This question is inspired by Green's Volcanoes in Orbit! The premise is that there is a 50-mile-high shield volcano (again, let's ignore the height implausibility) with a slope of about 2-3 degrees, at its base. In my case, this is a rare pyroclastic shield volcano. I calculated that if the mean slope is maybe 4 degrees, then the volcano should have a diameter of roughly 900 km. That is a lot of usable land - the size of a decent-sized country!

I figured that people might as well as use this land for something - mainly the extreme lower slopes (i.e. up to 5,000 - 10,000 feet). You might see small towns and farming communities. The problem, of course, is that if the volcano erupts, it will likely release pyroclastic flows that will surge down the mountain, destroying or burying most things in their path.

Now, people would have 2-3 hours' notice of an eruption, given the typical speed of these flows, and so they could prepare. They'd need to either evacuate or shelter in place, preferably protecting their town (or both) in some way. My current idea calls for domes about 1 km in diameter, 500 meters tall, that come up from the ground to encircle each small town (and yes, these would be very small settlements - more like villages than towns.

Just to be clear, I have the above setup well-planned out. I'm not asking about any of that.

There is going to be a chance that someone may be outside when the flow hits, either doing maintenance on the dome or trying to escape in vain. There's also the possibility of trying to survive if a dome collapses. I'd like to design them a survival suit that will save them from the extreme heat and forces. The person may end up buried in ash, but they can survive for a short amount of time, and maybe (just maybe) be rescued.

What would be the best material to make this suit out of, using current technology? It would need to be resistant to temperatures of hundreds of degrees Fahrenheit, as well as possibly protecting the wearer from impacts from ejecta. Obviously, it does need to be wearable, flexible, and hopefully not too bulky (although bulkiness is okay, if need me). If there's no possible material, then that's also fine.

By the way, fire suits are not very effective in many cases; I had considered them but have since rejected the idea.

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    $\begingroup$ Some quick google-fu says Pyroclastic flows can be 1,000°C, I'm pretty sure there is nothing wearable that will keep you alive. I don't have the time for a full answer, but I'd imagine equipment that could quickly dig a hole in the ground, put you in it, seal it then keep you alive and announce your location would be more viable. $\endgroup$ – Kyyshak Nov 9 '17 at 16:59
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    $\begingroup$ If it's a shield volcano it isn't going to produce pyroclastic flows, at least not ones large enough or often enough that people would have to be constantly prepared for them. $\endgroup$ – Keith Morrison Nov 9 '17 at 19:10
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    $\begingroup$ Use the same material that you are making your domes out of. Since a pyroclastic flow is hot enough to melt steel, your citizens have obviously already found a material that provides enough protection, and have used it in their domes. $\endgroup$ – Justin Thyme Nov 9 '17 at 20:46
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    $\begingroup$ even if you found a material that can withstand pyroclastic flow, how do you keep the temperature inside the suit within a habitable range, if you can't do that, you'll be baked in an "oven" suit $\endgroup$ – am05mhz Nov 10 '17 at 5:54
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    $\begingroup$ Even if you DO survive a pyroclastic flow, how do you plan to dig yourself out of several meters of now solid rock? $\endgroup$ – BgrWorker Nov 10 '17 at 9:00

14 Answers 14



You don't make a suit to survive a pyroclastic cloud. Much like a hurricane the problem isn't that the wind is blowing; the problem is what the wind is blowing.

Sure you could make a 4 ton mech suit; won't stop it from getting trashed by a 6 ton flaming rock.

A pyroclastic cloud is much like an avalanche, only that it can contain temperatures hot enough to melt steel and gases capable of killing you in seconds.

Your only option is find very strong cover, tuck your head between your legs, and pray.

For your education on pyroclastic flows:

Here is a link to Wikipedia on the eruption of Mount St. Helens

  • You are talking about an explosion equal to the strength of several nuclear explosions
  • Temperatures hot enough to melt steel
  • Rock debris the size of boulders traveling at speeds greater than 200 mph
  • Toxic gases that can liquefy lungs in as little as a few breaths

There is no engineerable solution that a human could wear to survive these conditions outside the realms of futuristic science fiction (which if allowed I prefer personal energy shields).

image of a pyroclastic flow showing the plume

Survivors of pyroclastic clouds usually survive from sheer luck and that they found a strong structure to hide behind/in, like a mine shaft .

Upon Realization of other facts

The target radius of this pyroclastic cloud is 800km at least (as the stated distance subject settlements experiencing a pyroclastic flow could be found in). Not to be confused with rock slides or lahars.

