# What would be an ideal breathable atmosphere for a planet so that fire couldn't start naturally?

I want to have an intelligent life-form on a planet, but I want this life form to be technologically limited because of the lack of discovery of fire.

What changes would have to occur in the atmosphere for this to occur, and what effect would this atmosphere have on any human life or human technology on the planet, eg. using fuel based thrusters in this atmosphere?

• Partial pressure of oxygen at sea level is about 0.2 atm. At a partial pressure of oxygen of less than 0.1 atm (equivalent to an altitude of 5500 m) very few things will burn in open air. Air-breathing engines will still work because they compress the air; and rocket engines don't use atmospheric oxygen at all. La Paz, the capital of Bolivia, is situated at an elevation of 3600 meters. The highest permanent human settlement is La Rinconada (50,000 people) in Peru, at 5100 meters above sea level. – AlexP Jan 18 '18 at 23:53
• Unfortunately you cant destroy the triangle of fire because as far as I know(having not particularly looked into the subject), Respiration is the only organic process I know to give off enough energy to run an animals body. Respiration is basically just combustion inside the body(this process could use something else than oxygen, probably); so to completely stop one, you would stop the other. So you can only go with various ways to inhibit fires use, like the methods mentioned below. I will also recommend a nocturnal race with night vision(or just a race with no vision), to limit there need. – Necessity Jan 19 '18 at 2:52
• Make an Ocean planet with aquatic inteligent life – jean Jan 19 '18 at 10:03
• @GrumpyCrouton - it's probably a failure of imagination on my part but I can't think of a way to smelt metal that doesn't involve fire. You could use a laser, I suppose, but that presupposes you can make metal, optics and generate electricity and so forth but again, how? I can't conceive of anything nearly energetic enough that doesn't require at least some components that definitely require fire. Like I say - my lack of imagination :-) I'd love to hear how it's done when you're ready, though :-) – Spratty Jan 19 '18 at 16:35
• @Necessity Metabolism is loosely analogous to combustion in that it combines compounds with oxygen to produce energy, but just because two processes share some properties doesn't mean they are exactly the same thing. Clearly, metabolism is different from combustion; one difference is that metabolism can take place at lower temperature. – Acccumulation Jan 19 '18 at 19:43

# Sparkling Pele's hairTiny tinfoil confetti!

How about we keep the ability to start fires artificially, but make enough changes so that fires do not start naturally?

There are two main causes that lead to natural fires:

1. direct heat from the sun
2. lightnings
3. lava
4. will-o-the-wisp

We need to change the atmosphere such that the direct heat from the sun is greatly reduced, and also to reduce the creation of rapid vertical movements of air masses. In the realms of science fiction, we need very fine metallic dust mineral fibers dotted with small pirite crystals floating in the air. This amazing fiber is produced without the pirite crystals by volcanoes and can naturally float in the air. In our story it is the result of some very nasty ancient volcanic explosions. The difference from the naturally occurring Pele's hair that I found on the internet, is that we are going to sparkle it with iron crystals. Note that Pele's hair is part of the mineral wools that are considered to be fire-retardants.

The fibers are glassy and sprinkled with highly reflective pirite crystals, thus it will be reflective, increasing the overall albedo of the planet, and it will be most dense in the tropics. The reason for the increased density is that the hotter air, being more rarefied, will cause a local accumulation of the fibers, hence increasing the local concentration, and as a by-product, the local albedo.

The minimum local density of the fibers will also be such that there is never enough difference of electrostatic potential to generate any meaningful spark. Any difference in electrostatic potential will be discharged between the pirite crystals harbored on the mineral fibers. Think of it like living inside a block of metal. All the charges will be distributed in the upper layers of the atmosphere, and ancient hominids will enjoy lightnings only at the boundary between the thermosphere and the exosphere. Considering that Pele's hair has a ridiculously high ignition point, good luck igniting anything up there.

Finally, although it is not part of the atmosphere, I would remove all those piezoelectric rocks, and place all volcanoes that are active during the evolution of mankind well under the sea. Plenty of free-air active volcanoes up to the Mesozoic, fill the atmosphere with the pirite-dotted mineral wool, and then bury all of the under hundreds of meters of water. There too, good luck seeing lava igniting anything.

Finally, to avoid even will-o-the-wisps, we need to add some methane-digesting bacteria to the environment. These otherwise harmless bacteria, which live attached to the floating mineral wool, use the pirite crystals as catalytic agent to degrade methane into CO2 and water, without burning it. This will also take care of local methane spillage.

Humans will need thicker nose hair to filter the metallic dust mineral wool fibers and prevent some nasty lung carcinomas. I think that natural selection will eventually favor homo-mustachios over homo-sapiens.

The beauty of all this is that we are still in a O2-rich environment. Happy breathing.

PS a big thanks to rek's, John's, and celtschk's constructive comments.

