We have replaced a lot of the old lines, as well as put markers in place, and have started documenting the most popular ones.

Thailand has enormous limestone formations, generating its unique topography. Limestone is the perfect breeding ground for dry caves to be formed. National projects have flooded entire valleys to supply hydro-power and preserve the rainforests. A lot of the previously dry caves in these national parks are now flooded and dive-able. Besides stunning panoramas resembling Lord of the Rings scenery, the caves now offer the prefect training grounds for shallow cave training with plenty of the decorative stalactites the novice diver expects to see.

Cave life seems to thrive as well in these caves flooded just over two decades ago, as shrimp, catfish and other fresh water fish come to inspect you.

Visibility may not always exceed 100 feet/30 metres, as some of the caves in the West may offer, but in return, the warm water temperature means most divers can shed their drysuit for a 3mm or 5mm wetsuit, or even board shorts for some of us die-hards.

Most cave courses or trips will start in the more shallow caverns, before heading to one of the many deep, dark sinkholes and thermal vents located further south.

The limestone ridge, stretching throughout southern Thailand is very old and has acidic water from the rainforest above which has carved enormous, mostly unexplored tunnels. Because of the limestone, Thailand has over 2000 caves, both wet and dry. Today less than 10% of these are known.

lilieThermal vents are deep springs, bringing up a variety of minerals and gases. This usually provides a turquoise, slightly milky water. And these vents are deep, very deep. One has even been explored up to 788 feet/239 metres. They also seem to offer a perfect source of nutrients as the surrounding jungles flourish. Divers often have to swim between water lilies, or have their nails manicured by fresh water cleaning shrimp.

Other sinkholes are enormous with entrances well over 300 feet/100 metres in diameter. Divers can easily enter scootering side by side, as the visibility can be well in excess of 100 feet/30 metres.

Most of the caves being dived now are easy access and have no strong flows in or out. This means the caves are dive-able for everyone year-round, as we are not limited by weather conditions.

If your holiday, however, isn’t solely focused on cave diving, Thailand also offers a fascinating culture, where everyone is smiling the entire day, and is ready to help out a total stranger. Thai food is rated best and most varied in the world, and even the pickiest among eaters will find mild, easy to digest meals. For the true adventurer, there are of course the spiciest of curries. One thing is sure; it is impossible to get hungry in Thailand. Thais love their food and will eat around the clock.

boat travel in ThailandLogistics in Thailand can be a bit challenging, but I strongly believe that it is all part of the Thailand cave experience. Four-wheel drive trucks are used to haul compressors, gases and cylinders from one cave spot to another. Lodging can be in true Indiana Jones’ style on a floating bamboo raft on a jungle lake, without cell phone coverage. Where this might be a desirable escape for most, the more discerning traveler can find cover in the most comfortable lodging with air conditioning, 3G, WiFi and fresh brewed coffee.

The variety in cave diving experiences found in Thailand are unequaled in comparison to any other part of the world.

Some information about the 2 most famous caves in Thailand:

Sra Keow Cave Details:

Distance from Phuket: 2.5 hours drive by car
Transportation: By car. The lake is 10×10 metres diameter.
Closest Town: Ao Nang
Depth: 249 meters 829 feet
Visibility: Between 3-20 metres
Temperature: Between 23-29 Celsius
Entrance: 2 small lakes connected to each other at 70 metres and at 205 metres depth.

Song Hong Cave Details:

Distance from Phuket: 4 hours drive by car
Transportation: By car. The lake is about 50×50 metres diameter.
Closest town: Thung Yai
Depth: 177 metres 589 feet
Visibility: Between 10-80 metres
Temperature: Between 23-29 Celsius
Entrance: 2 small lakes connected to each other at 40 metres depth. One entrance at the north-east side at 80 metres depth. (unexplored yet)

Thailand has 10 multilingual TDI Cave Instructors in all parts of the country that can offer a variety of specialties as Cave DPV, Cave Sidemount, CCR Cave and support for deeper expeditions. These instructors have actually set up their own cave instructors group and maintain a healthy communication on cave access, repairs and incidents.

