This is the follow-up question to How could an underwater civilization develop electricity?, as mentioned there.

In that question, I never addressed how my civilization could have discovered/used fire. In our world, this would be a huge issue, because fire was the precursor to most of the entirety of our technology. However, I figured that it might be different underwater.

  1. How would the civilization discover fire?
  2. How could the civilization use fire?

Some details about the civilization:

  • They are octopus-like, insofar as they have tentacles for manipulation of objects.
  • They have gills.

I can't give more details about the level of technology or what other technologies exist, because I have no idea how earlier fire would be discovered (or at all).

So, how can an underwater civilization use fire?

Something I should clear up: This civilization doesn't necessarily have access to electricity yet. I'm guessing that they might have discovered fire first, but I'm not sure how this could have been achieved. I apologize for posting the questions in the reverse order to how they would most likely have been chronologically relevant.

  • $\begingroup$ Could they discover it on shore? As in, they peek out of the water to see what they can see, and they see a forest fire or something. $\endgroup$
    – Martin_xs6
    Commented Dec 9, 2015 at 21:41
  • 1
    $\begingroup$ @Martin_xs6 I've intended for them to be deep-sea creatures, so chances are slim for that. $\endgroup$
    – HDE 226868
    Commented Dec 9, 2015 at 21:43
  • $\begingroup$ fire is simply a by-product from a chemical reaction the gas molecules become very excited that they glows (black body radiation), I imagine water molecules when heated to high enough temperature under extreme pressure they will probably glow too maybe different freq not visible light if the condition is right! $\endgroup$
    – user6760
    Commented Dec 10, 2015 at 1:15
  • $\begingroup$ "That just raises further questions!" $\endgroup$
    – RonJohn
    Commented May 10, 2017 at 0:51

4 Answers 4


With Electrolysis.

They developed electricity before fire. That's good, now they can use that electricity to separate 2H2O into 2H2 and O2.

Bubbling the hydrogen and oxygen into any kind of container will allow them to have a collection of gas which is the perfect mixture for burning.

If they don't have electricity yet, then what they will more likely use in place of fire is any exothermic reaction that can take place underwater. For instance chlorine and acetylene bubbles mixing underwater.

The discovery of sodium, or any other higher period group one metals, while mining would lead them to discover exothermic reactions in the first place. Careful extraction and handling of these metals could make them available for testing. As their understanding of, or at least experimentation in, chemistry expands they could eventually learn to create thermite.

Of course, none of this prevents them from using fire on the surface. Which they may be familiar with from ship fires or fires on or near beaches.

  • $\begingroup$ I should have clarified that they didn't necessarily develop electricity before fire. I wasn't sure which would come first. $\endgroup$
    – HDE 226868
    Commented Dec 9, 2015 at 21:33
  • $\begingroup$ @HDE226868 Now we know, it's electricity first :) $\endgroup$
    – Samuel
    Commented Dec 9, 2015 at 21:33
  • $\begingroup$ How are they going to ignite it, they have an explosive not fire? also how are they going to isolate materials like sodium in water, most primitive chemistry becomes impossible since liquids don't stay isolated and dissolvable solids redisolve immediately. $\endgroup$
    – John
    Commented Nov 4, 2019 at 14:29
  • 1
    $\begingroup$ @John With an electric spark. The scenario where they have electricity is the only one where they need an ignition source. $\endgroup$
    – Samuel
    Commented Nov 8, 2019 at 23:40
  • $\begingroup$ @Samuel and how do you create an electric spark underwater, they won't have wires, and you can't build up a static difference underwater, organic sources can't generate a spark either. $\endgroup$
    – John
    Commented Nov 9, 2019 at 0:45

I don't think 'fire' is exactly needed before electricity. On land, man was mimicking the effects of Lightening.

What I think is absolutely necessary is Heat. Underwater, especially deeper underwater as you say your story is based in, you have hydrothermal vents creating islands of heated water as well as gasses bubbling up from these vents.

But I'm more in favour of the second source of heat leading to your electricity.

You also have underwater lava eruptions creating 'pillow lava'. Being underwater and with a little precaution you can get right up close to it.

An Image taken from the DailyMail (of all places) just show you how close your octo people could get...It's similar to sitting around a campfire? :) Pillow Lava

As you can see, it also creates steam. STEAM!!! I think your octo people had pillow lava, heat and steam, steam engines and then electricity!!!

I've done no research into this so this is at all, But it's the first thing that came to mind when I thought the problem out.


Underwater heating, cooking, metal-smithing and so forth will likely be done via magnetic induction, this would be an incredible breakthrough for them, the difference coal-fire made for us.

Edited by request.

As Samuel pointed out assuming this civilisation has discovered electrolysis they'll have an ideal mixture of oxygen and hydrogen to create fire as we know it, or at least explosive combustion. I think this is a safe assumption given that these intelligent aliens are clearly intended to be a civilisation of tool users like ourselves, an underwater analogue of humanity. Electrolysis wouldn't be an easy discovery, nor would venturing onto land and encountering/starting fires there, but there's nothing strictly preventing these discoveries so yes for the sake of WORLDBUILDING an underwater civilisation could totally develop fire.

They just wouldn't care.

What they need is a way to cook their food, heat their homes, forge their metal and fend off their enemies, they need to be able to create heat in a way that's useful to them, so I ask you of what practical use is gaseous fire to an underwater civilisation?

  • 1
    $\begingroup$ While I generally agree that that would make a huge difference for them. Induction is a tad more complex than fire. And it could be argued that without fire, we would never have develop that technology. $\endgroup$ Commented May 20, 2016 at 4:21
  • $\begingroup$ Gold is conductive, melts at a relatively low temperatures (could be refined in a crucible at volcanic vents) and in high purity is soft enough to be shaped with simple tools, so assuming they've discovered electricity even if they don't fully understand it they could still discover induction by experimentation. $\endgroup$
    – Cognisant
    Commented May 20, 2016 at 4:33
  • $\begingroup$ So they need some warm/fire-like basis before. $\endgroup$ Commented May 20, 2016 at 4:37
  • $\begingroup$ Large chunks of relatively pure gold have been found on the surface before, google the "Welcome Stranger", I'm sure that could have been hammered into wire and bent into a coil at room temperature. $\endgroup$
    – Cognisant
    Commented May 20, 2016 at 4:47
  • $\begingroup$ Welcome to the site Cognisant. I like the direction your going but your post doesn't really answer the questions that were posed in the OP. If you can take a moments to edit and address the questions what you currently have would be great additional information. $\endgroup$
    – James
    Commented May 20, 2016 at 6:19

Don't forget they would likely eventually also discover radioactive isotopes which may help in their endeavor to heat things without actually making fires, they could use heat vents near the cracks in the mantel to do any smithing needed, but this is all from a mind that is used to think above water and with materials and elements currently known and discovered here. Are we assuming that this is on earth? Since there are a lot of unknowns at this time, for example, this may be an underwater civilization, but, similar to us being an above civilization, we use water, what is to stop an underwater civilization from using air as a catalyst for fire or other things they may have needs for? Is there air? I assume there are other gasses since they form naturally under water either way. ( this is just a thought vomit without proper cohesion, I just woke up apologies lol)


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