Are fog nozzles not the answer?
Thornton’s Rule: Two Questions
- The first question that could reasonably be asked about Thornton’s Rule is this.
- Is there any difference in structure fires that might affect Thornton’s Rule?
Clayton Huggett of the National Bureau of Standards, Washington, D.C., examined this question in an article appearing in 1980 in FIRE AND MATERIALS magazine. Since almost all structure fires involve incomplete combustion, the question narrows down to what effect incomplete combustion has on Thornton’s Rule.
After examining this question in detail for various fuels and products of combustion, Dr. Huggett reaches the following conclusions.
- The rate of heat release in a fire can be estimated with good accuracy from two simple measurements, the flow of air through the fire system and the concentration of oxygen in the exhaust system.
- The heat release from a fire involving conventional organic fuels is 13.1 kj/gram of oxygen consumed with an accuracy of ±5% or better.
- Incomplete combustion and variation in fuel have only a minor affect on this result. Appropriate corrections can be made if necessary.
- The oxygen consumption technique of heat release measurement is adaptable to a wide range of applications ranging from small- scale laboratory experiments to very large scale fire system tests.
Notice the third conclusion that fire behavior in an actual structure fire has only a minor effect upon Thornton’s Rule. So this is conclusive proof that the validity of Thornton’s Rule as a scientific law that governs fire behavior in structure fires.
The black smoke referred to is proof positive that these fires involve incomplete combustion. This conclusion is a second reason why Frederick’s assertion about the heat content of plastics is irrelevant. The heat content of plastics is calculated assuming complete combustion. Since complete combustion seldom occurs in structure fires, their heat content is seldom fully released. The best evidence of this fact is the pictures and descriptions of fires given by Fredericks himself. The black smoke referred to is proof positive that these fires involve incomplete combustion. So there should be complete agreement on this significant fact about structure fires.
