ICD safety

The ICD Safety section closes the Plan step. It sets what the planner should object to when you change what you are breathing. With no helium in the plan it carries a single note and no controls; add a trimix or heliox mix and the cards appear: When Checks Apply, then the checks themselves in three titled groups, Composition, Partial Pressure and Switch Conditions.

Every check is Enabled or Disabled, and a disabled check is not evaluated. Most pair a control that turns the check on with a number that says how much is too much. Raising a number widens what passes. A failing check raises an error against the plan; the schedule is still computed and shown.

When checks apply

• Minimum Dive Depth (m), starting at 80: the shallowest dive whose gas switches are checked. A plan that does not reach this depth raises no counterdiffusion finding, whatever its mixes and switches are.

It is the depth of the dive that decides this, not the depth of the switch. On a 90 m plan every switch is checked, the 21 m deco switch included; on a 45 m plan none is. Counterdiffusion scales with the inert pressures involved, which is why the checks start held to deep diving. Set it to 0 to check every dive.

Composition

• N₂ Fraction Increase with Max N₂ Increase (% pts), starting at 20: how far the nitrogen fraction rises across the switch.
• He Fraction Decrease with Max He Decrease (% pts), starting at 15: how far the helium fraction falls across it.

This pair reads the mixes alone, so it catches a large change of composition wherever in the water column you make it. Switching from 18/45 to 32 % raises nitrogen by 31 points and drops helium by 45:

ICD: gas switch 18/45 → 32% at 30m - N₂ fraction increase 31.0% exceeds limit 20.0%
ICD: gas switch 18/45 → 32% at 30m - He fraction decrease 45.0% exceeds limit 15.0%

Partial pressure

• ppN₂ Increase with Max ppN₂ Increase (bar), starting at 0.5: the same nitrogen rise, measured as a pressure at the depth you switch.
• ppHe Decrease with Max ppHe Decrease (bar), starting at 0.5: the same helium fall, at that depth.

This pair is the same two events weighed by depth, which is why both pairs exist: a change that is modest by fraction can still be severe at 30 m.

ICD: gas switch 18/45 → 32% at 30m - ppN₂ increase 1.24 bar exceeds limit 0.50 bar
ICD: gas switch 18/45 → 32% at 30m - ppHe decrease 1.80 bar exceeds limit 0.50 bar

Switch conditions

• Switch at Ceiling, set to Block or Allow: whether a switch made at or above the decompression ceiling is objected to. It reports the ceiling it found, as switch at deco ceiling 21.0m.
• EAD Consistency with EAD Tolerance (m), starting at 2: how far apart the two gases’ narcotic depths may be.

Narcosis is the one you can check by eye. At 30 m, 18/45 narcoses like 8.8 m and 32 % like 24.5 m, a gap of nearly 16 m against a 2 m tolerance:

ICD: gas switch 18/45 → 32% at 30m - EAD mismatch: from 8.8m to 24.5m (diff 15.7m)

Next

Those five errors are one gas change on one dive. ICD violations covers what the planner does with the schedule afterwards, and where the failures are listed.