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I am writing a story where a person suffers from a medical condition where the gut produces too much of a liquid called diphosphane. Diphosphane is pyrophoric past a certain small concentration, and in the story, a character has something wrong with his gut which causes him to produce too much of this liquid. One day when he is sitting in a chair with two relatives, the diphosphane levels in his gut reach a critical amount - self-igniting and causing all the other flammable materials (methane, hydrogen, and other gasses) in every part of his gut to ignite at once.

What is a realistic outcome of this? What effects would happen and what would the witnesses seated next to him see and hear? Would there just be an uneventful ''pop'' sound, or full on Spontaneous Human Combustion?

Also, assuming that the oxygen in his gut is sufficient. (ie, this condition causes oxygenation of the gut, as well, until it is around 16-21% oxygen.)

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    $\begingroup$ ... and the doctors just let this happen? $\endgroup$ – John Dvorak Jan 31 '20 at 17:33
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    $\begingroup$ you are right that there is methane (or other flammable gases) in the stomach, but no oxygen. So just sticking a match in there will not ignite the methane. Moreover, even Diphosphane itself only burns in the normal air. So it will cause an irritation, but no explosion. $\endgroup$ – Bald Bear Jan 31 '20 at 17:33
  • $\begingroup$ I've tweaked the tags to attract those with the appropriate specialties. (also since science-based shouldn't really be used alone). Feel free to revert the edit if you feel it's appropriate. $\endgroup$ – A Rogue Ant. Jan 31 '20 at 17:33
  • $\begingroup$ @user535733 I edited my original post for clarification. $\endgroup$ – Lars Knowles Jan 31 '20 at 17:41
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    $\begingroup$ Unless they have somehow sealed his intestines just a lot of flatulence. $\endgroup$ – John Jan 31 '20 at 22:26
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Unless there's some other really bizarre things going on in this person's digestive tract, this isn't possible. As commenters have pointed out, it's not enough to have flammable materials, you need oxygen too in order for anything to burn, and there's just not enough of it in the digestive tract

Under normal conditions the oxygen concentration in intestinal gasses is 15-16%, with 5-6% carbon dioxide and the rest nitrogen. This isn't sufficient for almost anything to burn, and that's not even taking into account all the other stuff in there that WON'T burn that's pushing down the total concentration of oxygen even further.

So, you're not going to get internal combustion within the digestive tract no matter what. you MIGHT get really explosive flatulation, but it's going to be more like a rocket than a hand grenade.

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  • $\begingroup$ I edited my OP for clarification, this is assuming the oxygen level is sufficient. Hydrogen, for instance, can burn in as little as 5% oxygen (explosive mixtures can vary, between 5-95%), and hydrogen is the most common gas in the intestines, making up approx. 50-70% of intestinal gas. $\endgroup$ – Lars Knowles Jan 31 '20 at 17:56
  • $\begingroup$ @LarsKnowles I'd like to see the source that's saying H2 is 50-70% of intestinal gas. $\endgroup$ – Morris The Cat Jan 31 '20 at 18:00
  • $\begingroup$ britannica.com/science/human-digestive-system/Intestinal-gas ''Intestinal gas The movement of gas through the intestines produces the gurgling sounds known as borborygmi. In the resting state there are usually about 200 ml of gas in the gastrointestinal tract. Its composition varies: between 20 and 90 percent is nitrogen, up to 10 percent is oxygen, up to 50 percent is hydrogen'' $\endgroup$ – Lars Knowles Jan 31 '20 at 18:01
  • $\begingroup$ You don't actually need oxygen, as some materials - gunpowder probably being the most familiar - contain their own oxidizer. So you could equate this to swallowing a large capsule full of gunpowder with an internal fuse that ignites it some time later. (Note that gunpowder doesn't actually explode, it just burns really fast. It's being confined, as in a gun barrel, that makes the explosion.) $\endgroup$ – jamesqf Jan 31 '20 at 19:22
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    $\begingroup$ And please mind that 15-16% oxygen is the concentration in stomach. Down in the intestines this concentrations falls to 2% article. $\endgroup$ – Alexander Jan 31 '20 at 20:26
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Spontaneous human combustion works on the wick effect. It's much like a candle. A small flame causes some of the fat in the person to melt and wick up into clothing or other nearby cloth. This burns just like the wick in a candle, producing additional heat. This melts additional fat. In ideal circumstances this can work its way across a large portion of a body.

So it's possible for the fat in a fat person's stomach to burn, but almost certainly not quickly.

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The contents of the gut just aren't under enough pressure to produce an explosion--terrorist bombs usually are in pressurized containers I believe, so that they release a large amount of energy all at once when then container breaks--otherwise, you have more of a bonfire on your hands.

the max volume of gas you're looking at in the gut is about 1-1.5 liters, which, if it was entirely hydrogen, would look a little less powerful than this: https://www.youtube.com/watch?v=Ficsu-OnAKw

Taking into account that the intestines are not rigid, and also that the body would dampen any explosion outwards, you're looking at a moderate amount of air being forced out the mouth and anus, and very serious scarring of the delicate intestinal tissue. It looks like there are articles sensationalizing the flammable gas that may be produced in your intestines, but on the flip side, scientists have found people who produce disphosphane in their gut, and these people did not spontaneously combust: a case study showing us not to expect a great explosion.

I haven't read it yet, but "The Fireman" by Joe Hill is a famous and well reviewed fiction work about spontaneous human combustion... that could provide some insight into how to write this. It is fiction, after all, so I wouldn't worry too much about the science behind it. If your dude explodes, he explodes. If none of your characters are doctors, then they just have to deal with the fact of the explosion and process that in their own way. Less is more here, as mentioning diphosphane will make readers think basically everything everyone in this thread has said.

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