Predicting Spill Plumes with the Fire Risk Zone Model B-RISK

Recent experimental research on spill plume entrainment has developed a range of empirically-based formulae for smoke management design. These formulae form the spill plume entrainment model in B-RISK, a new fire risk zone model. This article describes the performance of B-RISK in predicting spill plume entrainment. Selected experimental data from the series of reduced-scale experiments used to form the new design formulae have been used for model validation, along with other full-scale experimental data from ‘hot smoke tests’ conducted to assess the performance of installed smoke management systems. B-RISK provides predictions of the plume clear-layer height that generally agree with experimental results within the range of experimental error. This gives confidence in its use to predict spill plume entrainment for smoke management design purposes.     

Uncertainty in Estimating the Fire Control Effectiveness of Sprinklers from New Zealand Fire Incident Reports

The current state of fire sprinkler effectiveness information has been found to be a limiting factor when comparing the fire risk for alternative building designs in New Zealand (Determination 2005/109: single means of escape from a high-rise apartment building. Department of Building and Housing, Wellington, 7). Data on the past performance of systems in real fires is one of the best sources of information to estimate future performance, but there has not been a detailed study on sprinkler effectiveness data from fire incidents in New Zealand published since Marryatt’s work (Fire: a century of automatic sprinkler protection-revised. Australian Fire Protection Association, Melbourne, 13), which was last updated in 1986 and included data from Australia. The current research looks at the quality and quantity of data available on sprinkler effectiveness from New Zealand Fire Service (NZFS) incident reports over the period of 2001 to 2010 to evaluate the data’s usefulness for risk-informed building fire safety design. A comparison is made between the number of sprinklers reported activated in the NZFS dataset, Marryatt’s study, guidance from PD 7974-7:2003 (PD 7974-7:2003: the application of fire safety engineering principles to fire safety design of buildings. Probabilistic Risk Assessment, London, 3), and NFPA data (U.S. experience with sprinklers and other automatic fire extinguishing equipment. National Fire Protection Association, Quincy, 12). Proposals to improve the collection and reporting process to increase the informative value of future NZFS data for risk-informed fire safety design are presented.     

Prediction of time to ignition in multiple vehicle fire spread experiments

This paper describes the application of the flux‐time product ignition criterion and the point source flame radiation model to predict the time to ignition in multiple vehicle spread scenarios. Ten experiments from the literature have been selected due to sufficiency of information required to apply the methods. The outcome of this work is to be applied to a risk‐based model for the design of car parking buildings to determine when and if a fire spreads between vehicles; therefore, the analysis suggests properties of a representative material that can reasonably account for those external vehicle components that are most likely to ignite first. The application of both methods to the complex problem of multiple vehicle ignition requires several assumptions and simplifications which are discussed in the paper.     

Selecting an ignition criterion methodology for use in a radiative fire spread submodel

Research is ongoing to increase the functionality of the fire zone modeling software BRANZFIRE, by converting it from a deterministic to a probabilistic model. One component of this work is the development of a radiative fire spread submodel for which a suitable ignition criterion method is needed. This paper provides details of that ignition criterion procedure and its implementation into the submodel. A list of requirements that the ignition methodology had to satisfy was established. Of the many different piloted ignition models available, the Flux–Time Product technique, and its associated ignition criterion, was selected to be incorporated into the fire spread submodel. This method provides a practical engineering approximation of when a secondary fuel item that is subjected to incident radiation will ignite that is commensurate with the accuracy of the overall model. Primarily to demonstrate the use of the technique in the submodel, a series of ignition experiments were conducted on a single example of upholstered furniture using the Cone Calorimeter apparatus, with specimens tested in both the horizontal and vertical orientation, under piloted and auto ignition conditions. The experimental incident radiation and time‐to‐ignition data, for the piloted ignition mode, was analyzed using a modified Flux–Time Product correlation procedure. To deal with the auto ignition mode, an empirical approximation, based on the modified Flux–Time Product procedure, is proposed. Data for use in the submodel was therefore also derived for the auto ignition mode, based on an experimental determination of the minimum ignition flux. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing the Sprinkler Activation Predictive Capability of the BRANZFIRE Fire Model

This paper describes an investigation into the sprinkler response time predictive capability of the BRANZFIRE fire model. A set of 22 fire/sprinkler experiments are simulated where the sprinkler activation time and the heat release rate (HRR) for each individual experiment had been determined. The experiments provided data for use in validating the sprinkler activation prediction algorithms in the BRANZFIRE zone model. A set of base case values were chosen and input files constructed for the simulations. The experiments were then simulated by the fire model using both the NIST/JET ceiling jet and Alpert’s ceiling jet options (which are the two ceiling jet correlations available in the BRANZFIRE zone model). The fire model included a heat transfer calculation for the temperature of the heat sensitive sprinkler element. Different sprinkler operational parameters such as the conduction factor, response time index (RTI) and the sprinkler depth below ceiling were also varied to assess the sensitivity of their effect on the activation time. Results showed that using the NIST/JET ceiling jet algorithm gave a closer prediction of the sprinkler response time in a small room than Alpert’s correlation. This was expected, since the former includes the effect of a hot upper layer while the latter applies to unconfined ceilings. The experiments available for comparison had been conducted inside an enclosure with a developing hot upper layer. The findings also signified that changing the sprinkler operational parameters can change the predicted sprinkler activation time significantly.     

