Rate-of-flow formulas for larger fires
Before leaving Warren Kimball’s two books, I would like to consider two paragraphs that appear on page 82 of the first volume. They are:
Theoretically, if water is applied in the form of fog with maximum efficiency, one gallon of water will generate 223 cubic feet of steam. And if water could be applied with 90% of its theoretical extinguishing capacity utilized, one gallon of water per 100 cubic feet of fire area might generate sufficient steam to cool a fire within 30 seconds. Possibly the same rate of application evenly applied on material which had been burning, ordinarily might be sufficient to prevent reignition of flaming although in some fires more water is required for complete extinguishment than for blacking out flame.
Such theoretical considerations seldom work out under actual fireground conditions. It is seldom possible, using hose streams, to apply water evenly and efficiently over an extensive fire area without using considerably more water than might be necessary…A desirable factor of safety where extinguishment is to be chiefly by hose streams would appear to be at least three to one and in many cases a factor of four to one would be justified.
Kimball did not present any evidence or research to explain this theory, nor did he give the source. It is more than just a matter of courtesy to cite the source of your information. An author has a professional responsibility to do so. The numbers that Kimball uses are:
- One gallon creates 223 ft3 of steam
- 90% of extinguishing capacity
- Cool in 30 seconds
- 1 gpm per 100 ft3
There is no doubt where these numbers come from. These numbers are the result of the research done by Keith Royer and Bill Nelson at the Fire Service Institute at Iowa State University. The 1 gpm per 100 ft3 is the r.o.f. of the Iowa r.o.f. formula. The 30 seconds is the discovery made by Keith Royer that all confined structure fires could be controlled within that time. The 90% is the safety factor built into the Royer Nelson formula in case not all the water is converted to steam. Taking 90% of 223 gives 200 that is the constant used in the Royer Nelson formula.
Kimball evaluates this theory by using the following words.
- Might generate
- Possibly or ordinarily generate
- Seldom work
- Seldom possible
All the evidence and research about this theory contradicts Kimball’s judgments. These are vague and imprecise phrases. There is no evidence or research to validate any of these judgments. In fact all the evidence and research about this theory contradicts Kimball’s judgments. Royer and Nelson, beginning in 1953, burned more than 75 structures of all kinds. The structures were instrumented, and the data produced was analyzed very carefully. The conclusions reached were founded solidly upon scientific facts.
The worst statement that Kimball made is that this theory “seldom works” Just the opposite is true. The combination fog attack on a confined structure fire works always provided it is properly done, and that is easy enough in theory as well as in practice. Kimball states that it is seldom possible to apply water evenly and efficiently over an “extensive fire area”. This statement is partly true since it is more difficult to distribute water evenly and efficiently in an open fire. However, it is not impossible, and there is nothing to prevent one from trying even though you are only partially successful. In other words, Kimball does not justify the assertion that it is “seldom possible”.