For any information on trips or courses, please contact


Rebreathers and Recreational Diving

by John E. Lewis, Ph.D.1:
rebreather diversThis article could have dealt with Boyle’s law, partial pressures, oxygen toxicity, and how rebreathers work. Unfortunately, it would be three times as long and could (probably would) prove to be boring. Therefore, I chose a more direct approach. I have designed a single day of recreational diving and compared the experience of three divers equipped with different scuba devices ranging from a common open circuit aluminum 80 ft3 tank using air, an identical tank but one equipped with 32% nitrox, and finally the recently introduced Hollis Explorer semi-closed rebreather.

The Dive Scenario

The day’s diving takes place from a boat that is positioned in an area with a wide variety of depths ranging from walls with maximum depths over 30 metres / 100 feet to reefs as shallow as 18 metres / 60 feet. The Captain of the boat has decided there are to be three no-decompression (NoD) dives separated by two hour surface intervals and are to include a mandatory safety stop of five minutes at 3 metres / 10 feet. He also insists that the divers surface with no less than 35 BAR / 500PSI in their tanks.

This boat does not have a compressor, and it follows that all of divers must bring the tanks necessary for the three dives. The first dive is a multi-level dive beginning at 30 metres / 100 feet followed by a 15 metres / 50 feet second depth option. The second dive is also a multi-level dive to a maximum depth of 24 metres / 80 feet with a 12 metres / 40 feet second depth option. The third dive is to be at a single depth of 18 metres / 60 feet. In order to be able to visit the three sites that the Captain has chosen in the time allotted, he insists that for the first two dives the divers not exceed a 60 minute bottom time.

The Divers and their Equipment

Bob, by far the oldest of the three, carries on board three aluminum 80 ft3 tanks filled with air (21% oxygen). He has been diving for over 40 years, and he has developed the particularly low value of air consumption (SAC of 0.5 cu ft/min)2. Mike has three new aluminum 80 ft3 tanks that are prefilled with 32% enriched air mix and sport Nitrox labels. Ordinarily he has a considerably higher SAC, but for this exercise we have made his the same as Bob in order that we can see what Nitrox brings to the table. Nick, by far the youngest, has a brand new Hollis Explorer semi-closed rebreather that is equipped with a steel 28 ft3 tank filled with a 40% nitrox mix, and he too has two backup tanks similarly filled with 40% nitrox. Nick has a SAC of 0.75 cu ft/min, which represents a more common value among recreational divers.

All of the divers are equipped with dive computers, and with one exception, all have been programmed to reflect a predetermined value of oxygen content. The exception is Nick’s Explorer that has been designed to optimize the dive time by choosing a value of the oxygen fraction in the breathing gas such that the no-decompression limit (NDL) equals the capacity of the device. This of course is subject to the maximum operating depth (MOD) dictated by an accepted value of PO2 = 1.4 atm. In addition, the dive time based on the canister life of the Explorer is limited to 120 min.

The First Dive

The results of the first dive are shown in Table 1, where TBT refers to the total bottom time. The dive times that were controlled by NoD limits are labeled as ND, by scuba capacity as CAP, and 60 for the Captain maximum specified bottom time.

Table 1

Depth (fsw) Bob (OC air) Mike (OC Nitrox 32) Nick (Explorer)
100 18 ND 30 ND 37 ND
50 22 CAP 12 CAP 18 (60)
10 5 5 5
TBT 45 min 47 min 60 min

As can be seen, Bob, the traditional open circuit air diver, was seriously disadvantaged at the first depth of 30 metres / 100 feet where the other two divers have significantly greater bottom times. Note that if Nick with a more common SAC had been using the open circuit rig, his TBT would have been less than 30 min.

The Second Dive

After a 120 minute surface interval, the Captain has moved the boat to a new dive site where the maximum depth is 24 metres / 80 feet. Again Bob is at a disadvantage at the first stop. However, it is interesting to note that Mike who gained eight minutes over Bob at the greatest depth, lost five minutes in total bottom time. Nick with the Explorer greatly surpasses both Bob and Mike at the first depth even with the imposed 60 minute TBT.

