Research On The Characteristics And Prevention And Control Measures Of Indoor Gas Explosion In Residents

In recent years,the number of gas consumers keeps increasing rapidly.However,due to the insufficiency of effective safety management for gas companies and safety awareness for residential users,a great number of safety hazards have not been found out and rectified in time.Thus,gas leakage and explosion accidents have occurred frequently inside residential buildings,which would pose significant human injuries and property loss in the surroundings.It is of great importance to perform on-site investigation,analyze the accident consequences,find out the accident cause and determine the responsibility body for gas explosion accident investigations and subsequent treatments inside residential buildings.In order to conduct above works,the initial accident scenario should be firstly identified,and then the evolution process and dynamic characteristics of gas explosion need to be analyzed inside residential buildings.Meanwhile,the effective prevention measures are proposed to control fire and explosion accidents,decrease the accident consequences and reduce accident losses.In this paper,the gas explosion accident of a residential user in Chengdu,Sichuan province is taken as an example.The numerical simulations are performed for different gas cloud filling regions and equivalence ratios prior to ignition to identify the initial scenario.In addition,the temporal evolvement process and spatial distribution characteristics of explosion overpressure and indoor temperature are analyzed.Furthermore,the effects of relevant parameters on the peak overpressures in the kitchen are investigated,and the Code for Design of City Gas Engineering is combined to propose effective prevention measures for the gas explosions inside residential buildings.This study provides a new analysis method and data reference for the indoor gas explosion accident investigation and subsequent treatment in the future.Therefore,the research works of this paper are provided as follows:(1)Based on comprehensive on-site inspections,gas company surveys and user consultations,the real accident consequences and personal injuries are determined at explosion scene,and the trace characteristics of floors,doors,windows and walls are analyzed in each room.Combined with the identification technology of physical evidence,the property of explosion accidents,ignition location and leakage sources are identified.Additionally,the follow-up investigation and research directions are defined in this accident.The results show that this accident is a conventional natural gas explosion,and the ignition source that caused this explosion accident is confirmed to be the lighting switch in the living room.However,the leakage source that triggered this explosion accident indirectly is confirmed to be the gas hose.(2)According to the CAD plane drawing and the damages of floors,doors,windows,and walls at explosion scene,a numerical model of gas explosion in a residential building is developed using the commercial CFD code FLACS.Subsequently,the reasonable time step,initial and boundary conditions and solution schemes are determined.In addition,three set of grids with a uniform cell size(0.18 m,0.15 m,and 0.12 m)are chosen to perform grid independence test in the entire computational domain,and the optimal grid quantity is determined based on the computational accuracy and cost.Furthermore,the numerical model which is the same as the experimental data in the literature is established.Meanwhile,the numerical results obtained from the present work are compared with the peak overpressures recorded by the different vent activation pressures and the volume blockage ratios of obstacles to validate the accuracy and reliability of the present model.The results show that a uniform cell size of 0.15 m is adopted to save time and improve the computational efficiency.The numerical results are both in good agreement with the experimental results for the different explosion scenarios,and all the relative errors are below±10%.It indicates that the present numerical model is valid to reproduce the experimental results.(3)The numerical simulations are performed for different gas cloud filling regions and equivalence ratios prior to ignition.In total,six kinds of gas filling schemes are chosen.To identify the initial accident scenario,the simulation results are compared with the overall damage consequences of building and injury degree of personnel.According to the initial accident scenario and the real consequences of each room,the adaptability and reliability of CFD model are further validated.Furthermore,the temporal evolvement process and the spatial distribution characteristics of explosion overpressure and indoor temperature are analyzed.The results show that the initial scenario prior to ignition is identified as that the entire fuel region is filled with flammable gas cloud of a volume of 9.7 m × 7.5 m × 3 m and a gas concentration of 8.6%.The simulation results reproduced by the CFD model are in good agreement with the real accident consequences based on the explosion overpressures and the corresponding damage criteria.During the explosion process,the overpressure distribution in a room is almost uniform and there seems little spatial difference.The instantaneous maximum temperature can reach up to 1953?,which is easy to cause secondary fire accidents.The maximum flame velocity is in the range of 34.3 m/s and 230.9 m/s.It means that the indoor gas explosion is a typical deflagration process,and thus the explosive products would not deposit and leave black smoke traces on interior walls.(4)According to the causes and essential conditions of explosion occurred,the active prevention measures of gas explosion are proposed in residential buildings.For example,how to prevent the leakage of indoor gas,how to prevent the formation of explosive vapor cloud,and how to control or eliminate the ignition source.The results show that these measures can all effectively reduce the probability of gas leakage and explosion accidents in residential buildings,like using gas cookers accurately,installing the leakage alarm instrument and automatic cut off valve,designing the placement of household facilities reasonably,as well as forbidding telephone and switching appliances after gas leakage.(5)A numerical model of gas explosion venting in the residential kitchen is developed using the commercial CFD code FLACS.The effects of relevant parameters on the overpressure peaks are investigated to propose passive prevention measures of gas explosion in residential buildings,including vent area ratio,the broken pressure of glasses and the mass per unit area of glasses.Additionally,the orthogonal experiment design and improved grey relational analysis are implemented to evaluate the relative importance of these relevant parameters,which can provide effective guidance for venting safety design of residential kitchen.The results show that the overpressure peaks decrease with the increase of vent area ratio.When the vent area ratio is less than 0.3,the overpressure peaks decrease rapidly with the increase of the vent area ratio.However,when the vent area ratio is larger than 0.3,the overpressure peaks are almost independent on the vent area ratio.There is a linearly-increasing relationship between the overpressure peaks and the broken pressure of glasses.The overpressure peaks increase with the mass per unit area of glasses.Based on the grey relational grade values,the effects of these relevant parameters on the overpressure peak are ranked as:the broken pressure of glasses>vent area ratio>the mass per unit area of glasses.