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Airships went out of fashion for a variety of reasons including:

  • Materials science level made constructing gas bags difficult. Cow-intestine were used to make the bags
  • Filling the airships with gas was expensive and eventually airplane fuel became cheaper
  • Lack of accurate weather forecasting and primitive IFR capabilities led to crashes
  • Materials science level made constructing a light-but-rigid airframe difficult and expensive
  • High profile accidents tainted public perception (R101, Hindenburg) and military perception (Arkon)

Today though, it seems that many of these challenges can be overcome with modern technology:

  • We can construct gas-bags using light materials (near future materials can construct even better bags)
  • We have accurate global weather forecasting and a mature air traffic control system
  • We can manufacture ultra strong lightweight composites like carbon fiber to build structures
  • Even disregarding electrical propulsion and solar panels, our propulsion technology is far more efficient today

Unfortunately, Helium has only gotten more and more expensive (we're due to "run out" eventually) and the only other viable lifting gas is hydrogen, which has a very bad rep. Still though, for decades, hydrogen airships were operated just fine and saw successful, extensive use in warfare and more limited deployment in the civilian sector. Furthermore, the people who built and operated these airships weren't idiots, and apparently deemed the risk of using hydrogen as "worth it" which leads me to believe that hydrogen airships aren't quite as idiotic as the high-profile accidents would lead us to believe. So, my question:

With modern (and near future) technology, could we build a safe hydrogen airship?

By "safe" I mean an airship that's roughly as safe as a modern commercial aircraft.

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  • $\begingroup$ Here is a historical video of USS Los Angeles landing at a naval station. Notice the manpower. $\endgroup$
    – AlexP
    Mar 1 at 13:24
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    $\begingroup$ @AlexP I get the problems, but a lot seem to be able to be solved/improved by modern technology. Computers, automation and new bays could make most of the landing crew obsolete. We don't need to have that many to soften the landing anymore. Regardless I'm curious to a 'safe' hydrogen ship. $\endgroup$
    – Trioxidane
    Mar 1 at 13:31
  • $\begingroup$ Please don't answer in comments $\endgroup$
    – L.Dutch
    Mar 1 at 13:32
  • $\begingroup$ Not building the ship out of thermite will help. (Yes, yes, the Hindenburg wasn't technically thermite, but close enough that it didn't help matters.) Incidentally, recommended reading: Hard Magic (alternate history with a bit of SF/F in which the zeppelin still reigns supreme... although the "fire mages" have a lot to do with that). $\endgroup$
    – Matthew
    Mar 1 at 13:38
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    $\begingroup$ @DWKraus, 1) hydrogen don't burn easily. It prefers to explode. 2) hydrogen emits UV light when reacting with oxygen, nothing much to see $\endgroup$
    – L.Dutch
    Mar 1 at 16:29
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Yes, but it would take time and money. If you do that they could easily be the safest form of air transport in the world.

When talking about Airships people assume they are soft, flammable/explosive, slow, can't handle any wind and crash if you look at them funny. You can see this in any question about airships on this site for example. It goes so far that people will actively seek disadvantages to make their arguments work, like saying they were loud (they weren't).

Jet engine aircraft have actually been in the same spot at one point. The first high-altitude jet engine aircraft were involved in several high profile crashes with the loss of everyone on board. This caused public opinion to think that aircraft broke apart for no reason, would explode and were generally unsafe. Without computer simulations to properly test what could have happened the only method of testing was using a physical plane and simulating the conditions of a flight several hundred to a thousand times to see what happened. At the time a ludicrously expensive and time intensive method. Yet the aircraft company did the test anyway, they found out that the shape of their windows caused stress fractures which caused all the crashes. The entire air industry learned from it and now we fly with rounded window edges and the public opinion isn't that aircraft crash randomly or explode anymore. If that test never happened it would have taken decades longer before anyone would have build a working jet airliner.

Airships were in the same position, only they never got tested (because they didn't know how). However with modern materials, simulations and capabilities we can make safe airships, just like we've made our aircraft orders of magnitudes more safe than our early aircraft designs. Airliners can take off and land with a burning engine that falls off halfway through flight nowadays!

The gas:

Hydrogen is one of the most flammable substances on earth, but only when it has enough oxygen. The interest in hydrogen cars and hydrogen fuel cells let to research into how safe it was to have them onboard cars and large fuel tanks compared to regular gasoline. They found out that due to how hydrogen burns it's actually safer compared to most types of fuel we use today. With the addition of more partitions between gas cells, more individual gas cells and other safety measures you can make it very safe. Let's compare it to the Hindenburg for example.

