Smoke Layer Height Research Articles

Numerical study on smoke exhaust system in a mall with mechanical make-up techniques

This paper shows a numerical investigation on smoke management techniques inside a large building. Fifteen numerical simulations were carried out using fire dynamic simulator FDS software. The effect of adding a mechanical exhaust louver on the roof inside the building is studied. This was carried out by varying the exhaust ACH and the configuration of the exhaust openings. Also, the effect of injecting fresh air into the building was examined by investigating the effect of changing the make-up air ACH and the location of the make-up air. All cases were analyzed by studying the smoke layer height, mean soot density and the mean temperature of smoke.It was observed that the smoke hazard decreases by increasing ACH, using multiple exhaust points, and adding make-up air. As compared to no smoke management, this enhancement reaches 71.18% for the smoke layer, 31.6% lowering the average temperature, and 38.4% decreasing the average soot density. These results were achieved when six opposed supply louvers and one exhaust louver were used for the smoke management system.

Scale modeling experiments of fire-induced smoke and extraction via mechanical ventilation in an underground hydropower plant

This study explores experimental research that investigates the characteristics of fire-induced smoke and mechanical smoke extraction systems in the main powerhouse of the Ludila underground hydropower plant. Experiments adopting the similarity theory were conducted in a 1/12 scale model, which in turn was verified through empirical formulas. Experimental results reveal that the cooling effect was so striking that the maximum temperature in the occupied zone was 27.35 °C, and the egress time was over 18 min under conditions of fire intensity of 3 kW. Moreover, the influence of fire locations on CO concentration and smoke layer height are discussed in detail. Furthermore, the effects on temperature variations, the smoke ventilation system layout and exhaust rates caused by mechanical smoke extraction are analyzed. A turning point of smoke layer descent speed was discovered at 0.6 dimensionless height, and this study also recommends the optimal layout of smoke exhaust ventilators that should be used to reduce underground excavation loads. This will help to retrench the initial investment and thereby render a guideline in the design of sustainable underground engineering.

A pilot study of shortwave spectral fingerprints of smoke aerosols above liquid clouds

Absorbing aerosols like smoke heat the atmosphere by absorbing solar radiation, and such heating is enhanced when aerosols are above liquid clouds. To reduce uncertainty in estimates of the aerosol radiative forcing, it is desirable to characterize the size, index of refraction, optical depth, and altitude of smoke aerosols and underlying cloud droplets. While past work with remotely sensed multi-spectral data have made progress toward such characterization, it remains unclear if those radiatively important parameters can be fully and simultaneously retrieved from shortwave hyperspectral measurements. This issue is studied here first by examining the spectral fingerprints of above-cloud aerosols in the shortwave region (wavelength from 330 nm to 4000 nm) using hyperspectral radiative transfer simulations. These simulations are further explored to analyze the information content for hyperspectral inversion of aerosol and cloud optical depths as well as their microphysical properties over an ocean surface. The analysis shows that the Moderate Resolution Imaging Spectroradiometer (MODIS), with limited spectral bands in the solar spectrum, has partial information required for retrieving the optical depth and the effective radius of smoke and cloud. In contrast, hyperspectral measurements have about 5 extra pieces of information (double the degrees of freedom for signals of MODIS), allowing for the retrieval of additional aerosol and cloud microphysical parameters, including the smoke layer height above cloud, the imaginary part of smoke refractive index, and partially the effective variance of cloud droplet size. Thus, hyperspectral measurements can provide valuable constraints on heating rate estimates of absorbing aerosols above clouds.

