Research On Sediments Combustion And Fire Safety Forecast In Air Duct Systems Of Buildings

When the dissemination of public epidemic and fire security become the main focus in nowadays, the HVAC (Heating, Ventilation and Air Conditioning) system, considered as the important building environmental equipment to improve indoor air quality and protect fire, has attracted more and more attentions. It has been certified widely that the HVAC system is the potential headstream of not only contamination but also the building fire as a result of its sediments. Consequently, it is very important to look deep into the dynamic performance of duct network and the mechanism of both sediments combustion and fire spreading. However, the current research are all concentrated on the system properties in normal condition and mechanisms of contaminant sedimentation and diffusion, but neglect the system properties and the fire breakout and spreading in the special situation. Therefore, in this dissertation, the combustion performances of the sediments and the characteristics and mechanisms of fire spreading in the HAVC systems are deeply analyzed by the way of spot sampling, experiments and numerical simulation from the angle of long-narrow confined space in the buildings in the fire research, based on the theories of long-narrow confined space in the buildings and some other traditional theories. The main research work and its conclusions are introduced as follows:(1) After reviewing the current fire research on the long-narrow confined space in the buildings, a three-phase theory is put forward on sediments sedimentation, sediments pyrogenation and ignition and fire spread, in which the air duct system is set up as geometry boundary, and sediments are taken as the research subject. Theory of the large eddy three-dimensional mathematics model for the fire burning in the narrow and long underground confined space is set up for the fire spread model and FDS (Fire Dynamics Simulator) software is adopted for fire simulation, which are all the theoretical basis of the research below.(2) The investigations of building environment and sediment existence were taken, and random sampling were adopt in several commercial and industrial buildings to certify the combustibility of sediments in the air duct system. It is approved that a mass of sediments in air duct system do harm to fire due to their existence and combustibility.(3) A model of the single air duct system for sediments combustion is established and several cases are finished according to the orthogonal design, and the variances of temperature and velocities of the air flow are also calculated. A new parameter of PFT* (Probability of Fire-happened Temperature) is put forwarded for the first time, and the factor analysis is taken finally for fire evaluation and forecast on air duct system.(4) A new experimental platform of actual-dimension single air duct system has been built in the lab, and accordingly the models of both homogeneous design experiment and control experiment are set up for sediments combustion in the air duct system. The new parameter of dynamic ignition temperature (T*) is advanced for fire characteristic on sediments in air duct system. The quantification theory is used to analyze the influence factors. Further discuss are made on the experiment data and simulation data. The hazardness of sediments to cause the fire and the validity of the model is further specified finally.(5) A model for sediments combustion in the actual-dimension compositive air duct system has been set up, and the comprehensive properties of the fire and the temperature field in the air duct system are simulated by the orthogonal design cases and comparative cases. The estimation and forecast of the fire spreading are completed combining the parameter of PFT* (Probability of Fire-happened Temperature). A full understand of the characteristics and mechanism of fire spreading in the air duct system is achieved based on the above analyses.(6) A new fire risk evaluation method in the air duct system is advanced and validated based on the current evaluation methods and the analyses of fire hazardness. Consequently, integrated control measures on the air duct system fire are brought forward based on the experimental and theoretic analyses in this dissertation, engineering application and related regulations.