Predicting toxic gas concentrations resulting from enclosure fires using the local equivalence ratio concept linked to fire field models

Fire field modelling is based on the techniques of computational fluid dynamics (CFD), which provide detailed variable solutions throughout the computational domain quickly, repeatedly and cheaply compared with fire experiments. A main component of fire effluent are toxic gases and one of the main toxic gases responsible for a significant number of fire fatalities is Carbon Monoxide (CO). Current engineering fire field models either ignore the prediction of toxic gas generation or require the use of detailed chemistry to predict toxic gas generation. These detailed chemistry models require considerable data which is not generally available for most common building materials. The main objective of the study presented in this thesis is to develop practical and reasonable engineering fire field models to simulate the production and movement of toxic gases in enclosure fires. The developed toxicity models should be capable of working within the framework of the current popular combustion models in fire safety engineering. In addition, the developed models should not rely too heavily on hard to obtain experimental data. The central idea behind the newly developed toxicity model is the use of the Local Equivalence Ratio (LER). The species yields as functions of the Global Equivalence Ratio (GER) and temperature are input parameters of this model. Correlations for most building materials are available from small-scale fire experiments. Similar approaches to this method are also developed using the CO/CO2 and H2/H2O mole ratios. The LER methodology is further refined by an approach which divides the computational domain for the calculation of toxic gases into two parts, a control region in which the toxic gases are dependent on the LER and temperature, and a transport region in which the toxic gas concentrations are dependent on the mixing of hot gases with fresh air. The toxicity model is then extended to two-fuel cases. In the two-fuel model, the LER is a function of the two mixture fractions, which are used to represent the mixture of the two different fuels, oxygen and combustion products. This model is useful in simulating residential fires, in which wood lining of sidewalls or ceilings is the second fuel. Finally, the transportation of HCI within fire compartments is considered. A mathematical model is developed to simulate the exchange of HCI between gas boundary and wall surfaces and the reaction of HCI with walls. All the toxicity models developed in this study can be integrated into the practical volumetric heat source approach and the Eddy Break-up (EBU) combustion model typically used in practical engineering analysis

A computational study of the characteristics of aircraft post-crash fires

Full-scale furnished cabin fires have been studied experimentally for the purpose of characterising the post-crash cabin fire environment by the US Federal Aviation Administration for many years. In this paper the Computational Fluid Dynamics fire field model SMARTFIRE is used to simulate one of these fires conducted in the C-133 test facility in order to provide further validation of the computational approach and the SMARTFIRE software. The experiment involves exposing the interior cabin materials to an external fuel fire, opening only one exit at the far end of the cabin (the same side as the rupture) for ventilation, and noting the subsequent spread of the external fire to the cabin interior and the onset of flashover at approximately 210 seconds. Through this analysis, the software is shown to be in good agreement with the experimental data, producing reasonable agreement with the fire dynamics prior to flashover and producing a reasonable prediction of the flashover time i.e. 225 seconds. The paper then proceeds to utilize the model to examine the impact on flashover time of the extent of cabin furnishings and cabin ventilation provided by available exit

Grouping strategies for MPS soot transport model and its application in large-scale enclosure fires

A soot transport model called Multi-Particle-Size model (MPS model) was developed to improve the prediction of soot movement by considering the uneven mass size distribution of soot particles and the influence of particle size on the gravitational settling. The model requires a sophisticated grouping strategy to divide the soot particles into several groups and determine the representative size for each group. In this paper, several soot particle grouping strategies and the method to calculate the representative sizes are developed with the aim of balancing the computational efficiency and the prediction accuracy of the model. The performance of the MPS model when different grouping strategies are applied is investigated through the comparison of the predicted movement of soot particles generated from several materials. Based on this analysis a grouping strategy that results in the identification of three groups is shown to be sufficient to represent the influence of particle size on the gravitational settling for a variety of combustible materials and the computational cost of the extra governing equations for the transport of soot particles in the groups is acceptable. Furthermore, the efficiency of the model is demonstrated by simulating soot movement in a large-scale industrial building with a high ceiling

