Zone Fire Research Articles

Bushfire resistance of external light steel wall systems lined with fibre cement boards

Bushfires/wildfires have become a widespread and frequent occurrence in many parts of the world. With the adverse effects of climate change and the increasing population in the Bushland Urban Interface (BUI)/Wildland Urban Interface (WUI), ensuring adequate bushfire resistance of buildings in bushfire-prone areas has become very important. Improving the safety and integrity of the external building envelope is identified as a solution to minimise the bushfire related building damage and losses. This paper presents the details of bushfire resistance experiments conducted on external Light gauge Steel Framed (LSF) wall systems and the results. These LSF wall systems were externally lined with fibre cement boards and exposed to both bushfire radiant heat and flame zone fire conditions under indoor and outdoor test conditions. The results have shown that the rapid increment of the heat flux led to sudden explosive failure of the wall system whereas the gradual increment of the heat flux resulted in a progressive failure. This study has highlighted the importance of external cladding integrity and thermal shock resistance of building elements to enhance the bushfire resistance of buildings.

Replicating the activation time of electronically controlled watermist system nozzles in B-RISK

This paper presents two series of enclosure fire experiments in which the activation time of electronically controlled watermist system nozzles and concealed sprinklers have been obtained. The first series experiments were aligned to the procedure given in the BS 8458 standard whereas the second series were configured to give slower growing fires than in the standard test.The activation of the two systems have been simulated in the B-RISK zone fire model. Activation characteristics for the concealed sprinklers have been taken from elsewhere in the literature. Representative activation characteristics for the electronically controlled watermist system nozzles have been determined. The selection of these characteristics has required a balance between the results from the two experimental series. By using an effective response time index of 20 m½s½ and an effective conductivity factor of 0.25 m½s−½ the predicted activation times are on average 14% slower across all of the enclosure fires.

Development and Validation of a Zone Fire Model Embedding Multi-Fuel Combustion

This paper presents the development and validation of a two-zone model to predict fire development in a compartment. The model includes the effects of the ceiling jet on the convective heat transfer to enclosure walls and, unlike existing models, a new concept of surrogate fuel molecule (SFM) to model multi-fuel combustion, and a momentum equation to accurately track the displacement of the smoke layer interface over time. The paper presents a series of full-scale fire experiments conducted in the IUSTI fire laboratory, involving different combinations of solid and liquid fuels, and varying the compartment confinement level. The model results are compared to the experimental data. It was found that for all fire scenarios, the experimental trends are well reproduced by the model. The SFM concept predicts oxygen and carbon dioxide concentrations in the extracted smoke to within a few percent of the measurements, which is a good agreement considering the sensitivity of the model to chemical formulas and combustion properties of fuels. Comparison with other measurements, namely average gas and wall temperatures, is also good. For the large fires reported in this study, the impact of the ceiling jet leads to a slight underestimation of wall temperatures, while the model gives conservative estimates for small fires.

Analysis of Zone Fire Models and their Application in Structural Fire Design

This paper is focused on a comparison of zone fire modelling software tools and their application in structural fire design. The analysis of the zone models is performed for five selected computer programs, namely Argos, Branzfire, B-RISK, CFAST, and OZone. The limits and input parameters ofthe zone fire modelling software tools are described. In each software, two variants of the analysed compartment are created for simulating two types of fire scenario, including the fuel-controlled fire and the ventilation-controlled fire. The burning regimes are defined based on two heat release rate(HRR) curves, determined according to EN 1991-1-2. The HRR curves parameters are used as the main input data into the fire modelling software. The fire simulation method in each fire modelling software is selected based on the software capabilities. Although each program requires a different amount of input parameters, the aim was to create the same model in all programs and to compare the results. The fire modelling software outputs are exported into a spreadsheet. Subsequently, a comparison of the resulting graphs is performed, particularly the heat release rate graphs and the upper layertemperature evolution graphs. The fire resistance assessment of a simply-supported concrete slab panel is performed for all zone fire models and then the results are compared. The fire modelling software tools are finally quantitatively and qualitatively evaluated and compared to assess their differences.

