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3.5 Fire safety study.
A CFD program (Computational Fluid Dynamics) was utilised to simulate the
station project and determine the possible advantage of the transversal openings
between all the arched roof membranes above the platforms, and this at the level
of their contact points. Considering the design’s lateral and longitudinal symmetry
axes, the analysis considers solely one quarter of the covering.
Two models were drawn up. The first model shows no opening; in the second
model an opening was made at the level of the lateral symmetry axis between the
arched roofs of 39 and 52 metres.
Air currents caused by the heat’s thrust develop in the case of fire. Considerable
convection movements occur in the area. The roof membranes, because of their
shape, create a collecting basin in which the smoke is trapped.
The study shows that openings placed laterally above the platforms improve
smoke evacuation. When comparing both models, it is clear that the model with
the lateral openings offers nothing but advantages. Firstly, there is less smoke
generated, and it remains confined to a single span. Secondly, we measure a lower
and more concentrated temperature increase. Thirdly, smoke is evacuated faster
because of the faster movement of the air molecules.
We can conclude from these pictures that the roof openings increase the safety
level of the area under the canopy, since they promote smoke extraction near
the centre of the fire. This structural composition can be considered as a kind of
compartmentalisation of the volume. In the case of fire, and aside from radiating
heat, there would be no smoke affecting the areas outside the compartment in
which the fire occurs.
Nevertheless, great attention was paid to the composition of the roof membrane
in order to avoid possibly disastrous situations, such as injuries caused by burning
debris falling or evaporation of hazardous substances. The material is non-
flammable and can withstand the high temperatures that can be reached under the
roof membranes. The structure will not collapse because of the high temperatures
occurring in the case of fire.
Figure 1: The model indicates the smoke density on a
scale of 0 to 1 (1= absolute smoke density).
Figure 2: The model shows the increase in tempera-
ture in case of fre and indicates the tem-
perature on a scale in °C.
Figure 3: The model indicates a vectorised represen-
tation of the air circulation on a vertical plane
in the case of fre. The model indicates the
vector’s speed in m/s.
Figure 4: The model indicates the dispersion of smoke
with an equal density. To improve rendering
legibility, only smoke dispersion with a den-
sity of 20% was calculated.
Figure 5: The model indicates the movement of an
air molecule in the considered module. The
air molecules are introduced into the model
on a horizontal plane of a height of 2m, and
follow their path depending the infuence of
the centre of the fre.
3 4 5 1 2
Model whithout openings:
Model with openings at the level of the lateral symmetry axes:
3 4 5 1 2