A forensic analysis of a fatal fire in an indoor shooting range using coupled fire and evacuation modelling tools

In this paper, coupled fire and evacuation computer simulations are used to numerically reconstruct a fatal fire that occurred in an indoor shooting range in Pusan, Korea in 2009. Of the 16 building occupants, 15 were killed and only one survived with serious injuries. The analysis demonstrates that these modelling techniques can accurately reproduce the outcome of this fire. The numerical approach is then used to forensically analyse the incident to determine what factors significantly contributed to the high loss of life. In particular, the occupant response times are analysed as is the impact of the flame spread rate on the polyurethane foam cladded walls of the shooting range. The results suggest that it is unlikely that anyone could have survived if response times were greater than 5 seconds. Furthermore, the analysis suggests that fatalities could not have been completely avoided even if the occupants had zero response time. In addition, it is demonstrated that gunpowder residue on the polyurethane foam walls is the critical factor in producing the high loss of life in this incident. The average number of fatalities could be reduced from an average of 14.9 in the reconstruction case with gunpowder residue on the polyurethane foam walls to an average of 0.1 if the walls are completely free of gunpowder residue. However, to completely eliminate fire related casualties, it is necessary to use a polyurethane foam wall cladding material with low flame spread rates together with an effective gunpowder cleaning system

Modeling the impacts of climate change on nitrogen losses and crop yield in a subsurface drained field

The effect of climate change on crop production and nitrate-nitrogen (NO3-N) pollution from subsurface drained fields is of a great concern. Using the calibrated and validated RZWQM2 (coupled with CERES-Maize and CROPGRO in DSSAT), the potential effects of climate change and elevated atmospheric CO2 concentrations (CO2) on tile drainage volume, NO3-N losses, and crop production were assessed integrally for the first time for a corn-soybean rotation cropping system near Gilmore City, Iowa. RZWQM2 simulated results under 20-year observed historical weather data (1990–2009) and ambient CO2 were compared to those under 20-year projected future meteorological data (2045–2064) and elevated CO2, with all management practices unchanged. The results showed that, under the future climate, tile drainage, NO3-N loss and flow-weighted average NO3-N concentration (FWANC) increased by 4.2 cm year−1 (+14.5 %), 11.6 kg N ha−1 year−1 (+33.7 %) and 2.0 mg L−1 (+16.4 %), respectively. Yields increased by 875 kg ha−1 (+28.0 %) for soybean [Glycine max (L.) Merr.] but decreased by 1380 kg ha−1(−14.7 %) for corn (Zea mays L.). The yield of the C3 soybean increased mostly due to CO2enrichment but increased temperature had negligible effect. However, the yield of C4 corn decreased largely because of fewer days to physiological maturity due to increased temperature and limited benefit of elevated CO2 to corn yield under subhumid climate. Relative humidity, short wave radiation and wind speed had small or negligible impacts on FWANC or grain yields. With the predicted trend, this study suggests that to mitigate NO3-N pollution from subsurface drained corn-soybean field in Iowa is a more challenging task in the future without changing current management practices. This study also demonstrates the advantage of an agricultural system model in assessing climate change impacts on water quality and crop production. Further investigation on management practice adaptation is needed

