Fire in a High‐Rise Building: Study of the Behaviour of Burnt Gases in a Ventilated and Unventilated Upper Compartment

In enclosure fires, density-driven vent flow through an opening to the fire compartment is directly dependent on the state of the fire and the evacuation of smoke and hot gases. If a fire is strongly under-ventilated, there may be heavy production of flammable gases. If a sudden opening occurs, e.g., a window breaks or a fireman opens a door to the fire compartment, fresh air enters the compartment and mixes with hot gases, thus creating a flammable mixture that might ignite and create a backdraft. In this article, we consider the critical flow approach to solve the classical hydraulic equations of density-driven flows in order to determine the gravity controlled inflow in a shipping container full of hot unburnt gases. One-third of the container’s height is covered by the horizontal opening. For the initial condition, i.e., just before opening the hatch, zero velocity is prescribed everywhere. When the hatch is opened, the incoming air flows down to the container floor and the hot gas flows out. The interface in between them (the neutral plane) can move up like a free surface in internal flows, making it possible to use the techniques of open channel hydraulics devised by Pedersen [1]. In this article the critical flow condition, known from classical hydraulics, is used providing a new equation for the vent flow problem. Two flow correction coefficients are considered at the opening, taking into account the uneven distribution of velocity (α) and the effect of mixing and entrainment (C). The value of these coefficients is evaluated using computational fluid dynamics simulations and physical model results performed for the same geometry. Together, these two coefficients form the flow correction coefficient used in practical formulas for vent flow in fire protection engineering. These are known to have a little different values for different geometries and flow situations. The resulting flow coefficient varies slowly with the density difference, shows a small variation with geometry and compares well with previously published data.

The U.S. Navy has now developed an N-Class division system to classify fire resistant boundaries in accordance with MIL-STD-3020, fire resistance on U.S. naval surface ships. The N-Class division is analogous to the commercial International Maritime Organization (IMO) system (e.g., A-Class) division. The key difference is that N-Class divisions are designed to have satisfactory fire resistance when exposed to hydrocarbon pool fire (UL 1709 fire exposure) following a shock event. In addition, N-Class is applicable to fire resistant divisions constructed from polymer composites structures when they meet the requirements of DDS-078-1. MIL-STD-3020 requires a hydrocarbon pool fire exposure (UL-1709 fire exposure) which provides a minimum average total heat flux of 188 kW per square meter (kW/m2) (60,000 British thermal unit per square foot/hour (Btu/ft2∣h)) within the first 5 min of the test exposure. At all times after 5 min, the average temperature within the furnace shall be maintained at a minimum of 1038 °C (1900 °F) and a maximum of 1149 °C (2100 °F) for the duration of the test. These fire conditions simulate a post-flashover fire scenario for shipboard applications. Performance is defined as the time period during which assemblies will continue to perform their intended function when subjected to fire exposure. The minimum duration of fire exposure is 30 min. Shock testing prior to fire resistance test is performed to ensure that fire resistance of divisions, with fire insulation, penetrations, and associated attachment methods, is not degraded in a combat environment. Shock test specimen size of 1219 by 3048 mm (4 by 10 ft) was selected to reduce the cost of shipping a full size fire test specimen of 3048 by 3048 mm (10 by 10 ft) or greater to the fire test laboratory. A full scale fire resistance test is still required for qualification purposes after successful completion of the shock test prior to fire resistance test. MIL-STD-3020 also permits AN-Class fire resistant divisions when fire threat is from common combustibles (Class A) and where liquid flammable (Class B) fire threat is non-existent. AN-Class divisions are those divisions formed by bulkheads and decks that are designed to protect against structural failure and prevent the passage of flame or hot gases when exposed to IMO Resolution A.754(18) fire exposure after shock testing. For all AN-Class divisions, including those with penetrations, the fire test duration is a minimum of 60 min. This paper will discuss fire resistance test results conducted using steel, aluminum, and composite substrates.