Full-scale immersed tunnel fire experimental research on smoke flow patterns

To research the smoke flow patterns and their effects on personnel evacuation during a tunnel fire, a full-scale model of an immersed 150 m tunnel was constructed, taking the Hong Kong–Zhuhai–Macao Bridge immersed tunnel in China as the prototype. A series of fire tests, including pool fires and vehicle fires, were developed to simulate a real fire scenario. The characteristic parameters describing the smoke flow were measured, including smoke layer height, smoke spread velocity, and CO concentration. Their development behaviors and main influence factors were explored, and finally smoke flow patterns were examined. The results showed that smoke stratification appeared, which was measured by smoke layer height. The smoke layer height distribution along the tunnel was found to obey a quartic polynomial trend (goodness of fit > 95%). From this, the safety distances were predicted to be 20 m in windy conditions and 80–90 m in still (no wind) conditions. Thus, the longitudinal velocity plays a leading role. Around the fire source or in still conditions, the buoyancy of the smoke is the critical factor driving smoke flow; the influence of other factors is no more than ±20%. However, other conditions depended on the ventilation state. CO concentration decreased sharply with increasing distance from the fire source. At a distance of 60 m, CO concentration decayed by 50%.

Prediction of natural and hybrid ventilation performance used for fire-induced smoke control in a large single space

This paper deals with a large single space building for smoke control when a fire happens. Two hybrid ventilations are investigated, i.e. natural ventilation through a roof opening combined with mechanical suction flow, and with mechanical jet flow. Pure natural ventilation is used as a benchmark. An experimental model was reproduced as 1/10 of the prototype. Under pure natural ventilation, the roof opening played an important role in exhausting but the smoke layer height descended rapidly. Influences of mechanical flows from sidewalls on the smoke distributions were found to be evident. Large eddy full-scale simulations were performed in which grid size of the fire-domain was determined to be 0.125 m being one half of the non-fire domain. The simulation results agreed well with the experimental ones. A total of 63 ventilation cases are further simulated, and it reveals that mass flow rates of the roof opening increase with the increase of opening area ratio or discharge velocity of inlets or heat release rate but with the decrease of exhaust velocity of outlets; under hybrid ventilation of mode 4, back-flow occurs under the roof opening when the exhaust velocity reaches up to 6 m/s, and the maximum smoke temperature and the CO concentration near the door is of the lowest indicating its best advantage in controlling the fire smoke; the smoke plume is more easily disrupted by jet flow than by suction flow. This study helps to promote the design and operation of ventilation system for large and high spaces when firing.

An experimental study on plug-holing in tunnel fire with central smoke extraction

A series of fire experiments were carried out to investigate the plug-holing in the road tunnel with central smoke extraction system. The smoke layer height and the temperature under the exhaust vent as well as the velocity in the upstream and downstream are measured and analyzed. The results show that with the increase of smoke exhaust rate, no plug-holing, incompletely plug-holing and completely plug-holing will occur in turn for the smoke layer under the exhaust vent. The height of smoke layer under the vent increases rapidly, while the temperature decreases quickly with the increase of smoke exhaust rate, until they become stable when the completely plug-holing occurs. The velocity difference between upstream and downstream of the vent firstly increases with the larger smoke exhaust rate, and then it starts to decrease in the transitional region of plug-holing. Similarly, it becomes stable when the completely plug-holing occurs. When Fr is<1.2, no plug-holing occurs and when Fr is larger than 1.8, the completely plug-holing occurs. It is transitional state for plug-holing when 1.2 < Fr < 1.8.

Real-time forecasting of fire in a two-story building using ensemble Kalman filter method

Accurate and reliable prediction of smoke development process is critical for building fire protection design. Although modern computers allow us to use sophisticated models, e.g. CFD, to simulate certain fire scenarios, the simulation time is often drastically longer than zone models. This paper applies a real-time forecasting method, Ensemble Kalman filter (EnKF) algorithm, to a zone model, CFAST, for the simulation of a full-scale fire experiment in a two-story building structure. The results of the CFAST simulation with and without the EnKF algorithm are compared to the experimental data. It shows that the EnKF algorithm can significantly improve the accuracy of the CFAST simulation of the smoke layer temperature and height. To solve the problem of filter divergence and further reduce the computational cost, a general statistical interference method, the bootstrap method, is added to the EnKF algorithm. It shows that the bootstrap method improves the accuracy with fewer ensemble members and less computing time, thus even achieving a real-time forecasting on a personal computer. A sensitivity analysis is also conducted in nine case studies for demonstrating practical engineering applications of the real-time forecasting process.

