Experimental And Numerical Study On The Characteristics Of Fire Natural Smoke Extraction In Ultra-high Z-shaped Atrium

With people’s demands for full development of green building, more and more architectural atriums adopt the scheme of natural smoke extraction in the design for smoke control. The structure of the Z-shaped atrium is relatively special which differs from the ordinary closed atrium, setting opening through outdoors on one side of bottom of atrium, which called natural air inlet, also on the other side of top which called natural air outlet. The consistent of the two layers opening platform and vertical atrium is similar to the Z-shaped atrium flow tunnel of smoke. The atrium space is connected with outdoors, its internal air can exchange with outside, it can get appropriate fresh air outside constantly while exhausts the air within the atrium to the outdoors.The atrium which over12meters is called the ultra-high Z-shaped atrium. Conventional mechanical smoke extraction methods do not fully meet the actual demands in case of fire safety for ultra-high atrium. There are many influencing factors on the inside and outside of ultra-high atrium, using the natural smoke extraction whether can ensure the fire safety needs study on the characteristics of natural smoke extraction of ultra-high Z-shaped atrium. In this paper, based on investigations upon research status of atrium smoke extraction, a study on a ultra-high Z-shaped atrium in full-scale fire experiment and numerical simulation was conducted. Firstly, the building structure and external environment such as weather condition are considered, formulating feasible full-scale fire experimental program. Secondly, the full-scale fire experiment in field is conducted from the smoke temperature, smoke layer height and the concentration of carbon monoxide which analyzed on the characteristic of atrium natural smoke extraction. Finally, we adopt the numerical simulation method to have further study on the natural smoke features of ultra-high Z-shaped atrium especially studying on the influence of characteristics of natural smoke extraction on the aspect of atrium height. According to the experiment of the atrium smoke flow situation, hazard occurrence time was defined as the time value of the designated floor smoke emerged which causing people in danger. Thus, we discussed the relationship between atrium height and hazard occurrence time.Under the condition of this paper, we draw the following conclusions:(1) Different from the traditional closed atrium, ultra-high Z-shaped atrium can exhaust the fire smoke timely, the smoke in atrium cause slight damage to people. Under the condition of ultra-high atrium traditional mechanical smoke extraction mode which is not fully applicable, the natural smoke extraction of ultra-high Z-shaped atrium can provide adequate security time for personnel evacuation;(2)Under windless conditions, the higher atrium height is, the longer hazard occurrence time is, the better effect of natural smoke extraction will be. The hazard occurrence time t and the atrium height h met certain exponential growth: t=y0+Aexp(h/α), atrium fire source position and atrium width had some influence on y0,A and α. Meanwhile, under wind conditions, when the wind was consistent with the air inlet direction, the natural smoke extraction of atrium performed better than windless conditions, the higher atrium height is, the better effect will be. When the wind and the external air outlet were in the opposite direction, smoke flowed backwards into the atrium, natural smoke extraction performed worse;(3)One side of the Z-shaped atrium is inlet air and the other is outlet air essentially, its special structure makes wind has a strong effect on natural smoke extraction suggest that the area suitability should be considered comprehensively when designing similar atrium.Taken together the full-scale fire experiment and numerical simulation results, under the conditions of the traditional mechanical smoke extraction modes of ultra-high atrium is not fully applicable, natural smoke extraction is an effective way to exhaust smoke. In this paper, the research results on aspects of natural smoke extraction will provide a reference on similarity of ultra-high Z-shaped atrium design, perfecting natural smoke extraction of the large space and performance-based fire protection assessment, etc.