Gas temperature measurements using fibre Bragg grating during fire experiments in a tunnel

Gas temperature measurements with thermocouples are affected by radiation. This effect means that the temperature measured by a thermocouple can be far from the actual gas temperature. To study this effect and to compare the thermocouple readings with the readings of a fibre Bragg grating (FBG) sensor, fire experiments were performed in a model-scale tunnel. In this paper the results from two such fire experiments are presented. The temperatures measured using thermocouples with different diameters and the FBG sensor are compared and discussed. The “true” gas temperature, corrected for radiation effects from the thermocouples, was calculated from the results from the thermocouples with different diameters. The results show that the temperature measured by the FBG sensor is closer to the “true” gas temperature than is the case for any of the thermocouples used in these tests.     

On Radiant Network Models of Thermocouple Error in Pre and Post Flashover Compartment Fires

Thermocouples are often used to obtain gas temperature measurements in compartment fires. Such measurements are subject to a thermal lag during fire growth, but the main problem is a steady-state error induced by radiant heat transfer at the thermocouple surface. This error is sensitive to thermal parameters of the flame, compartment structure, thermocouple surface and combustion products; and is also influenced by the size and position of both the flame and thermocouple. The literature contains models of varying sophistication to enable an assessment of steady-state error. A model is now proposed that makes use of the concept of radiosity. Developed from radiant network theory, the model can be applied to both pre-flashover and post-flashover conditions. Experiments have been performed using different sizes of thermocouple and the models compared. The simpler models pre-date the more sophisticated and predict much larger errors than the latest published and current versions.     

BRE large compartment fire tests—Characterising post-flashover fires for model validation

Reliable and comprehensive measurement data from large-scale fire tests are needed for validation of computer fire models, but is subject to various uncertainties, including radiation errors in temperature measurement. Here, a simple method for post-processing thermocouple data is demonstrated, within the scope of a series of large-scale fire tests, in order to establish a well characterised dataset of physical parameter values which can be used with confidence in model validation. Sensitivity analyses reveal the relationship of the correction uncertainty to the assumed optical properties and the thermocouple distribution. The analysis also facilitates the generation of maps of an equivalent radiative flux within the fire compartment, a quantity which usefully characterises the thermal exposures of structural components. Large spatial and temporal variations are found, with regions of most severe exposures not being collocated with the peak gas temperatures; this picture is at variance with the assumption of uniform heating conditions often adopted for post-flashover fires.     

Determinations of the fire smoke layer height in a naturally ventilated room

According to the case-based reasoning of natural ventilation designs in recommended Green Buildings, an investigated model space was proposed in this study. FDS simulations and full-scale experiments were carried out to measure the impact of natural ventilation conditions and the installation of a natural ventilation shaft on smoke layer descent during different fire scenarios. The feasibility of using the N-percentage rule to determine the fire smoke layer height in a naturally ventilated space was also investigated.In a non-fire room, the smoke descent curve determined from the FDS simulated temperatures is consistent with the experimentally measured temperatures and visual observation of the smoke layer. However, the thermocouples in the fire room are affected by direct burning and fire radiation, and the experimentally measured temperatures cannot be used to determine the smoke height. Under these conditions, FDS simulations can be used to compensate for the lack of experimental measurements. In fire scenarios without outdoor winds blowing into the building's interior, FDS simulations can reliably model the fire smoke layer height. When outdoor air blows into the interior, it causes the smoke layer temperature to become unstable. Thus, the temperature will not be thermally stratified, and the use of the N-percentage rule is not recommended.     

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.     

Interaction of a water mist with a buoyant methane diffusion flame

This work describes observations and measurements from the interaction of a fine water spray from a hollow cone nozzle, with purely buoyant diffusion flames from a natural gas ceramic-plate burner located directly underneath the nozzle. The burner plate was instrumented with thermocouples cemented on its upper and lower surfaces to assess the influence of the spray on the burner temperature. A set of thermocouples was also used to measure plume centerline temperatures above the burner plate. An imaging system was used to record the presence of droplets near the burner surface, and a narrow angle total radiation detector was used to measure changes in local flame radiation. A limited number of measurements of the steady state O₂ and CO concentrations along the plume centerline were also carried out.

