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Abstract

Smoke flow inside buildings is a major cause of death in the event of fire. Presently, fire or smoke doors are used, together with smoke control systems, to avoid smoke flowing beyond the boundaries of the fire compartment. In this research, it is proposed the use of downward air curtains to stop smoke flow, which will not impair visibility in escape routes. The methodology followed in this research includes: (i) the development of an analytical model that relates the relevant characteristic quantities of a plane jet with the characteristics of the environment in which the fire develops, (ii) small scale experiments with saltwater modelling to assess the convective parameters that control the smoke tightness of the curtain, (iii) CFD simulations to assess the performance of a full scale air curtain near a fire source and (iv) fire experiments with a full-scale test specimen. In this paper both the analytical model and the saltwater experiments are presented. Test results confirm that vertical downward air curtains are able to avoid smoke flow through openings and show a good agreement with the theoretical model for predicting the minimum exhaust rate from the fire compartment. It has been shown that the exhaust flow rate depends on the air curtain flow rate and on the fluid heat expansion due to fire. Test results also make it possible to assess the minimum nozzle velocity to avoid smoke leakage.

4. Conclusions

In this paper, a set of equations has been developed, which describes the fire smoke tightness of a downward air curtain applied to an opening. Saltwater modelling was used to study the convective performance of this kind of flows and the experiments made it possible to draw the following conclusions: 1. Downward curtains may be successfully applied to avoid saltwater flow through an opening, but require exhaustion in the compartment. 2. Small scale saltwater tests show that the convective process described by the theoretical model is correct; therefore, this convective part of the model is expected to be applicable for obtaining smoke tightness of openings during fire events (adjustment of the model for fully turbulent flows will be required). 3. The test results show that the minimum jet velocity required to obtain the saltwater tightness of the opening may be given by Eq. (32). 4. Minimum saltwater exhaust flow rate from the compartment is given by Eq. (29), which agrees with Eq. (15) of the theoretical model. To obtain the minimum smoke exhaust flow rate, the term corresponding to smoke expansion due to heating must be added. Full-size experiments, including a prototype of the air curtain and using a fire source, will be developed to verify the smoke tightness model and to adjust the model for fully turbulent flows.