Getting the most out of your training: a closer look at TDI courses

Advanced Nitrox and Decompression Procedures

This course is essentially where sport diving ends and technical begins. Sure it used to be different, but these days most divers will tell you that technical diving begins when dive plans require mandatory decompression stops, and in the diver development we offer at Technical Diving International, that usually translates into a combination course make up of Advanced Nitrox and Decompression Procedures. This combo builds the knowledge and skill base that supplies a strong foundation for all kinds of advanced diving, in all sorts of conditions.


Participants in this program will have the best chance of success if they are experienced divers who have been using the dive kit that the program calls for (large volume single with H or Y valve, manifolded doubles, etc.) on several “workup dives.” TDI’s Intro to Tech is a great prerequisite too, although more and more divers are taking this new course as a stand-alone simply to improve the way they conduct sport dives, and have no intentions of going tech.

If you are thinking about signing up for Advanced Nitrox and or Decompression Procedures, here an overview of what you might expect.

Course Goals

Graduates from this course should be proficient divers capable of planning and executing simple staged decompression dives using nitrox and oxygen to optimize their decompression.

In order to graduate, candidates should be confident, divers who understand the basic principles and practices of staged decompression diving, and who are able to demonstrate proficiency and comfort while diving in a wide range of conditions – such as current and variable visibility.  Graduates should also have a firm, realistic grasp of their personal limits – body and mind — and the breadth of their comfort zone.

Course Scope

This course usually consists of four phases or components: Classroom sessions, Fieldwork(dryland drills), Skills building and assessment dives, Working or Graduation dives.

Academic sessions for this combo course run approximately 12 hours with about another four hours for fieldwork. The course also calls for at least six to eight dives and often requires four to five very busy days to complete. Many TDI instructors will add an additional evaluation dive before the classroom sessions and some courses will run for one or two days more! A lot depends on the size of the class (four student maximum) and the skill level of the candidates.

Candidate Prerequisites

Candidates for this course should have experience diving in the conditions in which the course is to be conducted. They should have a fundamental grasp of buoyancy and trim, and be familiar with the gear they will be wearing for the course.

Candidates should also be in a position to supply their personal equipment as outlined in Suggested Equipment Checklist

Course skills

All TDI courses have a listing of specific skills required of candidates for successful graduation. Candidates may also be asked to demonstrate mastery of skills required for courses that are prerequisites to the current course. In this case, this would be basic nitrox. Here for reference are those skills:


Use TDI tables to plan a nitrox dive taking advantage of EAD calculations

Create a simple written dive plan for a nitrox dive to an appropriate depth (MOD calculated with p02 between 1.3 and 1.6 depending on environmental conditions)

Demonstrate correct use of oxygen analyzer

Demonstrate correct tank management and labelling

Conduct simple pre-dive briefing (may be simulated if dives are not part of program)

Program nitrox computer – if used — with appropriate oxygen percentage if used


Here are the skills for Advanced Nitrox:

Review of Nitrox Skills

Land Drills

Calculate and Log CNS loading for each dive including cumulative exposure where appropriate

Demonstrate correct use of oxygen analyzer including optimal procedure for calibration

Demonstrate understanding of gas labelling

Demonstrate adherence to conventions regarding prep of equipment for Oxygen service

Program nitrox computer with appropriate oxygen percentage if used

Pre-dive Drills

Use START* before every dive

Stress analysis and mitigation

*START is Sdrill (OOA drill and Bubble Check), Team (buddy equipment checks), Air (gas matching), Route (entry/exit and planned path underwate)r, Tables (depth, duration, waypoints and schedule)

In-water Drills

Demonstrate buoyancy control (ability to hover at fixed position in water column without moving hands or feet)

Show good awareness of buddy and other team members through communications, proximity and team oriented dive practices

Demonstrate ability to manage freeflow from primary regulator in controlled fashion (shutdown cycle), and switch to back-up regulator.