A-Evac: The Evacuation Simulator for Stochastic Environment

We introduce an open-source software for fire risk assessment named Aamks. This article focuses on a component of Aamks—an evacuation simulator named a-evac. A-evac models evacuation of humans in the fire environment produced by a zone fire model simulator. In the article, we discuss the probabilistic evacuation approach, automatic planning of exit routes, the interactions amongst the moving evacuees and the impact of smoke on humans. The results consist of risk values based on fractional effective dose and are presented in the form of various probability distributions and evacuation animations. The intended scope of Aamks is buildings, e.g., offices, malls, factories rather than stadiums or streets. We present the need for such software based on the current state of research and existing engineering tools in the probabilistic risk assessment domain. Then we describe a-evac and its details: geometry, path-finding, local movement, interaction with fire, and visualization. Given the above scope, the article contributes to the domain of probabilistic risk assessment by proposing: (a) stochastic approach to evacuation, (b) velocity-based model for evacuation, (c) evacuation software that interacts with fire conditions and zone fire models.

An improved two-layer zone model applicable to both pre- and post-flashover fires

The present paper proposes a sub-model for two-layer zone models to describe heat and mass transfer across the interface between the upper and lower layers as a result of the temperature difference between the two layers. The sub-model is integrated into a two-layer zone fire growth and smoke movement model, which now can predict both pre- and post-flashover fires. The comparison of the numerical predictions of the improved model and experimental data shows that the improved model produces better temperature and heat release rate predictions for both pre- and post-flashover fires than the previous model. Compared with hybrid models consisting of a two-layer zone model and a single-layer zone model, the improved model has no transitional difficulties in switching from the pre- to the post-flashover state and it produces more reasonable temperature gradients for post-flashover fires.

Application of the CFAST zone model to the Fire PSA

The integrity of the cables located in the target room is very important in the Fire PSA, because the CDF and CCDP are changed according to the results of a cable integrity that depends on the surrounding gas temperature. The conservative assumptions used in the Fire PSA typically specify that all of the equipment and cables of a room would fail when a fire happens in the room. But the realistic assessment of a fire risk by using a fire simulation tool has become necessary in the Fire PSA as described in the ANS Fire PRA Standard. This paper evaluates the cable integrity of eight pump rooms in the nuclear power plant by using the CFAST zone fire model. The upper layer gas temperature of each room is estimated, and an analysis based on the results of model simulations is used to judge the cable integrity. According to the analysis results, the integrity of the cable located in the upper layer in the pump rooms is maintained without any thermal damage, and the CCDP is reduced to about the half of the original CCDP. A fire safety assessment for dominant pump rooms by using a fire modeling tool is seen capable of evaluating the consequences of a fire scenario, of reducing the uncertainty, and of developing a more realistic Fire PSA model. It is considered that the fire modeling can satisfy the requirements of the ANS Fire PRA standard related to a fire modeling, and improve the quality of the Fire PSA.

Extended Rankine approach for bi-axially loaded steel columns under natural fire

Up till now, there has been limited research work conducted on bi-axially loaded steel columns under fire conditions. Under normal ambient temperature, the load-bearing capacity of steel columns is governed by the interaction of strength and stability considerations, which gives rise to the Rankine method. The authors extended this method to predict the fire resistance of steel columns subjected to bi-axial loading under standard fire curve. Basically, the authors developed an interaction equation based on failure surface to account for the effects of axial load and bending moments in two directions. Predictions from the proposed approach were benchmarked against a well-established finite element program SAFIR for steel columns under standard fire conditions. The same approach is then extended to include natural fire curves. To model a compartment fire with different geometries, thermal characteristics of boundary walls, different fire loads and ventilation factors, a zone fire modelling program Ozone was used. Coupling Ozone to SAFIR, the failure times of steel columns in a compartment fire were predicted. These numerical predictions were compared with those from the proposed approach and reasonable agreement was obtained.

Transfer of Architectural Data from the IFC Building Product Model to a Fire Simulation Software Tool

A standardized, object-oriented building product model for buildings is introduced that can be used as a means of electronic exchange between various software tools. The ability to transfer architectural data between a commercially available computer-aided design (CAD) program and a widely available zone fire simulation tool illustrates the applicability of this model in fire engineering. This article describes the software developed to interpret the building product model and the test buildings used to verify the exchange process. In general the building geometry, topology, and other properties can be transferred satisfactorily but some inconsistencies exist due to the structure of the building product model, the CAD implementation of the model, and the simplifications required by the zone modeling approach.

