In an alternative reality, people where capable of taking information from the future, and thus, they decided to not only to replicate future technology for the betterment of manking, but also future war technology.

Including, but not limiting the use of exoskeletons and mechs with life support systems and so on.

One specific faction decided it would be a great idea to make the use of a "sulfuric acid Piranha solution flamethrower", which they simply spray sulfuric acid like a flamethrower and melt anything that is organic.

(although it wouldn't be that useful against other exoskeleton-powered armies)

It is a brutal weapon for a brutal faction, but would that be considered a war crime under today's geneva convention? Or it would be a grey area of the convention?

As far as I could find, the geneva convention prohibits mass murder chemical weapons that poison the water, the earth and the air with the intention of indiscriminately killing every civilian or soldier, plant and animal alike.

However, the sulfuric acid spray/liquid will simply be neutralized after some time in contact with the carbon content on the air and land itself.

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    $\begingroup$ This feels like more of a Law StackExchange question to me. You are asking in the context of a scifi story, but you are asking about whether a specific chemical that actually exists would be banned under a specific law that actually exists, so it seems like there would be an objective legal answer to this, or at least a realistic legal case to be made. $\endgroup$
    – Atog
    Commented Jun 18, 2023 at 23:46
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    $\begingroup$ Does your alternate reality have a treaty of sorts in place against their use? If not, there's nothing preventing their use. If so, does it really apply to anyone and everyone, or only to certain parties (e.g. the UN chemical weapons convention doesn't apply to countries that never ratified it, neither does any other treaty the UN cooks up). $\endgroup$
    – jwenting
    Commented Jun 19, 2023 at 8:12
  • $\begingroup$ I don't think you need technology from the future to make a sulfuric acid spray gun. I also question how useful such a weapon would be. Keep in mind in order to spray it, you must make it, and transport it, and carry it. Instead, you might want to come up with some sort of fictional acid that works the way you're envisioning. $\endgroup$ Commented Jun 19, 2023 at 16:42
  • $\begingroup$ @GrandmasterB not too hard to do any of that with sulphuric acid. The actual usefulness of the weapon would depend on its intended use. It'd definitely not be all that effective, certainly not after an initial "oh god what did they come up this time" phase shortly after its introduction. Protective clothing is simple, but might be slightly cumbersome depending on climate. $\endgroup$
    – jwenting
    Commented Jun 20, 2023 at 3:29
  • $\begingroup$ @jwenting "Quick, everyone, cover yourself in this baking soda!" :-) $\endgroup$ Commented Jun 20, 2023 at 5:41

9 Answers 9


Yes and No.

I'm going to start this with 'I am not a Lawyer'.

Protocol III to the Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons which may be deemed to be Excessively Injurious or to have Indiscriminate Effects

This is the part that is relevant.

So, initially:

  1. "Incendiary weapon" means any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or a combination thereof, produced by a chemical reaction of a substance delivered on the target.

(a) Incendiary weapons can take the form of, for example, flame throwers, fougasses, shells, rockets, grenades, mines, bombs and other containers of incendiary substances.

Would seem to be pretty clear that your Acid throwers are in violation of this section.


(b) Incendiary weapons do not include:

(i) Munitions which may have incidental incendiary effects, such as illuminants, tracers, smoke or signalling systems;

(ii) Munitions designed to combine penetration, blast or fragmentation effects with an additional incendiary effect, such as armour-piercing projectiles, fragmentation shells, explosive bombs and similar combined-effects munitions in which the incendiary effect is not specifically designed to cause burn injury to persons, but to be used against military objectives, such as armoured vehicles, aircraft and installations or facilities.

See - this is where it gets interesting. White Phosphorus illumination shells, are legal. White Phosphorus used against people - technically illegal.

The difference between War Crime and not War Crime could be the after-action report of 'We fired 3 illumination shells, to help our forces retreat' vs the reality of 'Let's shoot the bad guys with everything we have and damn the consequences'

There have been many instances throughout history where certain militaries (who provide a lot of funding to certain NGOs) are 'allowed' to get away with dubious interpretations of this article, whereas other militaries (who are generally seen as 'the bad guys') tend to get treated with a much more literal interpretation.

This is also the paragraph where the urban myth about .50BMG Barrett rifles only allowed to be aimed at someone's belt buckle because it's not Anti-Infantry, it's anti-Material comes from.

And so for your weapons system - if it's primary use was as an anti-armour/Anti-exoskeleton weapon - there is potential and precedent (see WP comment) that you could get it through. If it's the primary infantry weapon, however - then probably not.