• You're forgetting two other natural sources: contact with lava, and decomposition ignition. – rek Jan 19 '18 at 4:47
• @rek I did not forget that. These two points are addressed in the paragraphs starting with "finally". – NofP Jan 19 '18 at 10:06
• You are aware that tiny metal pieces can burn, especially in an oxygen-rich atmosphere? You cannot ignite a rod of steel, but you <em>can</em> ignite steel wool. I'd expect your metallic dust atmosphere to be highly explosive. Hopefully nobody discovers a way to make fire on it, or it will be the end of life on that planet. – celtschk Jan 19 '18 at 17:07
• You can't have all lava is underwater and still have significant amounts of dry land. And you still don't have a way to stop decomposition ignition. – John Jan 20 '18 at 5:12
• The only way all your eruptions will be subglacial is if you are in a Snowball Earth situation and then you have other issues. Also, subglacial eruptions tend to melt the glaciers and produce massive explosions and mudslides. – bon Jan 21 '18 at 8:30

High oxygen environment.

Low oxygen environment might work. But how dull.

I propose a high oxygen environment. This scheme has been bandied about here before. Advanced civilization in high oxygen atmosphere. Your environment would be 35% O2 (like Earth in the Carboniferous) or higher. You could have constant high humidity or rains to decrease wildfires. Artificial fires would burn explosively and near-uncontrollably. Domesticating fire would be like domesticating african elephants, or cape buffalo - not technically impossible, but extremely dangerous.

Plus: giant dragonflies!

• Domesticating fire in a high-oxygen environment is easy: burn it in an enclosed volume so you can control the air inflow, and thus, the rate of combustion. This was probably one of the earliest fire-related discoveries in the real world, since people have been using it since before recorded history. – Mark Jan 19 '18 at 0:33
• internal combustion engines before hot diners. – user25818 Jan 19 '18 at 0:41
• @Mark: good point about enclosing fire, but keep in mind that Humans used fire for thousands and thousands of years before the technology to actually control it came along. I believe chances are best that in this environment, fire would be a force of pure terror for any intelligent beings just as it is for wild creatures. Higher oxygen PP is a novel solution for the question well worth considering! Also, yes, giant dragonflies!~! – elemtilas Jan 19 '18 at 1:15
• No offense, but this just won't work. There are three sides to the fire triangle, fire, fuel, and heat. Remove any of them, and the fire stops. To control the magnitude of the fire, you just need to limit the amount of fuel, or heat. Heat isn't so easily controlled, but fuel still is. Instead of kindling, you start fire with medium sized sticks. Surface area of fuel goes down, relatively, so the chemical reaction of the fire proceeds at the same rate. Gotta -1 this because it doesn't work. – kingledion Jan 19 '18 at 1:23
• @kingledion There are three sides to the fire triangle, fire, fuel, and heat Did you mean oxygen, fuel and heat? Recursive fire triangles sound really dangerous! – xDaizu Jan 19 '18 at 9:07

Add something to the atmosphere that suppresses fire.

If there was 5-7% Halon over the whole planet fires could not exist. Respiration would still work, though there are toxicity concerns.

There are several fire suppressing gasses, though an atmosphere's worth of any of them existing naturally is doubtful, and it decomposes into terribly toxic products and destroys ozone. So this may just move the handwaving back one step.

• @kingledion - not true, halon inhibits burning process itself. In real life firefighting systems, halon gets injected into a compartment that has fire burning, so that its concentration goes to 3-7% level. This amount of extra gas would be way to small to notably displace any oxygen. And yet this amount is sufficient to stop the fire. – Alexander Jan 19 '18 at 1:41
• Halomethanes are CFCs, which, as we all know, destroy the ozone layer. Not much life at all would evolve on such a continually-sterilized-by-UV planet. Besides, it decomposes into very toxic byproducts. – RonJohn Jan 19 '18 at 13:10
• @RonJohn: Maybe if the planet orbits a red dwarf (which produces much less UV), it doesn't need an ozone layer. And toxicity is relative to the species. Note that oxygen was highly toxic to early life on earth; a hypothetical species on that halon planet would certainly have evolved so that the decomposition byproducts are not toxic to them. The more interesting question is: Where does that Halon come from? – celtschk Jan 19 '18 at 16:59
• IMHO halone-containing atmosphere can't stand the test of hard science, but worth exploring for a story. In addition to origination/decomposition problems, there would be a big problem with concentration. Because halones are much heavier than air, they would gather in low-lying areas, making air there unbreathable. On the other hand, at higher altitudes their concentration would not be sufficient to have the desired fire-suppressing effect. – Alexander Jan 19 '18 at 18:19
• @celtschk the problem there is that while red dwarfs have very little UV in their normal spectrum, when they flare they deliver massive amounts of it to any planets orbiting in the habitable zone. To the extent that it's an open question if a notionally earthlike planet could retain at atmosphere at all, or if the flares would inevitably strip it away. – Dan is Fiddling by Firelight Jan 19 '18 at 18:44

I'll take the boring option.

