Method for comparison of different fire extinguishing technologies – Part 3.
How can we improve the success rate of the Storage Tank fire fighting? We have good news for the Fire Experts: we have the opportunity for positive influence on the measured efficiency by changing the parameters of the tank fire fighting.
The optimum performance we can achieve in two steps:
- to find the best technology, then
- to choose the most effective foam material that has the highest synergy effect with the best technology.
What points shall be examined, and improved?
- The most effective, and still economic foam solution application rate
- The possibly shortest burning time, to prevent air pollution
- The sufficient foam blanket thickness we would like to produce
- The most advantageous foam introduction method (geometric shape)
- The appropriate arrangement of foam supply, especially in extreme climatic conditions (arid and polar territories)
Let us begin to examine the influence of the above mentioned points to the η
The strongest influence was found at the Foam Solution Application Rate. Of course we may talk only about the foam that was introduced to the inside space of the tank. The aiming loss (at over the top applications by foam canons) do not have to be considered. This waste is decreasing the efficiency.
The higher the application rate, the higher the efficiency is.
We can understand the reason of this phenomenon.
Figure 1. shows the function of η versus the actual application rate.
The higher the application rate, the faster the foam front movement towards the center of the hydrocarbon surface will be. Faster movement leaves less time for the fire to damage, to “eat” our foam.
The efficiency- vs- application rate has two significant characteristic points.
At low application rates we find the “critical application rate“. Below this value the extinguishing time is infinite, in other words we cannot extinguish the fire. The fire continuously destroys all of the foam that is introduced.
The application rate is too low, the situation is hopeless.
The second one is the “inflection point“, that helps us to find the optimum application rate. The derivative of the curve shows maximum at this point, and that determines the most effective range of foam application rate.
Why is the burning time so important?
TOTAL BURNING TIME = PREPARATION TIME + EXTINGUISHING TIME
- PREPARATION TIME
Detection, alarm, approaching the scene, assembly
Depends on the applied strategy:
Fixed, semi-fixed, or mobile
- EXTINGUISHING TIME
Depends on the applied extinguishing technology and techniques
Critical intervention time for 40+ m diameter tanks:
DELAY FROM IGNITION TO FIGHTING AND THE CAUSED DAMAGES
- 0 – 3 minutes: minor damages
- 3 – 10 minutes: damages in cables and seal fabrics
- Burning > 10 minutes: deformations, tank to be taken out of operation, severe damages
We shall keep the burning time as short as we can.
The best solution is to engage fast response fixed systems.
We, and the authorities are sensitive for environment pollution. The possibly shortest burning time prevents the air pollution.
The fire of a 80 000 m3 Hydrocarbon Storage Tank produces 14 tons of black carbon.
IN EVERY MINUTE!
To be continued on 31. March, 2014.