Introduction As urbanization accelerates, highway tunnels are proliferating across China. Owing to their semi-enclosed geometry, the primary objectives in a tunnel fire are immediate smoke extraction and toxic-gas dilution to rescue trapped occupants. Yet current research struggles to capture long-range smoke spread in full-scale tunnels and often overlooks how the relative position between fans and the fire source affects flow patterns. Methods Therefore, this study investigates highway-tunnel fire smoke and occupant evacuation using full-scale experiments, theoretical analysis and FDS simulations. Results Under low-intensity fire conditions, the critical longitudinal wind speed ranges between 1 and 3 m/s. Ventilation velocity shows a positive correlation with smoke-layer thickness near the fire source, while back-layering length is negatively correlated with fan speed. Fan location significantly influences temperature, visibility and CO volume fraction. The closer the fan is to the fire, the lower the temperature, the higher the visibility and the smaller the CO volume fraction, all of which favor evacuation. At constant walking speed, shortening the fan-to-fire distance reduces both the required and available safe egress times, thereby accelerating evacuation. Discussion By linking back-layering length, temperature, visibility and CO volume fraction to evacuation time, this work provides both theoretical foundations and real-time data for tunnel emergency response, enabling rapid intervention and safeguarding lives and property.

In this study spread of smoke from a possible fire in a University building and the evacuation time of occupants were simulated. Fire dynamic simulations (FDS) have been done for natural and forced smoke evacuation with different scenarios; at the same time, evacuation simulations have also been done for various scenarios for different exits at the building. While occupants move through changing CO, CO2, and O2 concentrations, Fractional Effective Dose (FED) was gathered to obtain results from both simulations. FED results were evaluated for poisoning risk of occupants. According to comparative results, the combination of scenarios that forced smoke evacuation by fan and evacuation of occupants from all exits at the basement of the building has the lowest FED value. On the other hand, depending on the fire source and smoke movement, sometimes occupants cannot use all exits. Therefore, evacuation simulation has been done separately from each exit and evaluated with all FDS results.

India has a vast geographic diversity and accordingly has diverse responses to changing climate. The more than expected variations in the temperature are causing alterations in the water cycle and stressing the regional water availability along with agriculture significantly. With the current climate change conditions with globally evident rising temperatures, India has to face the challenge of sustaining its rapid economic growth along with ensuring food security to its increasing mainly agriculture-dependent population. The purpose of this research was to investigate the spatiotemporal variations in maximum and minimum temperature in terms of monthly and annual trends in west-flowing river basin of Kutch, Saurashtra and Marwar (WFR-KSM basin). The trend was calculated and assessed in ProUCL5.0.00 and ArcMap 10 software using 36-year Indian Meteorological Department (IMD) maximum and minimum temperature grid (1° × 1°) data from 1969 to 2004. The direction and magnitude of annual and monthly trends were calculated for every grid using Mann–Kendall (MK) test and Theil–Sen’s (TS) slope. The trends in annual, maximum and minimum temperature were spatially analyzed annually and for every month from January to December. The majority of the area exhibited increasing trend in minimum and maximum temperature annually and in all the months from January to December. In annual maximum temperature, all grids exhibited positive slope ranging from 0.01 to 0.03 degree Celsius per year. In annual minimum temperature, majority of the grids (81.25%) exhibited positive slope ranging from 0.01 to 0.04 degree Celsius per year and none of the grids exhibited negative slope. Monthwise trend in maximum and minimum temperature also indicated rising trend in majority of the grids, with few grids identified with declining trend mainly along the eastern border of the basin.

