This phenomenon has been given the name “pyrophoric carbon” by some and it is somewhat controversial, most of the discussion being in the USA.
Ignition of wood has been reported where hot water pipes penetrate timber members over a long period of time and the temperatures involved may be as low as 75°C. Some say that, because this has never been reproduced in the laboratory and there has never been a generally accepted theory, it does not exist.
Others point out that seeing it happen in the laboratory or the existence of an accepted theory is not a problem if there is a reasonable body of evidence that it has taken place – and there have been many such incidents reported. I subscribe to this view. There is a good treatment of the subject in Vyto Babrauskas’s Ignition Handbook.
The important thing to remember is that wood does not have a specific ignition temperature, ignition depends on temperature and the time that the temperature is maintained. It seems reasonable therefore that very long exposures may result in ignition at quite low temperatures.
One word of warning though, you should not put this forward as a source unless you have some pretty good evidence to support it.
Hope this is helpful.
Stan
