Post-flashover Fire Research Articles

Evaluation of the Field Model, Fire Dynamics Simulator, for a Specific Experimental Scenario

The new version of the fire dynamics simulator, FDS version 3.01, is verified by a series of full-scale fire tests. Experiments are carried out in a compartment similar in size to the ISO-9705 room calorimeter. Gasoline pool fires of different diameters are used to give different heat release rates. The ventilation factors of the compartment are adjusted to produce flashover. Fire-induced flow, temperature, and pressure fields in these different physical scenarios are calculated using the FDS software. The predictions for temperature and radiative heat flux of a post-flashover fire in the specific configuration tested are in reasonably good agreement with experimental results even when the flame occupies most of the room volume.

Assessment of Fire Hazard in Small News Agents in Transport Terminal Halls

A large amount of combustibles are stored in small newspapers and magazine shops in terminal halls known as news agents in the Far East. Fire safety for those small shops located in crowded public transport interchanges should be evaluated carefully. In carrying out fire hazard assessment, the possible heat release rates should be estimated so that consequences of a fire can be assessed. As the shops are small with easily ignited combustibles, transition to a postflashover fire would be rapid. Therefore, the resultant heat release rates should be measured by burning those combustibles under flashover conditions. Hazard assessments based on full-scale burning tests for postflashover news agent fires performed in remote areas in China are reported in this paper. The effect of reducing the heat release rate by discharging water mists is illustrated. Such fire suppression systems are recommended for use in such shops.

Analysis of work on smoke component yields from room-scale fire tests

Smoke Component Yields from Room-Scale Fire Tests (NIST Technical Note TN 1453) has recently been published. This was expected to be an important work in developing concentrations and yields of toxicants that could be used for evaluating the usefulness of small scale smoke toxicity apparatuses (or fire models) for use in the prediction of the toxicity of materials and products in real fires. However, the work has a number of uncertainties that limit its potential for use as a reference. There are three major problems with this work. First, the post-flashover concentrations of CO are too low (as recognized by the authors who recommend that this part of the data not be used). Second, the post-flashover concentrations of the main toxicants measured (HCN and HCl) were much higher than found in most studies. Third, the precision of the data was inadequate. The consequence of the first two issues is that the work seriously overestimates the toxicological importance of gases known to have only minor effects in post-flashover fires, such as HCN and HCl. The very low concentrations of toxicants measured at pre-flashover conditions might have a value not discussed by the authors: an indication that pre-flashover fires of the type conducted here do not generate extremely toxic atmospheres. Accordingly, the report does not provide reliable characteristic room scale combustion gas data that can be used for validating small-scale furnaces.

The Behaviour Of Multi-storey Composite Steel Framed Structures In Response To Compartment Fires

This paper presents a summary of the PhD research project “The behavior of multistory composite steel frame structures in response to compartment fires.” The original assumptions, conclusions and suggested further work of the thesis are revisited and newly discussed in the context of structural fire engineering design post 9-11. The aims of the original PhD research were to extend the understanding of whole frame structural response to fire beyond the research carried out on the Cardington frame fire tests by studying configurations not identical to Cardington, to allow extended application of the at the time new techniques, in real design. Serious post-flashover fires in real buildings in the 1990s had shown that whole frame response of composite steel structures was significantly better than previously thought and it seemed that the amount of passive fire protection applied to steel was conservative. In addition it was clear our understanding of real structural fire responses including alternative load bearing mechanisms in fire could result in a more robust approach to structural design. The events of 9-11 and recent tall building fires around the world have meant that fire resistance ratings of tall building structures are being scrutinized again but this time the issue is whether the ratings are adequate or should there be alternative means of engineering structural resilience in fire, especially if total evacuations and extreme events like fire spread to multiple compartment floors are to form the basis of design for tall buildings in the future. The conclusions of this work are that the beam spans (6-9 m) considered by the PhD research were short in comparison with some modern construction particularly in high rise design. The design fires considered by the sensitivity analysis were severe but could be exceeded if fire spreads via the façade to the compartments above. Conclusions resulting from the sensitivity analyses carried out with regard the effects of different fire scenarios and the effects of different edge restraint on the structural behavior of a composite floor remain valid. Runaway failure (a rapid increase in mid-span deflection) was observed in the analyses conducted as part of the PhD research but local cracking and rupture or unzipping of reinforcement could not be modeled. These kind of failure modes were not observed at Cardington and this is a shortfall of the tests in terms of ultimate limit state design. A suggested piece of further work resulting from the PhD was a test to failure of a composite slab. However, there is currently still no experimental evidence to check if reinforcement rupture or unzipping type failures in a composite floor should be a concern. In contrast recent research since 9-11 is beginning to identify potential global progressive collapse mechanisms in different long-span floor systems. Failure mechanisms are being validated against evidence from real fires such as WTC 1, 2 and 7. It is clear that key possible failure mechanisms of composite frame structures in fire are still to be quantified and understood.

