Numerical Modelling of Simultaneous Heat and Moisture Transport in Fire Protective Suits Under Flash Fire Exposure and Evaluation of Second Degree Burn Time

An improved numerical model is developed for coupled heat and moisture transport in fire protective suit exposed to flash fire. This model is combined with Pennes' bio-heat transfer model and subsequently, second-degree burn time is estimated using Henriques' burn integral. Natural convection is considered inside the air gap present between the multilayer clothing ensemble and the skin. Comparisons of temperature and moisture distribution within the multilayer clothing, air gap, and the skin during the exposure are presented considering combined heat and moisture transport and only heat transport. Effect of moisture transport on the protective performance of the fire protective suit is shown. Impact of both horizontal and vertical air gap orientations on second-degree burn time is studied. Effect of temperature-dependent thermo-physical properties, relative humidity, fiber regain, different exposure conditions and fabric combinations for the fire protective suits on burn time is analyzed.

Reduced Combustion Mechanism for Fire with Light Alcohols

The need for sustainable energy has incentivized the use of alternative fuels such as light alcohols. In this work, reduced chemistry mechanisms for the prediction of fires (pool fire, tank fire, and flash fire) for two primary alcohols—methanol and ethanol—were developed, aiming to integrate the detailed kinetic model into the computational fluid dynamics (CFD) model. The model accommodates either the pure reactants and products or other intermediates, including soot precursors (C2H2, C2H4, and C3H3), which were identified via sensitivity and reaction path analyses. The developed reduced mechanism was adopted to predict the burning behavior in a 3D domain and for the estimation of the product distribution. The agreement between the experimental data from the literature and estimations resulting from the analysis performed in this work demonstrates the successful application of this method for the integration of kinetic mechanisms and CFD models, opening to an accurate evaluation of safety scenarios and allowing for the proper design of storage and transportation systems involving light alcohols.

THERMAL AND OVERPRESSURE HAZARDS MODELLING AND SIMULATION: A CASE STUDY OF REFINERY FIRED HEATER

Crude oil-fired heaters are associated with considerable fire and explosion hazards. The heaters present higher risks at later operational life due to ageing, wear and obsolescence. It is therefore important to re-evaluate such heaters to determine the adequacy or otherwise of the existing safeguards. This paper presents results of studies on hazard levels in aged fired heaters through quantitative consequence modeling method. A number of credible failure scenarios were considered. In particular, characteristics of potential jet fires due to Liquefied Petroleum Gas (LPG) leaks from hole sizes: 15, 30, 50 and 100 mm were investigated. For the 100 mm hole size, it was found that thermal radiation level of up to 37.5 kW/m2 could be experienced within 25 m radius of the heater, which is enough to affect nearby operators severely and could also adversely affect critical pieces of equipment around. Fireball potential with peak thermal density of about 12.5 kW/m2 was also observed within 2 m radius. For the 100 mm hole size, lower flammability limit of the fuel could be attained within 16 m downwind which poses flash fire risks. Overpressures of 1.02, 1.14 and 1.21 bar could be experienced at 30, 6 and 4 m respectively away from the fired heater which could result in partial demolition of structures that are within the radius.Overall, the results indicate that the risk profile is very sensitive to leak sizes, operating and atmospheric conditions as well as the fuel quantity being held, among others. For the chosen case study, higher integrity protection layers, in form of safety instrumented systems, relief, blow down and alarm systems, are recommended. Keywords: Downwind distance; Consequence modeling; Radiation intensity; Flame length; Overpressure; Toxicity; Liquefied Petroleum Gas.