In the early 1980s. SFP was awarded a contraCt by the Direction des Recherches et des Etudes Techniques @RET), a French Defence Agency involved in advanced research, to demonstrate the feasability of a hot gas valve (HGV) to handle highly aluminized popellant gases for Solid Rocket Motor (SRM) applications. This HGV using new carbon-carbon and carbonceramic composite materials was designed to withstand a flame tempature of 3,600K. U ' b o tests were conducted in 1986. Both tests were sucessful. different operating modes were evaluated. The fmt valve o p t e d in a bang-bang mode, while the second was designed to nin in a proportional mode. After presenting the program contents, this paper describes the detailed HGV design and the pre-6re testsconductedonkeycompo~nts, the test results and the post-test analyses. I Thrust vector control WC) using hot gases bled from the motor chamber and injected through the nozzle exit cone wall has been seen for several years as one of the most efficient TVCsystems. So,thisconceptwasthomughly investigatedin theearly 1%0s,butthemaindifficultywastodeviseanHGV able to withstand high flame temperature of aluminized propellants. The initial studies led to heavy and bulky HGVs and the fmt trials failed through lack of pop materials. There fore, the intewt in such aTVC concept declined. Recently, emerging new thermostable composite materials with shucnual capabilities over a wide range of temperatures resulted in a new way of tackling the HGV demonsuation. Consequently, five years ago, the Societe Europeenne v CoDvrlght 0 American Institute of Aeronautm and 1 de Propulsion (SEP) offered the DRET to demonstrate an HGV for a TVC application. This proposal was based upon SEP's developed and manufactured mbon-carbm and carboncaamic materials, which were regarded as the key to overcoming the HGV challenge. Demonstrating the HGV operation was to be the crucial stage of developing a TVC system by secondary injection of hot gases bled from the motor chamber. Thisprogramwasintendedtofiretestthedemonstrationof such a device using composite carbonarbon and carbonceramic materials of SEP's nD (n-Directionnal) and SEP's NOVOLTEX families. The program scope is presented in Table 1 and consists of three major tasks. TASK 1 Designing an HGV using SEP's nD and 3D-NOVOLTEX fine woven &n rein forcements with carbon or ceramic matrices. Analysing and conducting mechanical tests on full-scale components to verify thermal and mechanical behaviors. TASK :Manufacturing and assembling two HGVs using various selected materials. TASK3:Conducting pre-fire tests, -Fire testing two HGVs embedded in heavy wall motors with : one opp-'..g in a bang-bang mode, -one operating in a proportional mode. Performing post-test investigations on fired components. Table 1 PROGRAM PIAN This p r o m was targeted at demonstrating a valving system running along with highly aluminized propellant 3.600K combustion products. The operational time was specified to fulfill ballistic missile mission without any failures due to mechanical 01 thermal shocks and without being plugd by any alumina deposits on key surfaces. v Meeting these requirements was achieved by using thermostable materials and by selecting the reliable pintle-valve operating concept This concept was picked because of its simplicity and its high ability to provide the valve with an efficient tightness as opposed to other concepts such as rotating dome-valves for example, whose operating mode &mons!ration could prove to fail because of alumina deposits. These above considerations resulted in the HGV design to be embedded in a heavy wall mom case as presented in Figure1 . The key components were : * high density carbon-cabon pintle (3). outlet nozzle (1) and casing (2), carbon-ceramic and carbm-carbon insulators, respectively (7) and (4). a silica phenolic hot gas inlet (S), metal actuator rod (5) and metal housing (6).

The variation of temperature and density in the hot, X-ray emitting gas around massive, group dominant elliptical galaxies can be understood as a combination of gas ejected from evolving galactic stars and gas that accumulates in the outer halo by secondary cosmic infall. Beginning with an overdensity perturbation in a simple flat cosmology, we can duplicate observed properties of the hot gas. At some early time we form the stellar galaxy and release supernova energy, conserving dark and baryonic matter. Using a potential appropriate to the large elliptical NGC 4472, we follow the evolution of intergalactic and interstellar gas to the present time when the computed gas density and temperature agree with X-ray observations of NGC 4472. If the hot gas and dark matter halos are subject to differential tidal truncations or mass exchanges between group members, then the correlation between $L_x/L_B$ and the relative sizes of galactic X-ray images can be generated. The physical properties of hot interstellar gas observed in bright ellipticals today are sensitive to the cosmic baryon fraction, the time of maximum star formation and the amount of ``feedback'' energy delivered to the gas by Type II supernovae at the epoch of galaxy formation.

On the fire resistance of structural steel elements derived from standard fire tests or by calculation

Hazardous waste storage, disposal, remediation, and closure

LiDAR-derived topography and forest structure predict fine-scale variation in daily surface temperatures in oak savanna and conifer forest landscapes

In response to several claims from Manufacturers that intumescent coatings could be used in place of fire insulation and provide equal protection to shipboard structures during a fire, U.S. Navy conducted an extensive investigation of several fire protective coatings for use aboard ship. These fire protective coatings included water and solvent based coatings, insulative coatings, and foams. The objective of this program was to identify passive fire protection (PFP) coatings for shipboard interior applications capable of meeting U.S. Navy (USN) fire resistance requirements (DRAFT MIL-PRF-XX 381) of 30 min rating with backside average temperature rise less than 139 C using UL-1709 fire curve (post flashover fire). This evaluation consisted of small scale fire, adhesion, and impact tests; intermediate scale room corner fire tests, and full scale fire tests conducted aboard ex-USS SHADWELL. The test results with steel substrate show that all candidate coatings failed to meet minimum U.S. Navy fire resistance criteria when used as stand-alone coatings. Furthermore, many coatings demonstrated poor adhesion, and fell off from the substrate during the fire test. These data have led the Navy to conclude that intumescent coatings tested in this study are not sufficient to protect shipboard spaces during a fire and are not equivalent when used alone as direct replacement for batt or blanket type fibrous fire insulation (mineral wool, StructoGard) installed aboard U.S. Navy ships. However, U.S. Navy smallscale fire tests have also demonstrated that some of the intumescent coatings, when applied over substrates such as Glass Reinforced Plastic (GRP), did reduce flame spread and smoke generation.