Simulating the effects of fuel type and geometry on post-flashover fire temperatures

This paper discusses the effect of fuel type and geometry on predicted compartment temperatures derived from computer modelling of post-flashover compartment fires. Many previous studies have investigated post-flashover fires with either wood crib or liquid pool fuels, but very few analytical or experimental studies have considered realistic wood-based fuels with different ratios of surface area to volume, combined with plastic-based fuels. A simple single zone fire model was used to calculate the temperatures in post-flashover compartment fires. The program includes a catalogue of furniture items, each with fuel mass loss rate evaluated on the basis of a constant regression rate on all exposed surfaces. The program also includes a pool-burning model and considers wood fuels and thermoplastic fuels burning together inside a compartment. Use of the model shows that the total fuels load alone is not sufficient to characterise a post-flashover fire. The fire temperature is highly dependent on the fuel type and geometry. For given ventilation and total fuel load, the resulting temperature depends greatly on the average thickness of the wood fuels and the presence of thermoplastic fuels. The ratio of the available fuel surface area to the ventilation opening is particularly important. Several fire scenarios involving different fuel types and characteristics are simulated and compared with Eurocode parametric fires.

A multi-layer zone model for predicting fire behavior in a fire room

A multi-layer zone fire growth model is developed to predict the fire behavior in a single room. The fire room volume is divided into an arbitrary number of horizontal layers, in which the temperature and other physical properties are assumed to be uniform. The principal equations for each laminated horizontal layer are derived from the conservation equations of mass and energy. The implemented fire sub-models are introduced, including combustion, fluid flow and heat transfer models. Combined with these sub-models, the zone equations can be integrated with Runge–Kutta method for the gas temperature and species fractions of each layer for each time step. The results of the sample calculations are compared with the experiments conducted by Steckler and the University of Canterbury. In general, a good agreement between experimental and theoretical results is obtained.

A multi-layer zone model for predicting temperature distribution in a fire room*

Abstract A multi-layer zone fire growth model is developed to predict the vertical distributions of the temperature in a single room. The fire room volume is divided into a number of horizontal layers, in which the temperature and other physical properties are assumed to be uniform. The principal equations for each laminated horizontal layer are derived from the conservation equations of mass and energy. The implemented fire sub-models are introduced, including the combustion, fluid flow and heat transfer models. Combined with thesesub-models, the zone equations for the gas temperature of each layerare solved by Runge-Kutta method for each time step. The results of the sample calculations compare well with the results of experiments conducted by Steckler et al.

Characteristics of Fire Scenarios in Which Sublethal Effects of Smoke are Important

A number of simulations were performed using the CFAST zone fire model to predict the relative times at which smoke inhalation and heat exposure would result in incapacitation. Fires in three building types were modeled: a ranch house, a hotel, and an office building. Gas species yields and rates of heat release for these design fires were derived from a review of real-scale fire test data. The incapacitation equations were taken from draft 14 of ISO document 13571. Sublethal effects of smoke were deemed important when incapacitation from smoke inhalation occurred before harm from thermal effects occurred. Real-scale HCl yield data were incorporated as available; the modeling indicated that the yield would need to be 5 to 10 times higher for incapacitation from HCl to precede incapacitation from narcotic gases, including CO CO2, HCN and reduce O2.

Understanding fire and smoke flow through modeling and visualization

Computer modeling and visualization are important tools for understanding the processes of fire behavior. Fire models range in complexity from simple correlations for predicting quantities such as flame heights or flow velocities to moderately complex zone fire models for predicting time-dependent smoke layer temperatures and heights. Zone fire model calculations can run on today's computers within minutes because they solve only four differential equations per room. Zone models approximate the entire upper layer with just one temperature. This approximation works remarkably well but breaks down for complicated flows or geometries. For such cases, computational fluid dynamics (CFD) techniques are required.