Performance-based fire safety engineering assessment of national museum of marine science and technology

Abstract The concept of ocean current and fishery industry is expressed from the architectural design in using crossed exterior corridors to perform ocean current. The contrast between modern and obsolete is represented by the staggered interior design and antiquated building structure of the heritage, which is used to be North Thermal Power Plant. It is therefore partial areas which cannot fulfill the article 79-2 of Building Design and Construction Regulation mandated by Taiwan government that stipulate the requirement of any void space over 3 floors. Requirement of smoke extraction system and smoke curtain is also exempted from article 188 of Standard for Installation of Fire Safety Equipment Based on Use and Occupancy. Performance-based design is adopted by fire engineering approach as an alternative. This project passed the expert panel review of fire engineering strategies and smoke management assessment. At the stage of construction by auditing and reviewing, full-scale hot smoke test was conducted due to the safety consideration raised by local government. The results of tests are significantly different from the simulation modelling and smoke management report approved by National Fire Agency, Ministry of Interior. Visibility in partial areas is around 10 m which is not regarded as a tenable condition. After the improvement of smoke management, the study of full-scale hot smoke tests and computational simulated results are carried out. Acceptance criteria, usually smoke temperature, smoke layer height and visibility in Taiwan, are reached regardless of differences between FDS model and on-site full-scale tested values. This project provided design considerations to designer during design process, including the environmental differences of internal and external building, local weather impact, and grid size used in FDS model. The limitation and discrepancy of chosen software among different versions should be understood so that simulation results would more fit the realistic circumstances.

Research on Fire Safety Evacuation in a University Library in Nanjing

Abstract To research the fire peril arrival time and evacuation situation when fire extinguishing system fails, in this work Pyrosim and Pathfinder software were used to; simulate the spread of smoke and human evacuation in a university library in Nanjing during fires. Through the comparative analysis of the temperature, smoke layer height, the visibility, CO concentration and FED value, the simulation results show that, the risk time of the library is 280s, on the fire scale of 4MW; the risk time of reading room is 125s, on the fire scale of 8MW. The evacuation simulation results indicate that the evacuation time of the entire library and reading room is 411s and 165s respectively. Finally, the fire safety of the library is evaluated by comparing the risk time and evacuation time. It is concluded that the exit of each layer is the first to reach the dangerous state; the direction of the hazardous area is also the direction of safe evacuation. The risk time of the library and the reading room, is the time when the height of smoke down to 2m. Therefore, the staff activity height, smoke volume and detection alarm and other factors, should be considered in the system design of smoke control.

A Study of the Effect of Make-Up Air Velocity on the Smoke Layer Height with Symmetric Openings in Atrium Fires

This paper presents full-scale test results and CFD modeling of smoke conditions in atrium fires in the case of symmetric make-up air opening arrangements. The atrium used for the experiments was equipped with a smoke management system capable of exhausting 132 m3/s. Thermocouple trees were installed to measure the temperature along the height of the atrium. The N-percentage method was used to determine the smoke interface height from the measured temperature profiles. Make-up air velocities of 1 m/s, 1.5 m/s and 2 m/s were selected to investigate the effect of make-up air velocity on the smoke interface height in the case of 4-side and 2-opposite side openings. The fire size varied from 1 MW to 5 MW to cover the effect of small, medium and large fires. FDS was also used to simulate the atrium fires in order to compare the predictions with the full-scale test results and evaluate the accuracy of the developed correlations. Results show that the limit of 1 m/s is too restrictive in the case of symmetric opening arrangements. A correlation is proposed based on the full-scale test results that can be used to modify the smoke layer height obtained using plume equations so that the effect of make-up air velocity on the smoke layer height is considered.