Inflight transmission of COVID-19 based on experimental aerosol dispersion data

Background: An issue of concern to the travelling public is the possibility of in-flight transmission of COVID-19 during long- and short-haul flights. The aviation industry maintains that the probability of contracting the illness is small based on reported cases, modelling and data from aerosol dispersion experiments conducted on-board aircraft. Methods: Using experimentally derived aerosol dispersion data for a B777–200 aircraft and a modified version of the Wells-Riley equation we estimate inflight infection probability for a range of scenarios involving quanta generation rate and face mask efficiency. Quanta generation rates were selected based on COVID-19 events reported in the literature while mask efficiency was determined from the aerosol dispersion experiments. Results: The MID-AFT cabin exhibits the highest infection probability. The calculated maximum individual infection probability (without masks) for a 2-hour flight in this section varies from 4.5% for the ‘Mild Scenario’ to 60.2% for the ‘Severe Scenario’ although the corresponding average infection probability varies from 0.1% to 2.5%. For a 12-hour flight, the corresponding maximum individual infection probability varies from 24.1% to 99.6% and the average infection probability varies from 0.8% to 10.8%. If all passengers wear face masks throughout the 12-hour flight, the average infection probability can be reduced by approximately 73%/32% for high/low efficiency masks. If face masks are worn by all passengers except during a one-hour meal service, the average infection probability is increased by 59%/8% compared to the situation where the mask is not removed. Conclusions: This analysis has demonstrated that while there is a significant reduction in aerosol concentration due to the nature of the cabin ventilation and filtration system, this does not necessarily mean that there is a low probability or risk of in-flight infection. However, mask wearing, particularly high-efficiency ones, significantly reduces this risk

Fire safety risks of external living walls and implications for regulatory guidance in England

External living walls (LWs) have aesthetic and environmental appeal, but these characteristics must not compromise fire safety. A review of legislation indicates there are no specific fire regulations or test standards for LWs in England. Furthermore, the 2013 UK Green wall guidance document (GWGD) contradicts current guidance in Approved Document B (ADB) for certain categories of buildings, yet ADB cites GWGD as “best practice”. We suggest the recommended reaction to fire testing methodology for LW systems (single burning item (SBI) EN13823/ignitability EN ISO11925-2 tests) is inappropriate for assessing their fire performance. Despite some limitations, the BS8414 full-scale test could be used to assess LW installations. While not identified in the GWGD or specifically recommended within ADB as a suitable test method for LWs, it is arguably more appropriate than reduced scale SBI testing, primarily because it accommodates full LW modules with planting, and uses a more appropriate fire size. To reduce testing costs, we propose the use of CFD fire modelling, or a modified SBI test to identify candidate LW products likely to pass BS8414 testing. Given the inherent variable nature of LWs and their associated fire properties, LW maintenance is considered essential for on-going compliance with fire safety requirements

Regulatory Network and Prognostic Effect Investigation of PIP4K2A in Leukemia and Solid Cancers

Germline variants of PIP4K2A impact susceptibility of acute lymphoblastic leukemia (ALL) through inducing its overexpression. Although limited reports suggested the oncogenic role of PIP4K2A in cancers, regulatory network and prognostic effect of this gene remains poorly understood in tumorigenesis and leukemogenesis. In this study, we conducted genome-wide gene expression association analyses in pediatric B-ALL cohorts to discover expression associated genes and pathways, which is followed by the bioinformatics analyses to investigate the prognostic role of PIP4K2A and its related genes in multiple cancer types. 214 candidates were identified to be significantly associated with PIP4K2A expression in ALL patients, with known cancer-related genes rankings the top (e.g., RAC2, RBL2, and TFDP1). These candidates do not only tend to be clustered in the same types of leukemia, but can also separate the patients into novel molecular subtypes. PIP4K2A is noticed to be frequently overexpressed in multiple other types of leukemia and solid cancers from cancer cohorts including TCGA, and associated with its candidates in subtype-specific and cancer-specific manners. Interestingly, the association status varied in tumors compared to their matched normal tissues. Moreover, PIP4K2A and its related candidates exhibit stage-independent prognostic effects in multiple cancers, mostly with its lower expression significantly associated with longer overall survival (p < 0.05). Our findings reveal the transcriptional regulatory network of PIP4K2A in leukemia, and suggest its potentially important role on molecular subtypes of multiple cancers and subsequent treatment outcomes