Browsing by Author "Benarous, Abdallah"
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- Ensaios experimentais e simulação numérica de vestuário de proteção individual de incêndio exposto ao calor radiantePublication . Pereira, Vitor; Piloto, Paulo A.G.; Khedouma, Nechab; Benarous, AbdallahNeste artigo é apresentado um estudo de avaliação do comportamento de um conjunto muito significativo, de tecidos para proteção individual de segurança de bombeiros, quando submetidos a uma fonte de calor radiante. São apresentados ensaios experimentais desenvolvidos na Universidade de Tsinghua (TU, China) e no Instituto Politécnico de Bragança (IPB, Portugal). São apresentados os resultados de 84 ensaios experimentais no IPB, sendo 72 ensaios realizados para baixos níveis de fluxo de calor incidente (5 [kW/m2]) e 12 ensaios realizados para níveis médios de fluxo de calor incidente (20 kW/m2]). Estes ensaios permitiram determinar qual a melhor combinação de proteção para diferentes conjuntos de materiais com 3 camadas (camada exterior com 6 tecidos diferentes, barreira térmica com 4 tecidos diferentes e camada interior com 3 tecidos diferentes). A melhor combinação foi determinada pelo conjunto de material que apresentava menor densidade de fluxo de calor transmitido (TB3/BT2/F1 para baixos níveis de densidade de fluxo radiante e TB1/BT2/F1 para níveis médios de densidade de fluxo radiante). É ainda apresentado um estudo numérico 2D, não linear transiente, para baixos e médios níveis de densidades de fluxo de calor incidente. O modelo numérico foi validado com os ensaios realizados na Universidade de Tsinghua. Estes resultados permitiram concluir que existe uma relação não linear entre o fluxo de calor incidente e o fluxo de calor transmitido, tendo em consideração o estudo paramétrico.
- Fire dynamics in open compartmentsPublication . Piloto, P.A.G.; Possoli, Ketlen; Junior, Luiz C.M.; Nechab, Khadouma; Benarous, AbdallahWith the aim to increase fíre safety in open compartments, such as open car parks, some correlative models were used to test the ability to recover both dynamics and thermal characteristics ofa ceiling-jet flow. The flow occurs when the fire plume impinges the ceiling and develops in the radial direction ofthe fire axis. Both temperature and velocíty predictions decisive for sprinklers positioning, fire alarms positions, detectors (heat, smoke) position and activation times and back-layering predictions. This investigation deals with a parametric analysis using different fire events, fíre scenarios and correlative formulations (Alpert, Cooper, Heskestad and Delichatsios, Motevalli and Marks). An advance calculation method (CFAST) based on a two zone model fonnulation was used to compare the results.
- Fire dynamics in open compartmentsPublication . Piloto, P.A.G.; Possoli, Ketlen; Junior, Luiz C.M.; Nechab, Khadouma; Benarous, AbdallahFire events in car parks have been a major problem for buildings,vehicles and humans.The main cause for fire propagation are the combustible materials of the vehicles. Ceiling jet flow occurs when the fire plume impinges the ceiling and develops in the radial direction. Both temperature and velocity prediction sare decisive for sprinklers positioning,fire alarms positions,detectors (heat,smoke) positions and activation times and back-layering predictions.
- Fire dynamics in open compartmentsPublication . Piloto, P.A.G.; Possoli, Ketlen; Junior, Luiz C.M.; Nechab, Khadouma; Benarous, AbdallahWith the aim to increase fire safety in open compartments, such as open car parks, some correlative models were used to test the ability to recover both dynamics and thermal characteristics of a ceiling-jet flow. The heat flow, coming from a burning vehicle, occurs when the fire plume impinges the ceiling and develops in the radial direction of the fire axis. Both temperature and velocity predictions are decisive for sprinklers positioning, fire alarms positions, detectors (heat, smoke) position and activation times and back-layering predictions. This investigation deals with a parametric analysis using different fire events (class of the vehicle) and two fire scenarios. Some correlative formulations were used: Alpert, Cooper, Heskestad & Delichatsios and Motevalli & Marks. An advance calculation method (CFAST) based on a two-zone model formulation was used to compare the results, as well as the CFD software ANSYS Fluent, based on the finite volume method. A total of 16 simulation results were obtained taking into consideration 2 different heights for the compartment (H=3m and H=5m), 4 different car classes (fire events), 6 radial positions (R) and two software (CFAST and ANSYS Fluent). The correlative model from Motevalli & Marks overestimates the dynamic characteristics in small compartments. The two zone model overestimates the maximum temperature in the biggest compartment and the CFD results for temperature and velocity are always higher than the other calculation methods.
- Fire protection durability of intumescent coatings after accelerated agingPublication . Thabet, R.; Benarous, Abdallah; Mesquita, L.M.R.Intumescent coating is a reactive chemical material, which is used as the main fire protection material to steel structures. When intumescent coating is exposed to fire, the chemical components in the intumescent coating react to cause the coating to swell forming a lightweight flame-retardant char to protect the steel substrate from excessive rise in temperature. However, exposure to long-term environmental conditions can cause the intumescent coating to lose some of the reactive materials, thus reducing the effectiveness of the intumescent coating over time. Because fire safety requirement is throughout the entire life of a building structure, which may last many tens of years, it is important to understand the long-term protection performance of intumescent coating under exposure to environmental conditions, [1].
