"Let’s look at the difference between the two. You agree that in 30 minutes at 298ºF smoldering ignition of wood can take place."

I will assume this. Would be very interested in any report of the testing that could be provided.


"You are not willing to believe that a 2x12 heated for off and on several years at 170ºF can cause the same condition because you do not have laboratory conformation."

The Theory of the self-heat of wood to thermal-runaway provides a model that allows a determination as to if this can occur. Bowes used this Frank-Kamenetskii theory with required inputs derived from oven testing to model wood beams exposed to high ambient temperatures. A nominal 2 x 4 requires a critical temperature of 175 degree C. 170 degrees F is 77 degrees F, thus, the theory does not support thermal runaway. There millions of homes with attics that experience temperatures around 77 to 100 degrees C for years. How many resulted in fires?

Your missing the point. You can not make the comparison between the tests you describe and the dimensional lumber exposed to ambient temperature. They are very different configurations with respect to the energy balance and the heat transfer.

Self-heating is all about the energy balance. If the rate of heat generation is greater than the heat losses, the temperature inside the wood increases. With an increased in temperatures comes an increase in the rate of chemical reaction (heat generation), which increases the internal temperature ....and so on and so fourth. The ambient temperature provides the energy to heat the wood. The theory of self-heating assumes that all of the heat losses at the surface of the wood go into the infinite atmosphere with no measurable increase in temperature of the atmosphere and the local exposing temperature. It is also how tests are conducted in a temperature-controlled oven.

Now, insulate and trap the air surrounding the wood and it it now a finite amount of air that can be heated by the thermal losses at the surfaces of wood. How the exposing temperature is increasing with time and not constant. This dimension lumber in the open is a very different scenario than an enclosure that is made of wood.


"With that being said and your reliance on test data to support your opinion, let me ask what testing you have that supports your opinion that 170ºF applied to a 2x12 over several years will not allow ignition of the wood to take place. Has any test been conducted with wood being subjected to this temperature for several years? Right now, all you have to my knowledge is wood in an oven short time in comparison to the several years and you are relying on that data to support your opinion. How can it be any certainty as to the accuracy of the test if one does not conduct a test that replicates the conditions that actually took place?"

There is a lot of testing that is described in the available scientific literature. There are also some good references that provide a review of this literature. Almost all of it is related to dimensional lumber exposure to an ambient temperature with the surrounding environment being an infinite heat sink. Your testing does not include an infinite heat sink and a new theory is required to construct a model.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com