Table 2

Depth (msw) Depth (fsw) Bob (OC air) Mike (OC Nitrox 32) Nick (Explorer)
24 80 30 ND 38 CAP 55 (60)
12 40 12 CAP 0 0
3 10 5 5 5
TBT TBT 47 min 42 min 60 min


The Third Dive

Finally the boat is anchored above a reef that has a constant 18 metres / 60 feet depth, and the Captain has told the divers that they no longer need to adhere to the maximum 60 min bottom time. All of our divers have switched to their clean tanks, and Nick has renewed the Explorer’s canister absorbent. The result is that with no constraint on bottom time, as can be seen in Table 3, Nick has more than twice the bottom time with the Explorer over the open circuit divers.

Table 3

Depth (msw) Depth (fsw) Bob (OC air) Mike (OC Nitrox 32) Nick (Explorer)
18 60 46 CAP 46 CAP 112 (IDEAL)
3 10 5 5 5
TBT TBT 51 min 51 min 117 min

Days End

We don’t see dramatic differences during the first two dives largely because of the boats 60 min bottom time limit. However, Mike by using Nitrox has had more time at the greatest depth as well as Nick using the Explorer. It is worth remembering that Nick has an average diver’s SAC of 0.75 cu ft/min whereas Bob, the elder, and Mike by caveat was granted the same low SAC rate of 0.5 cu ft/min. Finally, on the third dive where the Captain removed the 60 min bottom time cap, the Explorer had more than twice the bottom time as the open circuit divers. It is worth noting that while the Hollis Explorer is semi-closed, during the entirety of these dives the exhaled gas never reached 10% of that of the open circuit divers.


Based on this example, the Hollis Explorer rebreather has a significant advantage over open circuit divers even those with exceptional breathing control that is 2/3 the SAC of the average diver such as Nick. The Hollis Explorer is not accurately characterized as “no bubbles.” However, the undeniably aesthetic appeal of quiet that is less than 10% of open circuit divers is of considerable potential value to any diver in addition to the increased ability to interact with wild live.

In 1989, the term “dive computers” was first coined to describe expensive and exotic devices that were known by no less than 27 different names. Less than ten years later, the term was common place and the majority of divers dove with one. I will be surprised if another ten years go by before the same cannot be said of the expensive and exotic devices known as … rebreathers, and for recreational divers, rebreathers similar to the Hollis Explorer have the potential to be the standard for the future.

1This article is an updated version of an original article by the author that appeared in the magazine Discover Diving in February 1997.
2Surface Air Consumption


4 Tech Diving Questions You Should Ask, But Never Do

by: Dr. Thomas Powell
tech diver with doubles
Scuba diving is a sport that a person can enjoy for an entire lifetime and never truly reach the end of training or educational opportunities. As the scuba community has expanded, many sport divers have started asking more and more about the world of technical diving and the opportunities that it has to offer. Technical diving is a realm that many new or long-standing sport divers often look at with awe, excitement, and desire. As technical instructors make educational opportunities available to a larger group of potential students, many unique and interesting questions often get asked. These questions are often critical to aid in the education of newly-minted technical students. When questions do not get asked, a student or a new technical diver may choose to test certain ideas that may lead to problematic situations or even injury. The desire to go deeper, see new things, and venture where few have gone before can cause individuals to become complacent about sensible actions. For that reason, the technical community has been a tight-knit and supportive group for many years. Understanding why answers to certain questions are important to know, but not to “test,” can go a long way toward helping a student become a more competent diver who builds a trusting relationship with his or her educator.

There are many questions that show an eagerness to learn but deviate from the tried-and-true standardized educational path. Of those questions, here are four examples with illustrations as to why knowledge is essential when partaking in the “advanced” levels of scuba diving:

How many dives do I need at the bare minimum to jump to the next course and training level?

