Are fog nozzles not the answer?
However, the fundamental principle in all of science is that a particular chemical process is invariant no matter whether is occurs in a laboratory fire or in a structure fire, or whenever it occurs—now or 50 years ago. Thus Thornton’s Rule is valid for the hydrocarbon air diffusion flame process (that we call fire) whenever and wherever it occurs.
There is a second important fact. Notice that Babrauskas’s statement refers to the “heat of combustion” of fuels, and that the heat of combustion is constant, or a near constant, for almost all hydrocarbon fuels. So plastics, as well as cellulosics, all release the same amount of heat per unit of oxygen consumed. Thus the greater heat content of plastics is irrelevant for determining the rate of heat release for structure fires.
This conclusion is reinforced by Dr. Babrauskas, in his article “Burning Rates” in the SFPE Handbook of Fire Protection Engineering (2nd Edition), when he states:
“If a correlation is simply attempted with the total specimen fuel load (heat content) long considered in building codes as a good predictor of fire hazards, Figure 3-1.7 shows that absolutely no correlation is achieved.”
In plain English, Fredericks argument is absolutely worthless, and is not accepted in fire engineering today. Notice the strong language, “absolutely no correlation is achieved”. In plain English, Fredericks argument is absolutely worthless, and is not accepted in fire engineering today.
This conclusion should be qualified for certain plastics. Bert Cohen in his article “Plastics and Rubber” in the l7th Edition of the NFPA Handbook, states that:
“Plastics other than cellulose nitrate are classified as ordinary combustibles…Nevertheless, unusually high burning rates, unusually heavy smoke production, and a higher heat content per unit weight are responsible for greater concern about the fire behavior of certain plastics”.
Many plastics are treated with inhibitors that retard flame spread. It is a fact worth noting that many plastics are treated with inhibitors that retard flame spread and increase ignition temperatures. In view of this, Cohen concludes that:
While there are no special hazards for most accepted uses of plastics, some exhibit burning characteristics that are considerably different from those encountered with the more traditional cellulosic building materials.”
So this narrows Fredericks argument down to a limited number of plastics. What is the best solution to the problem? Certainly there is no justification to abandoning fog nozzles. A more appropriate and direct solution is to identify the hazardous plastics, fix them, or better yet ban them.
