What a technical dive log should record: trimix and CCR

A recreational log entry can be five lines long. A trimix or rebreather dive can't. It uses more gases and more equipment, and it builds up more oxygen exposure. Each of these leaves something to write down, and each one matters later when you or someone else has to reconstruct what happened.

This guide covers what to record after a technical dive. It does not cover how to plan one. There are no gas choices, limits or decompression numbers here, and there shouldn't be in a logbook either. Those come from your training, your agency's standards and your team's procedures.

Why the detail matters

Your logbook is your proof of experience. Training agencies set their entry requirements in logged dives, and some count unit-specific hours:

• TDI's public course pages ask for proof of 100 logged dives for Trimix Diver.
• Advanced Trimix Diver asks for 100 logged dives, 25 of them deeper than 30 metres.
• Mixed Gas CCR Diver asks for a verified log of 50 rebreather hours over at least 50 dives on the specific rebreather, with fewer hours on the specific unit if you have hours on another CCR that TDI recognises.

Requirements differ between agencies and change over time, so check the current standard for your course. They all have one thing in common: a vague log can cost you a course place.

The second reason is reconstruction. The Rebreather Forum 3 consensus recommends that every rebreather record and allow download of its functional and dive data, so that dives can be reconstructed with as many relevant parameters as possible. A good written log puts that data in context: what you set, what you carried, and what you decided.

Commercial rules point the same way. For each dive outside the no-decompression limits, deeper than 100 fsw or using mixed gas, OSHA's 29 CFR 1910.423(d)(2) requires depth-time and breathing gas profiles to be recorded. That rule is written for commercial diving operations, but the principle carries over: when the gas changes, the record has to show it.

The basics still come first

Every technical entry still needs the ordinary fields, filled in properly:

• Date, start time and time zone
• Site name and location
• Maximum depth and total run time, as recorded by your dive computer or controller
• Water temperature, visibility and current
• Team members and their roles
• Dive objective (training, survey, cave push, wreck penetration)
• Dive computer or controller: make, model, serial number and firmware version

The serial and firmware details look like overkill until a device fault or a recall makes you ask which dives a unit logged.

Gases and switches

Record each gas the way it was in the cylinder, not the way it was planned:

• Analysed oxygen and helium percentages for every mix, plus who analysed it and when
• The label on the cylinder, written exactly as it appears
• Each gas switch: the time, the depth from your computer and the cylinder you switched to
• Any switch that didn't go as briefed, such as a late switch, a missed switch or a switch back. Add one line on why.

If you imported the profile from your dive computer, check that the switches came across. Some files carry gas changes and some don't. A short note such as "switch to deco gas not in the download, added by hand" keeps the record honest.

Cylinders

A technical dive can involve more cylinders than a recreational one. A small table per dive keeps them clear:

Write down what the gauges showed. Don't round numbers to make them look tidy.

Rebreather (CCR) specifics

A rebreather adds a second layer of records: the unit itself and how it was run.

The unit

• Make, model and serial number
• Your hours on this unit, carried forward from the last entry. Agencies count unit-specific hours, as the TDI requirement above shows.
• Pre-dive checklist completed, and which checklist version you used. RF3 recommends that manufacturers publish carefully designed checklists, and that training agencies build a culture where using them becomes second nature.
• Oxygen sensor checks and calibration, recorded the way your manufacturer and training ask you to record them

The loop

• Setpoints used: the setpoint values set on the controller and when you changed them, such as at the start of the descent or during the ascent. Record what you set; this is not a place to choose values.
• Diluent: the mix as analysed, the cylinder and its start and end pressures
• Oxygen supply: the cylinder and its start and end pressures
• Scrubber: the absorbent type and the time-in-use figures your manufacturer asks you to track. Log the time before and after the dive, so the next dive starts from a known number.

Bailout

• Each bailout cylinder carried: its gas, volume and pressures
• Any bailout event: the time, the depth, the cylinder used, the reason and how the dive ended. Write it down even if nothing went wrong afterwards.

The data file

Download the controller's log after every dive and keep the original file with the entry. The written log tells you what you meant to do. The download shows what the unit recorded. You need both.

Oxygen exposure records

Technical divers track two kinds of oxygen exposure:

• CNS exposure. DAN describes central nervous system oxygen toxicity as the main form seen in diving. Dive computers and planning tools often show it as a percentage of a published limit, sometimes called the "CNS clock".
• Pulmonary exposure, usually expressed in OTUs. TDI explains that one OTU is earned by breathing 100% oxygen at one bar (absolute) for one minute. DAN notes that pulmonary toxicity matters mainly on very long technical dives, such as extended cave or rebreather dives. TDI adds that rebreather divers on multi-day trips can build up significant totals.

For the log, the rule is simple:

1. Record the CNS % and OTU values your dive computer, controller or software displayed, and name the device or program that produced them.
2. Over a multi-day trip, keep a running total in the same format, so the history is in one place.
3. If a device didn't show a value, leave the field empty. Don't estimate one by hand and write it in as if a device had measured it.

What counts as acceptable exposure is not a logbook question. Your training and your team's procedures answer it.

Deviations, incidents and signatures

Note anything that departed from the plan, with times: equipment faults, gas loss, lost team contact, a skipped or extended stop, a bailout. Keep it factual. If anything happened that could have a medical side, follow your team's emergency procedure and get qualified medical help. The logbook only records it.

For training dives, have your instructor sign or verify the entry. For other dives, a teammate's signature or verification adds weight when you apply for your next course.

Where DIVEOPS PRO fits

DIVEOPS PRO is a record-keeping tool, not a dive computer or planner. Three parts of it are built for this kind of log:

• A technical record for each dive. You choose open circuit or rebreather (CCR) and enter a setpoint for CCR dives. You can add up to eight cylinders with roles including bailout, diluent and oxygen, with oxygen and helium percentages, volumes and start and end pressures. Stops are logged as performed, planned against actual. The record has one setpoint field, so note any setpoint changes in the dive notes. It plans nothing.
• Imported profiles and an OTU estimate. UDDF imports bring in the depth profile, the cylinders and the gas switches where the file contains them, so they don't have to be typed again (see Moving your dive history). Imported dives are saved as open-circuit records and can't yet be edited in the app, so type a rebreather dive in by hand if you want the CCR fields. For dives with an imported profile, DIVEOPS PRO shows an OTU estimate worked out from the recorded gas timeline. It is labelled unvalidated, so check it against your own device. On a rebreather dive it uses the loop ppO2 only if the file carries it; otherwise it works from the cylinder gas, which doesn't reflect the loop, so record your controller's own figure instead.
• Gas and pressure calculators for cross-checking your records. They are reference aids, not independently validated, so verify every result.

Start logging your technical dives

Technical Pro covers trimix, heliox and nitrox records, CCR and bailout records, multi-cylinder gas and stop records and the per-dive OTU estimate. See what's included on the pricing page, then start the 30-day free trial and log your next dive in full.