The effective radius of the Mount St. Helens pyroclastic cloud was only 31km which means this cloud needs more than 16X the energy of Mount St. Helens to reach the described area of effect. Also the heat blast from that eruption killed trees far beyond the knock down zone used in the calculation above.

Not even thermonuclear warheads have this kind of yield (individually).

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    $\begingroup$ My response to that is to have a suit whose job it is to bury you and help you breathe. $\endgroup$ – Mad Physicist Nov 9 '17 at 21:56
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    $\begingroup$ According to the question, waiting to be dug out is fine. I am curious how deep the flow actually is once things cool down. It is easier to carry a dune-style thumper than to dig yourself out. $\endgroup$ – Mad Physicist Nov 9 '17 at 22:11
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    $\begingroup$ You will have 2-3 hours to send a distress signal with your exact location. The search radius will be a few tens of meters at most. $\endgroup$ – Mad Physicist Nov 9 '17 at 22:33
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    $\begingroup$ My favorite image of a pyroclastic flow aftermath, which gives you an idea of the energy and damage involved. That was a steel reinforced concrete column, and those are rebar bent in the direction of flow. volcanoes.usgs.gov/vsc/images/image_mngr/1200-1299/… $\endgroup$ – John Nov 10 '17 at 2:13
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    $\begingroup$ According to Indiana Jones 4 a refrigerator protects you from a nearby nuclear explosion, so it might work in this case, too. $\endgroup$ – AndreKR Nov 10 '17 at 8:31

Make a balloon suit instead of a fire suit

Protecting a person from the dangers specified will require all the available payload space they have, ie, knights in shining armor don't carry anything else except for their armor and weapon. A suit that can withstand the temperatures, heat and pressures involved in a fast moving pyroclastic flow will be difficult or impossible to build unless the suit carries a robust power source, possibly in the megawatt range. Assuming this suit isn't really an exoskeleton that can carry itself plus the occupant, some trade-offs will need to be made in the level of protection provided.

Keeping someone cool when in such close proximity to super heated air will require active cooling (which is heavy to carry) along with some extremely good thermal insulation (also heavy). Combine this with impact armor to fend off the very heavy rocks that will be wrapped up in the flow; all told this is going to be very heavy and highly restrict the workers movement. For someone out hiking on the plains around the volcano carrying that much equipment will be unacceptable; especially if eruptions are fairly uncommon. For a worker, operating at heights who also may need to be moving heavy things as a part of repairs, being weighed down with a powersupply, rigid armor and HVAC unit strapped to their back will be the utmost in inconvenience. This sounds very much like an armored version of the Manned Maneuvering Unit (MMU). The MMU weighed over 300lbs fully loaded, I don't see how adding impact armor to that will make it any lighter.

So, let's not try to solve unsolvable problems. The best approach will be to get that person up and out of the pyroclastic flow's path as quickly as possible. The OP states that there should be many minutes or hours of warning from when a flow commences.


  • Must be man portable, the lighter the better. The smaller the entire package the better.
  • Must permit the user to move and work while wearing the suit.
  • If not worn, the suit must be very easy to put on quickly.
  • Must be easy to disassemble and test.
  • Must aide in discovery and rescue efforts
  • Must prevent the wearer from going too high; avoid hypoxia conditions.

Any escape method involving an engine will fail because it's too heavy. Non-rigid wings like a paraglider won't work because you can't be assured that you'll have a nice slope to run down for take-off. Hang-gliders suffer from the same problem as paragliders in addition to bulkiness.

The "suit" is actually just a lightweight harness or seat attached to a very large mylar ballon. In addition, there's a bottle of highly compressed helium to inflate the ballon. (I'm handwaving that a bottle strong enough to hold sufficient compressed helium isn't also very heavy. Perhaps it will at least be compact.) The suit should also have a gas scrubber in it since you may very likely drift into the volcano's fumes.

The point of this suit is not to survive direct contact with a pyroclastic flow but to avoid the flow altogether. Surviving contact and maintaining something that is man portable with current or near-future tech this is impossible. Full stop.

Intent and Limitations

The design of this suit assumes that there is ample warning of the arrival of the flow for the balloon suit to be setup and put aloft. Without warning, this suit won't save you. Since you're already aloft and the shock wave of the initial explosion is many tens of kilometers away, if you can get significantly above the flow, you should be okay. Highly turbulent air around the flow might suck you down but then you just got unlucky. Sorry. This suit is also not designed for escape from locations close to the initial explosion as those can send smoke, ash and rock many tens of thousands of feet in the air, well above a humans ability to breath.

