sdi tdi erdi

SDI vs. TDI vs. ERDI – What’s the difference in the diving courses?

We get questioned a lot on what the difference is between SDI, TDI and ERDI courses, so we decided to put it out there where it’s easy for everyone to find when they start doing research.

Are You Ready for Trimix? – Students VS. Instructor Perspective

by Instructor Trainer: Jon Kieren and Diver/Student Jordan Greene:
trimix diver

Instructor Perspective

Jon Kieren:
Day one of a TDI Trimix Course can be intimidating. It usually includes an evaluation dive with your instructor to ensure your skills are up to par before proceeding, as well as an academic review session to evaluate where your dive planning and emergency procedures skills are at presently. While this evaluation day is not typically a go/no-go situation, it gives the instructor an idea of what (if any) remedial work will need to be completed before moving forward. How do you know if you’ll be ready?

The first step will be to determine if the TDI Trimix Course is the appropriate next step for you. This is a personal decision that you need to make on your own, but your TDI instructor can be an excellent resource when trying to decide what your next step is. Do the dives you want to do regularly require trimix training? If not, maybe you should focus your dive training efforts on something that will more directly benefit your diving goals. If they do, then you’re on the right path.

Are you willing to make the investment? Yes, trimix diving is expensive, but it is also time consuming. Many divers have no problem coughing up the cash for the gear, gas fills, and training, but then fall short on making the time investment to keep their skills fresh. Are you willing and able to commit to diving at least once or twice a month? Are you willing to dedicate most of your dives to shallow water practicing skills? If not, your skills can quickly deteriorate after your course leaving you with an expensive plastic card.

Next up, are you mentally prepared for trimix diving? Trimix diving involves depths reaching 100 meters/330 feet and decompression obligations ranging from 30 minutes to several hours. Any emergency must be handled in the water, failure to do so can almost certainly result in serious injury or death. These situations are stressful for just about anybody, but if you are not mentally prepared to be in those situations, you will likely not be able to handle them. How do you handle stress? Can you solve multiple equipment failures in limited to zero visibility without panicking? Your TDI Trimix instructor will teach you techniques to cope with these types of scenarios, but you have to be mentally prepared to be put in those situations before you even get in the water.

Finally, are you a good enough diver? This is difficult for most divers to answer honestly. By now you’re a certified technical diver, at a minimum TDI Advanced Nitrox and Decompression Procedures certified, and you have made at least 100 dives. You’re a pretty experienced diver by this point. Whether your skills are where they need to be to begin TDI Trimix will be a decision that ultimately your instructor will make, but it’s important to be honest with yourself as well. We all want to think we’re the best divers in the universe, but this is typically far from the truth. A buddy with a GoPro camera filming you practice can be a great tool to help you evaluate your own skills. Some simple drills can be done to quickly evaluate your current skill level:

  • Valve Drills- How quickly can you identify shut down a malfunctioning regulator/valve? At trimix depths, mere seconds count when gas is hemorrhaging, and being able to isolate and control the situation will be critical in your TDI Trimix Diver course.
  • SMB Deployment- While the practical use of this skill varies drastically from environment to environment; it is ALWAYS an excellent test of a diver’s ability to handle a complex task quickly and efficiently.
  • Fin Kicks- Modified Flutter Kick, Frog Kick, Back Kick, and Helicopter Turn; can you perform each of these efficiently and without sculling your hands?
  • Stage/Deco Cylinder Handling and Gas Switches- Can you remove and replace your stage/deco cylinder and make gas switches effortlessly without skipping a beat? Trimix training will begin adding additional stage/deco cylinders making basic cylinder handling skills extremely important. These dives also often require up to 2 or more gas switches on a dive, additional gas switches means more opportunities to make a fatal mistake.
  • AND MOST IMPORTANTLY- can you perform all of the above while hovering within a 1 meter/3 foot window and in proper trim? How about without a mask?

