Imagine there is a rise in crime rates over the last couple of weeks in a small town in medieval age Europe. The victims abruptly combust into flame in broad daylight according to multiple eye-witness accounts.

A detective, who is investigating the case, notices a pile of ashes and the badly burnt belongings such as jewellery and clothing at the scene. The identity of the victim is established by eye witness accounts or from their belongings.


All Spontaneous Human Combustion (SHC) cases are only observed under sunlight (moonlight or lights from lamp are not known to contribute this phenomenon).

According to eye witnesses, the victims do not show any signs before combustion.

SHC takes a couple of minutes.


The story involves a trader from the East who wishes to operate a mining business on a sacred mountain; however, the locals believe that a terrible calamity will befall this small town if anyone dares to disturb the sacred mountain (extra background).

  • My question is how can I explain a SHC when bathed in sunlight?

  • Is there any substances produced in our body that is flammable and that could be catalyzed to magnify the effect?

What kind of substances are colorless, odorless and tasteless and, when ingested or breathed, can achieve this results?

  • $\begingroup$ Google "Game Theory Creepers"... Watch the video until the end $\endgroup$ – Jimmy360 May 11 '15 at 2:05
  • $\begingroup$ Ill Research more, but such a high percentage of our body is already at and end state of combustion (water) that its hard for us to burn...might require a magic component to explain this $\endgroup$ – Twelfth May 11 '15 at 3:22
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    $\begingroup$ Let's be clear on one thing - people can burn. Just like candles. The conditions only require a starting fire that is hot enough to rend fat. The problem with SHC as a 'mystery' is that all credible forensic attempts to investigate it find a plausible ignition source outside the body. That is, most of these people caught their clothes on fire, slumped over, and subsequently burned violently enough that the fat in their body could serve similarly to a tallow candle. $\endgroup$ – Sean Boddy May 11 '15 at 3:27
  • $\begingroup$ i read about real case study that the victim of SHC actually combusted from inside out therefore leaving their limbs and shoes unsrathed. $\endgroup$ – user6760 May 11 '15 at 3:42
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    $\begingroup$ That one was probably Henry Thomas of Wales, sitting in a chair. It is likely the sequence started with his shirt catching fire, his death due to inhalation of flame, and the subsequent liquefaction and burning of most of his torso and upper legs. The feet and shoes were on the floor and unaffected - the burned out skull rolled away. Gruesome but explainable. $\endgroup$ – Sean Boddy May 11 '15 at 3:49

@CortAmmon is on to something by mentioning white phosphorous. There are several chemicals which become unstable and exothermic when exposed to sunlight. Things to look into are high-nitrogen energetic materials and fluorinating agents. The trick is going to be finding something that is unstable and energetic enough to combust when exposed to sunlight, but stable enough to not burn or blow up when touched.

Many explosives become unstable when exposed to sunlight (see Fundamentals of Naval Weapons Systems 12.7.3). Nitrogen based explosives are one good candidate. Carbon disulfide is another which turns into white phosphorous. The effects of WP on humans are horrifying. The miners may have a significant amount of a dangerous substance accumulated in their clothing, particularly if there is insufficient water around the mining site to wash.

Flipping through books such as the Handbook of Emergency Chemical Management or Wiley Guide To Chemical Incompatibilities can lead to things like Amine-o-Methoxyphenylamine

Combustible liquid (flash point 210F)... Heat or sunlight contributes to instability; sensitive to all forms of light. Incompatible with strong oxidizers, with risk of fire or explosions... Exothermic decomposition with maleic anhydride. Increases the explosive sensitivity of nitromethane. Attacks some forms of plastic, rubber and coatings.

Sounds like pleasant stuff!

Another fantastic source of twitchy and highly energetic compounds is the Things I Won't Work With section of Derek Lowe's In the Pipeline blog. If nothing else, its an interesting read.

Just today I was reading a soon-to-be-published paper... They've prepared titanium tetraazide, of all things. One titanium and twelve nitrogens: whoa! Podiatrist appointment! See you later!