Application of the EnKF method for real-time forecasting of smoke movement during tunnel fires

Real-time prediction of smoke layer temperature and height of tunnel fires are crucial in guiding emergency rescue. However, current fire simulation tools are often not able to provide reliable modeling results due to poorly known input parameters and model errors. Besides, fire modeling are subject to computer resources, for instance, fire modeling by computational fluid dynamics (CFD) tools is often time-consuming. Moreover, sensors located in tunnels can only detect certain physical quantities within a certain level of uncertainties. In order to gain more reliable predictions of temperature and smoke layer height of tunnel fires in real time, a proposed method, inverse modeling based on Ensemble Kalman Filter (EnKF), is presented in this study to improve the predictability and address problems of demanding computer resources of tunnel fire simulation by doing data assimilation. The basic formulas of EnKF method are introduced and the application of EnKF to tunnel fires is implemented by connecting the fire simulation tool, CFAST, with a data assimilation software, OpenDA. In current study, observation data are generated under the framework of Observation System Simulation Experiment (OSSE), i.e., synthetic observations are generated by CFAST simulation assuming true value of control parameters are known. Studies are conducted to show the feasibility of real-time predicting smoke movement during tunnel fires. Results show that prediction performance are improved after applying the EnKF method compared to the standalone tunnel fires modeling.

Numerical simulation of dormitory building fire and personnel escape based on Pyrosim and Pathfinder

To analyze the fire risk in dormitory buildings, one dormitory of a university was taken as the subject to build a model using Pyrosim. This paper has analyzed the temperature, visibility, smoke layer height, heat flow, and smoke movement with all windows and doors opened and compared these with conditions when the fire origin room had closed windows. The results show that, with all windows opened, the highest temperature area is the fire origin room and the fire floor temperature is higher than the other floors. The closer to the fire source, the lower the visibility. With window closed, the fire origin room temperature and heat flow are much higher than with window open while the smoke layer height is much lower. Horizontal corridors and stairs are more seriously influenced by the smoke. When all windows are opened, rooms above are more seriously influenced by the smoke. Pathfinder simulation results show that the best time to escape is within 164.8s. In order not to affect the safety of personnel evacuation, the width of exit doors should be no less than 3 m and stair width should be no less than 1.75 m.

A Study Regarding Smoke Exhaust from an Atrium Type Building in a Fire Situation

This paper presents the analysis of the effect of smoke exhaust and hot gases from an atrium type building using techniques for numerical simulation of a fire situation. Several scenarios regarding smoke exhaust are considered for that purpose and the variation of the following parameters is monitored: minimum and maximum temperature of hot gases as well as the smoke layer height inside the atrium. Using engineering techniques, the development of fire, in compliance with the European legislation has been modelled, by means of a specialized computer program in order to simulate the phenomena of both the fluid flow and the heat transfer manifested in a fire situation.

A Simple Solution of the Smoke Filling Equation

Thirty four years after the enclosure smoke filling equation was first published by Zukoski, Novozhilov found an exact analytical solution for the case of constant fire heat release rate (HRR). This exact solution is fundamentally important in theory, but quite complicated. In this note, a simple solution is reported for the same case. Because of its simple visual appearance, the formula of this solution can be easily calculated on a hand calculator or on a spreadsheet. Comparing with the exact solution, the relative error of this simple solution is from −5 to 5% in the range where the non-dimensional HRR is larger than 0.001 or the non-dimensional smoke layer height is larger than 0.2. This range covers most practical cases.