For the conditions tested, the plume-to-spray thrust ratio was large, resulting in negligible direct penetration of the droplets into the fire region. A consequence of the low spray thrust was an almost droplet-free region above the flame. The observed cooling of the ceramic burner when the spray was applied was due to decreased radiant emission from the flame as well as deposition and evaporation of droplets entrained into the plume near the burner. The centerline plume temperatures did not change significantly upon application of the spray, at least within the error limits of thermocouple measurements. However, there was a significant decrease in O₂ and an increase in CO concentrations along the plume centerline upon application of the spray. An energy balance on the ceramic-plate burner, together with the experimental data, yielded estimates of the water deposition rate on the burner surface.     

Temperature measurement in fire test furnaces

A study of errors associated with temperature measurement in fire endurance test furnaces has shown that conventionally used thermocouples are subject to large time constant errors in the first 20 minutes of a standard test.     

Effects of PPV Attack on Thermal Conditions in a Compartment Downstream of a Fire

There have been relatively few technical studies conducted on the effects of PPV on compartments downstream of the fire. Live fire tests in an acquired house were conducted in order to study the effect of PPV attack on the thermal environment downwind of the fire. Temperature measurements were made using 40 thermocouples located in a fire room, hallway, and downstream room referred to as “the victim room”. Video camera and infrared camera images were taken in several locations to visually record the progress of the fire and firefighting. A total of eleven cases are reported in this study. These cases correspond to three different fan configurations: no fan, a 45.7 cm (18″) diameter fan with a volumetric output of 3.06 m³/s (6,500 CFM), and a 61 cm (24″) diameter fan with a volumetric output of 4.31 m³/s (9,130 CFM). Two venting strategies were used: venting the fire room and venting the victim room. Fluctuations in environmental factors such as wind and the inherent statistical variation common in fire testing made it difficult to draw many absolute conclusions. In general, however, we found that cases with fire room venting and fan application had somewhat higher fire room or hallway temperatures when compared to cases without fan application. We also found that cases with victim room venting and fan application resulted in higher gas temperatures in the victim room at the higher elevations than both fire room vented cases and cases without fan application.     

Application of field model and two-zone model to flashover fires in a full-scale multi-room single level building

This paper presents a comparison of the results from a computational fluid dynamics (CFD) model and a two-zone model against a comprehensive set of data obtained from one flashover fire experiment. The experimental results were obtained from a full-scale prototype apartment building under flashover conditions. Three polyurethane mattresses were used as fuel. The CFAST two-zone model (version 2.0) was also used to predict results for this flashover fire test. The mass release rate, gas temperature, radiation heat flux and gas compositions (O₂, CO₂ and CO) were measured. A CFD program, CESARE-CFD Fire Model, has been developed and was used also to predict results for polyurethane-slab fire. A simple flame spread model was incorporated into the CFD program to predict the mass release rate and heat release rate during the fire instead of providing it as an input as is required for most zone and CFD models. It was found that the CFD model provided reasonable predictions of the magnitude and the trends for the temperatures in the burn room and the species concentrations, but over-predicted the temperatures in the adjacent enclosures. From a life safety perspective, the CFD model conservatively predicted the concentrations of CO and CO₂. The predicted temperatures from the CFAST fire model agreed well with the experimental results in most areas. However, the CFAST model under predicted the temperature in the lower layer of the room of fire origin and the concentration of CO in most areas.     

