Uncommon thoughts about commonly used suppression equipment:
“The Missing Tip” and Optimum Handline Flow in 2 ½-inch Hose
Author: Dennis J LeGear, Capt. Ret. Oakland Fire, CA
(Part I) The Need to Address Maximum Deployable
Handline Flow in 2 ½-inch Hose
There has been a flood of information over the last two decades in the fire service in regards to nozzles and flow rates. This has mainly focused on initial flows in 1¾-inch attack handlines. The significance of flow rate has been overlooked in 2½-inch handlines. Many interrelated factors indicate the need to address optimum 2½-inch handline flow rate. Several are: modern hydrocarbon fuel loads, rapid fire development, energy efficient building construction, reduced staffing, and longer fire development before initial extinguishment efforts. Taken together, these factors push the fire service to address the need to deliver more water through the initial attack handline. This situation begs the question, has a potentially very useful nozzle and flow rate been overlooked in the 2½-inch handline. To simplify the discussion, smooth bore tips are used as template examples with an ideal nozzle pressure of 50psi. The argument has been scientifically made and proven for water application in either a straight stream from a fog nozzle or, preferably, a solid stream, and that this represents today’s best practice for stream selection for structural fire extinguishment. The goal of this discussion is to address optimum flow rate. To be sidetracked into a debate regarding 30 degree fog vs. solid or straight stream would hinder this purpose.
“A Quantitative Approach to Selecting Nozzle Flow Rate and Stream” parts one and two by Jason N. Vestal and Eric A. Bridge (Oct 2010, Jan 2011; Fire Engineering) illustrates just how many influences there are in nozzle/stream selection and flow rate. Vestal and Bridge cite National Fire Protection Association (NFPA) 1710 recommendations that the sum of the flow of the first two handlines placed into operation at a structure fire be a minimum of 300 gpm, and that the first handline flow a minimum of 100 gpm. They discuss, at length, several National Institute of Standards and Technology (NIST) studies regarding flashover research, heat release rate, and the heat absorbing capacity of streams. This article represents the most detail-oriented and exhaustive look at effective initial handline flows and stream selection that I know of to date.
Vestal and Bridge also discuss nozzle reaction, stream quality, reach, penetration, type of stream, and unintentional reduction of gpm flow with an emphasis on kinks in the line. Heavily touched upon is the ability of crews to effectively manage and deploy handlines, focusing on nozzle pressure and nozzle reaction. Vestal and Bridge also make a strong case, citing a litany of research and data, that most first-due urban engine companies are arriving at the time of greatest concern in fire development: slightly before, at, or just after flash over. Reading both parts one and two is strongly recommended; for they represent a definitive scientific examination of what first arriving companies are facing today at most common residential structure fires.
Vestal and Bridge conclude that a minimum initial fire flow of 160 gpm is needed in 1 ¾-inch hose and based on kinks that reduce attained nozzle pressure on the fire ground they recommend a 15/16-inch smooth bore tip. This is a logical choice even though the 15/16-inch smooth bore tip is rated at 185 gpm at 50 psi, as a few kinks and or poor line management can reduce flow to around 160 gpm. Most of the discussion regarding handlines in the modern fire service has been centered on 1¾-inch hose because that is the size of line used most often. Logically, if there has been such a need for greater flow in the 1¾-inch attack handline, one must also examine the flow rate of the 2½-inch attack handline.
The two common smooth bore tip sizes used on 2½-inch attack handlines are 11/8-inch and 1¼-inch. Their respective flows at 50psi nozzle pressure are 266gpm and 328gpm. For reasons stated below, this article shall propose the consideration of a 1 3/16-inch smooth bore tip, which provides a flow of essential 300 gpm at 50 psi. (This flow and nozzle reaction could be achived by a fog nozzle designed to flow 300 gpm at 50 psi)
In the author’s fire service career, three things have dictated the choice of initial attack handlines. If a handline could not properly suppress a fire, based on the below principles, then the engine company would start an aggressive master stream attack with the goal of moving towards an interior operation, if viable, after initial knock down. The three guiding principles in decision-making are as follows:
1) Critical flow rate. William E. Clark’s principle of “critical flow rate”, described as the minimum flow in gpm needed to extinguish a given fire, is discussed in detail in his book Firefighting Principles and Practices (34). One must make sure the handline will, at the minimum, meet the “critical flow rate”. Optimally, the actual flow rate will far exceed the “critical flow rate”. This will lead to rapid knock down, thereby having the most life saving and property conserving potential. He went on to say, “When a fire continues to burn after water has been applied, it is for one of two reasons. Either the water is not reaching the burning material, or it is not being applied at a sufficient flow rate”
2) Hydraulics. Is the handline pumped properly? Is the flow attainable with the length of the stretch and the size of the hose? Is there adequate reach and penetration? David P. Fornell, in his Fire Stream Management Handbook, addresses these issues.
3) Deployability. Once the two above criteria have been met, does the handline have a nozzle reaction manageable by a reasonable number of personnel? Can it be advanced while flowing and maneuvered through a structure with inherit obstacles such as furniture, doors, staircases, etc. Fornell described, at length, the advantages of having the lowest possible nozzle reaction while still maintaining an effective stream. Retired FDNY Chief Vincent Dunn also expressed the strong opinion that flows in excess 300 gpm were of large caliber and considered master streams, in which mechanical aid should be provided to maintain adequate control and safety. (Dunn 102)
In this article the color scheme in most tables dictates that red highlighting represents negative consequences. The green highlights represent positive consequences. The yellow highlighting represents the limits of flow and nozzle reaction for handline operations. Below is Table #1. It includes five commonly used smooth bore tip sizes and the proposed 13/16-inch smooth bore tip. The two most commonly deployed smooth bore tips are the 7/8-inch tip and the 15/16-inch tip. Both are used on 1¾-inch attack handlines. Both meet the NFPA 1710 recommendation of 300gpm combined flow if two lines are pulled, pumped properly, and devoid of significant kinks. Respectively, they produce flows of 161gpm and 185gpm at 50psi nozzle pressure. Nozzle reaction and flow for the chart were calculated by the equations given at the bottom. In addition, those flows have been reproduced via flow test, plus or minus 5gpm by hand-held pitot gauge.
PLEASE CLICK ON LINK BELOW for remainder of article and the ability to print. If your an Engine Guy, You need to read this. I appreciate Dennis taking the time to put it in print.
Article By; Dennis Legear, Retired Oakland Fire Department