Investigation of Survival/Hazard Rate of Natural Ester Treated with Al2O3 Nanoparticle for Power Transformer Liquid Dielectric

Increasing usage of petroleum-based insulating oils in electrical apparatus has led to increase in pollution and, at the same time, the oils adversely affect the life of electrical apparatus. This increases the demand of Mineral Oil (MO), which is on the verge of extinction and leads to conducting tests on natural esters. This work discusses dielectric endurance of Marula Oil (MRO), a natural ester modified using Conductive Nano Particle (CNP) to replace petroleum-based dielectric oils for power transformer applications. The Al2O3 is a CNP that has a melting point of 2072 °C and a low charge relaxation time that allows time to quench free electrons during electrical discharge. Al2O3 is blended with the MRO and Mineral Oil (MO) in different concentrations. The measured dielectric properties are transformed into mathematical equations using the Lagrange interpolation polynomial functions and compared with the predicted values either using Gaussian or Fourier distribution functions. Addition of Al2O3 indicates that 0.75 g/L in MRO has an 80% survival rate and 20% hazard rate compared to MO which has 50% survival rate and 50% hazard rate. Considering the measured or interpolated values and the predicted values, they are used to identify the MRO and MO’s optimum concentration produces better results. The test result confirms the enhancement of the breakdown voltage up to 64%, kinematic viscosity is lowered by up to 40% at 110 °C, and flash/fire points of MRO after Al2O3 treatment enhanced to 14% and 23%. Hence the endurance of Al2O3 in MRO proves to be effective against electrical, physical and thermal stress.

Modelling of accidental phenomena related to leakage and tank rupture of a vehicle converted to LPG

Purpose Liquefied petroleum gas (LPG), known by its ecological qualities, making Algeria has since the 1980s carried out a policy of development of LPG fuel in substitution of traditional fuels and especially petrol. However, following a series of accidents (fires, explosions, etc). that occurred in 1999, 20 years after the introduction of the LPG in France these incidents led to the search for the strengthening of the safety of the installations by better or new technical and/or organizational measures. This strategy consists in establishing a balance between environmental protection and economic profitability while ensuring the safety aspect. Design/methodology/approach The approach used is quantitative risk analysis authors have identified the potential accident scenarios that consist of leakage and rupture of tanks depend on bow tie. According to the latter using PHAST software, to model these scenarios (thermal, overpressure and dispersion) and their effects on human beings and goods. Findings In this paper, it was noted that there are scenarios such as (jet fire, dispersion), are affected by atmospheric conditions (wind speed humidity), the stronger the wind, the higher the LPG spread unlike instant scenarios (1.3 s for the fireball and millisecond for the explosion) that have not been related to climatic conditions because they have a short duration on the one hand, and on the other hand, a safe distance is given in each phenomenon. Finally, some instructions for drivers and installers have been identified by protective and preventive action. Originality/value Based on a quantitative risk analysis, this work involves modelling potential accident scenarios such as (fireball, jet fire, flash fire and explosion) in the event of a gas leak and rupture in the tank. It aims to sensitize drivers and LPG kit installers, even to get a clear view on these accidental phenomena and how to avoid them.

Numerical studies on an accidental flashfire at a water fun park by FLACS software

A severe accidental fire with ?explosion? resulting from spraying coloured corn flour powder occurred at a water fun park in Taiwan. The possible fire scenarios were studied in this paper using Flame Acceleration Simulator(FLACS). Environmental conditions including wind action and solid boundary conditions were deduced based on government fire investigation and video records, and were used as the input parameters in simulation. Simulation results indicate that upon ignition of the sprayed powder, the maximum overpressure in the open space was only 0.03 bar gauge, with a dust flash fire generated without having an explosion. These environmental conditions or parameters and the simulation results together would give a fire scene that agrees with the accident observed, indicating that appropriate environmental parameters had been identified. Therefore, CFD simulation with carefully selected parameters can be used to reproduce explosion scenarios and to identify key factors in supporting accident investigations.

