The Application Research Of Water Mist Fire Extinguishing System In Car Paint Room

With the government’s continuous support to automotive industry, China automotive production and sales go into a dramatic growth phase, as a result, more and more auto factories are built. Paint shops are highly dangerous because of its complex manufacturing technique, electrical equipments and extensive use of combustible liquids, especially in the paint shop spray booths with volatile paint, solvent are mostly A and B flammable liquids, so in the event of a fire, it will cause serious losses. Water mist fire extinguishing system is widely used in various paint workplaces, because it is safety and environmental protection, efficient water-saving, electrical insulation, and easy to install and maintain.This paper studies water mist fire extinguishing system’s approach in the automotive paint shop spray chamber by full-size entity fire experiments and computer simulation research.1、Entity fire experimentIn entity fire experiments, I choose three different methods to extinguish paint fire in order to analyze their performances, like water mist fire extinguishing systems, water sprinkler systems and foam fire extinguishing systems. It divides into three parts Throughout the experiment.(1) Pre-testPre-test discuss specific paints combustion and compare the fire risk of varnishes and paint. Paint combustion can be divided into four phases:the initial phase, severe burning phase, decay phase and extinguish phase. According to the results of comparison, it has a higher temperature, more CO production and lower O2concentration when varnishes were burned, it is obvious that varnish has a greater fire risk. so i use varnish as fuels in fire extinguishing experiment.(2) fire extinguishing experimentFire extinguishing experiment consider to use water mist fire extinguishing systems, water sprinkler systems and foam fire extinguishing systems to compare their fire extinguishing performance.Having no obstacle in fire experiments, water mist fire extinguishing systems, water sprinkler systems and foam fire extinguishing systems are able to success. however, comparing their capacity of cool-down, radiant heat barrier, fire purification, oxygen cutoff and suffocation, water mist system has a greater advantage.Having an obstacle in fire experiments, water mist fire extinguishing systems, water sprinkler systems and foam extinguishing systems are able to control the fire successfully, these extinguishing systems almost have no difference in cool-down and radiant heat barrier, while in fire purification, water mist system has a greater advantage.(3)water distribution experimentWater distribution experiment comparing the difference between water mist fire extinguishing systems and water sprinkler system in water consumption and water distribution uniformity. Through the Water distribution experimental mass flow calculation, the water consumption of water sprinkler system is14.2times the water mist system, at the same time, water distribution experimental data variance show that variance of water sprinkler system is three orders of magnitude higher than water mist system. In summary, water mist system’s water distribution uniformity have advantages obviously.2、Computer numerical simulationFDS software give some numerical simulation analysis to show the fire extinguishing effectiveness on water mist system saving a fire of automotive paint shop spray booth. It focus on the impact of spray booths vertical ventilation, water mist droplet size, droplet ejection speed and obstacles to extinguish the paint fire.the result of numerical simulation is clear:In the interaction of water mist fire and paint, water mist have a significant effect on fire source’s surface cooling and oxygen cutoff. To prevent indoor oxygen be replenished, the vertical ventilation systems should be closed through a linkage control at the time of opening water mist. Under simulated operating conditions, water mist’s droplet size of100～300μm have better fire extinguishing than the diameter of400,500μm. Under a certain ejection velocity, the larger droplet velocity, the better fire extinguishing, it has been confirmed that droplet’s Injection speed of10m/s have better effect than that of3m/s and5m/s. However, in order to prevent lateral spread of flame, jet speed should not be too high. In the automotive obstacle fire, part of tiny droplets of water mist can bypass the obstacle into the fire zone to exert a cooling effect because of flame entrainment. therefore water mist system can control the fire barrier effectively, it can be used in automotive paint shop spray booths.