Strategically delivering water to burning commodities is one of the most effective and robust means of suppressing accidental fires. Because of its unparalleled performance and versatility, water-based fire suppression is used extensively. Although the basic cooling (gas and surface) and O2 displacement mechanisms associated with water-based fire suppression are easy to identify, developing detailed models to support fire suppression analysis remains a high challenge.
It is understandable that progress to establish analytical capabilities for evaluating suppression performance has been slow. However, the absence of this analytical capability has locked the fire safety industry into a costly empirical spiral that inhibits innovation.
In fact, water-based fire suppression could be viewed as the quintessential fire problem (i.e., water vs. fire). Historically, empirical observation and full-scale testing have been the answer to this problem, but as the practice of fire protection engineering develops beyond prescriptive codes and standards toward performance-based design, there is a need to equip researchers and designers with analytical tools based on fundamental knowledge to address the fire suppression problem. In addition to the need for fire suppression model developments, an experimental database would be useful to provide a comprehensive data set and knowledge base to promote a more detailed and quantitative understanding of fire suppression phenomena by fire researchers and practitioners.
It should be noted that analytical tools are readily available for the design of water supply systems to ensure adequate flow to fire suppression nozzles. At the same time, analytical tools based on Computational Fluid Dynamics (CFD) have been widely adopted for evaluating fire behavior. Yet, at the center of the fire suppression problem is, of course, the nozzle of the fire suppression system, the "business end" of the system, so to speak. Following this point, a variety of fire suppression nozzles have been developed to contend with a myriad of fire scenarios. Despite their variety, these nozzles (and systems) are all designed with the goal of suppressing the fire by strategically dispersing the water. Strategies vary from surface cooling by transient localized flooding (hose and monitor systems), surface cooling by distributed uniform surface wetting (sprinkler systems), to gas cooling and dilution by gas wetting (mist systems).
Although the basic suppression strategies are straight forward, the underlying physics governing spray initiation (i.e.,atomization) and the associated nozzle discharge characteristics are poorly understood. As a result, engineering analysis of these devices is riddled with empiricism – from design conceptualization to performance evaluation. Unfortunately, lack of knowledge regarding spray generation has limited the utility of computational tools for fire suppression problems. Admittedly, a number of problems (e.g., pyrolysis models for dry and wet materials) need to be solved before predictive capability of water-based fire suppression is realized. Nevertheless, the ability to accurately predict the spray generated for fire suppression is an obvious and unquestionable requirement as well as a natural starting point.
The uncertainty in defining the initial spray and related discharge characteristics makes analysis of spray dispersion and the associated fire suppression performance difficult from the very beginning. A number of recent advancements in the measurement and analysis of fire suppression sprays have been communicated in the literature.1-5 These experimental and analytical advancements have provided clarity in characterizing these complex sprays while creating critical pathways for the development of computational-based approaches to support the design and evaluation of water-based fire suppression systems (Figure 1). In this body of research, it is the author's intention to demonstrate how advanced measurements and analytical capabilities can be used to achieve detailed descriptions of fire suppression sprays useful for insight, model development, and engineering analysis.
One could imagine, for example, a significant first step in the analysis of fire suppression would be to develop predictive capability for the volume flux of water delivered to a target area or region. Accomplishing this goal would not only be scientifically noteworthy, but practically useful because much of the fire suppression engineering practice and even regulation is based on the delivery of critical volume fluxes of water. It is the author's hope that recent advancements in sprinkler spray research, conducted by the author and others, will demonstrate that complex sprays do yield themselves to quantitative treatment and that this progress will inspire similar developments in other fire suppression applications.
Andre Marshall is with the University of Maryland.
- Ren, N., Blum, A., Zheng, Y., Do, C. and Marshall, A. "Quantifying the Initial Spray from Fire Sprinklers," Fire Safety Science – Proceedings of the Ninth International Symposium, International Association for Fire Safety Science, London: 2008.
- Ren, N., Blum, A., Do, C. and Marshall, A., "Atomization and Dispersion Measurements in Fire Sprinkler Sprays," Atomization and Sprays, (2009), Vol. 19, p. 1125 -1136.
- Zheng, Y. & Marshall, A. "Characterization of the Initial Spray from a Jet In Crossflow," Atomization and Sprays, (2011), Vol. 21, pp. 575-589.
- Ren, N., Baum, H., and Marshall, A. "A Comprehensive Methodology for Characterizing Sprinkler Sprays," Proc. Combust. Inst., (2011),Vol. 33, pp. 2547-2554.
- A. W. Marshall, "Unraveling Fire Suppression Sprays," Fire Safety Science – Proceedings of the 10th International Symposium, International Association for Fire Safety Science, London: 2011.