A Multi-layer Zone Model For Predicting Fire Behavior In A Single Room

A multi-layer zone fire model for a single compartment was developed to predict the vertical distributions of the temperature and the gas concentrations. The basic concept of this model is to divide the fire room volume into an arbitrary number of horizontal layers, in which the temperature and other physical properties are assumed to be uniform. Considering the mass and the enthalpy flow rates through the layer interfaces and the opening and the heat transfer rates for each layer, the zone equations for the temperature and the species mass fractions are derived. The results of the sample calculations are compared with the experiments conducted by Steckler et al. From the comparison, it is considered that the model can be a practical tool to predict the behavior of fire in a room, although continuing effort may be necessary to improve the prediction.

Using Sensor Signals to Analyze Fires

Building fire sensors are capable of supplying substantially more information to the fire service than just the simple detection of a possible fire. Nelson, in 1984, recognized the importance of tying all the building sensors to a smart fire panel [1]. In order to accomplish a smart fire panel configuration such as envisioned by Nelson, algorithms must be developed that convert the analog/digital signals received from sensors to the heat release rate (HRR) of the fire. Once the HRR of the fire is known, a multiroom zone fire model can be used to determine smoke layers and temperatures in the other rooms of the building. This information can then be sent to the fire service providing it with an approximate overview of the fire scenario in the building. This paper will describe a ceiling jet algorithm that is being developed to predict the heat release rate (HRR) of a fire using signals from smoke and gas sensors. The prediction of this algorithm will be compared with experiments. In addition, an example of the predictions from a sensor-driven fire model, SDFM, using signals from heat sensors, will be compared with measurements from a full-scale, two-story, flashover townhouse fire.

Ventilation effects on combustion products

The effects of fire ventilation on combustion products are expressed in terms of relationship between concentration of products and equivalence ratio, Φ. For well-ventilated fires, Φ < 1.0, where mostly heat and products of complete combustion (such as CO 2 and water) are generated. For ventilation-controlled fires, Φ > 1.0, where mostly products of incomplete combustion are generated with very high concentrations in a transition region for Φ between 1.0 and 3.5. The high concentrations of the products of incomplete combustion are dangerous to life and property. For halogenated materials, this condition occurs for Φ < 1.0. The non-flaming region for fires is found to exist for Φ > 3.5. Correlations have been developed for the prediction of concentrations of products at various Φ values for the assessment of combustion toxicity and smoke damage hazards by zone fire models, such as Hazard 1. The correlations show good agreement with the measured concentrations. The concentrations of the products of incomplete combustion depend on the chemical structures of the materials. For the same Φ values, the carbon monoxide concentrations are higher for materials with oxygen atoms in the structure, whereas smoke concentrations are higher for materials with carbon and hydrogen atoms in the structure. The results of the study suggest that it is necessary to examine the combustion behaviour of advanced materials for use in aircraft and other critical applications at various Φ values, along with the toxicity experiments.

Fire Modeling Tools for Fse: Are They Good Enough?

Performance-based building codes presume the existence of models which can predict neces sary fire scenarios. The author examines today's state-of-the-art zone fire models and finds that many crucial aspects of fire physics and chemistry are not included in these models. Six specific limitations are discussed. These limitations are commonly overcome in fire reconstruction and litigation when large-scale tests are commissioned. Since such testing will normally not be affordable for the design process, it is essential that the gaps be filled. The gaps are seen to be partly due to funding limitations within the research organizations. Thus, it is suggested that cooperative research may be the best strategy.

The Pressure Equations in Zone-Fire Modeling.

The nonadiabatic nature of low-speed combustion and fire, in which strongly exothermic reactions produce large temperature variations but only mild pressure variations, can cause difficulty when integrating zone models of enclosure fires. Examples of simple zone fire models are examined to illustrate the analytical nature of the problems encountered. These difficulties arise in the solution of the equations for the pressure in general enclosures because the pressure equilibrates much more rapidly than other dynamical variables. Singular perturbation methods and phase plane analyses, together with numerical integration of the nondimensionalized equations, are employed to study the stiff nature of the equations. We conclude that many of the difficulties associated with numerical integration of zone fire models may be circumvented by appropriate analysis of the zone fire model equations.

Analyzing and Exploiting Numerical Characteristics of Zone Fire Models.

Analyzing and Exploiting Numerical Characteristics of Zone Fire Models.