At this level of training, all of your basic technical diving skills need to be second nature in order to ensure you will be able to handle the additional task loading of more complex dives as well as equipment failure and other emergency scenarios appropriately. Your TDI Trimix Instructor will help you refine many of these skills and help you with managing emergencies; however, taking an honest look at yourself and your current skill level will greatly help you prepare for your class.

Once you have decided that the TDI Trimix Diver Course is the next logical step, have committed to making the time and financial investment to both the training and keeping up your skills, determined you are mentally prepared to conduct trimix dives, and have made an honest self assessment of your skills, it’s time to get in touch with your TDI Trimix Instructor and start planning your training. Use our Instructor Locator Tool to find an instructor near you.

Student Perspective

Jordan Greene:
trimixWhen technical diving was introduced to me, the TDI Trimix Course stood out in particular more than any other course. Not to undermine the magnitude of any other courses or to discredit the knowledge and skill each one built upon my dive education, it was something about the science of it. The idea of using a gas not commonly or naturally utilized in human physiology for the purpose of exploring a deeper reach, a manipulation even was fascinating to me. This course and type of diving seemed so far-fetched when I started my first tech course (TDI Intro to Tech), it was something I saw as intimidating. Learning the fundamentals of technical diving and being exposed to new types of equipment, configurations, skill sets and understandings made a Trimix course seem mountains above my ability at the time. Building up to performing decompression dives to depths of 100 meters/330 feet (TDI Advanced Trimix) would become a long, hard, time consuming (and expensive) dedication; one that I would happily pursue over time. A Trimix course is by no means a weekend course and requires a great amount of focus and dedication, whether your just starting technical diving or you have accomplished your prerequisites to this course (Advanced Nitrox, Decompression Procedures , 100+ logged dives), honestly ask yourself if deeper diving on mixed gasses is a path you would like to follow. Do you have the time and dedication to learn and maintain skills? Do you have the mental ability to apply the knowledge? Can you handle emergencies scenarios in stressful situations while maintaining a clear train of thought? Are you ready for a Trimix course?

These were my initial thoughts when starting out in my technical training and actually still remain as my thoughts today, though the intimidation and fear factor has been greatly replaced with confidence, understanding and ability. As I mentioned before, a trimix course does not happen over a weekend or week, many months of preparation and experience must be built up prior to starting a trimix course. As with any education or skill, a strong foundation must be built to ensure a sturdy structure can stand. Without a strong understanding of what trimix diving entails, one might not be as thoroughly physically and mentally prepared; training and building upon your current skill set should be routinely enforced before entering into your trimix course. Ultimately it is the student’s decision to move onward to this course, and with the advice of your trimix instructor, it may be determined whether you’re ready or not. As a student, you should be well versed and confident in the practices of your Advanced Nitrox/Decompression Procedures certification including physiology, gas planning, labeling, analyzing, switching and application of corresponding skills. These skills can quickly deteriorate, so it is very important for a student to constantly refresh them in shallower water environments often. Work closely with your instructor for evaluation and areas of improvement; take advice with an open mind. Emergencies can arise at any moment and the more practice a student can have mapping and executing these drills, the better. Valve drills, assortments of fining and kicks, deco cylinder drills, gas switching, low/no visibility comfort, strong current comfort and SMB deployment all need to come natural at the point of entering your trimix course. If one point could be greatly enforced and underlined, it would certainly be to follow your instructor’s guidance for planning, skills assessment, and knowledge development. Your instructor will truly be your greatest asset in determining if this is the right course for you. Ultimately, you should appreciate any advice given, even if it isn’t what you would like to hear. After all, diving is supposed to be fun and your instructor wants you (and themselves) to preform these complex dives as safe as possible. The time commitment and financial investment in a TDI Trimix Course is significant, but remember, the payoff is just as great if not more. The reward will be more than just exploring a deep wreck or over head environment. The discipline and confidence the training and course provides can be applied throughout your diving career and applied to many future courses. Contact your TDI Trimix Instructor and discuss your thoughts on moving forward with this course, be honest with yourself and your instructor about your skills and ability to determine if this is indeed the right course for you.