Balloon Suit Procedures

  1. Identify that the flow is coming and escape is impossible any other way.
  2. Unpack harness and seat. Put this on.
  3. Ensure the Mylar ballon attachment points are corrected linked to your harness. You don't want to get 100 feet up then realize that only one link is done.
  4. Inflate the balloon. The balloon should have sufficient capacity to lift a 250lb man.
  5. Ensure that the balloon has inflated then drift up into the sky. You made it!
  6. The balloon should automagically manage height for you to prevent hypoxia.


  • The balloon may have a tear in it or get a tear in it. This is a fatal failure. Helium balloons don't produce lift with a big hole in them.
  • You may drift into the volcano itself. In this case, you still die but at least you died with a good view.
  • Safeties to keep you below 10,000 feet fail and you die of hypoxia/exposure. Again, at least you got a good view.
  • Land in the water and drown. Today just isn't your lucky day. At least you didn't burn to death.

Recovery Efforts

Mylar film and most anything made out of aluminum will be highly reflective to radar. After an eruption, the local air traffic controllers can look for slowly drifting dots on their radar to identify people who have escaped the eruption and may need rescuing.

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  • $\begingroup$ Perhaps the balloon could be combined with a paraglider as well; once you're in the air, you deploy the paraglider and cut the cord to the balloon. Now you have control, and you don't need to worry about climbing up too high. $\endgroup$ – Skyler Nov 9 '17 at 19:42
  • $\begingroup$ Having owned a paraglider, they are not light or compact. Well, they're lighter than a hangglider but I wouldn't want to carry a balloon+charging bottle and a paraglider. I like the idea but I don't think it's feasible. $\endgroup$ – Green Nov 9 '17 at 19:45
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    $\begingroup$ This does nothing to prevent the burning shards of rock (which are part of a pyroclastic flow) or the hot gases flying through the air at lethal speeds) $\endgroup$ – anon Nov 9 '17 at 20:06
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    $\begingroup$ The reach of the pyroclastic flow of mount St. Helens was 24Km high, and happened in minutes. With that kind of warning you might as well have driven out of town. or pre make subterrainian shelters $\endgroup$ – anon Nov 9 '17 at 20:24
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    $\begingroup$ You'd be better served by strapping a rocket to your back and wearing a wing suit. Balloons are slow, difficult to steer, and as some others have noted, filling and carrying a large enough balloon is not very feasible. $\endgroup$ – fyrepenguin Nov 10 '17 at 5:27

No, nothing you could carry will allow you to survive a pyroclastic flow, and nothing that cannot survive a large bomb explosion will survive one either.

THis is what the forces involved can do, this was a steel reinforced concrete column, that has had several inches of its surface scoured away by a single event, the forces involved also ripped the top off bending the steel rebar in the direction of the flow. And that is before you get to the heat and toxic gasses.

enter image description here

If you try to resist the flow you die, period. Getting pushed along with the flow is slightly more survivable, in the sense that getting hit by a freight train then dumped in a fireball is more survivable than getting thrown in an industrial meat grinder.

Worse as as shield volcano the rare pyroclastic flow will be mostly explosive flows, which do things like this. That was a tree. You are basically asking for a portable ground zero nuclear blast shelter.

enter image description here

You do not describe pyroclastic flows, you do not have hours of warning you have seconds. You may be thinking of ash falls or possibly gas surge, those are potentially survivable and ash falls give some warning.

You describe a impossibly large volcano but that does not change the physics. That only leaves you with two options either the volcano is shallow enough to that the flows never come anywhere near the villages, dissipating its energy long before then, or it is steep enough to keep up the energy needed to keep the flow moving in which case the villages have a few seconds of warning becasue the flow is moving near the speed of sound.

Remember a pyroclastic flow is moving many tons of material with friction being the dominate force, the further it need to to travel the more energy and thus velocity it needs*. This is the simplest accurate (enough) model of a pyroclastic flow distance, speed, slope relationship, modeling it as a pseudo-fluid. This one is more accurate but the math is much more difficult. As you can see the friction generated is immense, the only way to overcome this is with very high energy, which means either a very steep slope or a very short distance. *To be fair there are slow moving flows but they don't occur on shield volcanoes and need some rather unusual conditions.

Since they are mass/friction driven and to keep it running for 1000km plus (radius at listed angle) requires a tremendous amount of force, to the point it is less a pyroclastic flow and more a shock wave for the majority of its travel distance. It is also impossible to achieve for a low slope volcano, so if you want a pyroclastic flow to reach your villagers they need to either live really close to the top (in which case distance is not a factor), or your volcano needs to be a lot steeper in which case the speed is so high the distance is a minor factor. Slarty is right as described the flow is not reaching the people at all or it is doing so in seconds.

