Do New York Nozzle tests prove anything?
In a series of three articles published in Fire Engineering in February and September 2003 and in February 2004, Jerry Knapp, Tim Pillsworth, and either Sean White or Christopher Flatley reported on a number of nozzles tests at Rockland County Training Center in Pomona, N.Y. The three articles are titled: “Nozzle Tests Prove Fireground Realities” .Reference to statements in these articles is made by article number and page number. For example, 1-72 indicates article 1, page 72.
The nozzle testing measured the air flow entrained by various types of nozzles that were held steady or moved in a certain way. This was done inside a compartment that was sealed to provide only one air intake and only one exhaust opening. It should be noted that none of these tests involved any fires or actual fire fighting. Also, while these tests did provide detailed information about various nozzles, none of the information obtained is really new. The fact that fog nozzles entrain more air than smooth bore nozzles has been known for a long, long time, as the authors recognize.
It is important to note that the amount of air entrained varies directly as the rate-of-flow. The authors cite William E. Clark’s book, Firefighting Principles and Practices, originally published in 1974.In another article in the National Fire Protection Handbook, Fifteenth Edition, (1981), titled: “Theory of Fire and Explosion Control”, Walter Haessler states that a fog nozzle at a 300 setting at 100 psi nozzle pressure induces 30 cfm into the water stream per gpm of flow. At 100 gpm that is 3,000 cfm. It is important to note that the amount of air entrained varies directly as the rate-of-flow. Haessler adds that this can be beneficial or harmful depending on its use. So you cannot assume that the fact that fog nozzles entrain more air automatically means that this is bad in any way.
First there is some data that is missing from these tests. With respect to fog nozzles, these authors state that data was collected from three separate fog nozzles. (1-74) A little later the article states that nozzles tested were “a low-pressure, constant gallonage fog tip and two automatic nozzles”. These nozzles were flowing at designed pressures and volumes. It would be helpful to know what nozzles were used and what the flow rates were. What are the designed pressures and volumes? As you know automatic nozzles maintain a constant nozzles pressure with varying rates-of-flow. The data for the smooth bore nozzle was provided. This nozzle was a 15/16 inch tip operating at 50 psi nozzle pressure and flowing 180 gpm. The hose layout was 100 feet of 1.75 inch hose.
However, a major weakness of the nozzle tests is the fact that this meter had a maximum limit Airflow was measured by a velocity/volume meter. However, a major weakness of the nozzle tests is the fact that this meter had a maximum limit of 2,000 cfm. (1-74). Thus, the actual air flow produced by these fog nozzles is not known. The authors estimate that the actual flow is three to five times the measured flow of 2,000 cfm, that is, 6,000 to 10,000 cfm. This is only a guess that is probably too high. This is higher than Walter Haessler’s data from the NFPA Handbook, Fifteenth Edition. Haessler’s data produces 5,400 cfm for 180 gpm flow for a fog nozzle at 300 with 100 psi nozzle pressure. Lacking any further data from the N.Y. nozzle tests, we cannot say that these numbers apply to the fog nozzles used. So we simply do not know how much air is entrained by fog nozzles based upon the author’s testing.