Behaviour of a small composite steel frame structure in a “long-cool” and a “short-hot” fire

This paper describes the results of finite element analyses on a small generic composite steel and lightweight concrete frame. It compares the structural behaviour of the frame during two different single floor compartment fires. The fire scenarios are modelled using Pettersson's (Fire Engineering design of Steel Structures, Swedish Institute of Steel Construction, Publication 50, Stockholm, 1976) post-flashover temperature-time curves assuming a fire load density typical of offices and opening factors of 0.02 and 0.08 m 1/2 . With an opening factor of 0.08 m 1/2 the model fire is characterised by high temperatures but a relatively short post-flashover duration (“short-hot fire”). In contrast an opening factor of 0.02 m 1/2 provides less ventilation leading to a post-flashover fire with lower maximum atmosphere temperatures but a longer post-flashover duration (“long-cool” fire). The two fire scenarios create contrasting structural behaviour because the duration of the fire dictates the gradient through the depth of the composite slab. In the “short-hot” fire the steel beams achieve high temperatures but only the exposed face of the concrete begins to respond to heating. The rest of the slab depth stays cool. In the “long-cool” fire an extended post-flashover duration allows heat to penetrate further through the thickness of the slab. The slab has a higher mean temperature, thus the gradient through the composite is lower. During the analyses the columns and edge beams were protected to provide 60 min fire resistance, primary and secondary beams were unprotected. The structural response to each fire is compared and explained.

Estimating Data for Incapacitation of People by Fire Smoke

Fire hazard and risk analyses establish the basis for providing conditions of safety for people, including those that are more sensitive to fire smoke than others. For this purpose, this paper develops a method for estimating, from information on lethal and incapacitating exposures for rats, smoke toxic potency values for incapacitation of smoke-sensitive people. For those engineering applications where the mix of combustibles is unknown, generic values are derived of the concentration of smoke that would incapacitate smoke-sensitive people in 5 min: 6 g/m3 for a well-ventilated fire and 3 g/m3 for an underventilated (e.g., post-flashover) fire. These values are estimated with significant assumptions in their derivation, resulting in an estimated uncertainty of about a factor of two. Further, there is a wide range of smoke toxic potency values reported for various combustibles, and some of these will lead to values significantly higher or lower than these generic figures.

The natural fire safety concept—full-scale tests at Cardington

As part of a European collaborative programme of research, the UK's Building Research Establishment has carried out a series of eight full-scale fire tests in a purpose-built compartment at Cardington in the United Kingdom. The work is in support of the development of the ECSC programme “Natural Fire Safety Concept, Full Scale Tests, Implementation in the Eurocodes, and Development of a Userfriendly Design Tool”. This test programme is distinct from the collaborative fire test programme carried out on the steel-framed building at Cardington to study the structural response of a building to fire. The tests have been undertaken in a compartment with overall dimensions of 12 m×12 m. The parameters considered in the tests have been defined from a consideration of the limitations of the current parametric approach adopted in Annex B of the ENV version of Eurocode 1.2 [1] and from the requirement to validate the program OZONE developed in the scope of a complementary research project. The tests have investigated the influence of compartment linings, fire load type and through draft condition on the severity of fully developed, post-flashover fires. Fire development in the pre-flashover phase and smoke movement are not considered in this programme although complementary tests carried out by the other partners to the research have investigated these aspects of fire behaviour. The objectives of the research are to gather high-quality data on the behaviour of post-flashover fires in realistic compartments and to use this information to validate the natural fire safety concept. This paper considers the predictive methods for determining the parametric temperature–time response in the Eurocode in the light of comparisons with the test results.

A tool to design steel elements submitted to compartment fires—OZone V2. Part 1: pre- and post-flashover compartment fire model

The computer code OZone V2 has been developed to help engineers in designing structural elements submitted to compartment fires. The code is based on several recent developments, in compartment fire modelling on one hand and on the effect of localised fires on structures on the other hand. It includes a single compartment fire model that combines a two-zone model and a one-zone model. In this paper, the description of this compartment fire model is given. The main model is first presented. It consists of the usual zone model equations fully coupled with the partition model equations. The partitions are modelled by the finite element method. The switch from the two-zone to the one-zone model is then explained. The vertical, horizontal and forced vent sub-models are presented, followed by the fire source and the combustion models. A comparison between this code and another compartment fire model NAT is made. The OZone calculations are then compared to full scale fire tests. Considerations as to how this model is used for the design of steel elements will be presented in a companion paper (Fire Saf. J., this issue).

