consumed for fire recurrence prevention amounted to 1.9 t (in 7.5 min) and 1.0 t (in 4.0 min), respectively. In other words, the amount of chemical inhibitor used in the extinguishing process was 67% that of water and 53% in the recurrence prevention process and the total average was 63%. Through the whole suppression process, while water was periodically and intermittently required, chemical inhibitor made it possible to discontinue application for 18.4 minutes.

In the previous experiments in part-1 using large cribs, more chemical inhibitor was consumed than water to extinguish the fire. This difference in required amounts in extinguishing process demonstrates different mechanisms due to great emphasis on the scale of the fire, i.e., extinguishment and suppression.

#### 2.3.3 Comparison of Effectiveness: Water and Chemical Inhibitor

Based on the tragic experience of lack of water during that earthquake, our main goal was to stop the spread of fire with as little water as possible.

The 18.4 minutes intermission by chemical inhibitor suppression process was 1.6 times (18.4/7.1-1) longer than the 7.1 minutes required to extinguish the fire. If the application rate after extinguishment to stop the recurrence of fire was at 500 liters/min, chemical inhibitor can complete all process in 9.1 minutes and it must be discontinued for the remaining 28.7 minutes after application started. Since the potential of penetration is high, the chemicals must be retained.

While the fire fighters need to be pasted along the entire 10 meter width with water, the use of chemical inhibitor makes it possible to operate in 42 meters width, 4.2 times $ (28.7/9.1 + 1) $ more efficient. The dynamic of the suppression of fire recurrence process indicates the efficiency must become larger as the extent of fire grows.

"The necessary treatment time for fire suppression " might be different because it depends upon definition where to point the time. In our experiment, we defined it as the time up to 51.3 minutes after ignition when the possibility of fire spread became small. Generally, fire continues burning with flames for 20 to 30 minutes, then the glow begins but easy to control. Thus, the selection of inhibitors and treatment method must be decided in accordance with this.

A condition that would be effective in suppressing the spread of fire enables swift operation and deployment of fire forces. Although the amount of water required in a given area might not differ much, chemical inhibitor is highly effective in preventing fire recurrence. If the burning area is left untouched in a real situation, fire will spread relentlessly in a short time. This characteristic of chemical inhibitor means that fire fighters are not required to remain in the extinguished area and enables to move to other locations to do their jobs efficiently.

The pitch (average treatment speed, interval) of water and chemical inhibitor during the fire recurrence prevention process is shown in Fig.8. If only surfactant solution is used as inhibitor, the pitch may be lengthened to some extent than water although the slope may keep the same. The difference in slope is thought as the effect of added MAP.

#### 3.2.4 Summary

(1) When the effects of chemical inhibitor and plain water were compared for suppressing the spread of fires in terms of required amount of water, chemical inhibitor remained close to 60%. This figure, however, is seen as a function of scale, the efficiency should be greater as the scale of fire grows.

(2) Chemical inhibitor was several times more effective than plain water in suppressing the fire spread on the lee side under high intensity fire conditions.