# Low oxygen environment

Boring, you say? What about developing live from the anaerobic organisms?

It'd be a lot of work, as they are some bacteria and such. But if you give aerobes no chance, your whole multi-cell and sapient life might be anaerobic. You'd need to fix prehistoric cyanobacteria for this, and then let the life cook and refine itself for few milliards of years.

Starters for further reading are: [1], [2].

• This is the most realistic answer. Normobaric hypoxic environments are already used on Earth in many places (like libraries and museums) to prevent accidental fires. Things like matches will ignite and burn, for example, while the oxidizer in the match head sustains the initial flame but it quickly goes out once the starter depletes and trying to use that flame to ignite something like newsprint simply fails. The fire just doesn't start. There is enough oxygen for humans to breathe, however. – J... Jan 19 '18 at 17:28

# Water world

If the planet is covered in one single ocean, no one would be able to start a fire until they discovered thermite or invented phosphorus torches.

You may have islands here and there, as long as they have nothing flammable on them.

Of course, the dominant intelligent lifeforms would probably be breast-singing, and possibly ram-ventilating mermaids/tritons.

As for the effect that would have on thrusters, those would be capable of operating just fine. The atmosphere over the ocean could be just like ours.

• I'm assuming ocean plant life would still be combustible once suitably dried out? Because at some point, something is going to wash up onto an island, or someone will experiment with "what happens with such and such when stuffed in a room filled with oxygen from the surface", and something will catch on fire. If fire is accidentally discovered, it'll be utilized just like the countless things our species have accidentally discovered. – Ellesedil Jan 20 '18 at 1:30
• can be combustible and is easily combustible are different things, no one is likely to discover fire from dealing with only dried seaweed, for one thing they have few ignition sources. – John Jan 20 '18 at 5:15

# Non oxygen based metabolism

The only way to do this is to exclude oxygen from the atmosphere.Anywhere that life depends on oxygen and creates an oxygen atmosphere will be fire prone, because of that same reactivity of oxygen. The only solution is to have life with a non-oxygen atmosphere.

Oxygen is probably impossible to find in an atmosphere in any planet without life, because it is too reactive. It will immediately bind with carbon, hydrogen, nitrogen, iron, or any of the other common elements in the universe (except helium, obviously). Over geological time, you simply won't find pure oxygen at human-like temperatures and pressures.

The choices are nearly endless, but here is a Wikipedia link about hypothetical bio-chemistries. You can pick one of these that allows metabolic pathways to operate without free oxygen.

Mobile life needs a chemical that reacts easily with most other chemicals to extract energy and nutritive byproducts. This chemical needs to be plentiful for life to thrive. So here on Earth we have oxygen. These are known as oxidizing agents, and there are many, but only a handful are gaseous.

The key takeaway here is that fire also requires an oxidizing agent, it needs to be plentiful - and it will occur where life is found because it's required for that life.

So wherever you have mobile life, that life will necessarily have all the ingredients to make fire, and fires will occasionally occur naturally in the same way that life occurred naturally.

We do have life that is based on non-oxidation reactions, though. Plants and non-mobile life forms use a different source of energy for their reactive processes - sunlight.

There's not enough sunlight, however, to form intelligent life due to the exceptional energy requirements of intelligence. If you irradiate a planet with enough energy to supply such demands you prevent the formation of the compounds needed to form even plants. Perhaps you could come up with a plant that lives mostly in shelter (underground) and exposes only its brain to a scorched earth scenario with enough radiated energy to power the intelligence, but I think that unlikely, and at that point what use is fire - or the lack of it - since the organism itself isn't free to move, or if it can does so only at a glacial pace.

The result is that the only possible way to form such a situation is by changing some other characteristic that allows fire - for instance having an aquatic society where oxygen exists, but other factors prevent fires.

Easy: High pressure, "low" oxygen world. For a really extreme example of this look at very deep scuba diving--there are realms where the proper breathing mixture is hydrogen/oxygen. Sounds like you have a big bomb strapped to your back but you don't--it won't burn because there's not enough oxygen.

The thing is, fire depends on the percentages. A low enough percentage of oxygen means the other gases absorb the heat, fire doesn't get hot enough to burn. However, our metabolic processes depend on the absolute pressure of the gases. At Earth's surface we breathe 3 psi of oxygen with about 12 psi of nitrogen mixed in. In space we used to use 3 psi of oxygen with nothing mixed in--our body does fine on this (but you need to be careful of the bends!) but we no longer use it because of the fire danger.