In short - If your team is 'the good guys', and the weapons system is used in such a way that there's enough plausible deniability (which would be a bit tricky with an Acid Thrower - but not impossible) that it's primarily an anti-armour weapon and the burn injuries to the individual are incidental, you might be able to get it through.

Also, as TheFatElectrician says - "It's not a War crime, the first time" and "Reality isn't what happened, Reality is whoever has the most sworn affadavits and after-action reports"

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    $\begingroup$ You appear to have overlooked section 2 of Protocol III: it only prohibits the use of incendiary weapons against civilian targets or military targets mixed in with civilians. $\endgroup$
    – Mark
    Commented Jun 19, 2023 at 6:45
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    $\begingroup$ You are mistaken in your inclusion of acids in the category of incendiaries. While some acids may have incendiary effects (and might be included as a result, IF that incendiary effect is the reason they're used as a weapon) not all do. $\endgroup$
    – jwenting
    Commented Jun 19, 2023 at 8:10
  • $\begingroup$ You might want to look at these: Regulations concerning the Laws and Customs of War on Land, annexed to Convention (II) with Respect to the Laws and Customs of War on Land, The Hague, 29 July 1899, Article 23(e). / Regulations concerning the Laws and Customs of War on Land, annexed to Convention (IV) respecting the Laws and Customs of War on Land, The Hague, 18 October 1907, Article 23(e). $\endgroup$
    – Trish
    Commented Jun 19, 2023 at 13:12
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    $\begingroup$ I agree with @jwenting that acids do not meet the definition of incendiaries which you quoted. While we use the term "burn" to describe the damage they do to human tissues, the text you quote specifies that the damage is cause by a chemical reaction which produces heat, flame, or both. They are referring to combustion. $\endgroup$
    – David42
    Commented Jun 21, 2023 at 12:29

White phosphorus usage in war is forbidden on human targets according to the 1980 convention of Geneva, because it causes deep and painful burns.

Similarly, expanding bullets are forbidden in war, because with their expansion cause excessive suffering to the target they hit (but curiously they are not forbidden in civilian use, like ammunition for police forces...).

Based on this precedents, and considering that piranha solution is akin to white phosphorus in terms of burn inducing capabilities, I would say it would be forbidden, too.

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    $\begingroup$ You say white phosphorus is forbidden, but numerous countries use it, perhaps most infamously the United States. It's a perfect example of the kind of gray area this question is asking about - it's "banned" but, partially because it isn't a weapon of mass destruction, pressure to enforce that ban is rather weak. $\endgroup$
    – Cadence
    Commented Jun 18, 2023 at 17:50
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    $\begingroup$ The Convention on Certain Conventional Weapons (the 1980 treaty you mention) does not ban the use of white phosphorus. It bans the use of white phosphorus and other incendiary weapons against civilian targets. Military targets, including military personnel, are fair game. $\endgroup$
    – Mark
    Commented Jun 19, 2023 at 6:38
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    $\begingroup$ "forbidden" ONLY for use by those nation states that actually signed and verified those treaties. Not all of them did, and of course terrorist groups, "freedom fighters", and groups like those are never signatories of any treaties so those treaties don't bar them from doing anything. $\endgroup$
    – jwenting
    Commented Jun 19, 2023 at 8:08
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    $\begingroup$ Expanding ammunition is legal outside of war because preventing overpenetration (endangering bystanders) is more important than the comfort of the target. $\endgroup$
    – towe
    Commented Jun 19, 2023 at 8:19
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    $\begingroup$ The deep and painful burns from white phosphorous have less to do with why it’s banned than the fact that it tends to spontaneously reignite when exposed to air as you’re pulling it out of a deep wound (making it a serious hazard to anybody treating patients who have suffered white phosphorous burns), and the fact that it’s actually rather nastily toxic aside from being highly flammable. $\endgroup$ Commented Jun 19, 2023 at 11:49

It will only exist, if it overcomes a meaningful threat; so, it would be legal if used against that threat.

Piranha solution is not a particularly useful biochemical weapon. The amount needed to cause any more than a surface level burn, and the speed at which it reacts is simply not good enough to weaponize. If it was worth weaponizing, it would already be classified by the OPWC a schedule 3 biochemical weapon, but it is not. So, if we are working on the assumption that your future tech people are smart, they would not even invest in such a weapon.