원자력발전소 주제어실 화재 시 공조모드가 배연성능 및 거주성에 미치는 영향 분석

본 연구의 목적은 원자력발전소 주제어실 화재시 운전원의 거주성을 평가하는 것이다. 운전원의 거주성 분석을 위해 FDS v.6.0을 사용하였으며 이를 통해 주제어실 화재 시 배연성능과 운전원의 거주성에 있어 도출되는 문제점을 확인하였다. 본 연구에서는 공조환기설비의 운전조건을 핵심변수로 지정하고 그에 따라 3가지 시나리오로 분류하였다. 수치해석결과, Case 1(공조설비 작동시)의 경우가 연기온도, 복사열, 광학밀도 및 연기층높이에 의한 영향이 가장 심각한 것으로 나타났다. 이에 반해, Case 2(공조설비 미작동시)와 Case 3(공조설비 미작동시 풍량 1.5배 증가 시)는 Case 1보다 더 안전한 것으로 나타났다. 약 820초경 연기온도를 확인한 결과, Case 1이 Case 2와 Case 3보다 약 63% 정도 더 높게 나타났다. 복사열에 의한 영향도 Case 1에서 가장 높게 나타나, Case 2 및 Case 3와는 최대 약 68% 이상의 차이를 보였다. 분석결과를 통해, 주제어실의 공조환기설비는 배연성능에 큰 영향을 미쳐 운전원 거주안전을 지키기 위한 주요 인자인 것을 확인하였다. 다만, 급기구와 배연구가 천정부에 동시에 설치되어 있어 Case 2와 Case 3의 경우 연기층높이에 있어 불연속적 패턴을 나타냈다. This study evaluated the habitability of operators for main control room fires in nuclear power plants. Fire modeling (FDS v.6.0) was utilized for a fire safety assessment so that it could determine the performance of the smoke ventilation and operator habitability with the main control room. For this study, it categorized fire scenarios into three cases depending on the conditions in the HVAC system. As a result of fire modelling, it showed that Case 1 (with HVAC) would give rise to the worst situation associated with the absolute temperature, radiative heat flux, optical density, and smoke layer height as deliberating the habitability and smoke ventilation. On the other hand, it showed that Cases 2 (w/o HVAC) and 3 can maintain much safer situations than Case 1. In the case of temperature at 820 s, Cases 2 and 3 were up to approximately 63% greater than Case 1 in the wake of ignition. In addition, the influence of radiative heat flux of Case 1 was even larger than Cases 2 and 3. That is, the radiative heat fluxes of Cases 2 and 3 were approximately 68% higher than Case 1. Furthermore, when it comes to considering the optical density, Case 1 was approximately 93% greater than Cases 2 and 3. Accordingly, it expected that the HVAC system can influence a the performance on the smoke ventilation that can be sustainable for operator habitability. On the other hand, it revealed an inconsecutive pattern for the smoke layer height of Cases 2 and 3 because supply vents and exhaust vents were installed within the same surface.

The Use of Fractional Factorial Design for Atrium Fires Prediction

In order to mitigate the excessive computational cost of atrium fire simulations, a novel methodology based on the use of the Fractional Factorial Design technique to obtain an experimental validated tool, in the form of a surface response model, capable to predict fire induced conditions is proposed. This methodology is supported by results from a Design of Experiments benchmark, which consists of a set of FDS simulations in the present work. Specifically, a $$2^{6-2}_{IV}$$ approach has been considered and applied to a 20 m cubic atrium. Thus, six factors have been considered, namely the fire Heat Release Rate (HRR) and location, the exhaust flow rate, the exhaust location and activation time, and the inlet vents area. Furthermore, the smoke temperature at the roof and 15 m high and the smoke layer height have been considered the variables of interest. Subsequently, a multiple linear regression analysis has been performed to predict and compare the steady and non-steady temperature profiles and the smoke layer drop with six novel full-scale atrium fire tests, and also with specific adjusted FDS models. In addition, this methodology has been extended successfully to predict the non-steady behaviour of the fire tests. At the steady state, the HRR and the exhaust flow rate have been found to be the most relevant factors. The results obtained with the proposed methodology show a good fit both with the fire tests and with the adjusted FDS models, with discrepancies mostly below 14%. For non-steady conditions, a time analysis of the influence of the six factors has been carried out. Again, remarkable good agreement with the time-dependent experimental results is achieved, with average discrepancies below 12%, being the larger differences found in the prediction of local effects, such as the smoke ceiling jet, for high HRR or when the make-up air influence is significant. The results turn this methodology into a powerful and useful tool for fire safety designs.

