Loss Prevention by the Use of Water - Where Do We Go from Here?
Publication Date: 2012-Jul-17
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Water in loss prevention: where do we go from here?
There are still things to be learned about this most useful fire-fighting agent. Further testing should be done to bring water-use recommended practices more closely into line with the reafities of hydrocarbon fires
R. H. Fritz and G. G. Jack, The M.
W. Kellugg Co., Houston, Texas
THE USE OF WATI".R to fight hydro- carbon fires deserves a new look.
There is obvious potential for fun- damental improvements. Water flow rates and application mode are the rigbt tbcal points. So we started our study with the paragraphs of
NFPA-15 devoted to (extinguish- ment and exposure protection).
A start from scratch. The refer- ences used to establish water-flow or coverage rates were not available.
We thereh)re first took an analytical appruach to determine what the theoretical water rate should be, based on its known playsigal proper- ties and a hypotbetical fire sceuario.
If a burning hydrocarbon pool is cooled below the ignition tempera- ture of its vapor, the fire will be ex- tinguished. Therefore, the water rate required to extinguisb a fire
Toward better water standards...
Caught in a forest fire, an animal will jump in a lake to protect itself from radiant heat. With a few ex- ceptions, industry uses a similar superficial approach. Advances have been made in understanding how water can best be used. And yet, superior talent and research money needed to advance progress has been hard to come by. In fact, much of the HPI's use of water in loss prevention focuses on NFPA-15. After reviewing NFPA-15, these authors conclude that, like the animals, we are still "jumping in the lake" for a solution to the problem.
ueed never exceed the rate which will cool the hydrocarbon below this temperature. Factors such as water droplet size and velocity do affect the water required to reduce the
temperature to lhis level, aod some data are availablê,ŵhich relate these factors to extinguishment, NFPA-15 stipulates neither the spray uozzle location nor the drop- let size or velocity, but only the ele- ments contributing to extinguish- ment. A water rate based on total energy absorption was thus consid- ered.
If water is applied from an over- head spray system and the drop|et size and velocity are such that all the water is evaporated before it reaches the liquid surface, then the water must absorb the total beat of combustion. The energy to be ab- sorbed was calculated fi'om the lin- ear regression rate of the liquid sur- face. This rate depends upon the back radiation from the flame into the pool and the la~ent beat of va- porization of the liquid at the pool surface,a Assume the burning hy- drocarbon has a specific gravity of
0.85, a heat of combustion of 18,000 Btu/lb and a la~ent heat of vaporiza- tion of 160 Btu/Ib, then the linear regression rate is approximately
0.33 in./min tbr the pool size se- lected. Assume also complete com- bustion. The water application rate required to reduce the products o...