A flamethrower is generally better than an acid gun because it sucks the oxygen from and heats the air. This means that it can kill and incapacitate enemies that it does not even touch. It also takes a relatively small amount of fuel and minimal technology to make a giant vaporous fireball as opposed to Piranha solution which only causes major on contact.

When it does come to biochemical weapons, you generally want to stick with gases, not liquids. This allows them to (like a flame thrower) harm by proximity and use less mass.

That is, unless their world includes something that they need a hydrochloric acid weapon to counter, that they can't beat with thier much longer ranged railguns, plasma cannons, etc. So, imagine that they have invented some future tech armor or shield technology that can stop heavy artillery and high energy weapons in its tracks, but is highly reactive with Peroxymonosulfuric acid, or maybe something like a "dune shield" that can only be penetrated by a slow weapon. Suddenly you have a reason to close range with an enemy to spray them with this acid. At this point, if the acid eating through the armor or bypassing the shield then causes horrific injuries to the underlying personnel, it is not a war crime.

This is because unless the chemical is specifically banned by the OPWC, the rules at play have exceptions for things that assist in overcoming your enemy's defenses like an how a thermobaric bomb can infiltrate a fortified position in ways that a self-oxidizing bomb can not; so, they are generally not seen as war crimes to use, even though they kill in relatively inhuman ways.

There is also another exception which is that you are allowed to use the weapon you have when it is all you have. For example, a 50cal riffle or machinegun is classified as an anti-material weapon and may not be used as an anti-personnel weapon. However, if all you have is a 50cal riffle and you find yourself in a combat situation where you are unable to switch to an approved anti-personnel weapon, then you are allowed to defend yourself with an anti-material weapon. So, if your anti-shield, acid gun troopers get ambushed by some unshielded enemy forces, then they are generally allowed to use the acid guns to protect themselves.

Lastly, if the awfulness of this weapon is deemed bad enough by international consensus, then Peroxymonosulfuric acid could become a Schedule 3 biochemical weapon and be banned, but that would have to be a specifically agreed upon by treaty.

Hazardous Material Warning: Piranha solution is not just Sulfuric acid. When sulfuric acid is mixed with hydrogen peroxide it makes Peroxymonosulfuric acid (Caro's Acid) which is an unstable explosive and a solid at room temperature. To liquify it, you need to heat it up to about 45°C. So, if anything ever goes even a little wrong with containment between your Peroxymonosulfuric acid and your heating element, your weapon will explode. In a combat environment, the risk of a high purity solution accidently exploding in your face is probably too high to be worth considering.


"Weapons of a Nature to Cause Superfluous Injury or Unnecessary Suffering"

What you discovered there is a type of weapon that is banned as a weapon that causes superfluous injury or unnecessary suffering. That is the overarching category that also includes Dumdum bullets, hollow points, White Phosphorous, napalm, Flamethrowers, and many many Biological or Chemical weapons - including Rainbow herbicides.

Use of such inhumane weapons was first declared illegal to use in a war with the Saint Petersburg Declaration of 1868, but the rules and customs of war were clarified especially with the various Hague and Geneva Conventions. Excerpts of those treaties pertaining to such weapons can be found on the site of the International Red Cross, but the most relevant are (emphasis mine):

Hague Regulations (1899)

Article 23(e) of the 1899 Hague Regulations provides: “[I]t is especially prohibited[t]o employ arms, projectiles, or material of a nature to cause superfluous injury.

Regulations concerning the Laws and Customs of War on Land, annexed to Convention (II) with Respect to the Laws and Customs of War on Land, The Hague, 29 July 1899, Article 23(e).

Hague Regulations (1907)

Article 23(e) of the 1907 Hague Regulations provides: “[I]t is especially forbidden[t]o employ arms, projectiles, or material calculated to cause unnecessary suffering”.

Regulations concerning the Laws and Customs of War on Land, annexed to Convention (IV) respecting the Laws and Customs of War on Land, The Hague, 18 October 1907, Article 23(e).

Additional Protocol I

Article 35(2) of the 1977 Additional Protocol I provides: “It is prohibited to employ weapons, projectiles and material and methods of warfare of a nature to cause superfluous injury or unnecessary suffering.

Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts (Protocol I), Geneva, 8 June 1977, Article 35(2). CDDH, Official Records, Vol. VI, CDDH/SR.39, 25 May 1977, p. 101, Article 35 of the 1977 Additional Protocol I was adopted by consensus.


