Numerical study of smoke extraction for adhered spill plumes in atria: Impact of extraction rate and geometrical parameters

In case of fire in an atrium, a smoke and heat control (SHC) system can be designed to improve safety inside the atrium. An important design criterion is the smoke free height in the atrium. This smoke free height is the result of a number of parameters, of which the fire heat release rate (HRR), the SHC extraction mass flow rate, the position of the extraction device or opening and the size and position of openings for make-up air are of primary importance. In the present paper, an extensive numerical study, based on computational fluid dynamics (CFD), is presented in which these parameters are varied. The presence of a downstand or balcony is not covered in the study at hand. From the results, a correlation is presented for adhered spill plumes in atria without downstand, relating the smoke extraction rate to the smoke free height in the atrium. The smoke layer in the atrium is illustrated to become multi-dimensional beyond a certain threshold value of the smoke extraction rate and existing correlations, which do not take this phenomenon into account, are not conservative. The position and exact size of the make-up air inlet openings are shown not to affect the observations, as long as the openings are sufficiently large.

► CFD simulations are used as ‘numerical experiments’ for parameter variation.
► A new formula is proposed for high extraction rates of fire smoke for adhered spill plumes in atria.
► Atrium height, width, length and fire heat release rate are included in the new formula.
► The size of the make-up air inlet opening can have significant effect on smoke extraction in atria.