The Hindenburg was a lighter-than-air craft, so to land it needed to vent it's hydrogen (or pump it into the same gas cell and fill the empty gass cell with air, the Hindenburg seems to have mostly vented it though). This hydrogen could have stuck around the craft when sparks for a flame occurred. Modern engines would be less likely to cause a spark and with the introduction of hybrid airships that problem goes away entirely. Hybrid airships get most of their lift from gas, but the remaining lift is generated by regular old wings and vectored thrust. This instantly also removes the need for mooring masts and allows these hybrid airships to land in rural area's where regular transportation cannot reach.

Another problem with the Hindenburg was that it's skin was made from flammable materials. As the flames kept burning across the airship's skin the hydrogencould mix with more oxygen and ignite, keeping the process going until it was so big it engulfed the Hindenburg.

As for that mix with oxygen, hydrogen is stored at atmospheric pressure. If you puncture the gasbag there won't be hydrogen spilling out as there's no pressure behind the gas to push it into the atmosphere around the ship. In WWI biplanes with incendiary ammo needed to first fire a couple of hundred shots into the airship, then wait a few minutes for diffusion to cause enough hydrogen to mix with the air before returning and actually setting that hydrogen outside of the airship on fire. If the airship's skin then also catches fire more hydrogen is quickly released to mix with the air and keeps the process burning. During WWII there was even a ship that got caught by Axis flak weapons twice, lost about 50% of it's lifting gas and made it home without going up in flames or crashing. Compare that to say an modern (or old) aircraft that would lose 50% of it's lifting surfaces in combat, very few aircraft are able to take that punishment and make it home.

It's speed:

Airships are seen as slow, lumbering beasts. Yet even the WWII airships could reach 130km/h. You could say "but compared to other aircraft that is slow", but that's an unfair comparison. It's like saying "ah but my racecar is faster than your truck". Yes it is! But your racecar cannot haul half as much cargo as my truck and my truck can do so for a lot less fuel per cargoweight carried.

It's safety measures:

A crash like the Hindenburg could have happened by venting hydrogen, which hybrid airships wouldn't have to deal with, or leaking. Leaking can be reduced by having more gasbags and redundant safety measures. Non-flammable envelopes and gas bags can increase safety measures, as can the application of self-sealing materials, buffers and compartimentalized gasbags. If one gasbag gets punctured or even burns up completely, the other gasbags can be insulated enough not to catch fire. Similarly you can reduce fire hazards by adding a helium mix to the hydrogen (if necessary by putting the hydrogen gasbag into a gasbag with helium). This means that the hydrogen will have a harder time mixing with enough oxygen to become flammable and stay flammable while not going for the full cost of a helium airship.

Another good safety measures is modern sensors. The Hindenburg couldn't measure it's leakage very easily and many airships crashed in storms or due to human error because sensors and modern weather control wasn't available. Just like ye oldy aircraft frequently crashed due to storms and human error because we didn't have the sensors and weather control data to keep them flying but those same measures have made them incredibly tough to crash (unless once again human error causes a lack of maintenance or design flaw).

Tl,DR:

Modern materials, sensors, knowledge, design, use of hybrid airships, safety measures and all the good stuff we've been using for modern aircraft would make a modern airship extremely safe. Their ability to get quite literally shot at and still make a safe landing several hours later makes them the safest, most resilliant aircraft available to mankind. The biggest hurdle is public opinion and the time+money to design good airships. Aircraft have been build for decades now, and when you look at the Airbus we see that even today a large aircraft design can be hard to pull off. Modern airships in the last decade or so have been build, but due to public opinion it is hard to find people willing to invest and use airships which is the main reason for airships to fail, not their actual safety. Airships are safe, it just takes time and money.

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Short answer: no, you can't make a safe hydrogen airship.

There are basic physical and chemical reasons for this.

First, hydrogen is the most flammable element, ignitable in mixtures with air from about 4% to 94% hydrogen. That means the smallest leak, in either direction, produces a hazard of (explosive) ignition, and a hydrogen fire is effectively impossible to extinguish (flooding with inert gas is the only practical method, and that carries an immense weight penalty due to the amount needed to flood an entire airship envelope).

Second, airships, by their nature, must be fragile. This is a machine that has to float like a soap bubble; the entire rigid structure and payload must have an overall density the same as that of air (at operating altitude, which is typically less than ground density). Any attempt to strengthen the airframe must generally be applied to making the same soap-bubble construction lighter, so the total hydrogen required to float is reduced -- because making the whole ship smaller is better than making it more rigid or stronger, both in terms of cost and safety.