Simplified Calculation Method for Determining Smoke Downdrag Due to a Sprinkler Spray

A simplified method has been developed to predict smoke behavior subject to a sprinkler spray. The method considers whether downdrag is likely to occur and the distance that smoke is then pulled down should downdrag be present. The method is validated using third party experimental data. Empirical equations are applied in the calculations to determine the heat loss from a smoke layer due to the sprinkler spray and therefore the smoke layer temperature. Comparative results show that the simplified method might expect the onset of smoke downdrag regardless the difference in temperature predictions. The empirical equation to predict the penetration depth of downdrag smoke is based on previous research and compared with third party experimental data. The predicted depths are acceptable for engineering use. For a 15 mm nominal sprinkler the water flow rate that leads to the onset of downdrag for typical smoke layers up to 2 m in depth is less than 100 L/min which leads to an operating pressure being less than 0.16 MPa. Experimentally data for sprinklers other than the 15 mm nominal sprinklers are unavailable and therefore the method should be used with care for any other sprinkler.     

Ignition performance of new and used motor vehicle upholstery fabrics

This paper examines the standards for fire safety in transport systems and in particular the test method for the flammability of materials within passenger compartments of motor vehicles. The paper compares data from ignition tests conducted in the cone calorimeter and the FIST apparatus with tests conducted using the FMVSS 302 horizontal flame spread apparatus. Ten materials were selected as representative of those used as seat coverings of private and commercial passenger vehicles. The time to ignition of new and used materials subject to exposure heat fluxes between 20 kW/m² and 40 kW/m² was measured. The results from the ignition tests were analysed using thermally thick and thermally thin theoretical models. The critical heat flux for sustained piloted ignition was determined from the time to ignition data using the thermally thin approach. Derived ignition temperatures from both the thermally thick and thermally thin methods were compared with measurements using a thermocouple attached to the back surface of materials in selected tests. The flame spread rates in the FMVSS 302 apparatus were determined and a comparison was made between the performance of the materials in the flame spread apparatus, the cone calorimeter and the FIST. The results suggests that a critical heat flux criterion could be used to provide an equivalent pass/fail performance requirement to that specified by the horizontal flame spread test although further testing is needed to support this. Copyright © 2004 John Wiley & Sons, Ltd.     

Benchmarking the Single Item Ignition Prediction Capability of B-RISK Using Furniture Calorimeter and Room-Size Experiments

This paper benchmarks B-RISK’s capability to predict item ignition in multiple object compartment fire simulations. A series of fire experiments have been conducted which measured single item ignition times under the furniture calorimeter and in the ISO 9705 room. These experiments used mock-up armchair, TV and cabinetry furniture items created from three common materials found in most households in New Zealand exposed to a 100 kW gas burner flame. B-RISK uses the flux-time product (FTP) method as the criterion to predict ignition of items, based on radiation received using the point source model (PSM). This paper presents an analysis of the B-RISK predictions compared to the experimental measurements. Due to the mathematical formulation of the PSM and FTP method, it is found that the predicted ignition time is sensitive to the distance between the radiative source and the item. Predicted ignition times of armchairs constructed of polyurethane foam were within 14% of the ISO 9705 room experimental results. However, for the furniture calorimeter experiments it is found that to get reasonable predictions of the ignition times for the mock-up armchair and TV items there is a need to account for the burner flame movement by adjusting the radial distance by 10–30 mm. Direct flame contact was required to ignite the mock-up cabinetry items and B-RISK was unable to successfully predict this ignition time.     

Predicting the Temperatures of Steel Members in the Cardington Fire Tests Using the THELMA Finite Element Model

A series of full-scale fire tests have been conducted in an eight-story steel frame building. Temperatures were measured in a number of protected and unprotected steel members at various locations. This paper compares the test data from one of those tests with predicted values calculated by a two-dimensional finite element thermal analysis package, THELMA. The paper considers the geometry of the members, the exposure conditions and the thermal properties of the fire protection material. It was found that THELMA made reasonable predictions for the temperatures in unprotected steel members. However, in protected members the comparison did not always exhibit a good match with the test data. This result was mainly attributable to insufficient measurements being available for the atmosphere temperature histories outside of the test compartment.