Fire hazards analyses and probabilistic fire safety analyses have demonstrated that fire can be an important contributor to core damage frequency and other major plant damage states of nuclear power plants.1 In this issue, fire modelling has been undertaken by a diverse set of contributors, including, nuclear licensees, technical safety organizations, and, in some countries, regulators, to assess the consequences of fires. One important aspect of fire related risk-informed and performance-based regulation is undeniably the availability of verified and validated fire models that can reliably estimate the consequences of a fire in confined and mechanically ventilated compartments. A number of members of the Organization for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA) expressed their interest in participating in a joint international research project on the topic of fire events to be carried out under the auspices of the NEA. The PRISME (French acronym for "Fire Propagation in Elementary Multi-Room Scenarios") Project was launched from 2006 to 2010 by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN, France) with their specially designed facilities in Cadarache. The three major research areas addressed by the PRISME Project included the confinement effect on the fire dynamics, the smoke propagation from the fire compartment to adjacent rooms, and the effect of the ventilation network on limiting smoke propagation. In total, five experimental campaigns consisting of more than 35 large-scale fire tests were carried out. The main experimental results and findings were presented in the first OECD/NEA PRISME summary report.2 In parallel to these experimental campaigns, PRISME partners evaluated the capabilities of various fire modelling codes to simulate fire scenarios based on the PRISME results. A number of benchmark exercises were conducted within an analytical working group of PRISME, which further advanced the knowledge on the predictive capabilities of the various fire codes being used.3-10 Some of these studies were published in the Fire Safety Journal, PRISME special issue.11 The experimental findings of the PRISME project and the analytical working group highlighted that confined mechanically ventilated fires were composed of physical complex phenomena to model. The outputs of the PRISME experiments and analysis allowed for the identification of further focused experimentations to address areas of uncertainty. These targeted areas formed the basis of the second PRISME Project. The second phase was launched on July 2011 and ended on December 2016. A total of nine countries signed the agreement to become PRISME 2 members: Belgium (Bel V and Tractebel-ENGIE), Canada (Canadian Nuclear Safety Commission—CNSC), Finland (Technical Research Centre—VTT), France (IRSN as Operating Agent and Électricité de France—EDF), Germany (Gesellschaft für Anlagen-und Reaktorsicherheit—GRS), Japan (Nuclear Regulation Authority—NRA and Central Research Institute of Electric Power Industry—CRIEPI), Spain (Consejo de seguridad nuclear—CSN), Sweden (Strålsäkerhetsmyndigheten—SSM), and the United Kingdom (Office of Nuclear Regulation—ONR). The project focused on advancing the state-of-the-art knowledge in smoke and hot gas propagation through a horizontal opening between two superposed compartments, fire spread on real fire sources such as cable trays or electrical cabinets, and fire extinguishing studies using fixed water-based suppression systems. In total, four experimental campaigns were undertaken comprising more than twenty large-scale fire tests within the IRSN DIVA facility in Cadarache. The last experimental campaign was defined based on the results and analysis of the previous three to ensure a cost-effective experimental campaign. In addition to the large scale fire tests, extra support tests for the characterization of fire sources, in open atmosphere, were performed to provide additional data for validation purposes. As in the previous PRISME project, the analytical working group evaluated the capabilities of various fire modelling codes to simulate fire scenarios based on the PRISME 2 results.12-15 The output of the PRISME 2 project has been summarized in the OECD/NEA application report.15 The objective of the first PRISME 2 experimental campaign, named VSP for vertical smoke propagation, was to investigate the vertical smoke propagation through a horizontal opening for fire scenarios in mechanically and ventilated compartments. A detailed description of the flow at the vent was one key issue of this campaign in order to provide detailed data to validate fire simulation zone models and more complex three-dimensional computational fluid dynamics (CFD) codes. The experimental setup was composed of two rooms (fire compartment and upper room) mechanically ventilated, with the fire source being a liquid pool fire. Two parameters were investigated: the buoyancy forces due to the temperature difference at the vent and the inertia forces due to the difference of pressure between the compartments. The effects of these parameters were investigated through the four VSP experimental tests. The results of these experiments are reported in this special issue in the paper Prétrel and Vaux, Experimental and numerical investigation of the smoke propagation in case of fire event within two confined and ventilated compartments connected with a horizontal opening. The objective of the second campaign, called FES for Fire Extinction System, was to assess the efficiency of two fixed water-based fire suppression systems. This topic is of great interest because such systems with water as extinguishing medium are often used to suppress fires in switchgear and cable rooms of nuclear power plants. Following initial sensitivity study, two key parameters were selected for investigation, droplet size distribution and water flow rate, to determine how they affect the efficiency of the water-based fire suppression systems. The fire tests investigated these effects by testing two types of industrial sprinkler and deluge nozzles with two water flow rates and two different activation times. A set of four fire tests was defined using a liquid pool as fire source. More details are given in the work of Vaux and Prétrel, Experimental and numerical study of the efficacy of water spray application in case of a fire event in a confined and mechanically ventilated compartment. On the basis of this experimental campaign, a theoretical investigation was undertaken, evaluating the concept of repeatability on large-scale fire tests. The results are reported in the paper by Prétrel and Querre, Repeatability assessment of large-scale fire experiment involving water spray system in a forced ventilated compartment. This original work provides important information for the validation of numerical simulations on this type of fire scenario. The third campaign, called CFS for Cable Fire Spreading, focused on studying fire spread for the two following configurations: fire spread over cables trays and fire spread from one electrical cabinet to other electrical targets, in mechanically ventilated fire scenarios. This campaign consisted of eight fire tests in the DIVA facility. The fire tests CFS 1 to 4 were composed of five horizontal cable trays and involved three electrical cable types, provided by the partners (GDF-SUEZ, VTT, and NRA). In addition, two ventilation renewal rates (high and low) were investigated. Some of these fire tests have been analyzed in the work of Zavaleta et al., Cable tray fire tests with halogenated electric cables in a confined and mechanically ventilated facility. Some other analyses can be found in Zavaleta and Audoui.16 The three, CFS-5 to CFS-7, fire tests involved fire sources represented by a real open-door electrical cabinet and three overhead cable trays. Specific objectives of these experimental tests were to investigate how effects of ventilation, fire dampers shutdown, and cable-type–influenced fire growth and spread in a confined and mechanically ventilated environment. The results of these fire tests are presented in the work of Zavaleta et al., Fire spread from an open-doors electrical cabinet to neighboring targets in a confined and mechanically ventilated facility. The final PRISME 2 campaign conducted tests in both open atmosphere and in the confined and mechanically ventilated DIVA facility. The open atmosphere tests were aimed at studying the impact of cable tray configuration on fire spread over multiple cable trays, including protected cable trays and slanted cable trays.17 The fire tests in a confined environment were designed to complement the previous FES and CFS campaigns. The work of Shirai et al., Experimental study of smoke effects on energized electrical cabinets located nearby a lubricant oil pool fire, reports on one of these tests. In addition to the characterization of these experimental fire tests and their physical analysis, the PRISME 2 project members wanted to share with the nuclear fire community the valuable and novel numerical work conducted during the scope of the PRISME 2 project. This learning is presented within this special issue. The modeling tools used in the various papers cover both fire zone models such as SYLVIA, lumped parameter models like COCOSYS, and highly complex three-dimensional models such as ISIS or FDS. The results provided by these different numerical studies undoubtedly make it possible to get further confidence in extending the validation domain of the different fire models. However, although improvements in fire modelling have been demonstrated, the application of these models for complex fire scenarios has illustrated the limitations of current modelling capabilities. This learning must be taken into account in future experimental programmes. In this direction, a number of recommendations have been provided by the PRISME 2 members for targeting further phenomena not exhaustively studied in PRISME 2. These phenomena are smoke stratification and spread, fire propagation between electrical cabinets, and electrical cable tray fires in confined and ventilated conditions. The ongoing follow-on PRISME 3 Project aims at addressing the above mentioned three phenomena and to provide answers to various issues of interest for nuclear fire safety analysis. The authors are grateful for the financial support of the participating OECD/NEA member countries to the joint OECD PRISME 2 Project. Moreover, they want to acknowledge the outstanding support provided by the members of the program review group for the many fruitful discussion during the PRISME 2 meetings as well as by the OECD/NEA secretariat making by their active and valuable contributions this activity a successful one: F. Bonte and C. Fourneau from Bel V (Belgium), E. Gorza and L.P. Kwahou Kesembo from Tractebel-ENGIE, (Belgium), A. Bounagui from CNSC (Canada), A. Matala and T. Sikanen from VTT (Finland), S. Hostikka from Aalto University (Finland), C. Lallemand from DGA (France), L. Gay, B. Sapa, B. Gautier, from EdF (France), T. Morii and S. Fujita from NRA (Japan), K. Shirai from CRIEPI (Japan), J. Peco Espinosa from CSN (Spain), C. Karlsson from SSM (Sweden), S. Ledin and L. Nyogeri from ONR (United Kingdom), A. Kelsey from Health & Safety Laboratory (United Kingdom), and Andrew White (NEA Secretariat).

