Air breaks

Cycle decompression off high-ppO₂ gas at a set interval: what triggers the cycle, how long each phase runs, and which algorithms honour it.

An air break interrupts decompression on a high-oxygen gas with a period on a leaner one, to hold down central-nervous-system oxygen exposure over a long stop. The Air Breaks card, in the Decompression section, schedules that cycle for you.

A 20-minute decompression interval broken by 5 minutes on 21/35

Once triggered (by CNS% or elapsed runtime), the diver breathes the primary deco gas or setpoint for the deco interval, then breaks for the break duration. This repeats until deco clears. Set the break gas and, in CCR mode, the break setpoint below.

Air Breaks

CNS Trigger

Runtime Trigger

Deco Interval

Break Duration

Break Gas

At least one trigger (CNS% or runtime) must be set for breaks to activate.

The fields

Air Breaks: on or off. A new plan arrives with it off, and the rest of the controls appear only once it is enabled.
CNS Trigger: a percentage between 0 and 100, starting at 80 %.
Runtime Trigger: a number of minutes. The cycle starts at whichever trigger is reached first, and a plan with neither set never triggers.
Deco Interval: minutes on the primary deco gas before each break, starting at 20 and greater than zero.
Break Duration: minutes each break runs, starting at 5, also greater than zero.
Break Gas: every gas in the plan by name, plus an empty option. A new plan has none chosen.
Break Setpoint (bar): rebreather plans only, between 0.20 and 1.60. Set it and the break is taken by dropping the loop setpoint rather than switching off the loop, and the break gas is not used.

Once triggered, the diver alternates the deco interval and the break until the decompression obligation clears. Break time is spent at the stop depth on a leaner mix, so the stop grows to compensate. Break segments appear as separate rows at the stop depth with the break gas named in the Gas column; read them in the Advanced view, which puts ppO₂ next to the gas.

Which algorithms honour it

Bühlmann ZHL-16C and Thalmann E-L both schedule air breaks. Thalmann GF Calibration does not apply them at all; its controls stay visible and editable and change nothing.

When the cycle is disabled

A break gas that is not in the plan disables the cycle, at Warning severity: “Air-break gas index N is out of range (M gas(es) configured); air breaks disabled.”
A zero or negative interval or break duration disables it too: “Air-break interval and break durations must both be positive; air breaks disabled.” In both cases the schedule is computed without breaks.

Contingency is next. Also worth reading: oxygen exposure, for what CNS % counts.