Related Articles

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.


3 Ways to Improve Your Air Consumption

musa diverby: Jon Kieren

The goal of every avid diver is simple: Spend as much of your life as possible underwater. On open circuit SCUBA, we all have one major limiting factor, the amount of gas we brought down with us (along with no decompression limits, but this article will only address gas supply). Most new divers will have the same reaction when diving with a group, “How does everyone else stay down so much longer than me?” While this quickly fades after just a few dives as the beginner starts to be more comfortable, their breathing will relax a bit, and they are diving just as long as most of the others in the group. However, there are always those exceptions in the group that are able to stay down twice as long as everyone else. What are they doing that’s so different? Do they have gills? Well, no, but some of it is simply physiology. Small people with tiny lungs simply breathe less. Their smaller bodies require less oxygen for metabolism, and it takes far less gas volume to fill their lungs. Much of the rest stems from these three simple tricks.

1. Relax.

This is the hardest part for newer divers. Being underwater is both exciting and also a bit stressful at first. When people are excited, their breathing rate tends to increase. As you breathe faster, you tend to breathe shallower. Fast shallow breaths are very inefficient for gas exchange, and your body starts to build up carbon dioxide (CO2). As CO2 builds up, your body’s natural response is to increase your breathing rate. It’s a vicious cycle that results in a vastly increased air consumption rate and shorter dives. Relax and focus on your breathing, with extra attention on the exhalations. Make sure you are ridding your body of all of the built up CO2, and you will see a drastic improvement in your air consumption.

2. Slow Down.

Scuba diving is not a race. We know it’s exciting and you want to see as much as possible, but you’ll actually see MORE the slower you go. Swimming fast means you’re working harder and breathing harder, which means you’re breathing through your tank faster. If you see something amazing, don’t chase after it, let it come to you. Critters don’t like to be chased around the ocean, and you’re probably not going to be able to catch whatever it is anyway. Slow down and take your time and you’ll be able to stay down significantly longer, and in turn see more.

3. Get yourself weighted properly.

Many divers, both new and experienced alike, have a horrible habit of diving over-weighted. Their thought process is typically “I’d rather have too much weight than not enough, because I can always add more air to my BCD.” While to some extent this is true, and you can become neutrally buoyant by adding more air to your BCD, your air consumption will suffer. This happens for two reasons, both which take a brief physics review to explain. First of all, adding weight to a diver increases the diver’s mass. Even though you have added air to the BCD to counter the gravitational pull by adding buoyancy, the diver’s mass has still increased. Increasing a divers mass also increases his inertia, meaning it requires more force to propel the diver through the water. More force means the diver’s body will need to metabolize more oxygen, creating more CO2, increasing the diver’s breathing rate. Not only does over-weighting increase a diver’s inertia, but it also will have a negative impact on the diver’s trim. When a diver falls out of horizontal trim, they are faced with increased resistance when trying to move through the water. More resistance means it will require more force to move the same distance. Starting to see how diving over-weighted can seriously impact a diver’s air consumption?

Relax, slow down, and get properly weighted and you’re on your way to improving your air consumption. Just like anything, practice makes better, and the only way to truly improve is to get out there and dive as much as possible. Working with an experienced instructor can help get your weighting, trim, and buoyancy control dialed in, while the rest just comes from experience.

The Secret Sauce for Surface Marker Buoy (SMB) Deployment

This article focuses on one specific aspect of deploying an SMB: methods for inflating the SMB.


Survivor or Statistic… Which One are You?

by Jon Kieren:
tdi diver and reefDive enough and you’re bound to have a few “incidents.” Technical dive enough and you’re almost certain to have at least a couple of “hits the fan” moments. TEACH technical diving at ALL, and it’s a whole other level of “pucker factor.” Knowing that we are going to have some sort of equipment malfunctions, environmental/navigation emergencies, and will just simply make mistakes at some point in our technical diving careers, how do we avoid becoming a diving fatality statistic? Follow the rules, keep things simple and conservative, stick to your training, practice, and stay calm.