You can isolate the stuff, it seems, as long as you handle it properly. It turns out that brutal treatments like, say, touching it with a spatula, or cooling down a vial of it in liquid nitrogen - you know, rough handling - make it detonate violently. I think that staring hard at it is OK, though. The authors recommend using everything you have for protection if you're zany enough to follow their lead: goggles, blast shield, face shield, leather suit (!) and ear plugs. Those last two suggestions are unique in my experience, and quite. . .evocative of what you have to look foward to with these compounds. (We don't have any leather suits around where I work, although I'm sure I'd look dashing in one.)

Another route is to work with the suspected causes of Spontaneous Human Combustion. SHC is likely not spontaneous at all, but often has a plausible ignition source: a cigarette, lamp or candle. What is interesting about it is how completely the victim burns. The victims are often elderly or alcoholic, leading to the explanation that they pass out, are accidentally lit on fire, and are so out (or already dead) they don't wake up. One plausible explanation is melted subcutaneous fat combining with the victim's clothing to act much like a candle wick.

You will likely have to bend and exaggerate the chemistry involved to get the effect you desire, but there you have several ignition sources and a fuel.


No, there is no known cause or anything resembling a cause for SHC. Generally speaking, the body has a vested interest in not combusting in sunlight, so it would have evolved to deal with any odd compounds that might cause it.

I would fall back on Sanderson's First Rule of Magic: The ability for an author to resolve conflict with magic is directly proportional to the reader's understanding of the magic.

That being said, the burns from white phosphorous grenades are notorious for their violent and inextinguishable flames with traumatic results. You'd need more than a trace of the material, but it might provide inspiration.

  • $\begingroup$ There is, though it is not well known. $\endgroup$ – Jimmy360 May 11 '15 at 2:09
  • $\begingroup$ @Jimmy360 And it seems it will remain not well known? Will you share it with us? $\endgroup$ – Schwern May 12 '15 at 19:08
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    $\begingroup$ @Schwern I might post an answer. $\endgroup$ – Jimmy360 May 13 '15 at 19:23

I'm not sure how you could contain it, but Chlorine Trifluoride could be your friend here, a sentence I doubt anyone else has ever said...

From the wonderful (although, currently broken) blog Things I won't work with, comes the excellent article on the substance. It states that the substance is a "stronger oxidiser than oxygen itself" and thus can burn things not normally considered flammable, such as concrete, asbestos, sand and water.

FOOF (dioxygen diflouride) is even nastier, although it is only stable at very low temperatures.

Now if you could contain the substance in a photosensitive compound, (particularly if it took a small while to completely break down) you might be able to form a dust that could ignite pretty much anything. Covered in a light blocking layer, a disturbance could leave for some nasty outcomes...

  • $\begingroup$ will these volatile chemical compounds blow up my victims because I still want some alibis alive to talk? $\endgroup$ – user6760 May 11 '15 at 7:00
  • $\begingroup$ Maybe if they only had a very small amount on them? $\endgroup$ – BM- May 11 '15 at 23:59

Because your SHC cases occur in public (rather than all the reported modern cases, which occur in solitude), you're in something of a pickle. However, I do believe that a sort of solution is possible.

As has been mentioned, soft tissue (but not fat) is essentially water, so getting any sort of combustion going is a losing proposition - the body will act as its own fire extinguisher. And somehow replacing the body's water with something flammable, like alcohol, will have obvious and dire metabolic consequences. It's very hard to see how a victim could be walking around with a massive replacement of water with something else.

But let us consider the alternative to soft tissue - bone. The skeleton makes up about 15% of the body by weight, with a nominal density of about 3 times that of water, so it's about 5% by volume. Now, what would happen if bones were (by some wild biochemical weirdness) replaced by a spontaneously flammable substance? Let's take nitrocellulose as a base line. The density of nitrocellulose is about 1.7 times that of water, with an specific energy of ~ 10 MJ/kg. So a 100 kg person with modified bones would have a skeleton comprised of ~ 8 kg of nitrocellulose, with an energy content of about 80 MJ.