Determination of flood parameters during the fire hazardous liquid spreading after the accident

Пролив пожароопасных жидкостей на свободную поверхность является одним из наиболее опасных сценариев аварии, приводящей к пожару. Для решения задачи по оценке параметров такого пролива было использовано численное интегрирование уравнений сохранения методом Годунова, на примере растекания пожароопасной жидкости по бетонному основанию. Возможности метода численного интегрирования позволяют спрогнозировать размеры пролива на текущий момент времени. Результаты расчета показали, что пролив объемом 245 м в течение 4-5 мин достигает равновесного состояния, после чего площадь зеркала пролива практически не увеличивается. Nowadays, various containers are used for storage and transportation of fire hazardous liquids. It is impossible to eliminate completely the possibility of tank depressurization and the scenarios associated with their destruction should be taken into account when developing technical solutions and organizational measures aimed at minimizing the possible consequences of such accidents. As a result of the flammable liquid spreading a mirror of the flood can form, from which subsequently the evaporation of combustible products occurs, which, when mixed with air, forms explosive mixtures. At a fuel concentration in the cloud above the upper limit of flame propagation, a fire development characterized by a flash fire is possible. If the concentration of vapors in the mixture with air is inside the concentration region of the flame propagation, a deflagration explosion is possible. In both cases, a flood fire can occur characterized by the formation of a high temperature flame. The initial task in predicting such accidents is to determine the surface area of the spilled liquid from which evaporation can occur. To solve this problem it is necessary to solve the hydraulic problem associated with the fluid spreading on a free surface having hydraulic resistance. Similar problems were solved in the practice of building design while determining the parameters of water movement along a dry riverbed. One of the forms of solution is the method of numerical integration of the conservation equations with the Godunov method, which is effective in solving problems of gas dynamics, as well as hydraulic problems. The calculation results showed that this method is applicable to the considered problem of forming a fire hazardous liquid flood on a free surface. Also, the results of the work indicate that a very significant volume of the fire hazardous liquid flood (245 m) reaches quickly enough a quasi-equilibrium state with a flood thickness of 0.03 ч 0.04 m.

Technical textiles for protection against Arc-flash fire: Savesplash®

Flash fire caused by electric arc is different than that caused by flammable liquids/fumes or combustible dusts. A suitable protective clothing for protection against electric arc-flash must be designed as per Indian weather conditions. Currently available garments are manufactured using two or three layers of woven/nonwoven combinations to achieve higher Hazard Risk Category (HRC) rating (level 3 and above). However, they are heavy and not comfortable to the end users. Savesplash® is a single layer inherent flame-retardant knitted fabric. Its arc rating was determined using ASTM standards. It achieved arc thermal performance value (ATPV) of 41 cal/cm2, breakopen threshold energy (E_BT) of 42 cal/cm2 and heat attenuation factor (HAF) of 94% when tested as per ASTM F1959/F1959M-14 which translated into an arc rating of 41 cal/cm2. This is equivalent to HRC level 4 ratings as per National Fire Protection Association’s NFPA 70E standard (USA). Further, cut and sewn gloves (HM-100) developed using Savesplash® fabric reinforced with leather on palm area achieved ATPV of 63 cal/cm2 and HAF of 94.5% when tested as per ASTM F2675/F2675M-13.

Quantitatively evaluating the effects of flash fire exposure on the mechanical performance of thermal protective clothing

Purpose The purpose of this paper is to determine the effect of flash fire exposure on the mechanical properties of single-layer thermal protective clothing. Design/methodology/approach The full-scale flame manikin tests were performed to simulate flash fire exposure. Two typical fire-resistant fabrics were investigated. The manikin was divided into seven body parts and the specimens meeting the requirements of tensile and tear strength standards were sampled. Fabric thickness, mass per unit area, tensile strength and tear strength were measured and analyzed. Findings The results revealed the significant influence of heat flux on both of tensile and tear strength. However, the regression analysis indicated the low R2 of the liner models. When the tensile and tear strength retention were reorganized based on the body parts, both of the multiple linear regression models for tensile and tear strength showed higher R2 than the one-variable linear regressions. Furthermore, the R2 of the multiple linear regression model for tear strength retention was remarkably higher than that of the tensile strength. Practical implications The findings suggested that greater attention should be paid to the local part of human body and more factors such as the air gap should be considered in the future thermal aging of firefighters’ clothing studies. Originality/value The outcomes provided useful information to evaluate the mechanical properties of thermal protective clothing and predict its service life.