We all want to learn more, grow as divers, and push some sort of limit in our individual sports, hobbies, and activities. Otherwise we would not grow at doing what we love. The problem is that becoming a better diver is not about the card, what course you have jumped into, or how high you can go within a hierarchy. Instead, scuba education is about getting more proficient, learning tricks that make diving easier and more enjoyable, and more than anything, PRACTICE. The point behind taking a training course is to learn how to perform certain skills and how to do new things (or become more skilled at certain things). The job of an instructor is to ensure that a student can safely complete tasks and perform as a competent diver. This does not mean that every diver who completes a new course is the best diver in the world at that particular training level. The education provides a diver the means and knowledge he or she needs to – go out and safely continue working to become better. Some divers may be ready to jump to the next level of training, while others may desire, need, or even be encouraged to continue diving and practicing. Similarly, participating in too many courses in a row may create an overload of information for a student. One of the best practices out there for any student is to partake in a class, and then GO DIVE! Once the student feels like he or she is ready, the next educational step should then be taken. Training should never be based on a baseline minimum number of dives, but instead on the readiness and preparation for a new program. A diver who looks at scuba education as a race to the finish may not take the time to learn the things he or she needs to know to stay safe and efficient in the water. The best way to make the determination regarding a person’s readiness for the next step in education is to ask the instructor and follow his or her guidance. The goal of any instructor from Technical Diving International (TDI) is to train and prepare divers to be competent enough to dive and be partners with his or her own loved ones. For this reason, a good instructor can help a diver make quality decisions about what steps to take and when, in regard to scuba education. Once a diver knows in his or her own mind that he or she is ready, and the associated instructor agrees, then it is time to safely take that next step.

Can I get by with my current equipment? Do I really need to spend money on something so similar to what I already have? I can cut some of this cost out, right? Why does my computer have to be replaced? Those things are expensive.

Technical scuba diving can be an equipment-intensive world within the overall realm of scuba diving. Many divers get into diving with fun new equipment geared toward sport activities. Depending on the type of diving a person is learning, new equipment may be needed. The best way to view equipment in scuba is to relate it to something else. If you were running a marathon would you rather wear your dress shoes in the closet at home, or would you rather wear a fitted set of stable and comfortable running shoes that would not blister your feet? Or, if you had a loved one who was in a medical emergency, would you want the ambulance coming to get that person to have quality modern life-support equipment or hand-me-down equipment from twenty years ago? Sometimes “it might work” is not the way to approach gear needs, especially involving life support equipment. A technical diver does not necessarily need the most expensive and newest top-of-the-line equipment, but he or she does need quality life support equipment that is both dependable and reliable. A technical student must remember that he or she may be venturing into colder waters, darker waters, soft ceiling scenarios, or even hard ceiling overhead environments. These situations call for redundant gear items and equipment designed for that type of diving. Similarly, many sport computers do not have the capability to plan for the use of mixed gas or decompression needs. Again, the job of an instructor, following the standards of TDI is to ensure that during training, a technical student learns about what equipment a diver at each training level needs in order to dive at that level in the safest way possible. Sometimes gear can be recycled for technical diving use, but money should not be the determining factor behind diving in a safe or unsafe manner. Instead, quality equipment should be obtained when possible, and learned (in regard to use) prior to partaking in advanced and potentially more complex diving activities.

Is my depth limit associated with the course a requirement or is it just a suggestion? I can go deeper if I feel prepared right?

Depth limits have been established by TDI with safety in mind. Instructors have been trained to show students why depth limits are important, and often depth limits are associated with gas, physiological reactions, and physiological needs. For instance, why would a person go to a certain depth if they could stay twice as long and dive more safely on a gas mixture different from air or nitrox? The person who wishes to push that limit without knowing a good answer to that question is not taking his or her time to either answer the question in an effective fashion, or is only entertaining technical scuba for the thrill of the moment rather than the love of the sport and the desire to do more. Similarly, TDI Instructors are required to take advanced students to specific depth ranges to complete many of the courses within the technical program. Technical students will get the chance to go “deeper” during training and not just simulate depth as an exercise. Pushing depth limits without knowing how to be safe, monitor physiology, or be prepared for problems can lead once again to injury or even death.

Can I use my shiny new gear to go straight into tech? I bought this yesterday and I am ready to roll!

