Steel Buildings in Europe

Part 7: Fire Engineering 7 - 15 Flame axis L z D f H Z 0 = 1,02 D + 0,00524 Q 2/5 z 0 Flame axis L h D H r The flame is not impacting the ceiling The flame is impacting the ceiling Required data: - Rate of heat realase: Q (W) - Distance fire Source-ceiling: H (m) - Diameter of the fire: D (m) Results: - Flame length Lf (m) : L f = -1,02 D + 0,0148 Q 2/5 -Temperature  (z) in the plume along the symmetrical vertical axis:  (z) = 20 + 0,25 (0.8Q) 2/3 (z-z0) -5/3  (z)  900°C Results: - Horizontal flame length Lh - heat flux received by the fire exposed unit surface area at the level of the ceiling at the distance r from the flame axis: h  = 100000 if y  0,30 h  = 136300-121000 y if 0,30 < y < 1,0 h  = 15000 y -3,7 if y  1,0 with ' ' h L H z y r H z      where r: is the distance from the flame axis to the point where the thermal flux is calculated (m) z: is the vertical position of the virtual heat source (m) D: is the diameter of the fire (m) Figure 5.2 Localised Fires (Annex C of EN 1991-1-2) For situations where the fire is not impacting the ceiling, a design formula is given to calculate the temperature in the plume at heights along the vertical flame axis. For situations where the fire is impacting the ceiling, some simple steps are given to calculate the heat flux received by the fire-exposed surfaces at the level of the ceiling. These models are most often used to calculate thermal actions (expressed in terms of heat flux resulting from a radiation part and a convection part) on horizontal structural members, such as beams. At the present time, no method is available for vertical steel members affected by a localised fire. The input data are the rate of heat release (RHR), the distance between the fire source and the ceiling, and the diameter of fire. The RHR is usually determined by using EN 1991-1-2 section E.4. These approaches are limited to cases where the diameter of fire D is less than 10 m and the rate of heat release of fire Q is less than 50 MW.