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How about a new, very gruesome method of execution?

The condemned person is placed in a vat filled with a low-concentration acid solution and he is kept alive as long as possible (IV feeding, breathing tube, etc...) using acid-proof apparatus while he slowly gets dissolved (the uppermost layer of the skin is dissolved in 24 hours, it takes 3 to 4 days to completely remove the skin, the muscles will vanish in a week or so, etc...

My question is:

  • How painful would this execution method be? Is it a good candidate for being the most painful and torturous death?
  • What equipment would be needed (I suppose everything should be acid-proof)?
  • What substances could be used for this execution method?
  • How to keep a person alive for as long as possible? Would mild painkillers be needed to prevent fainting? I suppose that there is no danger of infection since acid kills most microorganisms.
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closed as off-topic by JDługosz, Youstay Igo, bilbo_pingouin, Gianluca, Hohmannfan Mar 23 '16 at 8:39

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – JDługosz, Gianluca, Hohmannfan
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Skin is remarkably resistant to chemical attacks. If/when I can find some links, I'll try to provide a quantitative answer. It's possible that weak acids won't appreciably harm human skin. I've accidentally exposed my skin to strong solutions of both nitric and hydrocholoric acid and as long as you can rinse it off within a few minutes, nothing much happens. If you don't get it rinsed quickly enough, then it feels a bit like being burned with hot water - but nothing makes the burning go away other than time. But the skin wasn't visibly damaged. $\endgroup$ – Jim2B Mar 21 '16 at 16:55
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    $\begingroup$ -1: To be honest, I totally hate such type of question. And I started discussion on Meta to see if I am only one or how does the community feel about it. Your opinions are welcome on the Meta $\endgroup$ – Pavel Janicek Mar 22 '16 at 12:49
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    $\begingroup$ In my opinion personal taste should not be a basis for down-voting a question. If you down-voted because of other reasons, please consider leaving a comment stating how the question could be improved. $\endgroup$ – fgysin Mar 22 '16 at 14:31
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    $\begingroup$ I didn't say that there was no reasonable ground for down-voting this question, I merely observed several down votes in short succession which were followed up with a meta discussion based on personal taste... $\endgroup$ – fgysin Mar 23 '16 at 8:11
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    $\begingroup$ -1: Because the question is poorly thought out and shows little to no proof that the OP did any thinking or research beyond "Hey I have this idea I think is cool" $\endgroup$ – dot_Sp0T Mar 23 '16 at 8:38
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Background on acids

Most weak acids won't kill or even harm a human. Human skin has a pH of about 5.5 (that's fairly acidic). Any acid weaker than this and even those somewhat more acid than this will have no effect (unless there's an underlying chemical reaction occurring besides the acid attack).

Phosphoric acid is one of the strongest of the weak acids. According the MSDS, long-term exposure of your skin to phosphoric acid can kill you. Because it has three $H^{+}$ available for disassociation, phosphoric acid has 3 possible pKas. The most acidic ($pKa_1$) is just above 2. That's very acidic but does not meet the definition of a "strong acid". A strong acid is one defined as having a pKa below that of Hydronium ($H_3O$) or -1.74. A one molar phosphoric acid solution can approach a pH of 1 (that's extremely acidic).

Skin Contact: CORROSIVE. Contact can cause pain, redness, burns, and blistering. Permanent scarring can result. A severe exposure can cause death.

But the reference didn't say how long that would have to be.

