|MadSci Network: Chemistry|
Joan, I hope this at least begins to answer your question:
In my dictionary I found the following definitions:
Spontaneous : happening or done quite naturally
Combustion : burning
Actually my dictionary is the oxford illustrated children’s and I didn’t feel the definition of combustion was very comprehensive. So I tried the Usbourne dictionary of science instead:
Combustion (or burning) : an exothermic reaction between a substance and a gas. Combustion usually takes place in air, when the substance which burns combines with oxygen. Substances can also burn in other gases e.g. Chlorine. Combustion does not normally happen spontaneously, it has to be started by heating.
(An exothermic reaction is one where energy is given out, usually as heat and also as sound and light)
So when we talk about spontaneous combustion we mean a combustion reaction which takes place apparently without energy being provided to start it off. (This energy would be the energy of activation, so spontaneous reactions have low activation energies)
Some things will combust spontaneously – petrol soaked rags left in the sunshine sometimes burst into flames. There is a page on spontaneous combustion of materials in the ‘fire investigations’ website – www.mhv.net/~dfriedman/arson/spontcom.htm It explains quite well what might happen when something just busts into flames. But it doesn’t deal with spontaneous human combustion (SHC), and I think this is what your question was really about.
In the Mad Scientist Archive there is an answer by Chris Larson to a question about spontaneous human combustion where he explains (better than I could) why people don’t generally burst into flames. ( message ID 853266056.Ch) Here he concludes that it is just not possible for people to burn unless they get set on fire. While there is no doubt that a human body will burn to ashes (think of all the people who are cremated) this requires a high temperature and some kind of ignition.
I’d like to go back to talk about activation energy a little bit – this is the energy you need to provide to start a reaction.
If you mix methane from the gas tap and air you form a very volatile mix, and in the right proportions an explosive one. When the methane burns it reacts with the oxygen according to the reaction
CH4 + O2 = CO2 + H2O
Methane + Oxygen = Carbon Dioxide + Water
a lot of energy is given out – the heat, light and sound of the fire. This is because the products (carbon dioxide and water) have lower energy, or are more stable, than the reactants (methane and oxygen) This difference in energy is equal to the energy released when the reaction occurs.
But : you will always need a spark or a match to start the reaction going - you have to provide the activation energy. This is like an energy hill that you have to ‘push’ the molecules over before they can react and fall down the other side of the energy hill. It doesn’t matter how much lower in energy (more stable) the products are than the reactants, you still have to push then over the activation hill. The ease with which a reaction proceeds is as much to do with the height of this energy barrier (which is different for different reactions) as in the difference between the products and reactants.
Once the first molecules have reacted they give out enough energy to allow some more to react, and they give out more energy so yet more can react – and so on. (a chain reaction in fact) In people there are lots of big molecules which when burned will form carbon dioxide and water, and release lots of energy in the process. So lots of heat is given out when a person is completely burned. However, people do not spontaneously combust because the activation energy barrier is too high. Even if put our hand in a flame the flesh would not catch fire because the body can take the heat away through the blood. (KIDS – don’t try this at home!!) When this heat transfer stops keeping pace with the temperature of the flame the skin would blister and eventually the hand would burn, but this would not be instant by any means.
However there are a number of recorded cases of humans doing just that and apparently spontaneously and instantly catching fire, and so there is something going on we don’t really understand.
There have been strange tales of people burning down without good reason for many years – in fact some people like to interpret some bible stories this way – but many of these are rather mythical accounts where the details have long been lost in the mists of time. However you can find some well investigated cases. Perhaps the most famous one is the death of Mrs Mary Reeser which you can read all about at www.improganda.com/~street/ detour/shc.html (although it might be as well to remember that this page is part of a site about paranormal happenings and so emphasises the mysterious nature of the case.)
Mrs Reeser was found by her landlady having apparently been burned to death – her skull had shrunk "to the size of an orange", and a shrunken skull is characteristic of a person who burned to death. She was nearly completely destroyed by the fire which, as in all cases of alleged SHC, had clearly been very hot and localised within a small area. The body was reduced to ashes but flammable objects nearby did not burn – in fact in Mrs Reeser’s case one of her legs, which she propped up on a small stool, remained intact and was found by the fire fighters.
It is difficult to say how many cases of SHC are reported. In England there are around 100 unexplained deaths in fires but how many of these are ‘genuine’ SHC cases is not known. In 1852 Charles Dickens’ book ‘Bleak House’ featured the death of a character Krook by SHC and Dickens said that "before I wrote that description I took pains to investigate the subject"
Two hundred years ago such a happening would probably have been thought of an act of punishment by a vengeful god. Now there are a huge variety of theories about how and why this happens It has been suggested that SHC is related to heavy drinking (perhaps ethanol in the blood would help combustion, although it would not provide that magic spark) and is more likely to happen to women. Although alcohol in the body may play a small part, you would die of alcohol poisoning long before you became significantly more combustible.