Real-scale fire tests of one bedroom apartments with regard to tenability assessment

Statistics reveal that people mostly die in bedrooms or lounges, from smoking-related fires. However, at present, little is known of this phenomenon, especially in terms of identifying which fire effects first injure people. Through several real-scale fire tests, two different sets of fire scenarios are explored in a single bedroom apartment. As in everyday life, the test room is equipped with furniture, clothes and items supplied from major retailers. It is heavily instrumented with sensors to record tenability-related data (thermocouples, heat fluxmeters, gas analyzer including 3 FTIRs, opacimeters and several cameras for video recording).The first set of tests explores a bed fire scenario, in which a person has fallen asleep, accidentally lighting its quilt, and then its mattress, e.g. with a cigarette or a small flame. The door and window remain closed during the entire test, and the fire decreases rapidly to become insignificant because of a lack of oxygen.The second set of tests explores a wastepaper basket fire scenario, with a first person leaving the room quickly, while a second person – who is potentially disabled – cannot leave the room. As the door remains open, there is enough oxygen supply, and the fire grows to flashover.The test results are designated as reference for calculation models validation. In addition, their interpretation in terms of tenability is presented; fire effects are classified and discussed. All this work also highlights the importance of smoke alarms in such premises.     

Measuring modified glass bulb sprinkler thermal response in plunge and compartment fire experiments

Automatic fire sprinklers use a heat sensitive element such as a glass bulb or fusible link to respond to the heat from a fire. The response of commercial fire sprinkler glass bulbs has been extensively characterised in convection-dominated dry gas flows but in real fires there may be more factors that influence the heat transfer to the bulbs such as radiation from the fire or cooling from adjacent sprinkler sprays. The time of activation is the only indication of the thermal response of typical commercial fire sprinklers using glass bulbs to a fire, but direct temperature measurement using a modified proxy may provide a better understanding of how sprinklers respond in a complex environment. Modified glass bulbs have been created that allow a thermocouple to be inserted in the bulb for direct temperature measurement. In this paper, the thermal response of sprinklers with these modified bulbs has been observed in hot-air wind tunnel plunge experiments and full scale room fire experiments. At the time of activation the measured temperature of the modified sprinklers was found to be higher than the nominal activation temperature specification for the unmodified sprinklers. For the compartment fires, a thermal response model generally predicted longer sprinkler activation times based on ceiling jet temperature and velocity measurements than was observed experimentally.     

热电偶补偿导线的正确使用

对补偿导线的使用原理进行了介绍,阐述了操作错误对热电偶温度测量结果的影响,并提出补偿导线的正确使用方法,以避免热电偶的测温结果出现较大误差影响热控工作其他环节。     

Air pumping action of a plume in a room fire

Air pumping effect of a fire plume to give higher intake rate through vertical openings in a post-flashover room fire will be discussed in this paper. The thermal balance equation was set up with known fire phenomena in a room. The hydrostatic model was applied to study the air intake rate through vertical openings. An equation relating heat release rate to room air temperature rise with empirical constants was then justified by reported experimental data on post-flashover room fire. The heat release rate was measured by the oxygen consumption method in that experiment. The predicted heat release rate from the empirical equation reported in the literature was observed to be proportional to the room air temperature rise as derived from hydrostatics. However, the proportionality constant is lower than the experimental value. A possible explanation is due to neglecting another fire phenomenon on air pumping action of the fire plume in a real room fire. Higher pressure differences across the door would give higher airflow rates across an opening. This would supply more air to give higher heat release rate as observed in the experiment. In this paper, the pressure due to air pumping of the fire plume is taken as a proportion of the hydrostatic pressure due to temperature differences between the upper hot layer and lower cool layer. Comparing the measured heat release rate with the estimated heat release rate due only to hydrostatics will give the air pumping action. The possible increase in heat release rate in a post-flashover fire can then be estimated accordingly.     