This paper presents the multiscale temperature structures in the Milky Way (MW) hot gas, as part of the XMM-Newton Line Emission Analysis Program, surveying the O vii, O viii, and Fe-L band emission features in the XMM-Newton archive. In particular, we define two temperature tracers, I OVIII/I OVII (O87) and I FeL/(I OVII + I OVIII) (FeO). These two ratios cannot be explained simultaneously using single-temperature collisional ionization models, which indicates the need for multitemperature structures in hot gas. In addition, we show three large-scale features in the hot gas: the eROSITA bubbles around the Galactic center (GC), the disk, and the halo. In the eROSITA bubbles, the observed line ratios can be explained by a log-normal temperature distribution with a median of logT/K≈6.4 and a scatter of σ T ≈ 0.2 dex. Beyond the bubbles, the line ratio dependence on the Galactic latitude suggests higher temperatures around the midplane of the MW disk. The scale height of the temperature variation is estimated to be ≈2 kpc assuming an average distance of 5 kpc for the hot gas. The halo component is characterized by the dependence on the distance to the GC, showing a temperature decline from logT/K≈6.3 to 5.8. Furthermore, we extract the autocorrelation and cross-correlation functions to investigate the small-scale structures. O87 and FeO ratios show a consistent autocorrelation scale of ≈5° (i.e., ≈400 pc at 5 kpc), which is consistent with the expected physical sizes of X-ray bubbles associated with star-forming regions or supernova remnants. Finally, we examine the cross-correlation between the hot and UV-detected warm gas and show an intriguing anticorrelation.