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  • $\begingroup$ As I stated in the question, the people in danger will be hundreds of kilometers away from the start of the eruption. Any flows that manage to make it to the bottom will indeed take hours, not seconds, to get there. This is not a normal volcano. $\endgroup$ – HDE 226868 Nov 10 '17 at 2:56
  • $\begingroup$ Check the edit. $\endgroup$ – John Nov 10 '17 at 3:02

Pyroclastic flows might not be able to reach the lower levels of such a volcano. In part because at such extreme altitude there would be very little air present which would hinder the formation of pyroclastic flows. Also the distance of travel from the top is rather extreme for such a flow.

But assuming neither of these factors were sufficient to prevent the arrival of such a flow there should be plenty of warning and the best solution would be to get into a sealable underground shelter which might be built in pyroclastic flow danger areas. Several metres of rock should provide enough insulation from the flow. Supplies of oxygen and a carbon dioxide scrubber could be installed to extend the time they would be useable for.

Unfortunately there is no special suit that can protect against the extreme forces of a pyroclastic flow.

If anyone had to venture far off track in pyroclastic flow country where there were no shelters I don't think any form of suit would save them, but there are two other possibilities:

Carry a portable shelter
This would be very bulky and inconvenient and would need to be contained in a vehicle but it should be possible to provide a degree of protection. Here’s my suggestion:

On receiving the warning the vehicle could be positioned so as to face away from the flow. Large steel shutters could be carried to deflect the worst of the flow over or around the vehicle. These could be erected quickly and anchored into the ground by drilling holes and using some suitable expanding bolt. Inside the vehicle would be a large steel drum with various layers of insulating material inside it perhaps half a metre thick, the team would enter this shelter by a sealable hatch and oxygen/carbon dioxide scrubber would be carried as previously described.

Carry an escape rocket
Plan B the truck carries an escape rocket. A small capsule capable of carrying 2-4 people. Think 4 ejector seats with the back of each forming a square covered by a light conical shell. Underneath a large rocket either solid or better still storable hypergolic propellants

When the team are inside they trigger the launch. The rocket guidance system automatically communicates with a central system that broadcasts the size and direction of the flow. The rocket guidance system then launches the rocket on a trajectory that moves the team out of harm’s way. Thwy can then eject and parachute to the ground many many miles away.

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    $\begingroup$ This answer is completely outside the OP's question, an escape rocket is not a defensive wearable material it is an escapes method. The vehicle solution stretches physics and the requirements thin, also by digging down you put urself in the position of being buried alive by debris. $\endgroup$ – anon Nov 9 '17 at 19:41
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    $\begingroup$ Yes thank you for pointing out my omission. Now corrected - there is no way to protect against a pyroclastic flow by using a wearable suit. The rest of the answer proposes some alternatives that I thought the OP might find interesting. How does the vehicle solution stretch physics? It would be relatively easy to construct the exit to minimise such problems and in fact much more rudimentary shelters are actually in use, I will add one to my answer. $\endgroup$ – Slarty Nov 9 '17 at 20:57
  • $\begingroup$ How much shutter would you need in an environment that can melt steel? Would a normal truck be able to carry enough? $\endgroup$ – Mad Physicist Nov 9 '17 at 22:13
  • $\begingroup$ @MadPhysicist how hot do you think Pyroclastic flows get? $\endgroup$ – Slarty Nov 10 '17 at 0:49
  • $\begingroup$ About 1000C, but I see that steel melts ~1500C, so point taken. $\endgroup$ – Mad Physicist Nov 10 '17 at 2:07

Going in the direction opposite to @Green, you could carry a suit that is designed for burial under the flow. The suit/kit would have the following items:

  • A set of explosive charges and a shovel to get you deep enough under ground to avoid getting roasted. Some hand waving might be required for something like this to dig a narrow hole straight down instead of making a cone.
  • A radio transmitter/satellite phone or whatever is plausible to transmit the coordinates of your burial site to home-base before the eruption reaches you/them.
  • An inflatable plug either made out of incredibly good insulation, or having a heat shield at the top. This will plug up the hole once you are inside, and keep the flow from actually reaching you. Aerogel with something like space shuttle tiles on top of it might work.
  • A compressed air supply, enough to last for the duration of an average eruption. Something along the lines of a souped-up SCUBA or a firefighter's tank should do.
  • Some device to produce mechanical vibrations for an extended period of time. This would be activated once the eruption was over to help pin-point your location for rescue parties. Especially useful if a boulder covers your hole. An EM signal like a radio would probably be better, but it might not penetrate the tons of rock surrounding you. In either case, you are relying on the rescuers having received your exact location from before the eruption.
  • A poison capsule or something similar in case you get buried for too long and it does not look like you are going to make it.