Deploy lift bag / or safety sausage correctly while maintaining position in water column (not in contact with bottom features or other structures)

Conduct appropriate safety stop while “hanging” from surface marker (lift bag)

Demonstrate ability to share “air” (back gas) with buddy as both recipient and donor in a controlled manner while maintaining position in water column.

Demonstrate correct body position (appropriate trim, such as horizontal / streamlined when moving forward)

Demonstrate proper stress analysis with self and team mates

Decompression Procedures Core Skills:

Skills review from previous TDI skills requirements

Land Drills

Demonstrate familiarity with basic hand signals (listing attached)

Selection and preparation of equipment suitable for soft overhead environment

Conduct team oriented drills (buddy checks) for lift bag deployment

Conduct team oriented drills (buddy checks) for switching procedure

Gas matching among buddy team

Pre-dive Drills

Use START* before every dive

Stress analysis and mitigation

In-water Drills

Demonstrate buoyancy control (ability to hover at fixed position in water column without moving hands or feet)

Show good awareness of buddy and other team members through communications, proximity and team oriented dive practices

Demonstrate comfort swimming on surface and at depth carrying single decompression stage bottle

Demonstrate ability to drop and retrieve single decompression cylinder while maintaining position in the water column

Demonstrate ability to deploy a lift bag solo and as member of team

Demonstrate controlled / staged ascent on lift bag / emergency ascent line (lost ascent line)

Remove and replace mask (deploy backup mask)

Demonstrate appropriate reaction to gas haemorrhage from manifold or first stage, SPG and primary regulator

React to BC inflator malfunction (disconnect LP hose, dump gas and orally inflate BC/Wing to neutral buoyancy)

Demonstrate ability to confirm gas switch(es) at depth with buddy/team members

Buddy breathing deco gas for at least one minute

Switch to back-up mask (remove and replace mask)

Demonstrate appropriate reaction to free-flowing deco regulator (feather valve)

Demonstrate appropriate (may be simulated) modifications to deco schedule in decompression emergency (over time, over depth)

Demonstrate tired diver tow at depth and on surface (30 meters lateral each)

Complete a horizontal breath hold swim at depth for 15 meters

Course Modules (Classroom)

Introductions, paperwork and course review

Textbook Review and Handout of Supplementary Materials (CD etc.)

Accident Analysis

Dive Planning

Gas Management

Equipment Selection

Dive Schedules (decompression planning)

Procedures before, during and after diving


General Review

Preparing for Open water sessions

Course Modules (Fieldwork)

Working with bags, reels, line and knots

Gas mixing (Ideal vs Practical) and tank preparation

Equipment selection and “editing”

Swimming techniques

Drills and muscle memory

Video Review and discussion

Here is a typical overview of the type of dives candidates may be asked to complete.

Please note: Your instructor may reserve the right to conduct staged decompression dives at shallower depths to account for sea conditions and other environmental stressors.

*Dive One — Skills in a controlled environment such as a shallow quarry 18 metres / 60 feet

*Dive Two — Skills in a controlled environment such as a shallow quarry 30 metres / 100feet

*Dive Three – Simulated decompression dive to 40 metres / 130 feet (Nitrox used to extend bottom time and / or shorten surface interval)

Dive Four – Required Decompression dive to 40 metres / 130 feet with decompression between 10 and 15 minutes (one deco gas)

Dive Five — Decompression dive to 40 metres / 130 feet with decompression time of more than 20 minutes (one deco gas)

**Dive Six — Decompression dive to 43 metres / 140 feet (one deco gas) with drifting deco (live boating)

**Dive Seven – Optional decompression dive to 27 metres 90 feet

*These dives may be conducted in one day

** These dives may be conducted the same day

N.B. Depths stated are maximums. Your TDI instructor may opt to conduct all dives shallower to compensate for local diving conditions and comfort of participants.

Graduates would be qualified to enroll in:

  • TDI Advanced Wreck Course
  • TDI Trimix Course
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