【 Weak current college 】 building fire smoke hazards and control-of-Power By 【 China power house network 】

This article discusses the construction of fire smoke generation and its harmfulness, smoke damage to the human body is mainly due to the combustion of toxic gas by asphyxia and stimuli on human organs, as well as high-temperature effects. Through the smoke flow law of, leads to the implementation of effective control of smog, and presents some typical cases fire escape method.
Keywords: buildings, fire smoke flow control escape
Modern building flammable decoration, the chemical fiber rug and foam padded furnishings, the fuel in the combustion process produces a large amount of toxic smoke and heat, as well as to consume large amounts of oxygen. In building fire, the smoke is hindered people escape, trapped in death. According to the United Kingdom on fire casualties because statistics show that as a result of carbon monoxide poisoning suffocation or other toxic smoke smoked deceased General total deaths in 40%-50%, while being burnt to death of people, mostly to asphyxia collapsed after being burnt to death. Therefore, understanding and mastering the smog in building fire, control the flow of smoke diffusion is the building fire safety systems are very important issues.
1 smoke generation and hazards
Smog is a material in the combustion process generated with gaseous, liquid and solid substances and air mixture. Generally it consists of tiny carbon black particles full combustion or incomplete so burning products, water and fuel combustion decomposition products. Flue gas composition and quantity depends on the chemical composition of fuels and combustion reaction conditions (temperature, pressure and combustion of quantity, etc.). United States National Institute of standards and technology, using the "N-gas models" in the prediction of building fire smoke toxicity size has been verified, the ordinary civil construction material completely toxic combustion products from small quantity of gas, the gas primarily CO, CO2, HCN, HCl, HBr. National fire science laboratory of the research proposed in the Associate Professor Yang, fire gas toxicity is reciprocal influences, such as NO2 and CO will bring together existing CO increased toxicity; and NO, there is common with HCN to reduce the toxicity of HCN. Building fire in incomplete combustion conditions, not only the CO, CO2 and water vapor, there will be alcohol, ether, organic produce, the amount of carbon containing substances, in conditions of insufficient oxygen combustion, there is a wide range of carbon black particles. Smoke in low temperature phase is smoldering, smoke particles in liquid, solid blue white smoke. When the temperature rose to 260 ° c and above, as a result of dehydration occurs, produce a lot of free carbon particles, smoke black or dark gray, when fire point temperature rose to more than 500 ° c, the carbon particle will gradually reduce the smoke is grayed out.
When the fire broke out, due to the combustion consumes large amounts of oxygen, making the air oxygen concentration sharply declined, people long in this low-oxygen environment, resulting in respiratory disorders, blinded, spasm, pale blue, even suffocation. The building when the fire burning ambition, will also produce large amounts of carbon dioxide, when staff contact 10% ~ 20% after the concentration of carbon dioxide can cause dizziness, coma, respiratory difficulties, even paralysis of the nerve centres, so that the system is experiencing people lose consciousness, leading to death. In addition, you can create on the human body has a strong stimulus for gases, one does not see the direction of the had a familiar environment becomes illegible its evacuation routes and exports. People smoke environment correctly determine direction out of danger of visibility minimum is 5 meters, when people view down to 3 m, fled the scene is very difficult. People smoke, psychology very unstable, it will have a dread that panic, to organize evacuation fire-fighting operations resulted in great difficulty. At the same time, the role of smoke, sunscreen on evacuation and rescue activities cause a lot of obstacles. Burns high temperature smoke, also contribute to the loss of one of the main reasons. High temperature not only may cause heart rate, body sweating, fatigue, and dehydration occurs very quickly, and will put people burn burned to death. Therefore, smoke damage to the human body is mainly due to the combustion of toxic gas by asphyxia and stimuli on human organs, as well as high-temperature effects.