Many new technical students do make the decision to purchase new equipment to support the needs and activities related to technical diving. These purchases may include new regulator sets, buoyancy compensation systems, dry suits, wet suits, masks, lights, and even fins. The problem is that many new students may be jumping into gear that they are not yet able to use in a confident manner. Once again, if you pay for one hour of training time at the gym, do you want forty-five of those minutes to be spent learning how to use the equipment? When a diver buys new equipment at any training level, that gear needs to get wet. The diver needs to strap it on in a safe and controlled environment and work out the bugs. Not knowing how to use or configure new equipment may lead to problems, a lack of focus, or a dislike of diving activities. For this reason, prior to starting any technical program, a diver should go to the water with his or her gear and do some sport dives to make sure he or she is ready to learn and enjoy a future class. The only time this type of situation does not come into play is during a program such as TDI’s Intro to Tech Course during which a diver may be trying new equipment and diving methods for the first time, and a lack of preparation may be considered part of the educational environment surrounding the course.

One other question that is often asked by new technical students revolves around training. New students, old divers, and anyone getting wet should remember that skill practice has a purpose.

I was doing these things long before this class. I already know this stuff so can we skip these steps and move on?

Many individuals have partaken in “technical” scuba activities over lifetimes of underwater adventures. Every dive shop knows old salty divers who went deep long before technical scuba was organized under TDI and other agencies. Similarly, many technical classes require that basic tasks be performed that sport divers have learned over time. These tasks may include the deployment of a lift bag, buoyancy skills, or basic physiological reaction tests underwater. Students may consider repeating old skill sets redundant and desire to move forward at a faster pace (eliminating skill steps). The problem with this request is that basic skills may not be the same in the technical realm of scuba. For instance, the diver may know how to deploy a lift bag, but can he or she deploy that lift bag while hovering in a neutral fashion next to a vertical wall at depth with gloves on? Technical instructors are often looking for more than basic single-skill competency. Instead, they are looking at how the diver handles his or herself while enduring various complicating factors. What was once a simple skill in warm Caribbean waters during an SDI Advanced Adventure Course may not be so easy in deeper and colder waters while wearing a redundant equipment load. Technical students must trust that skill sets have a purpose, and once again practice is a good thing. Working through skills and trying to become more competent at what someone may consider a basic task is what makes a diver “better.” So while a diver has the attention and time of an instructor, the best value is to do everything he or she can, new and old, in the hopes of establishing a better understanding or receiving possible advice from someone who has done it countless times.

No question is a bad one. Education and understanding is essential to safe diving practices and learning programs. Instructors should be ready to answer questions or at least find information for students as knowledge is requested. It is always better to ask and learn rather than push the unknown within a community that may have sensible answers already developed based on experience and knowledge. Technical diving is about learning the complex nature behind advanced scuba diving activities while developing independent proficiencies; so ask questions and then take the time to enjoy and use what you learn.

– Dr. Thomas Powell
Owner/Instructor Trainer – Air Hogs Scuba, Garner, NC


Technical Diving Resources

by Jon Kieren:
tdi divers researching

Books – The texts listed are all excellent resources for any active technical diver, or anyone who is interested in beginning their technical diver training. Some of the titles are instructional manuals, while others are non-fiction stories of exploration.