I'll try to found out required exposure duration later but I have to go to some meetings :)

Mechanism of death by phosphoric acid exposure

This is the reference for the following quote:

/SIGNS AND SYMPTOMS/ Symptomatology (after ingestion or skin contact): Corrosion of mucous membranes of mouth, throat, and esophagus, with immediate pain and dysphagia. The necrotic areas are at first grayish white but soon acquire a blackish discoloration and sometimes a shrunken or wrinkled texture; the process is described as a "coagulation necrosis". Epigastric pain, which may be associated with nausea and the vomiting of mucoid and "coffee-ground" material. At times, gastric hemorrhage may be intense, and the vomitus then contains fresh blood. Profound thirst. Ulceration of all membranes and tissues with which the acid comes in contact. ... Circulatory collapse with clammy skin, weak and rapid pulse, shallow respirations, and scanty urine. Circulatory shock is often the immediate cause of death. Asphyxial death due to glottic edema. Late esophageal, gastric and pyloric strictures and stenoses, which may require major surgical repair, should be anticipated. Signs of obstruction commonly appear within a few weeks but may be delayed for months and even years. Permanent scars may also appear in the cornea, skin and oropharynx. Uncorrected circulatory collapse of several hours' duration may lead to renal failure and ischemic lesions in the liver and heart.

So it sounds like the first issue you need to solve is keeping acid completely away from the airway. Damage to the airway could rapidly lead to death.

You need to worry about circulatory shock. I'm not sure whether this is directly caused by the acid or whether this is caused by your body's reaction to the pain and damage caused by the acid. You might solve this by IV fluids. If you can keep blood volume up with IV fluids, then organ failure is less likely.

Then you should consider means of preventing bleeding. Initially this will involve keep the acid away from vulnerable tissues (e.g. mucous membranes and airway). But eventually, the acid will begin forming ulcers on the skin and the patient will begin losing blood that way too. You can make up for the volume of blood lost with IV fluids, but eventually they'll lose enough to die.

Once the blood becomes exposed to the acid through those ulcers, I imagine the acid bath will begin to severely alter the patient's blood chemistry. Eventually, their body will begin dying from the inside and there's not really anything you can do to keep them alive once the blood's pH drops too low.

Answering your questions:

  • Very painful - imagine being burned to death by exposure to boiling water. It won't kill quickly.
  • A vat, breathing tube (airway must not be exposed to the acid), IV fluids (wound site must not be exposed to the acid), a restraint system to keep the patient fixed in place and not able to leave and/or hasten the process.
  • I think phosphoric acid (the acid used in most soft drinks) would work nicely. You might be able to use a weaker acid for the same result.
  • I don't imagine that you could keep the person alive for longer than days if you insisted on total immersion - so infection isn't an issue. If instead, you kept them restrained and simply poured acid on different portions of the body, you might be able to extend this much longer.

But I'm totally guessing on the duration. I could be wrong by quite a bit. There's not much research data available on this topic.

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  • $\begingroup$ First it depends on concentration, then it depends on what kind of exposure... of course they don't tell you duration as it has little to do with it since they say severe exposure $\endgroup$ – Erik vanDoren Mar 21 '16 at 20:37
  • $\begingroup$ Your soft drinks contain phosphoric acid instead of carboxylic acid? Also, phosphoric acid is a HIGHLY STRONG acid (not weak, up there with Sulfuric), do not confuse weak with dilute. $\endgroup$ – Aron Mar 23 '16 at 0:56
  • $\begingroup$ Circulatory shock will not set in, the hydrostatic pressure would help to maintain the volume of fluids in the body. However it would be correct that death would occur due to the altered blood chemistry. To be honest, injecting the acid straight into the blood would perhaps produce similar effects... $\endgroup$ – Aron Mar 23 '16 at 1:02
  • $\begingroup$ @Aron, please read about weak acids. Phosphoric is one of the strongest of the weak acids. However, it is not a strong acid (strong and weak acids have a specific meaning in chemistry en.wikipedia.org/wiki/Acid_strength#Determining_acid_strength). pH of ~2+ is very acidic but not as acidic as the strong acids. $\endgroup$ – Jim2B Mar 23 '16 at 2:09
  • $\begingroup$ A strong acid is one that is more acidic than Hydronium $H_3O$ (pKa = -1.74). Phosphoric is not (pKa ~ +2.15). $\endgroup$ – Jim2B Mar 23 '16 at 2:24

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