Better Use of Water for Fire 

Suppression 

E.J.P. Zegers, P. Fuss, J.W. Fleming, B.A. 

Williams, A. Maranghides, and R.S. Sheinson 

Chemistry Division 

Introduction: Environmental concerns over the 

past decade have provided new impetus for expanding and improving the use of water for Navy fire protection. Traditionally, fire suppression in selected Navy 

shipboard compartments has been provided by Halon 

1301 (CF,Br), whose production has been banned 

in the United States and other developed countries 

because of its depletion of stratospheric ozone. Nonbrominated fluorocarbons, while ozone safe, are less 

effective, carry space and weight penalties for Navy 

platforms, are significant global warming agents, and 

produce toxic hydrogen fluoride (HF) gas in extinguishing a fire. 

Water is perhaps the oldest firefighting agent, but 

it can be difficult to implement in many situations; 

because, unlike Halon, it is a liquid. Droplet size, transport, evaporation rate, and suspension time are all 

critical parameters in determining the effectiveness 

of a water-based suppression system against a given 

fire threat. Although water-based fire suppression has 

been the subject of empirical tests for many years, 

the interaction of liquid water droplets with flames 

has received surprisingly little systematic study in laboratory settings. The identification of the factors important in determining water’s effectiveness as a fire 

extinguishing agent is a prerequisite for better implementation. The Navy Technology Center for Safety 

and Survivability has a coordinated program, combining fundamental laboratory studies of water/flame 

interactions with real-scale fire tests, to provide the 

Navy with implementation particulars for water mistbased fire protection systems. 

Water Mist Fire Suppression: Traditionally, 

water has been used as a firefighting agent in the 

form of relatively large drops. Typical sprinkler systems produce water drops having diameters on the 

order of a millimeter. Such droplets are useful at cooling smoldering surfaces, but are relatively ineffective 

at suppressing combustion of gaseous or liquid fuels. 

The large size and low surface area/volume ratio 

means that relatively little of the water evaporates in 

the length of time the droplet spends near the fire. 

Thus the cooling provided by the water evaporation 

and dilution of the oxygen and fuel by the resulting 

water vapor are not efficiently achieved. For this reason, most water-based fire suppression systems use 

more water than would be needed if the thermal and 

dilution effects could be properly utilized. 

Fine water mists, having diameters of 200 microns or less, circumvent these difficulties by allowing better droplet vaporization, but they are more 

difficult to produce. The tradeoffs between efficiency 

and engineering difficulties in droplet generation and 

delivery must be determined. 

Laboratory Studies: In assessing the applicability of water mist fire suppression systems, one must 

answer the question “how effective can water be 

under ideal conditions?” We have investigated water 

mist inhibition and extinguishment in two types of 

laboratory flames and find that, under suitable conditions, water mist can be as effective as Halon 130 1. 

Figure 11 shows data taken in a nonpremixed 

propane/air counter flow flame, to which suppressants (Halon and water droplets of various sizes) 

were added to the air stream.’ Addition of the suppressant to the air stream is the most typical scenario for most fire threats. The extinction strain rate 

plotted in Fig. 11 is a measure of flame stability. Effective fire suppressants lower the extinction strain 

rate as shown. Data for water and Halon, plotted on 

a mass basis, show that over the range of droplet 

sizes tested (20 to 50 microns), smaller droplets are 

more effective. Furthermore, water droplets of 14 

and 30 micron diameter are considerably more effective than Halon, while droplets of 42-micron diameter are comparable to Halon in extinguishing this 

particular flame. 

The degree of burning velocity reduction is also 

an indication the effectiveness of a fire suppressant. 

Figure 12 shows data on the burning velocity of 

premixed methane/air flames containing submicrometer diameter water These droplets are 

small enough to completely evaporate during the short 

residence time (approximately one millisecond) in the 

flame region. In this type of flame, the effectiveness 

of the submicron water droplets is comparable to the 

findings for Halon 1301 in Refs. 2 and 3. Comparison of the water data to measurements with nitrogen 

and CF,, two well-studied gaseous agents that are 

chemically inert and inhibit combustion by cooling 

and dilution of the available oxygen, indicates that 

the expected effect of water evaporation is achieved 

in this environment. 

Achieving the maximum effectiveness of water 

in real fire scenarios is more challenging. The small 

drops that are most effective in the flame may evaporate before they reach the fire, while larger drops 

may be too large to be entrained in the air flow and 

get to the fire, especially for obstructed or cluttered 

areas. The key issues to understand are mist drop 

size and distribution in the protected space. 

‘k ’ 

Toward Implementation: Realistic large-scale 

tests are currently underway at NRL’s Chesapeake 

Bay Detachment to develop water mist system implementation solutions to protect Navy shipboard flammable liquid storerooms against different fire threat 

scenarios (Fig. 13). These tests combine a powerful 

array of instruments to determine droplet sizes, velocities, and number densities at various locations in 

the test compartment, as well as the in situ measurement of oxygen dilution by the evaporating water 

mist, for truly understanding suppression by water 

mist. The detailed suppression mechanisms studies 

in laboratory flames combined with well instrumented 

full-scale studies is providing design guidance to the 

Navy for implementing water mist as an effective and 

reliable Halon alternative. 

[Sponsored by SERDP and NAVSEA] 

References 

E.J.E? Zegers, B.A. Williams, R.S. Sheinson, and J.W. Fleming, 

“Dynamics and Suppression Effectiveness of Monodisperse Water 

Droplets in Non-Premixed Counterflow Flames,” Proceedings 

of the Combustion institute 28 (2000) (in press). 

’T. Noto, V. Babushok, A. Hamins, and W. Tsang, “Inhibition 

Effectiveness of Halogenated Compounds,” Combust. Flame 

D.J. Parks, N.J. Alvares, and D.G. Beason, “Fundamental Flamespeed Measurements in Combustion Gases Containing CF,Br,” 

Fire Safety J. 2(4) 237-242 (1980). 

112( 1-2) 147-160 (1998).