Wind tunnel tests on compartment fires with crossflow ventilation

When a fire occurs in a room at ground level or a compartment located in the higher floors of a very tall building , the strong ambient wind will play an important role in fire spreading and smoke movement behavior. However, wind effect on compartment fire in cross ventilation condition has not been fully studied so far. In the present study, an effort has been made to study the wind effect on compartment fire in cross ventilation condition through experimental investigations. The experimental fire was generated by 250 ml n-heptane on the floor center of a cube enclosure with two opposite vents on the walls. The inside and outside gas temperature profiles at different vertical and horizontal locations were recorded by two thermocouple matrixes. The ambient wind velocity was set to 0, 1.5 and 3 m s⁻¹. It is observed that the ambient wind would enhance the fire severity by increasing the compartment fire temperature and reducing the time to flashover. The spilled-out flame/plume would extend horizontally farther with the increase of wind speed. Simple theoretical analysis shows that there is a critical wind velocity, or a dimensional number, to differentiate whether the gas flow across the vents is bidirectional or unidirectional, which is believed to influence enclosure fire behavior greatly.     

Performance of Different Temperature Sensors in Standard Fire Resistance Test Furnaces

Defining a methodology for measuring temperature in fire resistance furnaces is a challenge. This paper presents and discusses the performance of six different types of temperature sensors in wall and floor fire resistance furnaces namely: the ASTM E119 shielded thermocouples, ISO 834 plate thermometers, directional flame thermometers, bare-bead thermocouples, Inconel grounded and ungrounded sheathed thermocouples. The Inconel grounded and ungrounded sheathed thermocouples provided comparable results to those of the bear-bead thermocouples and are most suitable when a fast response time is desirable. Because of the fast response time and good durability, grounded and ungrounded junction thermocouples are well-suited for use in controlling the temperature in fire resistance standard test furnaces. The predicted and measured incident heat flux in furnaces controlled by either the bare-bead or grounded and ungrounded sheathed thermocouples are in good agreement.     

A comparison of a FLOW3D based fire field model with experimental room fire data

This paper describes the application of a fire field model based on the FLOW3D CFD software to the simulation of fire induced flows in domestic sized rooms. Several scenarios are examined consisting of various sized fires, fire locations and door sizes. Comparisons are based on upper-layer room temperatures, mass fluxes in and out of the fire compartment and door-way vertical and horizontal temperature and velocity profiles. For most cases the model agrees reasonably well with the observed trends, however the results suggest that significant mesh refinement is required to produce results in quantitative agreement with experimental results. A close examination of the horizontal door-way velocity profiles highlights the need for careful modelling and experimental practices in this region.     

Comparison of FDS predictions by different combustion models with measured data for enclosure fires

The performance of mixture fraction models FDS4 and FDS5 is investigated under different global equivalence ratios (GER). Predictions of heat release rate (HRR), upper-layer temperature, and CO yield are compared with measurements considering their sensitivities to the lower limit of fuel, mixing time scale, and turbulence model constants. When using FDS4, the inclusion of an extinction model can result in significant variations in both total and volumetric HRR prediction. When using FDS5, the mixing model constant has significant effects on volumetric HRR prediction. At low GER (<0.23), the prediction of upper-layer temperature shows dependency on both the lower fuel limit and the mixing model constant, but the predicted temperature is always lower than measured temperature, with deviations in excess of 30%. At higher GER (0.53<GER<0.81), the upper-layer temperature prediction shows significant dependency on the mixing model constant but can be over-predicted, with deviations up to 24%. The variations of CO yield prediction with lower fuel limit or with the mixing model constant show an opposite trend to that of upper-layer temperature. Furthermore, the prediction of CO yield shows a much greater dependency on the Smagorinsky constant and on the turbulent Schmidt number than do those of HRR and upper-layer temperature.     

应用FDS进行单室火灾场模拟分析

本文基于成熟的火灾模拟方法,和建筑烟气扩散领域的理论及实验成果基础上,应用美国标准技术研究局开发的场模型工具FDS,对单室火灾进行了场模拟分析。结果显示：火源的释热率值、房屋的单室门窗状况等对着火房间内热值、烟气浓度以及温度场的分布特性的均有主要影响,随着火源释热率的增大,室内热烟气的温度迅速升高,而且房屋的通风面积越大,火灾发展越剧烈,上层热烟气温度越高,室内整体温度也越高。本文的研究结果对于房间内火灾控制具有一定的参考价值。