that the use of water and chemicals in the unburned area was ineffective for intense fire intensity. Therefore, in this experiment, we waited until 3 meters deep area B was entirely involved in flames, and then inhibitors were sprayed, using a hand-held hose for each, for an area of 10 meters in width. This was done from both sides at 500 liters/min. The burning in area A was left untouched. When a flame appeared to spread through area B, minimal water was sprayed at 250 liters/min this time in order to extinguish the recurred fire in area B. This process was repeated until the flames closest to areas B disappeared.

#### 2.2.2 Structure of The Experiment Site made of Waste Materials

Waste wood materials used in the experiment consisted of a mixture of various construction wastes. An experiment site of the size H2m × W20m × L15m shown in Fig.7 was made. The first external surrounding row was made by stacking pallets vertically in order to keep the assembly from collapsing. Only pallets were used for 5 meters deep, including the suppression target area 3 meters deep, to facilitate the burning and water penetration. In the other area, approximately 80% pallets and 20% construction waste materials were mixed avoiding overlap.

The load density (fire load) of only pallets was calculated to be approximately $ 320 \, kg/m^2 $ (per plan area). The surface area of exposed wooden material, excluding the overlapped portions, was approximately $ 42 \, m^2/m^2 $ and the total surface area was $ 115 \, m^2/m^2 $ .

### 2.3 Results and Assessment

#### 2.3.1 State of Fire Spread and Suppression

Ignition was done at time as scheduled. A fire that started at the lower part of the assembly was pushed into the structure by wind, then appeared again in the upper surface 2 meters behind the edge. For a while, participants were anxious if the fire were burning unevenly, but soon the waste wood started to burn in a near perfect straight line along the entire 20 meters width. However, since the flames slanted to the leeward, the upper surface of the structure tended to ignite more quickly than the substantial lattice burning as they caught fire from radiation or from licking flames. Fires in such sections tended to extinguish automatically as soon as the flames were gone, so the burning did not necessarily continue. Although 3 meters deep suppression area was assumed in advance based on spray tests, we could not spray well this time as the blast of hot air blew to the leeward. We were soon forced to switch to watering the cribs horizontally. When the experiment finished, we had extinguished only the fire area 1.2 meters deep, which was approximately the width of a pallet, and regarded it as the substantial fire suppression area.

#### 2.3.2 Amount of Inhibitors Required to Suppress the Fire

Fig.8 shows the time and amount of water used in extinguishing and in suppressing process. The detailed time process are reported in Ref $ [5] $ . When the fires were extinguished, the amount of water and chemical inhibitor used was 5.4 t (in 10.8 min) and 3.6 t (in 7.1 min), respectively. From the extinction point until the end of the experiment (51.3 minutes after ignition, or 37.8 minutes after start of application), water and chemical inhibitor

Fig.8 Relationship between quantity of inhibitors used and time after ignition