Fire Safety Science Digital Archive

A series of fire suppression experiments was conducted to evaluate the efficacy of physical scaling of water mist suppression of solid combustible fires in enclosures. Wood crib fires were used in this evaluation. The experiments were conducted in a 1:3 scale ratio based on the Froude-modeling-based scaling relationships. The parameters considered in the evaluation were: enclosure size, door opening size, water mist spray condition, fire size, fire location and fire-shielding condition. The two geometrically similar enclosures measured 1.22 × 1.22 × 1.22 m and 3.66 × 3.66 × 3.66 m. Two door opening sizes for each enclosure were tested to evaluate the ventilation effect: 0.30 × 0.61 m high and 0.61 × 0.61 m for the Scale-1 enclosure, and 0.91 × 1.83 m high and 1.83 × 1.83 m for the Scale-3 enclosure. Two wood cribs were configured for each enclosure to produce maximum free-burn fire heat release rates of 22 and 47 kW for the Scale-1 experiments, and the corresponding maxima of 340 and 740 kW for the Scale-3 experiments. Besides matching the peak heat release rates according to the scaling requirement, an attempt was also made to scale the free-burn fire growth developments. The two water mist sprays used in the previous suppression studies for gas and pool fires were employed in the present study. In each enclosure, nine ceiling-mounted nozzles were arranged in a 3 × 3 pattern with equal nozzle-to-nozzle and nozzle-to-wall spacing. The experiments showed that the fire development during free-burn and water mist application in general could be reasonably scaled for the wood crib fires in enclosures, but more sensitive to the scaling imperfection of water mist sprays as compared to the case for gas and pool fires. The thermal environment inside the enclosure was also reproduced reasonably well in different scales during water mist application as expected from Froude modeling.