Thermal capacity of water is 4200 J/kg-deg C, so raising a kg of water to boiling will take ~ 294 kJ, and boiling that water will take ~ 2.3 MJ/kg, for a total energy requirement of ~2.6 MJ/kg. As a result, ignition of a nitrocellulose skeleton will only destroy ~ 30 kg of soft tissue.

Well, nearly half-way there.

Now let's look at fat. An overweight person might have on the order of 30% body fat (more for women). If, in addition to the bones being replaced with nitrocellulose, the composition of the body's fat were changed to 70% nitrocellulose, you'd have more than enough energy available to reduce the body to ash.

The process would presumably begin with ignition of "bone" at one of the extremities where there isn't much flesh, and the advancing ignition zone would ignite the modified fat to complete the job.

Are there problems with this? Oh yeah. Regardless of the perversity of the biochemical process required to modify bone and fat, at least 2 issues arise. First, nitrated hydrocarbons are toxic. Exposure to materials such as nitroglycerine and nitrocellulose will kill at quite low doses, so how the altered materials would be sequestered without killing the host is anybody's guess. It's magic, I suppose. Second, the modified bones would no longer (without some really serious handwaving) be able to support the growth of bone marrow, and the immune system would go to heck in a handbasket.

EDIT - And another problem - how do you get muscles to attach to the new material? END EDIT

But those are left as an exercise for the reader.

  • $\begingroup$ "Overweight" and "medieval age" don't sound to me to be very likely to occur together. $\endgroup$ – user May 11 '15 at 9:41
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    $\begingroup$ Among peasants, no. Among the wealthy, rather more. $\endgroup$ – WhatRoughBeast May 11 '15 at 13:02
  • $\begingroup$ @MichaelKjörling Being overweight was, at times, considered a fashionable affectation. "Look at how rich I am; I can afford to eat all I want and don't have to do any labor". See also: long fingernails, high heels and other fragile clothing. It could give the story a classist tinge if only the rich are combusting but the poor seem relatively immune. $\endgroup$ – Schwern May 12 '15 at 19:13
  • $\begingroup$ @Schwern That's a really good point. My initial thought was more along the lines of making it common among the population, but your proposal could certainly provide an interesting twist to the story being told. $\endgroup$ – user May 12 '15 at 20:06

One alternative method comes to mind:

  • A weapon concentrating daylight, possibly through lenses and/or mirrors. It would have to be very powerful and accurate to get the result you describe. More of a steam-punk method.

  • $\endgroup$
    • $\begingroup$ The question is tagged science-based. No vampires. $\endgroup$ – Schwern May 12 '15 at 19:09
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      $\begingroup$ Oops missed that tag. $\endgroup$ – Bookeater May 12 '15 at 19:13

    The body is full of water. How do you react in a "burning" way with water? I've heard of a goo invented in medeval times that would catch fire on contact with water, but could not find in using Google. What I did find, other than alkali metals, seemed to be redox reactions that are allowed to take place only after powers are disolved in water.

    Sunlight? Light on the skin or clothing I assume, since it would not reach inside the body to something that you swollowed.

    You would need a great deal of whatever substance; on par with the size of a person.

    It doesn't look likely.

    You could have a flying drone shoot napalm, so you can only be targeted outdoors. If he wants to keep an air of mystery and builds a hoax around some actual events, the daytime-only can be explained as at night it would be visible and a glowing spray seen (the spray is invisible in strong light).


    What about alkali metals, such as lithium, building up and deposited within a fat layer inside a diseased liver? (Like, substances tend to find each other. Some become volatile only when enough has accumulated and lithium can do this, I believe.) Once it has built up enough to become reactive the only requirement is for water to breach the fat and cause the reaction.

    I don't know if this is possible and I may be wrong about the build up of lithium, but I know lithium is found in some water and is unreactive till it is extracted and compounded. So, if you got the info to confirm or correct me this would be welcome.

    • $\begingroup$ Welcome to WorldBuilding.SE! It would be good if you could look for the information you are missing as you most likely know where you have heard of this and might therefore get better results when searching to enrich your answer. If you find it please edit your answer. And if you have a moment please take the tour and visit the help center to learn more about how the site works. Have fun! $\endgroup$ – Secespitus Jul 7 '17 at 9:10

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