Radiant heat flux to external surfaces from escaping and extrusive flashover flames

Current practice when predicting safe separation distances between buildings is to assess the radiant hazard posed by flames and hot gas visible across the vent. The vent is treated as a radiating vertical surface with a representative temperature. A method is proposed for calculating the radiant heat flux to external surfaces from hot gas and extrusive flame emerging from a vent in a compartment wall containing post-flashover fire. An experimental study has been made to examine the validity of the method for extrusive flames unaffected by wind.

Application of Water Mist Fire Suppression Systems in Small Retail Shops

Protecting small retail shops packed with combustible goods by sprinkler system might not be too satisfactory. Any delay in system activation will lead to a flashover fire. Also, there might be serious water damage which is not good for shops selling expensive items. Alternative fire protection systems should be searched for. Water mist might be effective for suppressing postflashover fires if the system is designed properly. Whether water mist fire suppression systems can be used in the small shops is discussed in this paper. Key factors affecting the system performance will be discussed. Potential application strategies are outlined. An example was used to illustrate the design of the system.

Post-Flashover Fires in Light and Heavy Timber Construction Compartments

A series of fire experiments was performed to study the gas temperature development and charring behaviour of timber construction compartments. The measured gas temperatures were 300-500 C lower than predicted by the parametric temperature-time curves of Eurocode 1 for unprotected and insufficiently protected timber structures. For structures protected with a double layer of gypsum plasterboard, the agreement was better. In all cases, however, the prediction was on the safe side. One protective layer of gypsum plasterboard delayed the onset of charring for 20 min. Using two layers, the delay time was doubled. Reduced charring rates for long exposure times were observed, resulting from the increasingly protective effect of the char layer withtime.

Post-flashover fires for structural design

One of the major difficulties in designing structures to resist fires is the selection of post-flashover design fires. This paper proposes modifications to the parametric equation for post-flashover fires given in the Eurocode. The proposal is based on design fires obtained from the COMPF2 computer program, after calibration to results from realistic test fires using judicious characterisation of the fuel in the input data. The proposed new equation gives a much better fit to the real fire data than the existing Eurocode equation, which predicts temperatures lower than those measured in tests.

Modeling the Impact of Post-Flashover Shipboard Fires On Adjacent Spaces

Post-flashover fires in shipboard spaces have pronounced effects on adjacent spaces due to highly conductive boundaries. A model has been developed which predicts the thermal environment in such spaces. The model is based on radiative and convective heat transfer involving the hot wall (common boundary between post-flashover and adja cent space), the cold walls, and a gray gas. This theoretical description is reduced to a set of simultaneous non-linear equations that are solved by a Newton-Rapheson method. Experimental data provided the input function for the hot wall, and the model predictions for the gas temperature and the cold wall temperature have been compared with the experimental data. The comparisons shown are conservative, but representative, in accor dance with modeling assumptions. Language: en

A methodology for obtaining and using toxic potency data for fire hazard analysis

A comprehensive methodology has been developed for obtaining and using smoke toxicity data for fire hazard analysis. This description of the methodology comprises (1) determination that the post-flashover fire is the proper focus of smoke inhalation deaths; criteria for a useful bench-scale toxic potency (LC50) measurement method; (2) a method which meets these criteria, especially validation against real-scale fires; (3) a computational procedure for correcting the results from the bench-scale test for the CO levels observed in real-scale post-flashover fires; (4) procedures for reducing the usage of animals and broadening the applicability of data by interpreting gas measurement data using the N-Gas Model; and (5) a procedure for identifying whether a product produces smoke within the ordinary range of toxic potency for postflashover fires.

Modelling Post-Flashover Fires With FASTLite

This paper describes the post-flashover use of the FASTLite program and illustrates typical output for a post-flashover fire in a single room. The program is shown to model heat release and fire duration in a rational way, but some calculated compartment temperatures appear to be too high. Suggestions are made for using the program in its current form and for future improvements. Language: en

Light Timber-Framed Walls Exposed to Compartment Fires

The objective of this project was to determine the equivalent time of exposure (to the ISO-834 standard fire), for a number of light timber-framed wall assemblies exposed to a range of time temperature curves characteristic of compartment fires.This analysis considered only the thermal behavior of the walls. Load bearing performance will be the subject of the next phase of the study.The overall method was as follows.(1) The data from four full-scale ISO-834 wall tests were used to calibrate a finite element model of the wall assembly developed using the TASEF program. Subsequently the model was validated using test on walls with different layouts.(2) A set of characteristic time-temperature curves for compartment fires was developed using the computer program COMPF-2, a post-flashover compartment fire model.(3) The finite element models of the walls developed in Step 1 were subjected to the time temperature curves developed in Step 2.(4) The temperatures within the wall assembly found in Step 3 were compa...