    • Follow the rules – In technical diving there are a lot of them. They are there for a reason, usually because someone (or several people) died. Whether it’s gas volume requirements, gas analysis, cylinder labeling, depth/penetration limitations, equipment requirements, pre-dive checks, equipment maintenance, etc., there simply is not a dive that is worth breaking these rules and risking your life. Technical diving carries enough inherent risks as it is, and these rules are there to help mitigate those risks. Don’t push it, and don’t get complacent.


    • Keep things simple and conservative – We’ve all read the stories. Divers who tried to go beyond what a reasonable plan would allow and came up short. Keep dive plans and objectives as simple as possible, and plan conservatively.


    • Stick to your training – You paid an instructor (probably several by this point) a lot of money to train you how to dive, don’t let that money go to waste. What’s the point of training if you’re going to ignore what you were taught anyway? Going beyond the limits of your training can place you in situations you are not prepared to handle, and can (and often does) lead to fatalities. Don’t put yourself in that position, stick to your training.


    • Practice – Dr. Anders Ericsson’s research on expertise found that it takes 10,000 hours of deliberate practice to become an expert at almost anything. Since then, it has been more refined and determined that this practice must include proper evaluation, feedback, correction, and reward to truly be effective. Try and put that into the context of diving. 10,000 hours of practicing valve drills before you become an expert. You better get in the water.

While 10,000 hours is obviously not a realistic value, it certainly puts things into perspective, doesn’t it? How many of your buddies consider themselves “expert divers?” How many hours do they have under water? The point here is not to shoot anyone down or deflate anyone’s ego, but instead to point out that everyone needs more practice. It is often said that in a true emergency situation, the BEST you can possibly expect to respond is the WORST that you perform in practice. Think about your last skills dive, the worst you performed any of those skills is how you will react in an emergency. Would you survive? Just because you went through a great Deco Procedures course, doesn’t mean you’re now an expert at decompression diving. You have a long way to go, and have only just begun to develop those skills.

  • Stay calm – In technical diving, panic kills. Plain and simple. If you allow yourself to go into “flight” mode in an emergency, you will become a statistic. That’s pretty heavy stuff considering we’re doing this for fun, right? Well, panic is the brain’s natural response when someone is beyond their comfort zone. A scenario we use to demonstrate the comfort zone with students is to ask them at their most vulnerable moment (maximum depth/penetration, near turn pressure, separated from the team, etc.) to mentally put themselves in the worst possible case scenario, like a catastrophic gas loss or silt out, and pay attention to their heart rate. If your heart starts to race just thinking about it, you’re probably outside of your comfort zone and should turn the dive. Knowing the limits of your comfort zone is extremely important and should be taken seriously on every technical dive. If there are any complications just before or during a dive, you need to re-evaluate your limits knowing that the error chain has already started. Each mistake or problem on a dive adds a link to this chain and reduces your comfort zone, and the likelihood of you staying in control in an emergency begins to vanish. Staying calm and within your comfort zone will drastically increase your chances of survival in an emergency by allowing you to rationally solve the problem instead of bolting for the surface.

We’re all in this to have fun, but chances are we’re going to run into a few problems along the way. As a technical diver you’ve been trained and given the basic tools to resolve those problems. As long as you stay within your comfort zone, keep your skills sharp, follow the rules, and try to keep things as simple as possible, you should be able to keep your name out of the accident reports.

3 Mistakes Most New and Veteran Divers Make

This article will discuss 3 mistakes that are common for new divers, how to avoid them, and how an experienced diver could easily end up making the same mistake..

6 Skills Every Technical Diver Should Master

Whether you are just starting your TDI Intro to Tech Course, or have over 200 Advanced Trimix dives, these six essential skills should be practiced on every dive.

