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By Dr. Peter Vogel, Gebäude-Technik-Dresden GmbH, Dresden, Germany
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During the planning and construction of open, large scale facilities
such as sports arenas, airport terminals, rail stations, and
convention centers, care must be taken to understand the
indoor air flow patterns in the event of a fire. If improperly vented
smoke builds up in regions where people are waiting to evacuate,
catastrophe can occur. Engineers at the consulting firm of Gebäude-
Technik-Dresden GmbH were contracted to study several scenarios for
a fire originating in the foyer at Messehalle 3, the new exhibition pavilion
in Frankfurt. The goal was to obtain information about the spread
of smoke and change in visibility depending on the time following the
start of the fire.
The Messehalle 3 exhibition center in Frankfurt
The foyer is an atrium that spans several levels - two mezzanine levels
above the ground floor and one additional floor above them. A
number of rooms and exhibition spaces open onto the foyer at all levels.
Using FLUENT and a mesh of about 2.2 million cells, a fire, located
on the ground floor, was modeled as a 2 m3/s source of smoke at either
100 or 800 °C. Several exhaust strategies, involving suction fans and
smoke aprons (used to segment the foyer) were simulated and compared.
Among other things, the smoke concentration on planes 1 m
above each floor level were studied. Based on the results, the decrease
in visibility was computed for each case.
Plain view of the mass fraction of smoke (%) on the ground floor (top) and first
mezzanine level (bottom) after 10 minutes, using an early design
The first case studied corresponded to the original building geometry
and a high temperature fire. It made use of exhaust fans operated
on the ground floor and first and second mezzanines, and no smoke
aprons. The results showed that for this scenario, the highest smoke
concentration (2%) was on the first mezzanine level above the fire, and
that it was less on the upper floors. In the smokiest areas, where emergency
exit lights are located, the visibility was computed to be about
20 m. Since the targeted smoke concentration was to be less than 5%
with a corresponding visibility of 10 m, this design was considered
acceptable. The success of the design was attributed to the development
of a layer of hot gas near the ceiling of the first mezzanine. The
stratified air temperature resulted in a pressure gradient that served as
driving energy to force the smoke through an available opening.
Mass fraction of smoke (%) on the ground floor (top) and first mezzanine level
(bottom) after 10 minutes, using the final design; the maximum is one-third that
shown in the top figure of an early design
A second case was run with the same boundary conditions as the
first, but with a cooler fire. With reduced buoyancy, the helpful pressure
gradient of the first case did not develop, so there was not an adequate
driving force to move the smoke from the area. Smoke concentrations
of 15% developed on the first mezzanine for this case. Because
of the challenges associated with the cooler fire, the remaining simulations
were run with smoke temperatures of 100 °C.
Other cases experimented with the placement of smoke aprons
hanging from the ceilings of one or more floors that serve to divide the
space into segments. Additionally, suction fans rated at 40,000 m3/hr
were tested in different locations. The best arrangement consisted of
fans in the roof of the first mezzanine level, as well as on the façade of
the ground floor level, and no smoke aprons. With this design, the visibility
near the evacuation routes for a cool fire was found to be about
10 m after 10 minutes, with a maximum smoke concentration (elsewhere)
of about 5%. This design was subsequently put into operation
at the pavilion.
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