If it works, the chances of immediate death are reduced greatly since you are not likely to drift off or be battered by the flow. There will still be a danger of the plug collapsing, as well as being buried too long, but over all it would significantly increase the chances of survival.

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    $\begingroup$ Partly in response to your comment on a different answer: Yes, I think this sort of thing satisfies what I was looking for. $\endgroup$ – HDE 226868 Nov 9 '17 at 20:09
  • $\begingroup$ Your suit also needs to be able to survive the sheer abrasive forces involved, if you can cut into it with a demolition saw it won't survive. $\endgroup$ – John Nov 10 '17 at 2:19
  • $\begingroup$ @John. What abrasive forces ? You are under ground in a hole covered by a ceramic shield. Only the ceramic is exposed, and it fits your requirement. $\endgroup$ – Mad Physicist Nov 10 '17 at 3:45
  • $\begingroup$ Explosives won't help you dig in soft ground (not unless you are trying to make a shallow wide hole which you are not), so you basically have ot dig a fox hole deep enough to be below ground scour so you are looking at half an hour of digging. And your plug is still subjected to the above abrasive forces which are also friction forces, generating lift. A ceramic shield of the right size and thickness to resist being ripped away would weigh more than a truck. $\endgroup$ – John Nov 10 '17 at 4:03
  • $\begingroup$ @John. Good point. Dig for an hour. You have two or three to do it in. The shield goes as deep as it can with you. It will be buried before it is torn away. $\endgroup$ – Mad Physicist Nov 10 '17 at 4:20

Your shield volcano is unlikely to make a pyroclastic flow.

http://www.geology.sdsu.edu/how_volcanoes_work/shieldvolc_page.html bold emphasis mine

Shield volcanoes are broad, low-profile features with basal diameters that vary from a few kilometers to over 100 kilometers (e.g., the Mauna Loa volcano, Hawaii). Their heights are typically about 1/20th of their widths. The lower slopes are often gentle (2-3 degrees), but the middle slopes become steeper (~10 degrees) and then flatten at the summit. This gives shield volcanoes a flank morphology that is convex in an upward direction. Their overall broad shapes result from the extrusion of very fluid (low viscosity) basalt lava that spreads outward from the summit area, in contrast to the vertical accumulation of airfall tephra around scoria-cone vents, and the build-up of viscous lava and tephra around stratovolcanoes. Cross-sections through shield volcanoes reveal numerous thin flow units of pahoehoe basalt, typically < 1 m thick. Pyroclastic deposits are minor (< 1%) and of limited dispersal, generally from flank eruptions associated with parasitic scoria cones, or from rare, localized hydrovolcanic eruptions.

Shield volcanoes produce liquid basaltic flows. These are destructive too but move along overland in an orderly manner. I have amused myself considering how flows of this sort might be diverted using giant barriers, large explosives, seawater jets to harden the lateral aspect, or the like.

There is no diverting a pyroclastic flow because it is moving through the air and the ground both and it is moving fast.

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    $\begingroup$ I too mentioned this early on however a shield volcano can have a pyroclastic flow. It is uncharacteristic not impossible but all that is required is for an occlusion to trap enough pressure for a chunk of the volcano to explode rather than 'gently' erupt. These kinds of explosions eject so much heavy material that the eruption column becomes to heavy and falls in on itself diverting a significant portion of the eruption columns energy horizontally than vertically. This inherently changes the shape of a volcano. $\endgroup$ – anon Nov 10 '17 at 15:13

Well, from your description, you want the people who are not in the villages or out in the open to be protected. You just need to place strategic shelters and give everyone who needs to go outside a device that can ping the nearest shelter and show a direction to it (or the device could just come pre-installed with the locations). Of course, since you're talking about suits or dome like structures that can shield from extreme heats, I'm assuming this is a high-tech era.

Since people will have a few hours advance notice of the danger, you don't even need that many shelters around. It would be easy to even walk to the nearest shelter (in an hour or so). A maximum of two hours of walking between shelters would ensure that you can get to the nearest one in one hour or less.

enter image description here

The shelters will not be as strong as the village enclosures of course, but the same goes for a suit. Though, these could even be holes in the ground, not really needing actual dome like structures as in the case of villages or expensive materials as in the case of a suit.

