# How to avoid respiratory and circulatory problems in a firebreather or flaming creature?

There are already questions like this (creature which set itself on fire for defense) and this (creature with flaming collar), asking about flaming creatures or creatures which ignite their bodies with different reasons also we have a lot of questions asking about dragons, fire breathing or fire manipulation, at each one are explained how the ignition mechanisms work, so gonna forget how those all creatures produce they fire and let's focus in how they survive their own fire (unless the way in which produce their fire could influence in this topic).

First with the respiratory problems, producing fire gives other unwanted by-products as fumes, water vapor, ashes and principally carbon dioxide and carbon monoxide, this latter being the principal problem: CO, is an extremely dangerous molecule to any living organism and till where I found there's no way to form resistance, cure or block the CO intoxication.

So the solution would be use blue fire based on different reagents permitting a complete combustion without the CO as by-product (I think that here the way of producing fire influences because if normal fire is difficult to justify, full combustion fire is even more difficult), but here is the problem that the required oxygen to produce the combustion is the same that the creature needs to breath, in relative constant use of fire as biological mechanism, practically its own fire will steal its air.

Maybe the solution could be hold the breath, but depending on the time and size this require excessive big lungs or reduce the metabolism which as a consequence reduces moving: just imagine using fire during a fight and have to stay still administering the oxygen, plus the own fire will make necessary breathing for reduce the internal temperature, while practically it is needed to fast moves to get away from the burns like fire dancers do, even having a higher resistance is inside the biological limits.

Circulatory problems are less again practically just related with oxygen transport and problems with CO, but other is the blood warming, at the dragon's question an answer mentioned that wings could be used as cooler due to their high vascularization, but that is a double-edged sword, if you start to surround yourself with fire your wings will increase overheating and if you do not have wings or have fire in one part of your body it is even worse. Also is very probable that a gigantothermic or endothermic creature will suffer heat easily than an exothermic creature.

And finally there are other problems like that its eyes will burn caused by smoke and dry out due to intense heat or having to adjust to the limits of its own fire, but I just mentioned these two systems because I consider them more related with each other.

So my questions is, how the respiratory and circulatory systems could "evolve" or be modified in flaming creature or fire-breather to resist its own fire and by-products?

(Go to this question for check what is a flaming collar creature)

• Frame challenge: Bear in mind that, in military flamethrowers, which are the nearest analog we know of for fire breathing creatures, the bulk of the combustion occurs at the target, which is ranged as far as 50 to 100 meters away when using maximum pressure. So the combustion gases may be less of a problem than one would think. One can watch YouTube videos (e.g. youtube.com/watch?v=2wAQSMGfmRc) of low pressure (short ranged) flamethrower demonstration and note that even at that short range that no special breathing apparatus is needed. Feb 28, 2021 at 6:37

Carbon Monoxide: What makes carbon monoxide dangerous is that it has a higher affinity for iron in hemogoblin than oxygen (aka the blood of animals such as mammals and reptiles). But not all animals use iron as the oxygen carrier in their blood. Insects, for example require carbon monoxide levels in excess of 50% for toxicity and some species require carbon monoxide concentrations so high I'm not sure if it's the carbon monoxide that is killing them or the fact oxygen has simply been displaced from the atmosphere.

Also, it is easier to form carbon dioxide than carbon monoxide so as long as you aren't burning in oxygen deprived conditions, carbon monoxide shouldn't really be produced so I really don't think carbon monoxide is an issue.

Eyes: Animals in real life do exist with clear eyelids so I don't think this is much of an issue.

Breathing: "Fumes" is a term that encompasses both smoke and vapours. Vapours are gas molecules that need to be chemically filtered. But smoke is actual solid particulates and can be mechanically filtered with things like HEPA filters. Shouldn't be too difficult to have the dragon have something similar to mechanical particulate filtering. Chemically filtering fumes is trickier but in real life we just use activated carbon which you could probably biologically work out somehow. Biology has a lot more tricks it can play with chemical processing anyways.

Perhaps the dragon could store lots of water and use the latent heat to keep the temperature at only 100C.

But honestly, all that is moot because marine mammals exist which can hold their breath for tens of minutes while performing intense activity. They have myogoblin in their muscles which participates as oxygen carriers rather than just their blood and lungs. Myogoblin in real life is iron-based so if carbon monoxide was actually a problem, which it's not, you just make up a non-iron based equivalent. So again, not really a problem.

• Are hemocianin an option for solve it?, or are there other option? Feb 28, 2021 at 5:58
• Possibly. I can't find 50% mortality numbers for hemogoblin and CO. But the CO P50 for hemocyanin for molluscs is 1-10mm Hg but the hemocyanin for arthropods is 100-700mm Hg. I'm not sure where hemolymph falls into this since it is only found in arthropods. It seems to be used to transport oxygen in only certain parts of some insects while the hemocyanin is used elsewhere. Weird. Note that the hemogoblin is much more efficient. If you want to stick with more conventional biology, ignore the carbon monoxide problem since it is not really one and treat your dragon as a whale or marine reptile. Feb 28, 2021 at 6:16

Those problems can be easily solved by not having a dragon being the biological equivalent of a lighter: if you keep a lighter on for more than few seconds, you will burn your thumb, right?

First of all, as a dragon you don't need to start the flame inside your body. You just need to prepare the suitable precursor and propel them out of your body, letting the flame starts once they are away from you. That's what the bombardier beetle does:

There are two large glands that open at the tip of the abdomen. Each gland is composed of a thick walled vestibule which contains a mixture of catalases and peroxidases produced by the secretory cells that line the vestibule. Both glands are also made up of a thin-walled and compressible reservoir which contains an aqueous solution of hydroquinones and hydrogen peroxide.

When the beetle feels threatened it opens a valve which allows the aqueous solution from the reservoir to reach the vestibule.

The net reaction $$C_6H_4(OH)_2(aq)+H_2O_2(aq) \to C_6H_4O_2(aq) + H_2O(l)$$ is very exothermic, and the released energy raises the temperature of the mixture to near 100 °C, vaporizing about a fifth of it. The resultant pressure buildup forces the entrance valves from the reactant storage chambers to close, thus protecting the beetle's internal organs.

As you see the above reaction has the additional benefits of not releasing any $$CO$$ or $$CO_2$$ and not consuming any oxygen from the air that the creature is breathing.

• That would the solution if the answer don't involve the presence of organisms that are able to resist the fire for some short time at their skin but aren´t able to resist the dangerous by-products and even generate fire direct over their "skin", this could be solved if exist an alternative for fire. Feb 28, 2021 at 5:55