Impact of high-rise morphology on gas temperatures during fires

Onyenobi, TC

Abstract

With the development and use of fire sensitive construction materials and furnishings,
and with the growing demand for high-rise development, there is an increasing need for
improved fire safety measures. Modern high-rise policies within the UK and USA
require a minimum fire safety standard. Current techniques employed to achieve this
which includes performance based approaches are the "passive" built-in approach e.g.
compartmentation etc, and "active" approach e.g. Sprinklers etc. Considering the
diversity of building morphologies of modern high-rises buildings made possible by
improved construction techniques and materials, this research investigates the
possibility of the building morphology becoming an additional consideration in the
"passive" strategy for high-rise fire protection. The focus of this research is on
gas/atmospheric temperatures while proposing the smoke element as a subject for
future studies. The aim of this study is to explore the impact of the morphology
(geometry) of a "central core" high-rise floor on fire within a real life context with
focus on peak gas temperatures and its development during the fire growth stages. In
order to achieve this aim, a set of objectives were developed based on critical analysis
of existing literature. To reduce the scope of work the study focuses on central core
high-rise types.
The research methodology adopted for this study was based on the need for a
contextual approach resulting in a robust ontological standpoint. To achieve the
research aim, the study was designed to have an exploratory positivist experimental
approach set within an interpretivist real life context. The case study method was
selected to meet the contextual and in-depth requirements of this study. Due to the
impracticality of erecting and burning a high-rise building for fire data extraction, the
case study was divided into two phases; a descriptive and exploratory phase to provide
the contextual physical and thermal information respectively. Descriptive data was
extracted from selected real high-rise buildings and multiple case methods which consisted of World Trade Centre New York and One Canada Square London were
adopted for data triangulation. The two cases were selected for their morphological
disposition and the extent to which they represent the wider high-rise population. Two
additional morphologies selected from survey statistics were generated which resulted
in four morphological cases used in this study. The exploratory data which attempted to
predict the thermal process within the high-rise was acquired using pre-validated
computational fluid dynamics (CFD) and zone model simulations. In order to further
inform the simulation results, data from two past small scale experiments (Informing
Case Studies [ICS]) were analyzed. Interviews were carried out with fire fighters & fire
engineers and findings discussed with that of ICS and literature to put the quantitative
findings within a qualitative context.
The result of the study revealed some key findings; firstly, when a central core high-rise
morphologies are dimensionally transformed, three morphological dynamics actually
take place. The morphological dynamics are as follows: boundaries are reconfigured,
regions at the sides of the central core are rearranged in relation to each other and
orifices from the central core edges to the boundaries are redimensioned. Secondly, it
was also revealed that temperature development and peaks are higher in the region
adjacent to the ignition region when these regions relate to each other in a flushed
manner (rectilinear) than when there is a set back. Thirdly, further investigation was
carried out on simplified representation of the "flushed" and "setback" arrangement
which revealed that for the adjacent regions, when the distance between the edge of the
core and boundaries exceeds 50% of the region width, the presence of a setback will
result in lower peak temperatures than when a setback is absent. From the study, region
rearrangement and orifice redimensioning, though they are effects of high-rise
morphology changes, were also found to be active morphological drivers when
considering gas temperatures during high-rise fires. The effect of the boundary
reconfiguration was not studied but was identified as the third morphological driver and
was proposed for further studies. These simulation findings were corroborated by
interview findings that suggested similarities between observation of real fires and
simulation findings in terms of fire development. However, ignited dislodged fuel according to ICS and interview findings, tend to fall close to original fuel hence has no
significant implication in terms of causing random remote ignition not accounted for in
simulation.

Citation

Onyenobi, T. Impact of high-rise morphology on gas temperatures during fires. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Aug 19, 2021
• Award Date: Nov 1, 2008