Pyrolysis. It’s a big word but a simple concept. As organic materials age and are repeatedly exposed to high temperatures, they are chemically transformed. So, with that in mind, here is a quick overview of wood stoves, fireplaces, and the danger of pyrolysis.
Pyrolysis is a process that takes place over time when organic materials, like wood or coal, decompose due to heat exposure—in other words, regularly heating an organic object to a high temperature. When that happens, the thermochemical process takes place, which is, yes, pyrolysis. In the process, the ignition point of organic material drops to as low as 200F. There are no visible warning signs for pyrolysis, and it can take years before it occurs, so you can be lulled into a false sense of security before a fire occurs.
Inspecting your fireplace, chimney, or wood-burning stove is the only way to stop a fire from pyrolysis. Why? Because there are no outward signs of pyrolysis, the only way to stop it is to catch the problem before it starts. It is also wise to have annual inspections to see other issues before they become expensive problems.

What is Pyrolysis?
How to Stave Off Pyrolysis