The explanations which you mention in your question are some of the theories around -
Electric fields in the body may short circuit in some way, but we have no evidence for the existence of such fields. (I haven’t been able to find anything about coffee beans causing SHC)
- Some sort of atomic chain reaction occurs to explain the ferocity of the burning and extreme heat. This seems plausible enough but does not explain how or why burning starts in the first place.
- Geomagnetic phenomena somehow cause SHC
- Particular people are born susceptible to combusting – ‘preternatural combustibility’. These people would not self-ignite but are capable of combusting if exposed to the right conditions (whatever these may be) and ignited.
- That ‘ley lines’ are connected to SHC sites – ‘fire-leynes’ are particular ley lines and towns lying on these lines are supposed susceptible to strange fires. (more on ley lines at www.goe.org/dowse3.htm )
- It has been suggested, as with most hard to explain phenomena, that aliens must somehow be responsible. They are alleged to do anything from destroy people using secret hidden ‘laser’ beams to kidnap the victims and ‘program’ them to blow up at a later date.
- Jenny Randles book (Strange and Unexplained mysteries of the 20th century) proposes that a poor diet results in an explosive combination of chemicals in the digestive system. This she claims, would explain why the only reported cases are from the western world – our diet is poorer than that in other cultures - and why there are not reports of animals spontaneously combusting in mysterious circumstances. This is a suggestion which may fit some of the facts but no mechanism has been given – I am not a biologist but I cannot see what your body might produce that would explode inside you! The energy produced when you digest your food is always released slowly and either used straight away or stored as fat, and I don’t think there is any way that this energy could cause you to blow up. Excretes is a way in which you convert chemical energy from your food into other kinds of energy again this is done in a slow controlled manner, and in any case the reports of SHC I could find involved a stationary victim.
I cannot find any evidence to support the suggestion that waves of any sort would cause SHC. Firstly I can see no mechanism by which a wave could cause something to catch fire; although an electro-magnetic wave carries energy, it is not possible that they could carry enough energy to set light to a person. High energy waves are gamma rays and they kill you by radiation sickness rather than burning you to death Secondly, if you consider the amount of background radiation of all types which we experience all the time then why should it suddenly cause some people to catch fire? Plenty of people go for x-rays and I’m sure we would hear about it if they were burning to death as a result. If you believe that ley lines are connected to radiation and that ley lines are also connected to radiation then I suppose you have link.
The closest thing to an ‘orthodox’ scientific explanation is the Candle Effect : the name was first used by D J Gee in 1965. It is suggested that the clothing and perhaps the chair the victim is sitting on catches fire and acts as a fuel to burn off the water in the body, making it more combustible. As this happens the clothing absorbs some of the body fat. in a poorly ventilated room once the oxygen ran out the flames would die down, and the fat soaked clothing would act as a wick allowing the body to burn slowly. (in about an hour and a half.) We assume that the victim is already dead when the fire starts or is incapacitated (asleep?) and probably dies soon due to smoke inhalation . (This might explain why drunk people are allegedly more likely to be victims – they do not respond quickly enough) The smouldering body would give off smoke which would contain grease from fats creating an oily film on the ceiling. (Such a stain has been reported in some cases.) The heat produced melts nearby plastic, wax and metal objects but the lack of oxygen means that things can no longer burn - paper would for example remain intact.
This theory seems quite plausible but it is questionable that the clothes would provide enough fuel to burn off the water in the body (9 or more gallons) and leave anything to act as a wick. There still needs to be some kind of ignition to provide the activation energy for the clothing to catch fire – perhaps dropped matches or cigarettes? It has also never been shown that burning of this type would produce complete localised destruction of a human body with enough heat to destroy bone.
Personally I am not convinced that this is one phenomena - it is possible that these deaths have a variety of different causes. The candle effect seems to fit the circumstances of Mary Reeser quite well but there have been cases where people are reported to have suddenly burst into flames in front of witnesses. Perhaps we will never be able to say exactly what happens in each case.
So really this is something which we cannot be sure about, it is up to you to choose the explanation you like the best! There are plenty of books around, and any book about strange paranormal unexplained phenomena type should devote a few pages to it. It is not well researched by ‘proper’ scientists and the reports available may be sensational and not quite accurate. As for trying to avoid becoming a victim, I suppose the best advice is not to drink too much, not to smoke and to install a smoke alarm – but even without special precautions I fancy this is something you are unlikely to come across except perhaps in the newspaper.
The accounts of spontaneous human combustion have given rise to a number of theories, both scientific and fantastic, regarding how it occurs. However, spontaneous human combustion has not been a reproducible phenonmenon, so it has been difficult to test these theories. In the absence of rigorous testing of spontaneous human combustion, it is impossible to determine if this phenomenon occurs, and by what mechanism it might occur. As Robin says above, you are most likely to encounter spontaneous human combustion through the newspaper, and readers should form their own conclusions about the reliability of the account, as well as the proposed mechanism.
Try the links in the MadSci Library for more information on Chemistry.