Nicholas A. Dembsey

Compartment fire experiments : Comparison with models

Abstract Twenty full-scale compartment fire experiments suitable for model comparison were conducted. Ceiling jet temperatures, surface heat fluxes and heat transfer coefficients which have not been previously reported are discussed. The ceiling jet temperatures 0·10 m below the ceiling show the effects of compartment ventilation, near-field entrainment conditions and burner location on the ceiling jet. Net and radiant incident heat fluxes to the upper and lower-walls and the floor are estimated. Combined (radiation and convection) interior heat transfer coefficients for the three surfaces are reported. As compartment fire models such as CFAST and FIRST continue to develop in sophistication, it is important that they be compared to experimental data. Data at three heat release rates: 330, 630 and 980 kW, are used to evaluate these comprehensive compartment fire models and two simpler models for the upper-layer gas temperature. CFAST predicts upper-layer gas temperatures 150–260°C hotter than the measured bulk outflow gas temperatures. The increased temperatures appear to be due to insufficient heat transfer through the compartment surfaces. FIRST predicts upper-layer gas temperatures that are slightly cooler (on average, 20C) than the measured bulk outflow gas temperatures. The two simpler models are within 40°C, on average, of the measured upper-layer gas temperatures

Accommodating perceptions of risk in performance-based building fire safety code development

Differing perceptions of risk by various stakeholders have long played a role in influencing the development of prescriptive-based building fire safety codes. As performance-based building fire safety codes are developed, differing perceptions of risk will continue to be a significant influence. In this paper, the concepts of revealed preference, risk factors, risk adjustment factors and risk conversion factors are discussed, and two methods to address risk perceptions in a performance-based building fire safety code are introduced. The first method proposes the use of risk factors to classify buildings in terms such as low, medium, and high risk. Each class of building would be assigned a risk adjustment factor. Similar to safety factors, risk adjustment factors would be applied during deterministic building fire safety design to provide an increased level of safety in buildings where the risk perceptions would mandate greater safety. The second method would be used with a probabilistic-based building fire safety design approach, and uses risk factors to develop risk conversion factors (RCFs). In the probabilistic approach, a maximum expected-risk-to-life (ERL) value would be established by the code, with appropriate RCFs being applied to adjust maximum ERL values depending on how the buildings fire safety risk is perceived.

Fire characteristics of cored composite materials for marine use

Abstract This paper presents results from Cone Calorimeter testing of two types of cored composite materials used in shipbuilding: a GRP/Balsa-cored sandwich and a GRP/PVC foam-cored sandwich. The observed phenomena of delamination, melting and charring of the core materials, and edge effects are discussed in the context of how they affect test results. The “standard” ignition data analysis method specified in ASTM E 1321 and Janssens’ “improved” method of analysis were both used to derive effective material ignition properties such as ignition temperature and kρc. The findings of the study indicate that Janssens’ method is well suited for analyzing the ignition data of cored composite materials. Derived material properties are used as input to Quintiere’s fire growth model in order to evaluate their influence on time to flashover predictions in the ISO 9705 Room–Corner test scenario.

A means to estimate thermal and kinetic parameters of coal dust layer from hot surface ignition tests

A method to estimate thermal and kinetic parameters of Pittsburgh seam coal subject to thermal runaway is presented using the standard ASTM E 2021 hot surface ignition test apparatus. Parameters include thermal conductivity (k), activation energy (E), coupled term (QA) of heat of reaction (Q) and pre-exponential factor (A) which are required, but rarely known input values to determine the thermal runaway propensity of a dust material. Four different dust layer thicknesses: 6.4, 12.7, 19.1 and 25.4mm, are tested, and among them, a single steady state dust layer temperature profile of 12.7 mm thick dust layer is used to estimate k, E and QA. k is calculated by equating heat flux from the hot surface layer and heat loss rate on the boundary assuming negligible heat generation in the coal dust layer at a low hot surface temperature. E and QA are calculated by optimizing a numerically estimated steady state dust layer temperature distribution to the experimentally obtained temperature profile of a 12.7 mm thick dust layer. Two unknowns, E and QA, are reduced to one from the correlation of E and QA obtained at criticality of thermal runaway. The estimated k is 0.1 W/mK matching the previously reported value. E ranges from 61.7 to 83.1 kJ/mol, and the corresponding QA ranges from 1.7 x 10(9) to 4.8 x 10(11)J/kg s. The mean values of E (72.4 kJ/mol) and QA (2.8 x 10(10)J/kg s) are used to predict the critical hot surface temperatures for other thicknesses, and good agreement is observed between measured and experimental values. Also, the estimated E and QA ranges match the corresponding ranges calculated from the multiple tests method and values reported in previous research.

Human Variability Correction Factors for Use with Simplified Engineering Tools for Predicting Pain and Second Degree Skin Burns

It is important that the practicing fire protection engineer has tools that are computationally easy to use to simulate thermal injury to the skin. This paper presents a brief review of skin damage...