If you look at the types of weapons that are banned by international treaty, a large portion of them (radiological weapons, poison gas, etc) are banned because they are indiscriminate. Large sections of the Geneva conventions (and similar) deal with what qualifies as a valid military target, what civilian targets are off-limits, and what precautions must be taken to ensure that civilian targets are not hit.

A rifle can be aimed, so you can ensure that it's only pointed at a military target. Poison gas cannot be aimed. It lingers, drifts in the wind, and otherwise moves unpredictably. There's no way to ensure that it's only attacking a valid military target and not civilians. Your acid weapon will almost certainly fall in the same category. Even if you could aim your liquid spray perfectly, the acid takes time to neutralize. Until then, it presents a hazard to any civilians that enter the area after the battle. It could be like an invisible mine field with no clear way to detect it or know when it has been rendered harmless. Spraying military personnel with acid also presents a hazard to civilian medics that attempt to treat them. For those reasons, I believe such a weapon would run afoul of the rules of war even if it isn't explicitly mentioned.

That being said, the weapon doesn't seem like a great idea to begin with. A strong, sudden gust of wind in the wrong direction means you're spraying your own troops. An enemy force advancing behind the protection of a powerful fan (like the downdraft of a VTOL or helicopter) could make the weapon useless or even turn it against you. Simply spraying water at the weapon can make the acid boil and splatter uncontrollably in all directions, including at its user.


This is a Frame Challenge

I believe you're asking the wrong question. While it's theoretically true that we could judge the morality of your weapon against today's Geneva Convention standards, I believe another matter would take precedence. But before that, let me point you to some useful resources.

The short answer here is that anything that has a higher chance of maiming the target than killing said target (e.g. flamethrowers) or that kills the target too slowly (e.g. flamethrowers) is likely to be banned under current treaties. But I really think this isn't the right answer or, at least, not the right point of view.

What would be banned? The transfer of technology from the future

If your alternative history is based primarily on existing Human history, then the advent of "time travel" (I'll use the term for convenience, I recognize you're only capturing information) will cause an unusually rapid series of legal efforts to control what can be transmitted (if anything) from the future. Frankly, I could easily conceive of a legal ban on all information garnered from the future.

Therefore, how the faction obtained the technology becomes more important to the discussion of morality than how heinous is the weapon?

I say this because the capacity to kill someone would be, in my opinion, less terrifying than the capacity to upset the status-quo of or destabilize economic systems, food supplies, power distribution, and I suspect propaganda. Who wants an acid-throwing weapon when you can...

  • Bring printing technology from the future that allows you to print perfect counterfeit money?
  • Bring replication technology from the future that gives you a ten-fold advantage in manufacturing?
  • Bring disease tech that can wipe out the enemy's food supplies (think viruses) or, conversely, cures and enhancements that would protect your own food supply?
  • Bring tech that enhances the volume or decreases the cost of power generation, or that protects the transmission of power?
  • Bring tech that improves your ability to tap into the news and entertainment services of your enemies, allowing you to spread propaganda or to disrupt their communications?

Frankly, I believe these and many other ideas are much, much worse than an acid-throwing weapon. They're the information-age's equivalent to weapons of mass destruction.

I believe the act of taking anything from the future would be deemed unfair and inhumane and would, itself, be quickly banned by treaty.

All the while said signatories to the treaty would be finding ways to collect the information and then make it look like it had been developed in the present timeline. Boys will be boys.

BTW: I assume you're ignoring all the paradox theories that this idea would trample on. I'm a fan of the grandfather paradox: the information you bring back from the future is that five years from now your spouse will be exposed in a lurid affair that scandalizes and ruins you. In a fit of rage, you kill your spouse. ("It doesn't matter that you don't know Randy! You're gonna sleep with'm Randy! It'll ruin me!" BAM!) This is kind of the movie "Minority Report" on steroids. Or, perhaps more on-point, bringing back the acid-weapon tech ends up killing the person who invented it before they invented it. Or you learn that company XYZ will be fantastically successful, so you convince the mega-corp that created the time travel to heavily invest in it... except that it was the lack of investment that caused the company to make a choice that led to its success and, having received investment too early, it fails. Access to future information (or too much future information) is, all by itself, inhumane.

And while I'm thinking about it, you could make the same claim about past information. Pretend that we suddenly had access (how is irrelevant) to a cache of complete historical information for each and every person on Earth since, oh... 500 B.C. Think about it. Really think about it. The "true history" of really big world-altering things like the reality/fiction of Jesus Christ will have equally bad effects on the individual as learning that your great-great-great-great-great granddaddy was a fiend who made his fortune in the worst possible way or that somebody had a perfectly good reason to assassinate Kennedy. Too much information from either direction would have mind-blowing society-altering effects. Might make a good book, though.


