I understand and agree with everything you have said and cited. But, back to what I was trying to find out, have you, or anyone else on this site, attributed the ignition source of a fire to a cellulose material being exposed to a temperature below its reported ignition temperature for an extended period of time? I truly do appreciate your taking the time to discuss this. I know this is controversial and we are working a case right now where we believe this may be the case. Dimensional lumber, right at the minimum clearance requirements, exposed to prolonged heat from a chimney pipe since 1978. Area of origin is within the chimney surround, and no other potential ignition sources present.