Helium SCUBA

Helium a gas for SCUBA diving.

Helium SCUBA Helium SCUBA Diving

With a boiling point of 4.2 Degrees Kelvin (-450 Degrees F) and an atomic number of 2, Helium is the second most common element in the universe but not so common on Earth. The US has most known deposits. It is a noble gas. Helium is inert, colorless, tasteless and non-explosive.

Air is about 21 % oxygen and 78% nitrogen with some additional gasses such as carbon dioxide.

NITROX is a blend of ‘air’ with increased oxygen, replacing some of the nitrogen. NITROX is a super gas for diving in water, generally shallower than the recreational depth of 130 feet of sea water (FSW). The decreased nitrogen allows SCUBA diving with more bottom time, shorter ‘off gassing’ on the surface before a repeat dive and shorter times to fly after the diving day is over. One problem with the increased oxygen is a number of diving medical issues primarily oxygen toxicity. Increased partial pressures of oxygen can produce a seizure especially when the PPO2 (Partial pressure of oxygen) is in the range of 1.6 to 2.3 atmospheres at periods of greater than 15 minutes.

Helium is a reasonable substitute for some of the nitrogen in air. Helium is a very light gas, actually second only to hydrogen. Helium is chemically inert and non explosive.

Bad issues are that helium is a relatively expensive gas, about $135 US for 242 Cu. Ft. (two of these should provide about 13 tanks of 33% with over 100 cu. ft. left over to begin filling about 9 additional SCUBA Tanks with Helium), and has high heat conductivity. It drains heat rapidly from a divers body. HPNS (High Pressure Nervous Syndrome) can also be a problem associated with diving, generally over 600 FSW.

Several of the major SCUBA Diving training organizations such as PADI, NAUI, PDIC and SSI offer training in this gas for diving.

If Helium is chosen to dilute the oxygen and nitrogen in air then there is the practical issue of getting Helium into a scuba diving tank. The rest of this article is dedicated to this issue.

Helium is generally available in storage tanks with a capacity of 242 and 160 cubic feet when pressurized to 2000 and 1800 pounds per square inch. The pressure in this tank must be greater than the pressure in the receiving tank when the desired amount of helium has been transferred. This dictates that the SCUBA diving tank must be empty (or virtually empty) to allow the transfer. Common Tri-mix (Helium, Oxygen and Nitrogen) call for 25 to 33 percent of Helium. Using the higher percentage (33%) you can see that 33% of a standard 80 cubic foot tank is 26.4 cubic feet. This 26.4 cubic feet must be removed from the storage tank.. When 26.4 cubic feet is removed from a 160 cubic foot storage tank then the pressure should have dropped from 1800 PSIA to about 1500 PSI. This number (1500 psi) is greater than the 1000 PSI required to fill an empty SCUBA diving tank to 33%. Therefore the Storage tank can deliver the 33% required for one 80 Cubic tank. An additional SCUBA tank can be filled to 33% Helium with the storage tank dropping to 1200 PSI but a third scuba tank can not be filled to 33% as the storage tank would drop to 900 PSI and 1000 PSI is required to get the SCUBA tank to 33%. A second storage tank is required to ‘top off’ the third tank to 33%. The original storage tank can continue to be drained to assist the second storage tank but a lower and lower ‘Fill’ % will come from the original storage tank. A total of 7 SCUBA diving tanks can be filled to 33% from 2 storage tanks as defined above. The remaining gas in the second storage tank can be used to partially fill additional tanks and they can be ‘topped off’ with a third storage tank and so on. A maximum of 8 standard tanks can be filled from 2 storage tanks of this capacity. The partially filled SCUBA tanks can then be topped of with a regular air compressor to the 3000 PSI mark. You should carefully analyze your finished tank for Oxygen and Helium and know what the partial pressures mean and at what depths you can safely use them.

If a SCUBA diving fill of 30% is desired then 3 tanks can be completely filled from a standard storage tank and the filling can continue as described above. The spreadsheet on the next page can provide the ‘fill’ information. The original storage can be practically drained to about 20 cubic feet.

Hypoxia Hypoxia is a condition of not enough oxygen in air to maintain life. The standard number of .16 ATM (Atmospheres) or PPO2 (Partial pressure of Oxygen) is generally considered to be the lowest safe number, although there is ample evidence that numbers above .10 -.12 are adequate for short periods of time.