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In 1902 Mount Pelée erupted and shot a pyroclastic flow over the city of St Pierre de la Martinique. There were many explicit warnings: tremors, ashes raining, small eruptions, blasts of sulfur, etc... however the city had not been evacuated, because an election was taking place.

The local politicians who had decided not to evacuate all died, along with about 30-40.000 people.

enter image description here


enter image description here


There were three survivors, and the one who is of interest here is this guy. He was in jail, most specifically inside this solitary confinement cell:

enter image description here

His cell was without windows, ventilated only through a narrow grating in the door facing away from the volcano. His prison was the most sheltered building in the city, and it was this fact that saved his life. The cell in which he survived still stands today.

So, this looks like a suitable shelter. Very thick walls, curved top, and high thermal mass. The door was not facing the flow so it held, however the super heated air still leaked inside the building and he suffered severe burns.

Another survivor had trouble remembering, but:

The most scientifically viable theory is that Leon jumped into the ocean when the flow hit, and while the now boiling water severely burned him, he otherwise escaped unharmed;[citation needed] other accounts suggest that he survived by "napping in [his] wood cellar"


From this data, the shelter needs to be able to resist:

  • burning air and toxic gases

Requires either an airtight shelter, or an airtight suit with a can of compressed air. Filters don't work when there is too much ash.

  • high temperature (but not for very long)

Needs insulation or simply thermal mass. If Sylbaris' cell had been airtight, he wouldn't have been burned. The thermal mass would have protected him. The wooden door held, the problem was it wasn't airtight.

  • high pressure shock wave, hurricane force wind, large rocks rolling very fast

Unless you got a personal flummoxon shield generator, nothing wearable will work. These will also destroy your "1km wide dome" since force is pressure times area, by the way. To survive a hit, a dome needs to be small, for example concrete dome houses.

Anyway, you need to bury some of these at regular intervals:

enter image description here

They're pretty cheap, also they have two exits! They are also very strong when protected by a few feet of dirt on top. Nice thing is that you already have them if your country has storm drains or a sewage system. Installing them is part of making roads, so you also have them for free.

The difficult part is the airtight seal. It would be expensive and require maintenance, so this will be the wearable part.

It could be a variant of the hamster ball proposed in another answer. This wraps around the user. It needs to withstand very high temperatures though. The layer of air between the two concentric "hamster balls" would provide a modicum of insulation, but not much. However the pyroclastic flow doesn't last very long, so the heat capacity of the body could be enough. It would probably be very uncomfortable.

A better solution: a bag which would inflate with quickly expanding foam. Handwave the material to be heat-resistant and quick to harden (not PUR foam, please, maybe instant-aerogel!). So you crawl into a pipe or a sewer, and inflate this bag, it will expand until forming a nice seal inside the pipe. Same at the other end of the pipe if it is open. Now, the heat capacity of the pipe and the surrounding dirt is on your side, so you will stay cool.

Then you wait it out with your air canister (or rebreather) and cut through the foam with a knife, saw, pocket laser or folding shovel when you want to get out. It can also self-decompose after a few hours if you can handwave the technology.

It is also transparent to radio waves, which comes in handy when you want to make a call.

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Inflatable hamster balls.

Have each person carry a backpack-sized survival kit that contains a ton of heat-resistant material and pressurized gas. When triggered, the hamster ball would surround the person in heat-resistant fabric and a thick, cushiony layer of air.

When they actually get hit with the pyroclastic flow, they'll be thrown out of the way and to safety- although they may end up bouncing all the way down the mountain if they don't have a way to deflate it internally. The mental image I have is something like a zorb:

enter image description here

Additionally, it's imaginable that the pressurized gas contains an oxygen component, allowing the survivor to breathe safely even if they do end up buried in ash. That'd increase your flammability, but I personally would be willing to take that risk- a 20% oxygen atmosphere isn't likely to spontaneously ignite and will give you a long breathing time.

EDIT: Some numbers, after requested by the comments. Diameter of hamster ball 2m, thickness of heat shielding = 1mm, density of shielding = 1.4g/cm$^3$, weight of air = 1.2kg/m$^3$. That gives us an absolute minimum of 5kg. The rest of the math depends on the compression technology available, but modern tech would probably be able to get it down to about the size of a scuba bottle, which adds another ~10kg. Not bad for a survival suit.

The perk of this method is that it isn't trying to survive being buried underneath a pyroclastic flow- it's going to be hit by the first object in the flow and either be thrown or carried away from the most dangerous parts. Imagine trying to hit a ping-pong ball with water from a hose.

