Gas Switch Calculator

Calculate the partial pressure differences between two gases for different ambient pressures

From Gas

O2:

HE:

N2: 40%

Use Setpoint: 1.3

To Gas

O2:

HE:

N2: 50%

Use Setpoint: 1.3

Show IANTD 5% rule column (experimental, disputed)

Depth [m]		ppO2 [bar]	ppN2 [bar]	ppHe [bar]	Gas O2/He	Density [kg/m³]
6	from	1.30	0.14	0.16	81/10	2.06
	to	0.80	0.80	0.00	50/0	2.14
	diff	0.50	0.66	0.16
10	from	1.30	0.33	0.37	65/19	2.34
	to	1.00	1.00	0.00	50/0	2.68
	diff	0.30	0.67	0.37
20	from	1.30	0.80	0.90	43/30	3.02
	to	1.50	1.50	0.00	50/0	4.02
	diff	0.20	0.70	0.90
30	from	1.30	1.27	1.43	33/36	3.7
	to	2.00	2.00	0.00	50/0	5.36
	diff	0.70	0.73	1.43
40	from	1.30	1.74	1.96	26/39	4.38
	to	2.50	2.50	0.00	50/0	6.7
	diff	1.20	0.76	1.96
50	from	1.30	2.21	2.49	22/42	5.07
	to	3.00	3.00	0.00	50/0	8.04
	diff	1.70	0.79	2.49
60	from	1.30	2.68	3.02	19/43	5.75
	to	3.50	3.50	0.00	50/0	9.38
	diff	2.20	0.82	3.02
70	from	1.30	3.15	3.55	16/44	6.43
	to	4.00	4.00	0.00	50/0	10.72
	diff	2.70	0.85	3.55
80	from	1.30	3.62	4.08	14/45	7.12
	to	4.50	4.50	0.00	50/0	12.06
	diff	3.20	0.88	4.08
90	from	1.30	4.09	4.61	13/46	7.8
	to	5.00	5.00	0.00	50/0	13.4
	diff	3.70	0.91	4.61
100	from	1.30	4.56	5.14	12/47	8.48
	to	5.50	5.50	0.00	50/0	14.73
	diff	4.20	0.94	5.14

Color in O2 col: ppO2 limits | Color in N2/He cols: partial pressure difference
Green: difference below 0.5 Orange: between 0.5 and 1.0 Red: above 1.0

IANTD 5% rule aka IANTD rule of fifth

The 5:1 ratio indicates that a diver should not switch to a gas that has a helium drop of 5% (actual percent by volume) for every 1% (actual percent by volume) increase in nitrogen content.

[Tom Mount, Joseph Dituri: Exploration and Mixed Gas Diving Encyclopedia (The Tao of Survival Underwater)]

In other words: "Limit your rise in N2 to one fifth of the drop in Helium as you ascend."

This calculation might be incorrect and/or contain bugs. Do not rely on this tool for your dive planning. Do your own calculations.

You are welcome to check the source code on GitHub and report bugs if you find some.