A Mathematical Approach to Estimate the Error During Calculating the Smoke Layer Height in Industrial Facilities

Abstract Engineering based calculation procedures in fire safety science often consist of unknown or uncertain input data which are to be estimated by the engineer using appropriate and plausible assumptions. Thereby, errors in this data are induced in the calculation and thus, impact the number as well as the reliability of the results. In this paper a procedure is presented to directly quantify and consider unknown input properties in the process of calculation using distribution functions and Monte-Carlo Simulations. A sensitivity analysis reveals the properties which have a major impact on the calculation reliability. Furthermore, the results are compared to the numerical models of CFAST and FDS.

Feasibility Analysis on Natural Smoke Extraction for Large Space Warehouse Buildings

In order to explore the feasibility of the natural smoke extraction of the undivided large space warehouse buildings, the paper analyzes the characteristics, factors and feasibility of natural smoke extraction of the undivided large space warehouse buildings which have been fire damaged, based on the idea of performance-based fire protection design. FDS software is used for fire hazard analysis of the building by simulating the fire scene temperature, smoke layer height and visibility during the natural smoke extraction. It draws the conclusion that: during natural smoke extraction, increased area of the smoke vent and heightened warehouse both, under certain conditions, can lower the fire scene temperature, slow the sinking of smoke and weaken the ground radiation so that the fire scene safety can be guaranteed even in the most unfavorable condition. However, to ensure stable smoke extraction and eliminate the influence from the external environments, some proven fire safety measures can be provided in certain positions.

Effects of Supply-exhaust Ratio on Smoke Exhaust Efficiency in a Large Machinery Space

The effects of supply-exhaust ratio on smoke exhaust efficiency in a large machinery space were studied numerically. The simulation model used was a certain machinery space on a naval ship and two types of fire source are provided. Various parameters, such as the smoke layer height, smoke concentration and gas temperature were considered. Results show that the mechanical exhaust system could decrease the gas temperature and smoke concentration, and increase the visibility in a machinery space fire. With the increase of supply-exhaust ratio, the smoke control efficiency is improved. Considering both of smoke control efficiency and consume of energy and cost for the typical machinery space, a value about 70% of supply-exhaust ratio is suggested to be used in mechanical exhaust system.

CFD modeling approach of smoke toxicity and opacity for flaming and non‐flaming combustion processes

SummaryCurrent engineer's methods of fire safety design include various approaches to calculate the fire propagation and smoke spread in buildings by means of computational fluid dynamics (CFD). Because of the increased computational capacity, CFD is commonly used for prediction of time‐dependent safety parameters such as critical temperature, smoke layer height, rescue times, distributions of chemical products, and smoke toxicity and visibility. The analysis of smoke components with CFD is particularly complex, because the composition of the fire gases and also the smoke quantities depends on material properties and also on ambient and burning conditions. Oxygen concentrations and the temperature distribution in the compartment affect smoke production and smoke gas toxicity qualitatively and quantitatively. For safety designs, it can be necessary to take these influences into account. Current smoke models in CFD often use a constant smoke yield that does not vary with different fire conditions. If smoke gas toxicity is considered, a simple approach with the focus on carbon monoxide is often used. On the basis of a large set of experimental data, a numerical smoke model has been developed. The developed numerical smoke model includes optical properties, production, and toxic potential of smoke under different conditions. For the setup of the numerical model, experimental data were used for calculation of chemical components and evaluation of smoke toxicity under different combustion conditions. Therefore, averaged reaction equations were developed from experimental measurements and implemented in ANSYS CFX 14.0. Copyright © 2015 John Wiley &amp; Sons, Ltd.