Third, as noted in comments, airships must be moored by their nose, which means each ship needs a circular space with a radius slightly larger than the length of the envelope. Where airliners can be parked with their wings interlaced, so passenger capacity of thousands will fit on a football field (either kind), a single airship that can carry a couple hundred won't quite fit in the same space. Plus, the airship (when moored outside) must be allowed to swivel around the mooring tower, like a ship turning at anchor with the tide or current -- because the wind shifts. There was an incident in which a complete wind reversal (180 degree shift without blowing in the intervening directions) flipped an airship vertically over the mooring mast -- and since the ship was intentionally heavy while moored, the weight of the ship collapsed the nose cone of the envelope frame.

Related to this, they can't be loaded and unloaded with passengers sheltered, the way modern jets are -- rather, the passengers would, at best, be carried to the ship by what amounts to a tall bus, and the ship would be subject to movement while attempting to load passengers and cargo (since it can't be rigidly tied down, due to its fragility).

There have been airship hangars built, which do a very good job of protecting the airship -- but they still take up a huge amount of (expensive) real estate compared to aircraft hangars (they're big enough to have their own weather inside), and it's a long, slow production to move the dirigible into and out of the hangar, with the slightest turbulence or crosswind being a recipe for disaster.

Another concern is "hydrogen embrittlement". Most if not all metals in contact with hydrogen will absorb the gas into the metal's crystal matrix. The hydrogen then causes defects to form in the lattice, resulting in the metal becoming brittle. If the hydrogen never gets into contact with the metal structure, well and good -- but hydrogen also diffuses through almost anything else (not quite as badly as helium, the molecule is bigger, but it still does it). This also means you can't prevent hydrogen leakage.

Finally, airships are slow. The Hindenburg -- arguably the most advanced airship ever in commercial service -- had a top speed of around 100 mph and cruised at about 80 mph (160 and 130 km/h respectively). It took days to cross the Atlantic from Germany to New York City. This was comparable to airplanes of the day, except that the Hindenburg could make the trip non-stop, where airplanes of the early to mid-1930s could not. However, since then, airplanes have increased speed by a factor of four or so (for commercial transports), and airships likely can't be made to do so, simply because of the amount of power required to punch that immense gas bag through the atmosphere. The highest cruise I've seen for a proposed modern airship was around 200 mph (320 km/h)

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    $\begingroup$ Thanks for the insights. Is there a reason we need to use a mooring mast? Can't we just tie down the airship in a single spot? Sure, the loads would be high because of the potential wind load but I don't think this is a deal-breaker. Also, I'm not looking for reasons to make them viable alternatives to commercial air travel and overcome the other disadvantages all airships have, this question is strictly about the safety (and engineering) of a hydrogen vs a helium airship, not a question on airship vs an airplane or helicopter viability in general. $\endgroup$
    – Dragongeek
    Mar 1 at 14:17
  • $\begingroup$ There are two elements in this answer: safety and commercial viability. Regarding safety wouldn't it be possible to have self sealing gas cells? similar to what was done on WW2 military planes for the fuel tanks. There would be a payload loss for sure but I have no idea of how much. When it comes to safety in regards to harsh weather it may be less of a problem if you start seeing the airship as a specialized vehicle in its own niche rather than in competition with commercial planes $\endgroup$ Mar 1 at 14:19
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    $\begingroup$ If you start considering the airship just for carrying bulky loads that would be unfeasable by plane then it starts to make sense. And it is exactly in this role that has recently been proposed by a German company. Said company did indeed go bust due to a number of reasons. But I don't see the idea completely unfeasible in its own niche. As sky transports of course transport would be done only if the weather is acceptable during the whole flight $\endgroup$ Mar 1 at 14:21
  • $\begingroup$ @Dragongeek: "Is there a reason we need to use a mooring mast?" Airships are ships, they always stay afloat. The mooring mast is the equivalent of a wharf / quay for a water ship. Airships don't land in the sense of an airplane, because they are not designed to support their own weight + weight of cargo. If for any reason you need to deflate the gas cells (so that the airship loses buoyancy) then you need to take it into a hangar and suspend it there; that would be the equivalent of a water ship going into dry dock. $\endgroup$
    – AlexP
    Mar 1 at 14:35
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    $\begingroup$ I don’t think you’re quite correct about the likelihood of fire. No matter how flammable the element, fire can’t happen without oxygen. If there is no oxygen in the balloon, then it will take quite some time for a balloon fire to become big enough to cause an immediate problem, giving the crew plenty of time to resolve the issue; especially if the balloon is divided into cells. It certainly helps if the airships are unmanned, although that might make fires too difficult to extinguish.IIRC, the Hindenburg had an issue of flammable paint on the balloon. $\endgroup$
    – Globin347
    Mar 1 at 16:57
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Yes, to some extent at least.

