Research Of Metallographic Analysis And Numerical Reconstruction Of Smoke Pattern In Fire Investigation

It is important to conduct fire investigation research since fire cost more and more damage.It is unlucky that most investigation and analysis methods are still experience based which means that there is little standard for judgment.Different investigators may make different conclusions on the same fire.At the same time, improvements of legal awareness and idea of the public also ask for precision and clarity of the fire investigation.It is important to improve technology and method of fire investigation and find new way to make correct conclusion based on a tighter work.To improve metallographic analysis in electrical fire investigation,digital image processing methods are adopted.A human-computer interaction algorithm which name is Live-wire is used and improved and with this work,crystal outlines are captured.To eliminate off redundancy information and digital date from the metallographic image,digital morphology methods are adopted and so the precise outline of crystals are captured.Then,effects of several segment descriptors on crystal categories classification are analysis and discussed.With the help of principal component analysis,key segment descriptors such as eccentricity,degree of circularity and variance of crystal checkmarks are determined to be used as the final parameters of the automatic classification.Cluster analysis results show that most crystals are digested correctly which there are still little problems in the classification. Some crystals are mis-classificationed.To improve the results,fisher discrimination method is adopted and the results show that cylindrical crystals and afterbirth-like crystals in two different metallographic images are distinguished correctly.To improve theoretical and the formation mechanisms of smoke pattern in fire investigation,the fourth chapter conducts research in the light of mechanical model of a single smoke particle.The kinematical model of smoke particle is given.This chapter also offers a conception of critical escape velocity of the smoke particle. While the velocity of the smoke particle after the collision with the wall is greater than the critical velocity,the particle will escape;while the critical velocity is greater, the particle will stay on the wall.The fifth chapter designed validation and usability experiments,the results show that as the HRR and combustion time of the fire source rise up,smoke pattern change from "V pattern + U pattern" to "V pattern + funnel pattern".By the comparison between numerical simulation results which used particle adhesion model and experimental results,it can be concluded that the particle adhesion model can give predict smoke patterns numerically and the accuracy is acceptable.The sixth chapter conducted a numerical reconstruction of a typical heritage building fire which is caused by electrical malfunction.By using method of the second chapter,metallographic image of copper wires which is gathered from the fire site is processed and the analysis results show that it is electric heat which ignited the combustibles near the socket.By using computational numerical simulation method,a fire reconstruction is conducted.The way fire and smoke spread is given and the accuracy is validated with the comparison with testimony of witness.Temperature and smoke density of key spot of the heritage building are given,and FID parameter is used to help find out how CO and CO₂ kill people in this fire.In order to improve safety and extend available safe egress time,water sprinkles are set in the second numerical case and it can be seen from the results that with the effect of the water sprinkles,temperatures of key spots are much more lower and so the smoke density, people have more time to egress.