Oxygen Toxicity Oxygen Toxicity is the condition of too much oxygen. At some point a variety of body reactions including seizures and convulsions may occur. The standard number 1.4-1.6 ATM is generally considered to be the maximum Oxygen exposure, although Doctors use highly elevated PPO2 including pure oxygen at 60 FSW (2.3 ATM PPO2) in hyperbaric Chambers with the patient at rest. The number of 1.6 PPO2 is achieved at 218 FSW using AIR as a breathing gas and 132 FSW when using NITROX-32. Many divers exceed these numbers including this writer.

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Helium SCUBA Tank Filling Data Ex:1 Helium SCUBA Tank Filling Data ex:2

Caribbean Dive shops with Helium coming soon for Tortola, Aruba, Dominica, Curacao, Saint Lucia and Barbados

The Data below shows for any given % of HE (Column one) the % of O2 and N (Columns 2 and 3) if standard air is used to 'top off' the tank after HE is introduced into a tank. Percent of Argon is showed only to allow the total to approach 100%. Then the maximun Depth in FSW (Feet of Sea water) is shown for 1.4, 1.6 and 1.8 ATM of O2. Green background is added to aid in following data across the table only. I used N=78.084%, O2=20.947% and AR=.934% as the composition of Air used to top off the SCUBA Diving Tanks.

%HE	*	% O2	*	% N	*	% AR	*	1.4 PPO2	*	1.6 PPO2	*	1.8 PPO2
40	*	12.6	*	46.9	*	0.6	*	334.6	*	387.1	*	439.6
39	*	12.8	*	47.6	*	0.6	*	328.6	*	380.2	*	431.9
38	*	13.0	*	48.4	*	0.6	*	322.7	*	373.6	*	424.4
37	*	13.2	*	49.2	*	0.6	*	317.1	*	367.1	*	417.1
36	*	13.4	*	50.0	*	0.6	*	311.6	*	360.9	*	410.1
35	*	13.6	*	50.8	*	0.6	*	306.3	*	354.8	*	403.3
34	*	13.8	*	51.5	*	0.6	*	301.2	*	348.9	*	396.7
33	*	14.0	*	52.3	*	0.6	*	296.2	*	343.2	*	390.2
32	*	14.2	*	53.1	*	0.6	*	291.3	*	337.7	*	384.0
31	*	14.5	*	53.9	*	0.6	*	286.6	*	332.3	*	378.0
30	*	14.7	*	54.7	*	0.7	*	282.1	*	327.1	*	372.1
29	*	14.9	*	55.4	*	0.7	*	277.6	*	322.0	*	366.4
28	*	15.1	*	56.2	*	0.7	*	273.3	*	317.1	*	360.9
27	*	15.3	*	57.0	*	0.7	*	269.1	*	312.3	*	355.5
26	*	15.5	*	57.8	*	0.7	*	265.0	*	307.6	*	350.2
25	*	15.7	*	58.6	*	0.7	*	261.1	*	303.1	*	345.1
24	*	15.9	*	59.3	*	0.7	*	257.2	*	298.7	*	340.1
23	*	16.1	*	60.1	*	0.7	*	253.4	*	294.4	*	335.3
22	*	16.3	*	60.9	*	0.7	*	249.8	*	290.2	*	330.6
21	*	16.5	*	61.7	*	0.7	*	246.2	*	286.1	*	326.0
20	*	16.8	*	62.5	*	0.7	*	242.7	*	282.1	*	321.5
19	*	17.0	*	63.2	*	0.8	*	239.3	*	278.2	*	317.1
18	*	17.2	*	64.0	*	0.8	*	236.0	*	274.4	*	312.8
17	*	17.4	*	64.8	*	0.8	*	232.7	*	270.7	*	308.7
16	*	17.6	*	65.6	*	0.8	*	229.6	*	267.1	*	304.6
15	*	17.8	*	66.4	*	0.8	*	226.5	*	263.5	*	300.6

Many SCUBA Clubs such as Pacific Coast Divers and Illinois Divers recommend Helium as a great substitute for some of the nitrogen and Oxygen in Air.