Experimental and numerical study on the fire resistance behavior of steel truss girder structure in double deck suspension bridges

Purpose The purpose of this paper is to analyze the phenomenon of makeup effect using numerical simulation and model experiments on seven different natural smoke extraction patterns of tall space. Airflow distribution and heat accumulation phenomenon in different cases are compared. The natural smoke exhaust system for tall spaces has many advantages, including low cost, no power and low maintenance cost. It is more advantageous than the mechanical type of exhaust. However, the internal air distribution is complicated since the large span spatial character. Effective and correct verification method is very important for the analysis of flow fields in tall spaces. Design/methodology/approach This study used fire dynamics simulator (FDS) software to simulate the fire scene. The model experiments are conducted to determine if the numerical simulation results are reasonable. A single-mirror Schlieren system, including an 838 (H) × 736 mm (W) square concave mirror, as well as the focal length of 3,100 mm was adopted to record the dynamic flow of hot gas. Six smokeless candles were burned in a 1/12.5 model in experiments to record the distribution of inflow, accumulation and outflow of airflow in the space. In addition, the thermocouple lines were mounted in the model for temperature measurement. Findings The results of numerical simulation and model experiments have proved that makeup air has a significant effect on the effectiveness of a natural smoke vent system. Larger areas of smoke vents will produce more heat accumulation phenomenon. In this study, the air inlet and vent installed on the same side have a better heat removal effect. Moreover, Schlieren photography technique is proved to be an accurate measurement method to record the dynamic flow of hot air immediately, directly and accurately. The dynamic flow behavior of hot gas in the model has been visualized in this paper. Originality/value At present, there is no examination method other than checking the smoke vent area to validate the effectiveness of a natural smoke vent system in Taiwan, as well as no requirements regarding the makeup inlet. The effect of makeup air in generating the effective push-pull phenomenon of airflow has been analyzed. In addition, the post-combustion hot gas distributions were visualized by using Schlieren photography technology in the model space, compared with the FDS simulation result and thermocouple recorded temperature. A verification method in the model experiments is established to determine if the numerical simulation results are reasonable.