Vent Size Effect on Self-extinction of Pool Fire in a Ceiling Vented Compartment

Abstract

The self-extinction behavior of N-heptane pool fire located in a ceiling-vented compartment is investigated experimentally. The compartment is a rectangular chamber of 1.00 m (L) × 1.00 m (W) × 0.75 m (H) with only a ceiling vent with sizes between 0 and 0.490 m × 0.490 m. Three sizes of pans with the diameters of 0.10 m, 0.141 m and 0.20 m were at the center of the compartment with similar initial fuel thickness. The impact of vent area on fuel consumption and flame extinction time is mainly examined as the result, meanwhile the local oxygen concentration near the fire source and the mass loss rate of fuel are also reported. The result shows that the pool fire burning behavior can be classified into four types according to the ceiling vent size. The extinction time te of first type of fire nearly equals to the closed condition, while it grows sharply with vent size for the second type of fire. When the fire belongs to the third type, te decreases with vent size due to the growth of fuel burning rate, and for the fourth type, te keeps constant again with the well-ventilated/condition. Based on species concentration, the ceiling vent size can be normalized into (ρ∞g1/2Av5/4)/(mF”AF). An empirical exponential relationship between self-extinction time ratio and the dimensionless ceiling vent size was proposed, and the results well ntegrate all the profiles of self-extinction time of different fire sizes.