Are fog nozzles not the answer?
This is where fire departments have gone astray. Using too much water causes massive thermal imbalance problems. In the attempt to solve these problems, new tactics and strategy were devised, tactics not based upon any scientific foundation. It is easy enough to misuse a fog nozzle. Open up your nozzle to full flow, and you will flow entirely too much water for your smaller fires.
So what is the answer to these problems? The answer is that fire fighters must learn how to properly use fog nozzles. After 50 years, it is about time to do so. While Fredericks is undoubtedly right in saying that misuse has occurred, I am not convinced that all fire departments do so. Many fire departments do make effective use of fog nozzles., and have done so in the past.
One important question remains in this discussion of the proper use of fog nozzles.
How is the right amount of water determined?
The answer to this question is postponed until an analysis of Part Two of Fredericks article.
PART TWO
Fredericks cites two things present today as justification for this statement. Part Two begins with an analysis of the modern fire environment that Fredericks says is “far more hostile and unpredictable than it was in the 1950s”. Fredericks cites two things present today as justification for this statement.
Plastics
Energy-efficient windows (EEW)
First, plastics. Fredericks states that the heat of combustion of plastics is, on the average, about twice that of ordinary cellulosic (wood based) fuels. Then he proceeds to a discussion of Thornton’s Rule that was presented in a 1997 article in FIRE ENGINEERING. Fredericks seems to indicate that Thornton’s Rule applies only to “laboratory findings”, or is valid only from a “theoretical, laboratory perspective”.
Fredericks does not state Thornton’s Rule, so before proceeding I think that it is a wise idea to know what we are talking about. DR. Vytenis Babrauskas, author of Appendix A in the 17th Edition of the NFPA Handbook, states Thornton’s Rule as follows.
“Recently, however, increasing engineering use is made of the observation that the heat of combustion per kg of oxygen consumed is nearly constant for most organic fuels, It can be shown that the value of
Δhl/ro = 13.1 MJ/kg for O2
is near constant.”
Only recently has the oxygen consumption method (based upon Thornton’s Rule) been used as the most convenient and practical means of conducting laboratory experiments. Thornton’s Rule existed long before this was done.