  1. Advanced Wreck Diving Guide – Gary Gentile
  2. Basic Decompression Theory and Application 3rd Edition – Bruce R. Wienke
  3. Basics of Rebreather Diving, The – Jill Heinerth
  4. Beyond the Deep: Deadly Descent into the World’s Most Treacherous Cave – William Stone, Barbara A.M. Ende, Monte Paulsen
  5. Blueprint For Survival – Sheck Exley
  6. Cave Divers, The – Robert Burgess
  7. Caverns Measureless to Man – Sheck Exley
  8. CCR Cave “Almost Simplified” – Dr. Mel Clark
  9. CCR Trimix Simplified – Dr. Mel Clark
  10. Deco for Divers – Mark Powell
  11. Deep Descent: Adventure and Death Diving the Andrea Doria – Kevin F. McMurray
  12. Deeper into Diving, 2nd Edition – John Lippmann and Dr. Simon Mitchell
  13. Diving in Darkness: Beneath Rock, Under Ice, Into Wrecks – Martyn Farr
  14. Diving into Darkness: A True Story of Death and Survival – Phillip Finch
  15. Diving Physics with Bubble Mechanics and Decompression Theory in Depth – Bruce R. Weinke
  16. Diving Physiology in Plain English – Jolie Bookspan
  17. Essentials of Cave Diving – Jill Heinerth
  18. Fatally Flawed – The Quest to be Deepest – Verna an Schaik
  19. Introduction to Technical Diving – Rob Palmer
  20. Last Dive: A Father and Son’s Fatal Descent into the Ocean’s Depths, The – Bernie Chowhury
  21. Mastering Rebreathers – Jeffrey E. Bozanic
  22. Mixed Gas Diving: The Ultimate Challenge for Technical Diving – Tom Mount and Brett Gilliam
  23. Physiology and Medicine of Diving, 5th Edition – Alf Brubakk and Tom Neuman
  24. Rebreathers Simplified – Dr. Mel Clark
  25. Shadow Divers – Robert Kurson
  26. Shipwreck Hunter: Deep, Dark & Deadly in the Great Lakes – Gerry Volgenau
  27. Sidemount Profiles – Brian Kakuk and Jill Heinerth
  28. Six Skills and Other Discussions: Creative Solutions for Technical Divers, The – Steve Lewis
  29. Staying Alive: Risk Management Techniques for Advanced Scuba Diving – Steve Lewis
  30. Technical Diving from the Bottom Up – Kevin Gurr
  31. Technical Diving in Depth – Bruce R. Wienke
  32. Technical Diving Handbook – Gary Gentile
  33. US NAVY Diving Manual
  34. Wookey Hole: 75 Years of Cave Diving & Exploration – Jim Hanwell, Duncan Price, Richard Witcombe


    • The SDI/TDI/ERDI website provides student divers direct contact with their local TDI facilities and Instructors via the Dive Center/Instructor Search Tool. You can also search hundreds of articles about technical diving on the TDI Blog. The Course Description Page gives potential students access to complete descriptions as well as the Standards and Procedures of almost all TDI courses offered.
  2. Rubicon Foundation:
    • The Rubicon Foundation Research Repository is a free digital archive of over 8500 searchable references on topics ranging from Diving Accidents and Fatalities, Decompression Sickness, Hyperbaric Drug Interactions, In-water Recompression, Oxygen Toxicity, and much more! This is by far the largest collection of diving references, and the foundation actively undertakes projects that:
      • Contribute to the interdependent dynamic between research, exploration, science and education;
      • Improve the available resources for students, professionals and the general public; and
      • Preserve the valuable natural resources that are vital to future endeavors.
    • The Rubicon Foundation is a non-profit organization, they accept donations to help support their projects HERE.

Forums – Forums and discussion boards can be an excellent source of information from active technical divers and instructors. It is important to use caution whenever you are taking advice from someone on the internet, however.


FREE Webinar – New VIP Program and How You Can Benefit

Thank you for attending our live VIP Webinar Q&A with VIP author Don Kinney and VP of Training Sean Harrison. If you missed it, you can watch the recorded version below. We would like to continue the questions and answers, so please ask away in the comments section at the bottom of this page and we will be sure to answer them.

International Training has completely reworked and updated its cylinder Visual Inspection Program (VIP). Because of this major update many issues have developed, and questions are being asked. International Training is sponsoring a webinar to update facilities and IT’s on this new program, its implementation, and to answer any questions.The webinar will be hosted by Senior Vice President Sean Harrison and the program developer, Don Kinney. Items to be covered include:

  • The changes in the new program
  • The marketing strategy during the initial implementation
  • The reasoning behind the required instructor fee
  • The plans for future IT Training on this new program
  • The plan to handle the 3 year refresh for the Instructors

The goal of the webinar will be to answer these questions and any other questions you may have. Please be sure an ask your questions below and we will do our best to answer them in a timely manner.

Sign up for VIP Course near you here