# If unable to procure Helium, are there any regulations against filling lighter than air craft with Hydrogen instead?

The price of helium is going up again, and it is very difficult to find suppliers without established contracts. If all possible safety measures are taken, are there still regulations by FAA or other that would prohibit use of hydrogen instead for buoyancy in lighter than air non-thermal aircraft?

The causes of the Hindenberg fire are well documented and studied so lessons learned such as sudden grounding when aircraft surface has accumulated significant electrostatic charge can be avoided through measurement and continuous static dissipation techniques used on current aircraft.

• Trying for the Darwin Award? – Jim Garrison Jul 11 '17 at 3:06
• The Hindenburg did fly successfully for 14 months before the fire destroyed it, so chances are you do have some up-time. Possible items of interest: an article in The Economist and an answer on the SE Aviation site – Koyovis Jul 11 '17 at 4:01
• If you decide to do this please do so far away from me. Or anyone else. – GdD Jul 11 '17 at 8:15
• In these times of widespread fears and precautions, using hydrogen as a lifting gas is completely out of the question. The real risk involved, however, can be estimated by remembering the long history of hydrogen-filled balloons and airships. Of course there have been cases of fires and explosions due to that gas, but most accidents were not hydrogen-related, but to bad weather, structural failure, human error, or engine trouble. – xxavier Jul 11 '17 at 11:13
• The balloons in the Coupe Aéronautique Gordon Bennett use hydrogen. It's not out of the question. fai.org/fai-slider-news/… – MJeffryes Jul 11 '17 at 16:52

The Hindenburg utilized aluminum flake in a nitrocellulose impregnated fabric. Materials have improved since then.

In the case of He, diffusion is inhibited by polar surfaces. For the He to diffuse through the membrane in a balloon, it has to disolve into the fabric layers prior to a barrier such as aluminum. I understand that lithium and beryllium foils have higher impermeability.

In the case of He, poly(ethylene terephthalate) is a reasonable barrier, and PET is commonly available in films (and soda bottles). It is rather polar, and serves to reduce solubility.

H is a different bird, in that it has low polarity, and different materials will aid in reduction of solubility. Butadiene-acrylonitride co-polymers have low polarity and may perform better with a low polarity gas such as H2.

The gas envelope questions are really materials science questions, and require a fair understanding of not only the mechanical properties, but even more so of the permeability, solubility and diffusivity of the copolymer you might consider.

The legality of using H2 rather than He2 may not be an issue, but even if it were, I am sure that waivers are possible.

A quick check of regs on gas balloons indicates that hydrogen may be used if the aircraft manufacturer approves the gas. So it appears there is no hard regulatory bar.

Checking with a source at NWS, who indicates their balloons are launched with H2.

• Can you give a citation for the relevant regulations? – Nate Eldredge Jul 11 '17 at 21:38
• See third paragraph for guidance wrt H2, He2 and other gasses. faa.gov/aircraft/air_cert/design_approvals/balloons The meat is in 14 CFR 31 which is airworthiness standards. 14 CFR 31.33 is suitability of materials. The manufacturer of the gas balloon will have limitations as to the gas(ses) that are approved for the envelope material. – mongo Jul 12 '17 at 1:09
• addendum, as well as the lift, etc. Since they have to test various materials, they may be disinclined to do extensive testing with gasses which are intrinsically incompatible with their envelope, or they could have an offering of an optional envelope suitable for other gas(ses). – mongo Jul 12 '17 at 1:19
• The Hindenburg utilized aluminum flake in a nitrocellulose impregnated fabric. Actually, nitrocellulose was rejected in favor of cellulose acetate butyrate due to the former's known flammability. The aluminum was a powder, not flake, and was in low concentrations in the doping emulsion. The Hindenburg's skin was flammable, but not particularly so. Even after the intense fire there were portions of the skin that were unburnt. – TomMcW Jul 15 '17 at 2:01
• @TomMcW I confirmed my sources and then did a few more searches on the construction materials and techniques. While there is substantial differences in reporting, I am inclined to agree with what you report. Thanks. – mongo Jul 15 '17 at 8:19

Hydrogen and Helium are quite different substances, you are likely going to need gasbags made of different materials to prevent (or at least limit) leakage through the sublimation of gas through the material.

So even if it is legal, it still isn't practical (and given that it's a massive safety risk my guess is it wouldn't be legal).

• I was thinking that Helium was actually more of a problem, since Hydrogen would typically be in the from of the molecule H2 – Eugene Styer Jul 11 '17 at 13:15
• @EugeneStyer an H2 molecule is smaller than an He atom, and can more easily penetrate fabrics and plastics. – jwenting Jul 11 '17 at 13:18
• And... then there's that whole violently explosive thing... – SnakeDoc Jul 11 '17 at 15:05
• @jwenting, what size are you using for a H2 and He2 molecule? The van der Waals radius is 120 and 140 respectively, approximately. That's not a big difference. Permability of a membrane is about the chemistry and materials properties much more than the molecular size. – mongo Jul 11 '17 at 16:45
• @SnakeDoc The Hindenburg exploded because of the gasbag coatings, not the H2. Ref: web.archive.org/web/20131102010145/http://www.h2carblog.com/… – Roy Tinker Jul 11 '17 at 17:29