Szerkesztővita:Dr.Szocs/Tároló
Új téma nyitásaSTORAGE TANK FIRE FIGHTING Comparison method of storage tank fire extinguishing technologies.[szerkesztés]
Instead of subjective opinions or anecdotal information, fire protection engineers require hard data for evaluation of fire extinguishment methods.
The most effective tool for objective comparison is the use of the foam application efficiency factor.
TERMINOLOGY[szerkesztés]
The Foam Application Efficiency Factor is a figure of efficiency that shows how effectively the foam was used during the fire extinguishment process. It sums up the characteristics of the examined fire extinguishment technology.
Fire Extinguishment Technology denotes the chosen foam quality, the foam application rate and the foam introduction method together.
Foam Quality is determined by the chemical and physical properties of the foam solution and the method of foam forming (foam generating).
Foam Forming Method may be aspirating, non-aspirating and self expanding foam system.
Self-Expanding Foam is prefabricated foam that is stored under pressure in a vessel till the fire fighting.
The Surviving Foam Volume
When the fire extinguishment is successfully finished, some part of the generated total foam volume is “surviving”, the rest is “lost”.
One can measure the foam blanket thickness then calculate the remainder of the foam volume in the storage tank at the moment of extinguishment.
Vsurv = F * haverage (1)
The value of Vsurv maybe measured under experimental conditions.
The Total Foam Volume
That is all of the foam that was generated by all means during the fire extinguishment process.
Vtotal = Iv * text (2), where
Iv is the foam volume flow rate [m3 / min], text is the duration of the foam generation [min].
The Foam Application Efficiency Factor
This figure shows how effectively the given technology utilizes the foam.
η = Vsurv/ Vtotal * 100 [%] (3)
η = effectiveness of foam usage [%]
EXPERIMENTAL FORMULA FOR DETERMINING η[szerkesztés]
η = F * haverage / Iv*text [%] (4)
SEARCHING FOR OPTIMUM EFFICIENCY[szerkesztés]
Three series of experimental measurements are needed in order to determine the optimum of η.
First, the effect of the foam application rate has to be tested.
At low application rate range, the value of η is 0. This means that with the given application rate the fire continuously consumes the introduced foam, therefore the fire cannot be extinguished.
Using this low application rate, (below the critical application value), it is not possible to extinguish the fire, text = ∞.
Secondly the different foam introduction methods must be tested, while the foam quality is constant.
Thirdly, a series of tests of the behavior of different quality foams must be tested at the proper application rate and the foam introduction method that gave the best performance during the first and second tests.
The value of η is 100% if the introduced foam forms the foam layer without any losses, using its full volume. This might happen in cold foam spread tests, using a very good quality and stable foam, which has a very low rate of spontaneous self-brake-down (long half drainage time).
REFERENCES[szerkesztés]
Dr. Szocs, Istvan: Research and Development of Environment Friendly Storage Tank Fire Fighting Technologies 2005, Zrinyi Miklos National Defence University, Doctorial Thesis.