Measurements of Smoke Behavior in Staircase

Abstract

In order to investigate upward smoke spread behavior in stair shaft, full-scale experiments were carried out for various combinations of opening conditions and location of fire source. Cross sectional area of shaft was 17. 3 m² and height was 25. 6 m. From experimental results, upward smoke spread was qualitatively classified into three groups. The first is the case with no vent above fire source. In this case, smoke rose up slowly by being mixed with air in upper part due to turbulent diffusion. Temperature decreased exponentially as height resulting in very small increase of temperature at the top of shaft. CO₂ concentration was gradually increased even at the top of shaft. The second is the case with a vent above fire source. In this case, rising velocity of smoke was large in comparison with the case with no vent due to stack effect. Temperature decreased as height similar to the case with no vent above fire source. However, CO₂ concentration above fire source was uniform. Flow resistance coefficient per story was estimated as about 29. 1. Finally, in case that fire source located at the top floor, downward smoke diffusion was observed. The principal polluted region expands to about half of floor height.