Fire protection systems in areas which are susceptible to water damage or where there is a significant weight penalty for water-based systems have historically used halon-based chemical fire suppression agents such as Halon 1301 (CF3Br). Halons are so effective at fire suppression that in the past it was not necessary to evaluate other options. However, hatons are also powerful ozone-depleting agents due to their ability to transport bromine into the stratosphere. This attribute of halons led to the ban of their manufacture in the industrialized world by the Montreal Protocols starting in 1995. Despite the urgent need to find an alternative replacement, no environmentally acceptable chemical agent as effective as Haton 1301 has been identified.
The deficiency in replacing chemical agents has lead to an increasing interest in fine water mists as fire suppressants since mists pose no adverse environmental or health issues and they offer the promise of meeting the requirements of protecting both water- and weight-sensitive areas due to the low requirements for total water flow, typically about one order of magnitude less than conventional water sprinklers. Water mist technology has already been found effective for extingushing fires in shipboard machinery, aircraft cabins, and computer rooms.
Unfortunately, there is to date no widely accepted interpretation of the critical concentration of droplets or the optimum droplet size required to suppress a flame, or more importantly, of the fundamental mechanisms involved in flame extinguishment by a water mist. One of the main obstacles to obtaining such understanding is the difficulty of providing a simple, well-characterized experimental setup for the flame front/water mist interaction. A weightless environment provides an ideal place to study this interaction by eliminating the distorting effects of gravity on the generation and prolonged suspension of a uniform concentration of droplets and on the complex flow patterns induced by natural convection between the flame front and the water droplets. The objective of the Water-Mist Fire Suppression experiment (Mist) is to provide information on the flame-front/water-rnist interaction by conducting a series of experiments on the Combustion Module (CM-2) facility in the STS-107 mission of the Space Shuttle. The results from these tests will be used to assess the feasibility of using water mists as the new generation of fire suppressants on earth as well as in spacecraft systems. In preparation for the orbital flights, numerical simulations and low-gravity ground experiments have been conducted to obtain the data necessary to define the test matrix and the important technical issues for the spacecraft experiments.
McKinnon, J.T., Abbud-Madrid, A., Riedel, E.P., Gokoglu, S., Yang, W., Kee, R.J., The Water-Mist Fire Suppression Experiment: Project Objectives and Hardware Development For The STS-107 Mission, Sixth International Microgravity Combustion Workshop, NASA Glenn Research Center, Cleveland, OH, CP-2001-210826, pp. 105-108, May, 2001.