Your first question is does the exposure to heat have an effect on which temperature will be needed to ignite wood. To answer this question, one must also answer the question is there a specific ignition temperature of wood. I do not believe one can say what the ignition temperature of wood is because of all the variables involved in the conditions needed for ignition. There are many different factors that will come into play when it comes to what temperature needs to be present for the ignition of wood. Without getting into all the aspects that can determine the ignition temperature of a specific piece of wood at a specific time, under specific conditions one cannot give a definitive answer to the question.

For almost 100 years, there have been incidents where piping that is being used for the transportation of steam and hot water has been responsible floor ignition of wooden structural members in buildings. The following a comment from Scientific America.

An insurance officer, visiting mills at Exeter, N. H., observed a steam pipe running through a partition, and in contact with the wood-work. The agent, although incredulous of danger, promised to cut out the wood around the pipes. A few days afterwards the wood was removed where-ever in contact. In the course of the examination, timbers in contact with the pipe, at a distance of three hundred feet from the boiler, were found to have been on fire.

I conducted research the information and photographs in Vyto’s book about there being ignition of wood structural members in contact with hot water piping. His information was correct. In fact, in Canada they believe this is a common occurrence when the pipe is fitted tightly through wood structures.

I have seen the testing you have talked about that refutes the idea of the exposure to different temperatures having an effect on the ignition of wood. I agree that they people doing the test have failed to replicate what has taken place as described in the actual events where fires have taken place. As with any scientific testing, does the fact that the test did not replicate and reach the same conclusion as to the reason that lead to ignition mean that it cannot happen? Most true scientist we’ll tell you no, it does not mean that it cannot happen. The fact that it’s hard to get around the documented cases where there was no other ignition source other than the steam or hot water piping passing through the structural member of wood. In a number of the cases where hot water was the source of heat, the investigator documented the sitting on the thermostat. In these cases, it was known that the temperature of water was below 212° Fahrenheit. If one believes that the ignition temperature would is in the 450°F range as cited in NFPA 921 Linda should not have been a fire, but there was one.

Know this may not answer all of your questions, but it may give you something to work with in your research.

Jim Mazerat
Forensic Investigations Group