Hisahiro Takeda

Critical phenomenon in compartment fires with liquid fuels

The objective of this paper was to analyze in detail the behaviour of liquid-fuel compartment fires and to present precise information on the whole aspect of the fire phenomenon for use in modelling compartment fires. Two hundred experiments were conducted to research the behaviour of liquid-fuel compartment fires as a function of the ventilation parameter A H and compartment size, where A is the area of the ventilation opening and H is its height. Especially the influence of the compartment on the burning behaviour was investigated, using various size compartments, and the total aspect of this influence was presented. A critical phenomenon was observed for a pertinent condition of the ratio of compartment size to fuel tray size. This phenomenon, which is closely associated with the enhancement of burning rate and oscillatory combustion, may be substantially controlled by the dynamic equilibrium between the rate of fuel gas supply and the rate of air supplied by ventilation. A maximum burning rate may be obtained at an extreme value on this equilibrium. For methanol pool fires, the maximum burning rate was up to 7.2 times the open burning rate. The temperature within the compartment near the maximum burning condition was unexpectedly uniform and isothermal, due to fluctuation of turbulent flames and recirculation of gas. These experimental results were compared with previous research in detailed discussion.

Model experiments of ship fire

Ship fire behavior was investigated using a reduced scale enclosure with the ventilation opening in the center of the ceiling in order to establish a reasonable ship fire model. The experiments were carried out using a PMMA sample installed in the center of one wall or the floor in the enclosure. The opening had two major effects on the model ship fire. One is to hinder the development of a hot gas layer. Hot gas released from the flame zone tends to escape the enclosure through the opening without heating the upper part of enclosure. Thus the fire growth was greatly delayed when compared to ordinary compartment fires previously studied. The other effect is poor ventilation. The fire was strongly controlled by poor ventilation, so the burning rate was suppressed at a very low level. After the whole PMMA sample was involved, the flame moved from the PMMA surface to float in the gas phase and turned to a dark blue flame due to poor ventilation. However, the puffing (oscillation) of ventilation was not observed in any opening condition. This was an unexpected result. And the fire was rather steady even under this poor ventilation condition. Probably “bi-directional” flow could occur in the ventilation opening.

New modeling of liquid or thermoplastic pool fires in compartment

A new model of compartment fires with liquid or thermoplastic fuels was proposed, in which a new concept of combustion efficiency based on the mixing process of fuel gas and fresh air was considered. This new concept was formulated by the parameter “μ” related to the residence time and mixing time. A simple one zone model was used in order to demonstrate the effect of the mixing process. Theoretical results were in good agreement with the experimental results of methanol and PMMA compartment fires, and especially the scale effect of compartment was predicted successfully. Further the similarity law for this scale effect was investigated, and the upper and lower limits of flashver were decided by use of a new number “F.” This F number was found to be the key parameter for the prediction of compartment fire behavior.

Experimental investigation of fire behavior in a 1/6 scale dual opening compartment

Compartment fire experiments were conducted using a reduced scale model to investigate the fire behavior in a single room with two openings—a door and a window. The concept of the equivalent opening height was introduced into this paper to discuss this dual opening (door and window) effect on the compartment fire behavior, comparing it with single opening compartment fires. The flame spread rate on the compartment floor, the mass burning rate of the solid fuel and the flashover time were strongly influenced by this dual opening effect. These results were investigated in terms of the equivalent opening height, H eq . The flame spread rate on the compartment floor could be well correlated with the square root of the equivalent opening height. The mass burning rate of the solid fuel in the post-flashover fire was discussed in terms of the equivalent ventilation parameter, ( ( A H ) e q ), derived from H eq , where A is the area of ventilation opening and H is its height. The burning rate in the dual opening compartment was lower than expected. Flashover time was minimum at about ( A H ) e q = 0.01 ( m 5 / 2 ) , but became longer than that in the single opening compartment. An oscillatory phenomenon was observed in the dual opening compartment as well as in the single opening compartment for floor fires. This oscillation was a symmetrical puffing in the dual opening compartment, but it could not be observed for wall fires.