Diving from #MyBuddysBoat

by Jon Kieren:

buddy's boat

photo by Aldo Ferrucci

#AreYouSureThatisaGoodIdea | #SupportYourLocalDiveCenter

As divers, it’s hard to imagine a better summer day than hanging out on your buddy’s boat, doing a little diving, maybe a little fishing, and just relaxing enjoying the sunshine. When all goes well, it’s the perfect way to spend a day out of the office, but what about when it hits the fan? Do you and your buddies have the equipment and skills required to handle the worst case scenarios? While a day out on your buddy’s boat can be a lot of fun, if you are not properly trained and equipped it is probably a better idea to spend a few bucks and head out with your local dive charter instead. Professional dive charters offer more than just a boat ride; they have trained staff and the necessary equipment to handle emergency situations, and could very well save your life. A few points to consider when deciding whether to head out on your buddy’s boat or dive with a professional dive charter are:

    • Equipment-If you’ve ever been on a dive boat, you’ve probably heard a safety briefing given by the captain or crew. This briefing typically outlines emergency procedures and describes/shows where to find emergency equipment onboard. This briefing is not just for show, this emergency equipment can save your life, and typically includes:
      • PFDs (life jackets)
      • VHF Radio-for hailing coast guard, EMS, other vessels, etc.
      • Fire suppressant devices
      • EPIRB- Emergency Position Indicating Radio Beacon
      • First Aid kit
      • Emergency Oxygen

Not only do dive charters stock this equipment onboard the vessel, the crew is trained in its use. Do you and your buddies have access to this equipment? Are you confident in your ability to use it in a high stress emergency?

    • Crew- Are you and your buddies experienced and qualified mariners and rescue divers? In the event of an emergency in/on the water, you need to have well trained personnel on hand to lend assistance effectively. Are you and your buddies trained and prepared to handle the following situations?
      • Distressed/Unconscious diver in the water
      • Fire on-board the vessel?
      • Weather suddenly turning while divers are in the water
      • Lost/missing divers
      • Decompression sickness and other diving injuries

Dive charters staff professionally trained and experienced crew members to assist and handle these types of scenarios. These crew members are often overlooked, because most of the time their skills are not required. But when there’s a problem, you will be glad they are there to help.

Unless you and your buddies are very experienced mariners and divers, we strongly recommend choosing to dive with a professional dive charter instead of heading out on the water alone. Dive emergencies happen quickly and unexpectedly, and having trained professionals and the proper equipment on site can turn a potential fatality into a minor hiccup in the day’s events. Next time you’re thinking about going diving, let the pros do all the work and head out with your local dive charter. To find an SDI facility in your area, click here.

Is Technical Diving for You?

by Jon Kieren:
intro to tech divers

Don’t knock it ‘til ya try it, right? Well, this also works the other way around when we’re deciding whether to pursue technical diving. Technical diving takes a specific mindset, skill level, and a substantial investment of both time and money; are you willing and able to meet these requirements? If you are unsure, there’s an option available to help you make up your mind before you fully commit yourself. It’s called the TDI Intro to Tech course.

Whether you are unsure of your ability to handle the equipment (there’s a lot of it), if you’re mentally tough enough to handle the stress of not having direct access to the surface, or even if you just want to know more about what is involved with technical diving before you commit, the TDI Intro to Tech course can help answer these questions. You will be introduced to the equipment and skills required for technical diving without the additional stress of a pass/fail situation, and without entering an environment or situation you are not comfortable with (increased depth, wreck or cavern/cave penetration, or decompression). This course will walk you through the special techniques, planning procedures and skills that set technical diving apart from traditional sport diving. It will show you how to improve your dive planning methods, in-water skills, and streamline your existing gear configuration.

The specific skills this course highlights are:

  • Advanced Buoyancy Control
  • Gas Management
  • Situational Awareness
  • Trim
  • Gear Configuration and Selection

After completing Intro to Tech, you will be armed with the information you need to make an educated decision about moving forward into the technical diving realm. To find an instructor near you, visit our dive center locator here. Also, check out our Events page for upcoming TDI sponsored Intro to Tech events in your area.