All the progress we have atm is helpful, all the new materials, and approaches - we definitely can do better than it was done 90+ years ago.

And LZ 127 had 590 flights, 17,177 hours, and 1.7 million km under its belt. And it had hydrogen as its lifting gas, so as hydrogen as part of its fuel, that Blau gas. And that isn't bad, even by modern standards.

with modern material and technologies, we sure can improve it, and expect more safety and miles on it.

However it does not mean we can do that immediately, this is interrupted technology, even if there are some modern versions of airships. But if we would like to have it to be used more, we will need to go through interations of development, testing, operation, improvements and maturing.

Hydrogen is not the only lifting gas, another one is methane - yes, it has half of the lifting power, but if we consider Blau gas as well the LZ average lifting 100k m3 hydrogen and 30k m3 of Blau gas average lifting density of available gas volumes was 0.370kg per cubic meter, and methane is 0.657kg - so the difference in lifting capacities is 70% of its hydrogen analog.

They used Blau gas for keeping the same buoyancy during the flight, but we, as carbon neutral party, can easily compress some percentage of co2 from engine exhaust for the same purpose, it does not require that much effort.

what difference it makes

permeability of hydrogen is notorious, and it is one of the challenges, to make things safer, and methane is better for our purposes by that aspect. So as it is available in great quantities off the shelf.

Methane also is a product and good portion of natural gas which is carried over long distances by LNG carriers and CNG carrier. They carry that gas in liquified form or in compressed one(at 250 bar), so as that gas is transported by pipes in huge volumes, where the pipes are available. Meaning there is a demand to haul it in big volumes.

All three approaches have their cons and pros, liquifying isn't free, pressure 250 bar is quite demanding for big volumes, pipes have to be built and they have no flexibility in where they deliver stuff, etc.

Airships could be another means to deliver natural gas - which could propel the development and mature of that technology.

Advantages are no need to liquefy the gas which dumps big installations dedicated for that, and basically, refueling may happen out of the well. Neutral buoyancy is achievable with pressures less than 2 bars which put less demands on the materials, less than 250, so as it within the capacities of materials we may use to build that airship.

So one LNG tanker is from 18'000 up to 266'000 m3 of liquified gas, 422 tonne per 1000m3 of liquid gas.

For a potential airship if half of the lifting capacity is the mass of construction of that ship then per each 400t of lifting gas it can carry 200t of cargo(oil as an example). or 1.25 bar with no cargo.

what other advantages it may have

Airships are not bound by land or sea - so one can have shortened, more direct routes aren't limited by restrictions of canals, delivery can happen when it needs to be, no need for pipes to shore/port.

with that "400t of lifting gas, it can carry 200t of cargo" there clearly is a problem, u can't unload more than 50% of that gas(can't is a bit too strong, but other approaches require more doings, not necessarily worth it), but there is also a thing other means will have a hard time to have - energy-free delivery using Jet stream's which are high altitude wind/air flows. (solar powered is also an option)

Those are proposed as a potential energy source because "Winds at higher altitudes become steadier, more persistent, and of higher velocity."[6], so as they were one of the factors behind Loon (internet access, worldwide through high altitude balloons, atmospheric Starlink equivalent)

All those winds also need some technologies and have their challenges and bring some difficulties, but wind power tries to comeback even on an oil tanker's so ...

what we are better at, than in old days

Variety of materials which are available to us today, and means to shape them and strengthen them with different kinds of fibers(basalt fibre is suffice no need for carbon) - that one is clear and obvious, so as helpful to make airship to come back.

Less obvious, for this application, ofter overlooked one - we are way much better at detecting things, in this case, gases leakages, etc.

if we combine that - in old days they had no other ways than have a single layer gas cell, but we can have a multilayer structure, a typical double-hull strategy used in the oil tanker industry.

There are 2 aspects to the design - detect leakages, and recuperate the loss of gases due to permeability or internal shell damage, and preventing mixing of it with air.

we can easily detect different gases at ppm concentrations (parts per million) or better which way less than any combustible mixture ratios(parts per hundreds). Thus we can be aware of what and why happens inside out lifting volumes, and offset some naturally happening processes(gas permeating) and small leakages due to wear and tear. And thus we can say when and what needs a service and most likely where it needs it and how much.