Twenty years of performance-based fire protection design: challenges faced and a look ahead

A review of two decades of worldwide experience using standards, codes and guidelines related to performance-based fire protection design for buildings has identified shortcomings in the interpretation, application and implementation of the performance-based design process, apparent inconsistency in the resulting levels of performance achieved and several opportunities to enhance the process. In a constantly evolving building environment, technical challenges have to be overcome because fire safety engineering still depends greatly on knowledge gained from scientific and engineering research across a broad range of disciplines (e.g., better understanding of the fire phenomena, the behavior and response of the building occupants/contents/structure to the fire, tools for engineering analysis and all the necessary data needed to support tool application). Political challenges also need to be considered as performance-based fire protection design requires the approval of the authority having jurisdiction and ...

The Role of Decomposition Kinetics in Pyrolysis Modeling - Application to a Fire Retardant Polyester Composite

This work assesses the effect of decomposition kinetics on overall pyrolysis behavior using experimental data from thermogravimetric analysis (TGA) and Fire Propagation Apparatus (FPA) experiments. TGA data are presented for an unsaturated brominated polyester resin (reinforcement free), and the FPA is used to investigate the pyrolysis behavior of a fiber reinforced polymer (FRP) composite slab with matrix comprised of the same resin tested via TGA. Three different kinetic models are fit to the TGA data: singlestep n th order, 3-step n th order, and 3-step n th order with one autocatalytic step. These kinetics models are then used to simulate the pyrolysis of a composite slab in the FPA, with thermophysical properties estimated by genetic algorithm optimization. It is shown that the two 3-step mechanisms provide nearly identical calculations of total mass loss rate (MLR) in the FPA, while the single-step mechanism provides similar, but quantitatively different, MLR predictions. Although no broad conclusions regarding the importance of multi-step thermal decomposition kinetics can be drawn on the basis of a single study, detailed reaction mechanisms may be superfluous unless TGA curves show multiple distinct reaction peaks and/or all thermophysical properties/model input parameters are precisely known.

Evaluation of common ignition models for use with marine cored composites

With the adoption of the High Speed Craft Code the importance of fire safety analytical tools has been elevated. Input data such as ignition properties of cored composite panels will be needed to simulate surface flame spread behaviour. The ease of customizing cored panels for high speed craft means that numerous panel systems are possible on one craft. Understanding how skin thickness and core composition effect ignition is important for efficient evaluation of ignition properties and for fire safety design simulations. To study the effect of skin thickness and core composition, ten material systems were evaluated in a Cone Calorimeter at applied heat fluxes of 20 kWm−2 to 90 kWm−2. The systems were a balsa core panel (core thickness 9.5 mm) with three different GRP skins, 1.5 mm, 3 mm and 8 mm, each of the three skins over a copper substrate, the three skins over a ceramic fibreboard substrate and a thermally thick GRP skin. Over the range of applied heat fluxes a change in GRP behaviour from thermally thick to non-thick was observed. The sensitivity of three simple ignition models to this change was investigated. It was found that the ignition models were not able to resolve the effect of skin thickness and core composition. Copyright

Use of Small-Scale Test Data to Enhance Fire-Related Thread, Vulnerability, Consequence and Risk Assessment for Passenger Rail Vehicles

Fires in passenger rail vehicles pose threats to people and to critical transportation infrastructure. Although relevant guidelines and regulations exist, current approaches lack details needed for comprehensive fire-related threat, vulnerability, consequence and risk assessment (TVCRA), particularly with respect to identifying the size of initiation fire necessary to ignite the interior lining materials, assessing the potential for a fire to encompass the entire vehicle, and evaluating options for reducing the overall energy of a fully involved vehicle fire. However, these shortcomings can be addressed cost effectively by obtaining fire properties of materials used in passenger rail vehicles through small-scale tests, applying a simplified flame spread screening approach using the test data, and incorporating the output into an existing fire TVCRA framework. With these enhancements, operators will be better able to link vulnerabilities and consequences to a range of fire threats, and have more robust data for informing fire mitigation and operational response decisions.

Improvements on Flame Retardant Properties of PET/Montmorillonite Nanocomposite Caused by Polyborosiloxane

A phenyl-containing highly cross linked polyborosiloxane (PBSiO) was synthesized as a flame retardant for polyethylene terephthalate (PET). We coated montmorillonite (MMT) clay, a very high aspect ratio and high specific surface area layered silicate with synthesized PBSiO to introduce synergism in flame retardation to the PET nanocomposite film that retained thermal and mechanical properties. This PBSiO has high thermal stability at the processing temperature (270-285° C) of PET and acts as a compatibilizer between PET and clay that are otherwise incompatible. During burning, the flame retardant PET containing PBSiO and MMT forms a protective borosilicatecarbonaceous intumescent char on the surface. Cone calorimeter tests were performed to evaluate key fire properties of the PET/PBSiO/MMT. The peak heat release rate (PHRR) of PET that contains 5 wt% PBSiO and 2.5 wt% MMT was reduced by 60% and similar trend in the reduction of mass loss rate of the nanocomposite was observed.