Patrick Van Hees

Influence of delay times and response times on heat release measurements

This paper presents results from the analysis of the calibration results from the 1997 single burning item (SBI) test round-robin. The influence of the method of determining delay times and response times for the parameters involved in the heat release rate (HRR) calculation, on the overall result of the HRR and the FIre Growth RAte (FIGRA) index is shown. A procedure to determine response times and delay times based on the analysis is proposed. Examples of how to find delay times and response times, and how time shifting the measured data according to these times influences the test results, are shown in detail. Finally a mathematical approach to analyse the influence of response times is given. Calculations are performed to show how the response time influences the result when heat output is changed in steps and how this can lead to incorrect measured data. Guidance on acceptable response times is given. Copyright

Performance of cables subjected to elevated temperatures

The time to damage, i.e., time to short circuit, and the corresponding temperature within the cable were recorded for two different data cables and one low voltage cable when subjecting the cables to an elevated surrounding temperature. In the experiments it was found that short-circuiting occurred at a certain temperature in the core of the studied cables. The heating of the cables was modeled with the aid of computer programs for thermal analysis and an analytical solution of heat conduction. The experimental results were used to evaluate the different models. Both the analytical solution and the use of the thermal analysis programs turned out to be promising. However, both the analytical solution and the use of computer programs such as TASEF require data of the thermal properties of the cables. This is a complication as such data are not easily accessible. To some extent the thermal properties of the cables could be estimated from the experimental results.

A Monte Carlo analysis of the effect of heat release rate uncertainty on available safe egress time

Available safe egress time is an important criterion to determine occupant safety in performance-based fire protection design of buildings. There are many factors affecting the calculation of available safe egress time, such as heat release rate, smoke toxicity and the geometry of the building. Heat release rate is the most critical factor. Due to the variation of fuel layout, initial ignition location and many other factors, significant uncertainties are associated with heat release rate. Traditionally, fire safety engineers prefer to ignore these uncertainties, and a fixed value of heat release rate is assigned based on experience. This makes the available safe egress time results subjective. To quantify the effect of uncertainties in heat release rate on available safe egress time, a Monte Carlo simulation approach is implemented for a case study of a single hypothetical fire compartment in a commercial building. First, the effect of deterministic peak heat release rate and fire growth rate on the predicted available safe egress time is studied. Then, the effect of uncertainties in peak heat release rate and fire growth rate are analyzed separately. Normal and log-normal distributions are employed to characterize peak heat release rate and fire growth rate, respectively. Finally, the effect of uncertainties in both peak heat release rate and fire growth rate on available safe egress time are analyzed. Illustrations are also provided on how to utilize probabilistic functions, such as the cumulative density function and complementary cumulative distribution function, to help fire safety engineers develop proper design fires. (Less)

Detection of a typical arson fire scenario – comparison between experiments and simulations

Abstract in Undetermined Between one and two school fires occur in Sweden every day. In most cases, arson is the cause of the fire. The most severe fires generally start outside the building and spread up along the facade and into the attic through ventilation openings in the eaves. Linear heat detectors can be placed on facades to detect these types of fires. Such devices detect fire when short-circuited at a specific temperature. In this article, an attempt to simulate linear heat detectors is presented. Data from small-scale and full-scale experiments are compared with these simulations. The small-scale experiments and simulations demonstrate that the cable failure model in Fire Dynamics Simulator can be used to predict detection in linear heat detectors that use short-circuiting as the means of signaling an overheated condition. The full-scale experiments provide a measure of the uncertainties involved, as well as the possibility of using simulations of linear heat detectors in a fire engineering design. (Less)

Room-Fire Characterization Using Highly Range-Resolved Picosecond Lidar Diagnostics and CFD Simulations

In fire safety engineering, the use of computational fluid dynamics (CFD) allows for detailed multidimensional calculations of important parameters, for example, temperature. However, increasing use of CFD models puts requirements on experimental validation, a challenge for many measurement techniques under harsh fire conditions. In this work, laser-based picosecond light detection and ranging (ps-lidar) was used for remote measurements in a ½-scale ISO 9705 room containing either a methanol pool fire or a methane diffusion flame. Spatially resolved Rayleigh thermometry was conducted in the vertical door plane and in a horizontal plane inside the room. Temperatures obtained by ps-lidar are compared with values from thermocouples located in the doorway as well as results from CFD simulations. The technique allows for quantitative thermometry provided that minimal particle scattering interferences are present. Measurements of detailed distributions of temperature and particulates clearly demonstrate the potential of ps-lidar for diagnostics in large-scale combustion.