- Fire protection durability of intumescent coatings after Iaccelerated agingPublication . Thabet, Rida; Benarous, Abdallah; Mesquita, L.M.R.The most common method of achieve the required fire resistance of structures and struc-tural elements is using passive fire protection systems, being the intumescent coatings the fire protection material frequently used. This work presents a research study about the ef-fects of aging on the fire protection performance of intumescent coatings. A commercial water based coating is submitted to an accelerated aging cycle, using a QUV accelerated weathering tester. These tests aim to simulate 10 years of the coating natural aging accord-ing to the European technical approval guideline (ETAG N° 018). The coating durability is tested comparing the fire protection efficiency of small steel samples submitted to a con-stant radiant heat flux exposure from a cone calorimeter as prescribed by the standard ISO 5660. In total, 28 tests were performed on intumescent coating protected steel specimens, in which 14 specimens were tested before the hydrothermal aging test and other 14 after ac-celerated aging. The experimental test results of the steel temperature evolution shows that increasing the intumescent dry film thickness, an increase of the fire resistance time is at-tained. After the accelerated aging cycles, the coating lose their ability to expand, resulting in an increase of the steel temperature of approximately 200 ºC, compared to the samples without aging.
- Numerical prediction of the incoming heat fluxes on firefighter protective clothingPublication . Dahamni, Salim; Nechab, Khadouma; Benarous, Abdallah; Piloto, P.A.G.Improving the performances of a firefighter protective clothing requires a better understanding of the conjugated thermal exchanges in the ambient-garment-body assembly [1]. As the protective clothing is believed to ensure, as long as possible, a skin temperature below the injury threshold, it is mandatory to quantify accurately the instantaneous thermal loadings provided by the fire source. Indeed, protective garments are commonly designed for incoming heat flux values that are recorded during isolated tests, under quasi-steady fire conditions [2]. Moreover, the scarce unsteady investigations devoted to heat flux predictions are based on presumed temporal laws for fire heat release and do not account for natural or mechanical ventilation effects on fire development.
- Numerical prediction of the incoming heat fluxes on firefighter protective clothingPublication . Dahamni, Salim; Nechab, Khadouma; Benarous, Abdallah; Piloto, P.A.G.The present study is a numerical attempt for the prediction of the incoming thermal flux on a firefighter protective clothing. The study focuses on ventilation conditions impact on the incident fluxes reaching the external garment’s face. A radiative and convective transfer modelling is considered for a 3D geometry compartment, equipped with a door, a window and subject to a localized fire, with stationary heat release rate (HRR) during a prescribed exposure time. An additive constraint on oxygen mass fraction threshold is considered to account for flame extinction. The outer layer of the protective garment is modeled as a solid medium, featuring both front (chest F) and rear (back R) sensors. The baseline case corresponds to a situation where the external temperature of the protective clothing and that of the fresh air adjacent to the firefighter's body are maintained at 25 °C. Despite the importance of mechanical ventilation devices in smoke clearance and temperature attenuation, critical values for ventilation flow rates may lead to tremendous heat fluxes revealing the apparition of backdraft situations
- Numerical validation of the fire performance of fire fighter clothing and experimental testsPublication . Pereira, Vitor; Piloto, P.A.G.; Benarous, AbdallahThis investigation is focused on the numerical modelling of experimental tests to evaluate the thermal performance of the fire fighter clothing. First a 2D numerical validation is presented to asset the thermal model and materials properties. This numerical model solves a nonlinear transient thermal analysis under low thermal radiation [1]. The numerical validation is based on the bench scale cone calorimeter experience test [2] or equivalent, exposing the fabrics to a low thermal radiation of 2, 5 and 10 [kW/m2], following the procedures of NP EN ISO 6942 [1] to determine the t12, t24 and the heat flux density transmitted to skin.
- Numerical validation of the fire performance of fire fighter clothing and experimental testsPublication . Pereira, Vitor; Piloto, P.A.G.; Benarous, AbdallahThe Fire Protection Clothe (FPC) of firefighters have been investigated over the last years in several terms to improve the safety of their users. FPC are designed to save the firefighters from excessive heat and fire conditions, allowing for a period of time, usually required for a rescue mission, fighting fire, or withdrawing from direct flame contact. The FPC fabrics are design in order to settle a certain degree of comfort to firefighters when exposed to accidental conditions. The heat source, intensity of fire, time of exposure, and other variables affect the protection of the FPC. The FPC is a multilayer assembly composed of various types of woven and nonwoven fabrics. Conventional fibres such as cotton, wool, and viscose and highperformance fibres such as aramid, polybenzimidazole, and polybenzoxazole (PBO) are used in FPC [1].