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    $\begingroup$ How much do you estimate a ball like that would weigh, and be able to sustain the heat of a pyroclastic flow on the outside surface without bursting or melting? $\endgroup$ – Mad Physicist Nov 9 '17 at 19:43
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    $\begingroup$ You are expecting 1mm of heat shielding to survive 1000 degree material moving at ~100mph? $\endgroup$ – Mad Physicist Nov 9 '17 at 20:01
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    $\begingroup$ When the hamster ball gets hit by the pyroclastic flow, it'll be shredded in seconds. Look at the aftermath pictures of the Mount Saint Helens eruption to see what a real pyroclastic flow will do to things like trucks, buildings, and trees. A good mental model for the leading edge of a pyroclastic flow is a sandblaster being fed by the exhaust of a blast furnace; closer to the volcano, substitute small boulders for sand. $\endgroup$ – Mark Nov 9 '17 at 22:50
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    $\begingroup$ Not going to work. A 3m hamster ball hit by sufficient material at 360 km/h will be subject to around 3,000 g of acceleration (unless the material squishes the ball to a pancake, thereby killing the occupant). You would need an enormous hamster ball (hundreds of meters across), able to quickly compress to absorb the shock, and reexpand slowly to dampen the acceleration. Or massive enough to slow the incoming ejecta, with the same effect. $\endgroup$ – LSerni Nov 10 '17 at 7:17

It's not possible. Lets suppose you have a magical air supply and a magical perfect insulator and you're behind something sufficient to protect you from the direct physical impact. (The latter is actually feasible--blast yourself a crater--it won't stop something dropping on you but it will channel most of it past.)

For a typical adult male I find a survival time of about half an hour before your own body heat kills you. Women have an even shorter survival time because they're smaller. (And note that I'm using just the basal metabolism. In practice you're going to have been exerting yourself, the time is even shorter.)

Now, for how to survive: You're a long way from the source of the eruption, the pyroclastic flow isn't going to be all that thick. You're going to need a survival vehicle that you take along if you're going too far from the shelters. Hop in, when the flow gets close you push the button and some solid rocket boosters kick you up a few miles. (You'll need an oxygen mask.) Once the boosters drop off you're left with a paramotor, deploy the chute at the top of your trajectory and fly away--the deadly flow is below you and you're going to be able to stay up a long time.

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It sounds like you want a situation where the disaster of a volcano is imminent, and so manageable as to be routine and not a disaster. Bad news, it's not a disaster.

Agreeing wholeheartedly with Will, pyroclastic flows blow things up. Here you should read 'things' to include, especially, shield volcanoes.

Since water is the usual ingredient in causing a pyroclastic flow on a shield volcano, you're doubly safe because the atmosphere is really boring 50 miles up - it doesn't rain on Earth even 5 miles up.

If you did, somehow, manage to have some sort of highly porous rock that connected an ocean to a lava flow, and manage to keep not only that flow going uphill, but not going so much as to destroy your preposterously high volcano, you have another problem. You've minimized the size of the pyroclastic event which means that the volcano erupting 450 km away is barely worth talking about - the fiery, noxious gasses will be dispersed, cooled, and somewhat neutralized by simply existing in the atmosphere in view of the sun.

If, instead, you're worried about lava (which is far more likely, given that it's a shield volcano), tons of people live really close to active volcanoes, but your volcano is huge. If lava managed to flow for the hundreds of kilometers from the caldera to the edge where humans lived (wildly unlikely), the odds of a human seeing the flow are minuscule unless the humans literally ring the entire volcano, including the riverbeds where the lava is likely to flow.

In other words, your volcano is too big to make the disaster routine and imminent.

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How do you survive this?

Pyroclastic flow

This is a pyroclastic flow. It's superheated gases (1000°C) pushing debris that can be the size of houses down the mountain. Since the gases are heavier than air, they tend to offer a cushion between the ground and the material which can help propel the tephra at speeds up to 400 mph. This is a superheated avalanche.

If we were talking lava flow, I think you could create something that can survive. But a pyroclastic flow as so much inertia and kinetic energy, I just don't see how you can build a suit to survive the impact, even with one of those mech warrior style suits.

Did you mean lava flow?

If we were talking about lava, I think you could create a suit that survives.

this material survives 2000 degrees.

There are materials such as carbon-x that can survive the heat. There are materials such as ceramat which can help insulate your body from the heat outside the suit. In addition, plates can be manufactured from ceramics that will offer further heat protection, or use as an insulator for your heels.

Lava flows generally form a crust on the surface as it flows away from the caldera. This acts as an insulator which helps the flow remain liquid and travel greater distances. You can walk on lava like this with street shoes. Well, until it suddenly isn't firm.

