Fire Safety of Facades

Abstract

Façade fires are a big concern due to past incidents and the large number of victims encountered. Vertical flame spread mechanism specific to this type of fires is a complex phenomenon with parameters that are often difficult to be coupled. Moreover, the architectural design of the façade assemblies further complicates the evaluation of the fire safety strategies.
The energy reduction requirements have led to an increased use of combustible insulating materials. Polystyrene is one of the first synthetic polymers used on a large scale for thermal insulation of the buildings. Due to its remarkable properties like transparency, high chemical stability and dielectric qualities it is the most preferred material among plastics. Although, polystyrene is a combustible material, it is still used on the construction market due to its highly insulating properties. Often designers need to make a compromise in the early stage of the building to achieve a balance between fire safety strategies and the energy reduction requirements. Since these requirements are strongly interrelated there is a continuous need for further improvement of the construction materials used for facades.
The main goal of this thesis is to quantitatively evaluate the flammability properties of different polystyrene compounds and to investigate whether the addition of graphene in their composition could enhance these properties.
The experimental measurements using graphene PS masterbatch have shown important improvements in the fire properties of the polystyrene compound. The interaction between graphene and polystyrene matrix generates changes during the chemical reaction of this thermoplastic material.
Numerical simulations using Fire Dynamics Simulator have been performed in order to validate the accuracy of the pyrolysis model embedded into this CFD package on one hand and to qualitatively compare the temperatures recorded during an external fire which replicates the testing conditions presented by BS 8414 procedure, on the other. Heat release rate curves obtained for the Microscale Combustion Calorimeter (MCC) numerical simulations, offered encouraging results as their shape closely follows the experimental studies.

Popular Abstract

Due to the energy reduction and efficiency requirements, the thermal rehabilitation of the existing buildings has grown up in the recent years across Europe. Thus, one of the most accessible and cost-effective technical solution to achieve this desiderate is represented by the external insulation with expanded polystyrene slabs.
Polystyrene is one of the first synthetic polymers used on a large scale for thermal insulation of the buildings. Due to its remarkable properties like transparency, high chemical stability and dielectric qualities it is the most preferred material among plastics.
Like any other organic polymers, polystyrene is burning, having a melting point around 2400 C and an ignition temperature close to 4270C. Since it is a combustible material it contributes to a rapid fire spread over facades leading to disastrous consequences involving loss of human life and property damage. Although, polystyrene is a combustible material, it is still used on the construction market due to its highly insulating properties. Often designers need to make a compromise in the early stage of the building to achieve a balance between fire safety strategies and the energy reduction requirements. Since these requirements are strongly interrelated there is a continuous need for further improvement of the construction materials used for facades.
One way to deal with this issue would be to develop new materials that can fulfill these requirements, or at least to be on an acceptable range for both fields. One of the goals of the proposed thesis is to evaluate a new polystyrene-based material using graphene properties.
Based on general results for flammability characteristics depicted from experimental studies, carried with small-scale and bench-scale testing instruments, this study provides a quantitative assessment for various types of polystyrene specimens which may be used as an insulating layer in the external system of the building facades.
In the preliminary stage, all the materials were tested using a Microscale Combustion Calorimeter which requires nanoscale samples in the order of a few milligrams. Samples were first pyrolysed and then combusted in a controlled atmosphere with pure nitrogen. Quantitative comparison at different heating rates shows important improvements in the results, when graphene is introduced in the polystyrene matrix. Overall flammability measurements with different instruments revealed an enhancement of the combustibility properties for the graphene polystyrene masterbatch.
The second part of the thesis is focused to qualitatively evaluate the fire behavior of the polystyrene insulation using numerical simulations. Numerical simulations using Fire Dynamics Simulator have been performed in order to validate the accuracy of the pyrolysis model embedded into this CFD package on one hand and to qualitatively compare the temperatures recorded during an external fire which replicates the testing conditions presented by BS 8414 procedure, on the other.
Heat release rate curves from the Cone Calorimeter measurements were then used in a qualitative study proposed to estimate the temperatures developed in a large-scale façade test in accordance to BS 8414 requirements. Samples tested in a horizontal position are intended to replicate a vertical façade fire. Due to a rapid melting of these plastic materials it is difficult to determine an accurate value for the heat release rate expected in a vertical fire. It turns out that temperatures are strongly interrelated to the heat release rate used for the simulations. Thus, it is important that a precise estimation of the input parameters in the simulation to be made. Although, temperatures generated by the fire source are well captured during the calibration and are in line with outdoor experimental studies, an accurate flame spread analysis is yet very complicated on a large-scale using CFD applications. Not only the size of the mesh it is a barrier for the flame spread simulation, but also the vertical spread of fire it is still a complex phenomenon which makes the numerical approach a hot topic among researchers.

• author: Branisteanu-Albulescu, Bogdan-Grigore
• supervisor: Patrick Van Hees
• organization: Division of Fire Safety Engineering
• course: VBRM05 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: polystyrene, graphene, façade, pyrolysis
• publication/series: LUTVDG/TVBB
• report number: 5589
• other publication id: LUTVDG/TVBB-5589-SE
• language: English
• id: 8983928
• date added to LUP: 2019-06-26 14:05:09
• date last changed: 2019-06-26 14:05:09