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Militia Y intends to burn massive amounts of wood in order to produce carbon monoxide to be used as an air contaminant in warfare.

Defence: to be asked as a follow-up question.

Time period: ancient (140 AD thereabout).

Plan: Arrive at battle site long before enemy arrives,

Settle massive load of wood in strategic places.

The rest lies in the bows of the archers (with flaming arrows of course).

Transport: Carried by massive griffins (on platforms tethered with steel chains).

Although! Militia Y would prefer to test a recent theory that wet wood produces more carbon monoxide

No worries, carbon monoxide also poses a health hazard in ventilated areas, thus, there might be feasibility of open air carbon monoxide poisoning.

However, realistically, is this strategy a little too fantastical, even for a fantasy world?

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    $\begingroup$ Hmm, if the first verified instance of carbon monoxide poisoning in open air happenned in 1998 (!) I would say that such an incredibly rare effect is of no use in combat. (And not that in the linked article only of the cases was genuinely in open air; the other was in a car, and yes we already knew that defective exhaust pipes leaking carbon monoxide inside the car are dangeous.) $\endgroup$
    – AlexP
    Jan 29 '20 at 16:57
  • $\begingroup$ It might be worth a look to look at worldbuilding.stackexchange.com/questions/166613/… $\endgroup$
    – Trish
    Jan 29 '20 at 17:21
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    $\begingroup$ This would be no worse than a forest fire. One has to be very close to fire to actually suffocate. $\endgroup$
    – Alexander
    Jan 29 '20 at 17:24
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    $\begingroup$ Your army might get a better result bringing weapons and armor to the battle instead of heavy stacks of wood to burn. However, smoke (with the right wind) can be an effective obscurant. Use smoke to hide key forces and obstacles and to interfere with enemy communications. $\endgroup$
    – user535733
    Jan 29 '20 at 18:35
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This will be totally ineffective in any open environment with a terrestrial atmosphere because carbon monoxide is lighter than air. As such any amount of CO produced will rise into the atmosphere away from the battle. Only in a confined space like a cave could this be considered as a weapon, where fire is already an extremely effective combat tool.

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  • $\begingroup$ I knew it would be too far fetched. $\endgroup$ Jan 29 '20 at 15:32
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    $\begingroup$ It would quickly rise away from the battle even if it was some denser gas, because it's the product of combustion, and it's hot. I suspect the heat has a bigger effect on the density than the composition. $\endgroup$ Jan 30 '20 at 20:42
  • $\begingroup$ Also, in an open environment the combustion process will produce CO2, not CO. You only get CO produced when burning something in an enclosed space without enough oxygen available to fully oxidise it. $\endgroup$
    – Mike Scott
    Jan 30 '20 at 23:16
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    $\begingroup$ Even carbon dioxide, wich is some 50% heavier than air at the same temperature, if produced by burning goes UP just because it is hot and thermal expansion overcomes the heavier molecules. $\endgroup$
    – fraxinus
    Jan 31 '20 at 15:19
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Any fire big enough to produce a useful amount of CO will also produce its own circulation. The heat of the fire will cause air to rise over the fire, and bring surrounding air in at the bottom. The bigger the fire, the bigger the effect. So the fire itself will drive the CO away from the location of the fire and disperse it.

Also, the evidence of many millions of Boy Scout and Girl Scout camp-outs is that fires do not tend to produce dangerous levels of CO near the fire. I have never heard of an outdoor situation in which there was any possible CO problem. Long before the CO gets you, the other components of the smoke and gaseous combustion products of the fire will get you.

The moment you get some kind of enclosure you can have significant problems. It would not take much. The bottom of a deep bowl-shaped valley might accomplish something if it was a very still day. The fires would have to be small and distributed around so as not to create large updrafts. But probably not from the CO, more likely from the CO2.

Or if you could lure the opposition into a cave or similar situation, you might get enough still air to have some effect.

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    $\begingroup$ The idea is still a no-go I take it? $\endgroup$ Jan 29 '20 at 15:37
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    $\begingroup$ @GroukåLimher, there's a reason that in the real world nobody used poison gas as a weapon until the Twentieth Century. You need an agent that is both toxic and heavier than air or it just blows away. Even then, conditions have to be right (mostly "wind, but not much wind, and blowing toward the enemy"). $\endgroup$
    – CarlF
    Jan 30 '20 at 14:32
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Burn your wood for the smoke, toxic and otherwise.

If you like the idea of burning lots of wood, go ahead and burn it. Especially wet wood will make a lot of smoke and smoke is a legitimate asphyxiant. Probably better than carbon monoxide because smoke makes you cough and choke, and also you cannot see your enemy - who you know must be there because her troops (including massive griffins and who knows what else) showed up enough ahead of you to set up all this smoke.

It might be possible, with smoky fires and medieval tech, to add other things that would be better chemical weaponry than CO. If you burn poison ivy (I think burn in a relatively cool fire) some of the oil gets aerosolized. Breathing that will seriously mess you up and can even kill. Breathing a little bit and coughing a lot will make you even more scared of the smoke. Your troops can throw bales of poison ivy or your world's equivalent on your fire once the enemy starts advancing through the smoke.

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    $\begingroup$ also, burn the stuff in barrels not open pits $\endgroup$
    – Trish
    Jan 29 '20 at 17:26
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    $\begingroup$ @Willk The poison Ivy idea is brilliant! Why didn't I think of that?! $\endgroup$ Jan 30 '20 at 5:45
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    $\begingroup$ Burning sulphur is also quite noxious. As is a whole lot of other things, but sulphur was the most common warfare smoke because the substance is relatively easy to obtain and store. $\endgroup$
    – toolforger
    Jan 31 '20 at 15:28
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This could work under one circumstance: militia Y is burning a plant with toxic/irritant properties, such as poison oak/ivy/sumac. (One problem fire fighters encounter with wildfires is encountering smoke produced by one of these plants burning. Get this irritant in your lungs, & if it isn't fatal the victim sure wishes it was.)

However as others have pointed out, this is not very practical. When armies in WWI used mustard gas in battle, they found it difficult to manage: all it took was one unexpected breeze, & the poison would blow into friendly ranks. And there is the challenge of finding enough of this plant to be worth the problem. As user535733 commented, your militia would be better off bringing armor & pikes than poison plants & wood to burn.

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I think such an action could be easily defeated. If I remember correctly Pliny the Younger describing how the Romans dealt with the eruption of the Vesuvius also wrote that they used cloths drenched in water to protect themselves from the smoke, that wasn't enough for Pliny the Elder, but it should be enough against a man made fire.

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