Are fog nozzles not the answer?
The second question that reasonably can be asked about Thornton’s Rule deals with the heat of combustion of hydrocarbon fuels. Since Thornton’s Rule does not deal with the rate of heat release of these fuels,
What if an unlimited supply of oxygen is available in a structure fire?
All scientists, or engineers, agree that the rate of heat release in a structure fire is limited by either
- the fuel surface area available to the fire, or by
- the oxygen available to the fire.
It is a scientific fact that the rate of heat release in structure fires is oxygen limited, or ventilation controlled, during most of their fire development. John A. Campbell, writing in the 17th Edition of the NFPA Handbook in his article “Confinement of Fire in Buildings”, states that:
“Considerable ventilation is required for a fully developed fire to burn at a fuel-surface controlled rate…Many, if not most, building fires will be ventilation controlled at least during the period of time in which containment is a consideration…The maximum intensity of a post-flashover room fires occur when ventilation is just sufficient to permit fuel surface controlled combustion.”
Except for the very beginning at ignition, a structure fire is ventilation controlled up to the time of maximum, or peak, intensity. Thus, except for the very beginning at ignition, a structure fire is ventilation controlled up to the time of maximum, or peak, intensity. Dr. Campbell cites as an example a 20 x 20 foot room with an 8-foot ceiling, with an exposed combustible surface of 800 square feet of ordinary combustibles. For such a room, over one fourth of the wall area would have to be open to shift to fuel surface area controlled combustion.
The amount of oxygen available does limit the growth in the rate of heat release. So for structure fires, the amount of oxygen available does limit the growth in the rate of heat release, and lead to incomplete combustion. The examples of structure fires cited by Fredericks in his article are perfect examples of this fact. Opening doors, or making other openings, lead to an increase in intensity of the fires because of the additional supply of oxygen made available. This is further proof of the validity of Thornton’s Rule as it applies to structure fires.
I think that Fredericks does grudgingly concede that Thornton’s Rule may have validity when he states
“Although these laboratory findings viewed independently may indicate that plastics pose no more of a hazard to fire fighters than the cellulosic materials of fires past…”