  • by double layers I do not mean something drastic, it can be the same gas cell, just two layers of the same(or not) material with some spacer in between in which we can have neutral gas flowing, carbon dioxide as an example(Dichlorofluoromethane, Propane, etc), a flow of which carries away any leakage and is collected in some membrane separator, to recuperate lifting gas, and place it back.

Those two factors are the main factors for my yes answer. uncertainties are mostly because advancement in other areas does not make us automatically good at designing and building airships. plenty of research and development needs to be made, and it needs to build some expertise at using them and ironing kinks we may oversee at the beginning.

practice makes perfect, and there are commercial use cases for the technology, beyond current use, to help development and usage. And in general, airships do make sense, not worse than current cruise sea ships. And that can allow visiting paces which not possible to reach by sea alone.

They do make sense as cargo delivery means, for medium and long distances. if no free energy of wind then they can't beat sea transporting, but at slow speeds(20-40kmh), they are not much worse than railroads efficiencies, which potentially places them at 3rd place in terms of energy-efficient means for cargo transporting.

So maybe one thing we are waiting for is another Elon Tusk, who has the money and a will/a taste for them

At least as it looks on a napkin, if we dive into details it may or may not look better or worse, but some development with modern approaches do happen so it not a totally dry field.

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Current tech no. Near future.... maybe safe?

Safe? Maybe. Practical? Doubt it.

To make a hydrogen airship safe, you need to design it such that a leak and flame does not lead to the destruction of the air frame.

If a modern Hindenburg was to catch fire while airborne, it should be able to recover after jettisoning some ballast. If it catches fire multiple times such that its losing lift and cant recover, it must be able to navigate towards an open area, set down in the field, evacuate all passengers and crew within 90 seconds of coming to a stop (airline standard).... without burning anyone or dropping them to their deaths!

Hydrogen in air burns at 2045 degrees C. So you need to find a substance that's:

  • is extremely light.
  • is extremely strong
  • is airtight
  • doesnt combust or melt at 2000 degrees C

And build your airship out of that.

Few layers of Graphene sheets for the gas cells, and carbon nanotubes for the structure. (Or carbon nanotubes for the whole structure if graphene seeps hydrogen). With melting temperatures of 3500-4000 degrees, these wonder materials will stand the heat. Graphene will loose strength after at a while at 900, but with a bit of experimentation a design could be found such that one gas bag leaking to air and igniting just burns out - it doesn't rupture its neighbours and cause a chain reaction.

Graphene is also light enough that you could double hull your hydrogen gas bags adding further safety, such that a puncture only leaks the tiny margin of hydrogen on the edge, rather then the entire bag.

No it wont make airships practical again - especially with aircraft manufactures actually looking at hydrogen powered aircraft. But they could be made safe from a fiery death.

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    $\begingroup$ Hydrogen will go right through graphene. The holes in the mesh are larger than a hydrogen molecule. In fact, hydrogen diffuses through most materials at some rate, even metals. $\endgroup$
    – Zeiss Ikon
    Mar 1 at 18:08
  • $\begingroup$ @ZeissIkon It's true that hydrogen penetrates graphene, but not because the mesh isn't small enough to block molecules the size of H2. How the penetration occurs isn't fully understood, but it seems to involve reducing the molecules to atomic hydrogen which can then chemisorb through the mesh. See here: physicstoday.scitation.org/do/10.1063/PT.6.1.20200330a/full $\endgroup$
    – camerondm9
    Mar 1 at 22:14
  • $\begingroup$ You've got the right idea, but your implementation needs work. You're better off using non-flammable materials and setting up airflow so that the airship's structure doesn't get hot during a fire. $\endgroup$
    – Mark
    Mar 1 at 22:28
  • $\begingroup$ this one is just a nonstarter, wrong way ash, sorry $\endgroup$
    – MolbOrg
    Mar 1 at 23:49
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Hydrogen-filled aerogel

An aerogel is a synthetic solid material with very low density - most of it is gas. Graphene aerogel, sans air, is seven times lighter than air. If it is filled with hydrogen rather than atmospheric air (mostly nitrogen), such an aerogel will be far lighter than air. Since hydrogen can't burn unless exposed to oxygen, you just have to seal the blocks of aerogel with a thin, airtight layer. If exposed to a lot of fire, I imagine that the material will be quite flammable, but it would not be explosive. It would probably be safer than tanks of jet fuel, which can be quite explosive. Compartmentalization between fireproof walls combined with gaseous fire suppression systems would likely making it very safe.

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