Validation of CFD Model for Simulation of Spontaneous Ignition in Bio-mass Fuel Storage

Both numerical simulations and experimental measurements of small scale spontaneous ignition with different biomass fuels have been performed. In the experiments, temperature history was monitored at five different locations inside the fuel bed. The measured temperature history was used for validation of comprehensive threedimensional computer simulations which were carried out using a parallel finite volume CFD code SMAFS (Smoke Movement and Flame Spread) developed by the first author. The computation was based on numerical solution of a set of governing equations including the continuity equation, extended Darcy momentum equations, energy conservation equations for both gas and solid phases, and mass conservation equations for different chemical species. With reliable material properties input data provided by separate measurements, it simulated the temporal state evolution inside the biomass fuel storage. In the simulation, consideration was given to a series of essential physical and chemical processes, including convection and diffusion in porous media, evaporation, condensation and heat generation which is mainly due to chemical oxidation. Numerical results were compared with experimental measurements, showing excellent agreement. (Less)

How could the fire fatalities have been prevented? An analysis of 144 cases during 2011-2014 in Sweden : An analysis

Approximately 80%–90% of all fire-related fatalities take place in residential occupancies. The risk groups are well known, but the effectiveness of different measures has been less investigated. In this article, fire investigations from 144 unintentional fatal residential fires have been systematically analyzed and technical measures that would have been effective in preventing each fatality have been identified. The result shows that, generally, a thermally activated suppression system (e.g. sprinkler) has the highest potential effectiveness (68%) followed by a detector-activated system in bedroom and living room (59%) or smoke alarm (37%). For smokers with home care, however, the potential effectiveness of a thermally activated suppression system and home smoke alarm was significantly lower (31% and 14%, respectively). This indicates that different measures are effective for different groups. In one-fifth of the cases, the victim could have evacuated but chose not to do so, primarily to attempt to extinguish the fire.

Modelling of Euroclass Test Results by Means of the Cone Calorimeter

An important part of introduction of the construction productive directive (CPD) is the introduction of the so-called Euroclasses for building products. The Euroclasses define the different fire classes within the European harmonised system. The major fire test method in this system for wall and ceiling linings, the so-called SBI test (EN 13823), is, however, an intermediate fire test and requires larger test specimens. This makes it difficult for industry to develop new innovative materials as large amounts of samples are necessary to run the test, which is also more cost expensive. In this chapter, a product development tool for this method will be discussed. The product development tool is a simulation model based on small-scale test data obtained in the cone calorimeter tests. First the model will be explained in this chapter. The next step is to show the validation of the model and give guidance on how to use the model for building materials. (Less)

Characterization of stone wool properties for fire safety engineering calculations

Prediction of the insulating capability of building products in fire conditions would support the product development process. Stone wool insulation is a widely used material in fire barrier constructions. Due to the combustion of its organic content, the temperature inside stone wool can rise above the temperature of the exposed boundary. This temperature rise is difficult to predict. An extensive test program was performed to obtain the thermal and reaction kinetic properties of stone wool. The test methods included modified slug calorimeter, thermogravimetric analysis, differential scanning calorimetry, micro-scale combustion calorimetry and bomb calorimetry. The thermal conductivity in elevated temperatures was similar for all the investigated products. Two positive mass loss rate and heat release rate peaks were observed in temperatures between 20°C and 700°C. Reaction kinetic parameters were obtained and used in a finite difference model predicting the temperature increase in stone wool upon linear heating.

Selection and evaluation of fire related scenarios in multifunctional buildings considering antagonistic attacks

Multifunctional buildings have become more common in the last years. At the same time the threat from antagonistic attacks has increased. This presents challenges for the fire safety systems in multifunctional buildings since continuity of functions, especially those considered to be of societal importance, need to be operational and at the same time antagonistic exposures may present more challenging fire scenarios. A method for selection and evaluation of fire related scenarios in multifunctional buildings, that also considers antagonistic attacks, has been developed. Based on literature review and interviews with stakeholders typical for a multifunctional building, specific problem areas that the developed method needed to take into account were identified. A first framework for development of fire scenarios, developed by the authors in previous work, was refined taking into account the identified problem areas resulting in the method described in this article. The method, still simple to use, provides guidance on how to determine assets needing protection, relevant protection objectives, exposures (both accidental and antagonistic), fire related scenarios and evaluation of scenarios. The method also takes into account the inherent probability of failure for active systems, security features, domino effects and damage to protection systems due to antagonistic attacks.