Prefacing this with IANAL.

The whole point of weapons restrictions within the Geneva Convention is to ensure that weapons either kill someone (in a reasonably quick fashion) or, if they're not killed, they're reasonably likely to recover following medical treatment.

Incendiary weapons are banned precisely because they're likely to cause a fairly slow death or permanent, painful disability should someone survive.

Now, as far as I'm aware, nobody's tried using acid throwers, so they've not been explicitly banned to-date and they probably don't come under chemical agents rules since they largely refer to gasses.

That being said, I wouldn't rate your chances at a war crimes tribunal of arguing "they technically weren't explicitly banned" when such a weapon would be so clearly against inhumane.

Also, when it comes to war crimes, it doesn't really matter if it's banned or not if you win the war and just refuse to accept the jurisdiction of the ICC...


It's a straight-up chemical weapon because of the fumes. It won't just burn skin, the fumes will burn lungs and that puts it squarely in the "banned chemical weapons" category.

Anyway, it's a stupid weapon. It will work once, and then the damaged unit will get on the radio and warn everyone else to don their gear designed to resist worse attacks than that. So it will be militarily worthless, and just savage civilians.

Worse, the enemy will feel entitled to respond in-kind, so you get to find out how long it takes them to put mustard gas in an artillery shell. Or worse - some countries say "we do not see a distinction between nuclear, chemical, radiological and biological weapons" - that's code for saying "we only have one kind of those, and we'll answer any such attack with that".



Unquestionably, yes.

A good rule of thumb is that if you wonder "is it a war crime to...", the answer is probably yes, and if that question involves chemical weapons, the answer is unquestionably yes.

There isn't much grey area really, the only question is who's going to bring you to trial.

War crimes and Geneva

First, I have to correct a few things about the question, because I have to.

The Geneva Conventions (plural) and associated Protocols (plural) are a series of texts regarding civilians, POWs, the wounded and sick, and more generally people. It gives rights and protections against mistreatment. In a nutshell, combattants can kill each other in the field of battle and that's pretty much it. They don't concern chemical weapons directly.

The Geneva Protocol (singular) is the one that concerns biological and chemical weapons. It is one of a few agreements on the topic. It isn't part of the Geneva Conventions, nor one of the Conventions' Protocols. It's a different thing. International law is funny like that.

War crimes are first and foremost crimes. Perhaps that sounds stupid said like that, but it's true. You have to charge specific people with specific crimes. And then you have to prove it. It's not enough to prove the crime happened, you have to prove the person you're charging did it. You know, like any crime.

Finally, because war crimes are crimes, you need two things: someone to prosecute, and the will to prosecute them. Winners don't prosecute themselves. Winners often don't prosecute losers for a variety of reasons (as part of terms of surrender, because they need someone to build rockets, etc). You can only bring to trial someone you have captured or who surrendered.

It's never Geneva

With that said, neither the Conventions or Protocol matter much here. The Rome Statute (PDF in English), which establishes the International Criminal Court, makes a non-exhaustive list of war crimes for which you can be charged.

Article 8 War Crimes

  1. For the purpose of this Statute, "war crimes" means:

(b) Other serious violations of the laws and customs applicable in international armed conflict, within the established framework of international law, namely, any of the following acts:

(xvii) Employing poison or poisoned weapons;

(xviii) Employing asphyxiating, poisonous or other gases, and all analogous liquids, materials or devices;

(xx) Employing weapons, projectiles and material and methods of warfare which are of a nature to cause superfluous injury or unnecessary suffering or which are inherently indiscriminate in violation of the international law of armed conflict, provided that such weapons, projectiles and material and methods of warfare are the subject of a comprehensive prohibition and are included in an annex to this Statute, by an amendment in accordance with the relevant provisions set forth in articles 121 and 123;

You can knock yourself out reading the annexes, going through other texts that regulate weapons of war, but really, when it comes down to it, acid burns are horrific and that's a fact. Purposefully causing acid burns should absolutely be consider "superfluous injury" and "unnecessary suffering".

You could maybe argue that this isn't the case, but if you find yourself arguing that it's because you've lost the war. I don't fancy your chances of winning that argument against a bunch of horribly disfigured witnesses.

Just use bullets, like a civilised person.


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