The development of a new small-scale smoke toxicity test method and its comparison with real-scale fire tests

A comprehensive methodology has been developed for obtaining and using smoke toxicity data for fire hazard analysis. This bench-scale method can simulate diverse fire conditions and identify extremely toxic smoke under both pre- and post-flashover conditions. However, incidence data show that most of the fire deaths in the U.S. occur outside the room of fire origin from smoke and toxic gases that are generated from a fire under post-flashover conditions. Therefore, the most relevant real-scale combustion conditions to simulate in the bench-scale apparatus would be the post-flashover conditions which are achieved by using radiant heat, a high heat flux, and correcting the bench-scale carbon monoxide (CO) results to agree with CO yields observed in real-scale post-flashover fires. The number of test animals (Fischer 344 male rats) is minimized by using the N-Gas Model to estimate the LC 50 value from the chemical analysis of the smoke. The current N-Gas Model predicts the toxicity of complex fire gas mixtures based on a large data base of experimental results of individual and mixed gases that include CO, CO2, reduced O2, HCN, HCl, HBr, and NO X. The prediction is checked with a small number of animal tests and an approximate LC 50 value is determined. The bench-scale results have been validated with full-scale room wall burns of a limited number of materials of widely differing characteristics chosen to challenge the system. The toxic potency values are assessed to determine if the smoke from a material or product is unusually or extremely toxic and can then be used in computations of fire hazard.

A New Design Approach for Steel Structures Exposed to Fires

There is a need to develop an analytical methodology for the design of steel framed struc tures exposed to fire to provide design engineers with an approach which will achieve a known level of performance. An important step in this process is the development of a simple technique for determining the thermal impact of a fire.Such a technique is presented in this paper for insulated steel structures. This approach involves a new technique to determine a post-flashover fire's time-temperature history. Based on this, a method is presented for determining the peak temperature in an exposed steel beam, as well as a means to determine an equivalent fire endurance rating based on the ASTM E119 Standard Fire Test. This work is an extension of the existing applications of the Normalized Heat Load Concept.1. Harmathy, T.Z. and Mehaffey, J.R. "Post Flashover Compartment Fires," Fire and Materials, 7, No. 2, p. 57, 1983.2. ASTM. Standard Methods of Fire Tests of Building Construction and Materials. Designation: E 119 ...

Protecting fire fighters exposed in room fires: Comparison of results of bench scale test for thermal protection and conditions during room flashover

Heat flux conditions measured in seven room fires are discussed. The conditions varied from just below flashover in a sparsely furnished bedroom to flashover and severe postflashover fire in a typically furnished recreation room. These heat flux conditions are compared with the protection level provided by fire fighter turnout coats conforming to NFPA 1971,Protective Clothing for Structural Fire Fighting. This standard requires that the turnout coat or pants assembly must protect the wearer against second degree burns when a heat flux of 84 kW/m2 (2 cal/cm2.s) is applied to its outside surface for a minimum of 17.5 seconds [“thermal protective performance (TPP) of 35”]. The results imply that fire fighters have only ten seconds or less to escape under most flashover conditions. However, the turnout coats provide good protection in many other fire situations. Practical definitions for flashover are given, and possible means for making the TPP test more relevant for research and development work are discussed.

Experimental investigation of fire behavior in a 1/6 scale dual opening compartment

Compartment fire experiments were conducted using a reduced scale model to investigate the fire behavior in a single room with two openings—a door and a window. The concept of the equivalent opening height was introduced into this paper to discuss this dual opening (door and window) effect on the compartment fire behavior, comparing it with single opening compartment fires. The flame spread rate on the compartment floor, the mass burning rate of the solid fuel and the flashover time were strongly influenced by this dual opening effect. These results were investigated in terms of the equivalent opening height, Heq. The flame spread rate on the compartment floor could be well correlated with the square root of the equivalent opening height. The mass burning rate of the solid fuel in the post-flashover fire was discussed in terms of the equivalent ventilation parameter, ( ( A H ) e q ), derived from Heq, where A is the area of ventilation opening and H is its height. The burning rate in the dual opening compartment was lower than expected. Flashover time was minimum at about ( A H ) e q = 0.01 ( m 5 / 2 ) , but became longer than that in the single opening compartment. An oscillatory phenomenon was observed in the dual opening compartment as well as in the single opening compartment for floor fires. This oscillation was a symmetrical puffing in the dual opening compartment, but it could not be observed for wall fires.