Intro to tech

Published by rdevanney on

Twinset valves

Intro to Tech


Intro to Tech is really a brand name for TDI’s entry-level tech course, which is undertaken using a twinset. This has always been the traditional equipment configuration for tech diving. It’s a solid platform that allows you to add additional equipment without changing the basic setup. The wing and backplate set-up used for diving in a twinset is also utilised in CCR diving.

TDI articles written by Richard Devanney outline decompression theory. Two divers at Silfra fissure undertaking a safety stop must obey the rules governing offgassing of nitrogen to minimise their risk of decompression sickness

A potential downside is that the weight can take some getting used to on land, especially with steel cylinders. A long walk to get in the water is unlikely to endear you to diving in a twinset. Smaller people, or anyone suffering from back problems might also struggle. In these cases, smaller cylinders can be used for twinsets- 2x 8L for example. Sidemount may also be a good alternative.


The main advantage of a twinset is the isolation manifold. Regulator problems mean that you can turn off the valve to that regulator, but still have access to the gas in both cylinders. That can take a bit of getting your head around, but with practise it becomes pretty straight-forward.


Similarly, if you are losing gas from the cylinder itself, you can isolate the tank and save the gas from your other cylinder. You cannot do this with sidemount, yet in reality, the likelihood of a burst disk or neck o-ring failure is very low. Your buddy should also be there to help.

Intro to tech training


The best way to describe an intro to tech course is to outline how I teach it. Courses comprise 6 dives minimum. Students learn how to set up the harness and backplate in detail. Every aspect of the twinset and regulator set-up is discussed, and weighting and balance are assessed.


Students need to pay attention when going through the equipment because on the next day, they will be presenting to me how to put it together, whilst discussing why they are doing it a particular way.


Land drills are practised before the dives. A large part of the in-water training involves understanding the manifold and learning how to manage gas. Getting familiar when on land in a gradual and incremental way first is a big help.


Each dive focuses on maintaining buoyancy, trim, and positioning, whilst undertaking tasks, skills, or controlled ascents. Back kicking is introduced as part of that, and other propulsion methods are practised.


Every moment of every dive is an opportunity to practice buoyancy and trim, whilst maintaining awareness of what’s going on around you. Skills that are practised include:


  • S-drill
  • propulsion techniques
    • helicopter turns
    • back kick
    • modified frog kick
    • modified flutter kick
  • Regulator swap
  • Mask removal and replace
  • Mask switch
  • Out of gas
  • Out of gas ascent
  • Out of gas exit, left, right, and single-file
  • LPI failure
  • Wing failure
  • DSMB deployment
  • Valve drill
  • “Boom” drills (manifold and regulator failures)


We also calculate your SCR- Surface Consumption rate, also known as SAC rate (Surface Air Consumption rate). This is done when resting and working and is the first step in gas management.


A big part of technical diving is dive planning, and this is introduced in the classroom by going through the basics of using dive planning software, and outlining how to follow a plan during a dive.


The latter part of the course consists of 3 parts:


  1. Practising following a dive plan
  2. Practising controlled ascents
  3. Introducing problems for you to have to deal with, such as simulated failures


The focus of controlled ascents is exactly that- control. Students need to be able to maintain buoyancy, position, awareness, and be able to communicate simply and effectively at all times. It’s pretty easy to let the air out of your BC and descend. But when decompression diving, the hard part is the controlled ascent, where there is little room for error.


The last dive usually involves the student leading the dive from start to finish and is essentially a fun dive.

For TDI’s intro to tech, the minimum prerequisites include:

  • Be 15 years old
  • Be an Advanced OW diver
  • Have logged at least 25 dives

Advanced nitrox

Tech diving courses