Liquid lava

If you have to escape on a more liquid lava, the thing that would make the survival more likely would be a modified version of snow shoes to distribute your weight. If you could walk on top of the crust, you could escape. The problems become evident if you ever spend time staring at a lava flow. Sometimes that crust gives away from it's own weight and collapses into the liquid below. Maybe that adds drama to your story, but it also adds drama to your survival.

The gases and air around a lava flow are super hot. You'd need a Self-Contained Breathing Apparatus (SCBA) because the air will be so hot it will instantly scar your lungs. The particulates from the silica will do the same thing. The other issue with lava in liquid form is that it tends to stick to things, then harden. Think of how mud works when walking through deep mud. It's hard to walk, mud sticks to your shoes, your clothes, but unlike mud, lava hardens into stone which makes mobility even harder.

Good luck with living on your volcano. It sounds intriging.

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The evidence of pyroclastic surges in the Vesuvius area AD 79

The Boat Sheds, a short video on the BBC

In the video snippet at about 10 seconds in you can see the depth of the ash deposited by the flows, the sheds where the original ground level the cliffs behind them were formed by the flows.

The heat (min 250c) and speed (100mph ave) of the flow will be the first two things to survive, anything not significantly unmovable could be destroyed by a flow. The impact damage can vary so smaller protection areas might easily survive a full on hit, it would depend on the exact nature of that flow, some are more super heated ash some contain small rocks and other debris much like a hurricane picks up as mentioned earlier. The heat can reach temperatures so great as to boil your brain in an instant and melt steel in seconds. Then you have to deal with the weight of the ash deposited by the flow on top of your protection a blanket that has buried you under tens of meters of hot ash and rock.

I would say that the best survival option for living in an area where this is common enough to be a worried would to go under ground.

Have the small towns be mostly a few meters below the surface, with the above ground buildings being made of easy to replace materials such as wood. The under ground parts of the shelter towns connected by tunnels to each other and supplies stores that could allow people to survive for several weeks without having to go topside.

Emergency exits may have to be built many miles away from the towns in case the flows are large enough to permanently block the normal exits from the underground town shelters.

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  • $\begingroup$ As was the case for L.Dutch's answer, this is interesting but doesn't answer my question. $\endgroup$ – HDE 226868 Nov 9 '17 at 18:54
  • $\begingroup$ @hde-226868 I was looking at the first part of your question. For the second part there is no current technologies that could be used to create a suit that would protect against all the dangers of a flow and still allow the user to be mobile. unless its in a locker in Area 51.. :) $\endgroup$ – Gawainuk Nov 9 '17 at 19:03
  • $\begingroup$ I've edited to make it clear what I'm looking for. Apologies if it wasn't totally clear. $\endgroup$ – HDE 226868 Nov 9 '17 at 19:10
  • $\begingroup$ Flows reach ~1000&deg;C but steel melts at ~1500&deg;C. $\endgroup$ – wizzwizz4 Nov 11 '17 at 10:48
  • $\begingroup$ ~wizzwizz4 The tempeture point where steel becomes soft enough to be mallable, which is the point where it will lose it's rigidity and an impact protection it offered is Stainless steel (Nonmagnetic) 1150c Stainless steel (Magnetic) 1095c. Carbon Steel (50%) 1230c and you'll still be cooked as there's no modern technology that would deal with the heat in a suit form.. :) $\endgroup$ – Gawainuk Nov 12 '17 at 12:44

I believe the material you are looking for is aerogel. It has an extremely low heat conductivity. However passive insulation won't be enough. Breathing near the flows will torch the lungs of anyone unlucky enough to be caught off guard. A breathing apparatus will be necessary in addition to protective gear.

Take a look at fire proximity suits to get an idea of the equipment necessary to survive high temperature.

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  • 2
    $\begingroup$ It seems that the answer to a large proportion of questions on this site is aerogel. $\endgroup$ – Gryphon Nov 9 '17 at 17:06
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    $\begingroup$ @Gryphon Aerogel is great, you can use it, for instance, to keep one turkey alive in your oven, 2hours at 180C. $\endgroup$ – qq jkztd Nov 9 '17 at 17:55
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    $\begingroup$ @qqjkztd Seems like the main difference between an oven and a pyroclasitc flow (besides the temperature) is the speed at which the surroundings are moving. I don't think aerogel would last long on the surface in a flow. $\endgroup$ – Mad Physicist Nov 9 '17 at 20:18
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    $\begingroup$ Aerogel is fragile stuff. It won't last long in a flow of boulders driven by hurricane-force winds. $\endgroup$ – Mark Nov 9 '17 at 22:46

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