So long as we have that 3 psi of oxygen (and no more than 12 psi for extended use) and no more than about .2% of carbon dioxide the other gases are irrelevant until they reach toxic levels. (Which is actually the depth limits for scuba diving--it's not the pressure that stops us, it's the fact that we reach a point where there's nothing that can be used as a filler.)

# Humans or just generic intelligent life it is?

Because if it weren't humans, things would immediately become very simple. Say, you have a planet, where oxygen exists in liquid form only. Then oxygen breating life form can drink it and breathe this way. If you have no other oxidizers lying around, you're set - starting a fire would require significant efforts, thrusters will work almost as usual using a liquid fuel mix.

• Just a heads up, oxygen becomes a liquid at 90K. That's around −182.96 °C, or −297.33 °F. Your lifeforms should be quite sluggish, when compared to us. – Renan Jan 19 '18 at 18:06

## 73% methane, 23% oxygen, balance inerts + water, 1atm pressure

Or in other words, an atmosphere that is already so fuel-rich combustion cannot sustain itself. Could aerobic life operate here? Sure -- the process of cellular respiration is essentially step-wise and controlled enough that all the methane can simply be kept aside where it doesn't bother anything. Uncontrolled fires would simply fizzle out before they got beyond the "hot ember" stage, though. The water cycle would still work as intended, although the nitrogen cycle would need to be altered with a non-nitrogenous atmosphere (most nitrogen would be either ammonium or nitrate/nitrite in soils, with a small amount as dinitrogen).

Taming fire on this planet would be an...interesting exercise. Instead of having to pipe fuels about like we do on Earth, the locals would be distributing and storing oxidizers, in order to get to a combustible mixture from what's already in the air. Perhaps their cars would run on dinitrogen tetroxide and their furnaces on nitrous oxide?

• Can the downvoter please explain why this idea wouldn't work, or what is wrong with this answer for that matter? – Shalvenay Jan 20 '18 at 4:42
• I am not the downvoter, but an atmosphere 73% methane 23% oxygen would spontaneously combust, resulting in an atmosphere of carbon dyoxide, water, and methane, with no free oxygen. – Luís Henrique Jan 20 '18 at 13:51
• @LuísHenrique -- not according to the flammability diagram for methane I've seen – Shalvenay Jan 20 '18 at 16:00
• @LuísHenrique -- see figure 2 in this paper -- if I'm reading that triangle plot correctly, the atmosphere I describe would be just off the bottom-left corner of their experimentally derived flammable region – Shalvenay Jan 20 '18 at 16:09
• I see... however I wasn't able to find out how much energy their ignition device provides, and how would it compare with natural phenomena, especially sunlight and lightining. Also, that is measured for 1,000 milibars atmosphere pressures; as your mixture is quite borderline, I am not sure that changes in pressure would not affect it. – Luís Henrique Jan 20 '18 at 21:09

No, it would not be possible via changing the air composition only.

Humans consume oxygen in the same way that fire consumes it - the process oxidizes material and releases energy. And it would be very difficult to allow breathing, but not burning. Humans can tolerate oxygen concentrations down to 16% (compared to normal 21%), while most flammable materials can burn at lower oxygen concentrations.

Minimum oxygen concentrations

• Oxygen concentration is meaningless. Oxygen partial pressure is what counts. And humans can adapt to live at half the oxygen partial pressure available at sea level; 800,000 people live in La Paz (Bolivia), where oxygen partial pressure is about 67% of that at sea level; and 50,000 people live in La Rinconada (Peru), 5100 meters ASL, with partial pressure of oxygen about 55% of that at sea level. – AlexP Jan 18 '18 at 23:59
• True, but think about the fact that every high elevation human settlement needs burning stoves for its existence. – Alexander Jan 19 '18 at 0:09
• The question asks for making fire hard to be discovered, not impossible. For example, wood may not burn in open air, but sprayed fuel oil will. – AlexP Jan 19 '18 at 0:25
• Hmm, I read the question as asking for a categorical "no fire environment", not just for making fire somewhat difficult. – Alexander Jan 19 '18 at 0:38
• Another example: US astronauts (in earlier days) had 20% ppa pressure of almost pure oxygen. Then it went horribly wrong, but this environment was perfectly able to sustain humans. – Oleg Lobachev Jan 19 '18 at 1:31

If all the "plant life" was non-combustible, and there were no standing pools of hydrocarbons, and no piles of combustible metals, it would be rather unlikely that an "intelligent" life form would discover fire.

The problem with the main assumption is that the "Aliens" even need to evolve in an oxygen atmosphere. No oxygen - no fire.

Or you could have an earth like planet, but the intelligent lifeforms evolve in the sea. Imagine if all the land mammals were wiped out by reptiles, on the earth, after some had returned to the sea. At some point, you might expect one of the marine mammalian species to achieve a very high level of intelligence. With no fire. No special atmosphere needed.