2 building fire smoke flow in
Large fire investigation found that the fire most lethal personnel did not die in fire room, but die in the near or far away, this indicates smoke in mobile and proliferation. Smoke diffusion in the horizontal direction of flow velocity, General 0.3 ~ 0.8m/s. In the vertical direction of flow velocity is typically 1 ~ 3m/s. The stair well, or pipeline chimney effect produces pumping pullout, smoke flow diffusion speed sometimes up to 5 ~ 7m/s. Building smoke flow and diffusion, in General, is due to the wind and the various ventilation system pressure difference, and because the temperature difference cause gas density difference of chimney effect, where the temperature and the temperature change is the smoke flow in the most important factor. When opening the door to the corridor room, smoke flows become more complex, it and building chimney effect, smoke, fire and temperature, and many other factors.
(1) building ventilation, air conditioning system on building pressure depends on the air supply and exhaust air balance status. If the air supply and exhaust air is the same, then the system pressure inside the building will not be affected, if more than one part of a gas exhaust, there will appear the pressurized air flows into the other part from there. Conversely, in exhaust gas of parts, exceeded the opposite phenomenon. Therefore, building ventilation, air conditioning system can follow a predetermined and beneficial manner designed to control the flow of smoke in a building.
(2) gas expansion. Temperature rise of gas expansion effect of smoke flow is more important factor. Under the gas expansion project, the law on fire during the burning of gas volume will expand 3 times, 2/3 gas will be transferred to other parts of the building. And expansion processes occur very rapidly, and caused considerable pressure, the pressure if measures are not taken, will force the smoke from the burning layer up or down to other parts of the building.
(3) chimney effect. When the roomThe air temperature is higher than outdoor, indoor and outdoor air density difference of buoyancy. Building the pressure in the upper part is greater than the lower portion of outdoor pressure, the pressure is less than outside pressure. When there are openings on the wall, through the opening at the top of the building, outdoor indoor air flows through the open lower;, indoor outdoor air flows. This phenomenon is building chimney effect. It is made of high buildings and outside air density difference, high-rise buildings of the external temperature is lower than the internal temperature of the air pressure difference from low pressure, the flow through the building up and then flows out of the building from above, this phenomenon is called is hot-pressing. In the low place external pressure is greater than the internal pressure, height, on the contrary, in the middle of a certain height, the same internal and external pressure, the presence of a neutral pressure plane. Chimney effect with the building of internal and external temperature difference and building height increases, in fire occurred at a lower layer, the chimney effect on shaft and a higher level of smoke pollution is particularly significant because the smoke rising from a low level to high level of potential. The chimney effect caused by pressure and airflow distribution, as well as the neutral pressure plane position, depending on the building compartmentation openings on gas flow restriction. Fire burning flown when, due to the large amounts of heat, the indoor temperature rises rapidly, building chimney effect even more significantly, the spread of the fire. Therefore the chimney effect on buildings of air mobility plays an important role.
(4) indoor wind direction, wind, wind speed on top has a significant impact on the smoke flow, and this effect with the building of the shape and size. Simply speaking, the wind makes the wind surface walls subjected to internal pressure, while the Lee side and both sides have facing of walls, flat-top-up pressure on. Both pressure air flow from the upwind side of the building, from the Lee side flow out of the building, building on top of the negative pressure on the top of the vertical ventilation ducts with a suction effect. At the same time as the horizontal wind pressure led to the rise of neutral surface, negative horizontal wind pressure led to the decline of neutral surface.
3 smoke control and escape
Evacuation operation time from the evacuation began to evacuate the end of time, which consists of walking hours (disperse from the farthest point to safe walking time) and exit through the queue time (calculation of all regional staff from export through time). And evacuation operations time prediction-related parameters and their relationship is shown in Figure 1.

Figure 1 and evacuation operations time prediction-related parameters and their relationship
In high-rise buildings evacuated due to fire takes roughly proportional to the height of buildings, General evacuation time longer, and in the stairwells and the building away from fire district formation of other local smoke situation unbearable time is shorter. Experiments in Canada shows that each layer of 240 people, through a 1.1 meters wide stairs to evacuation, a building of 11 floors of a building evacuation time need 6.5 minutes, a 50-building evacuation time needed 2 hours 11 minutes, but a high 100 m of the building in case of non-stop, smoke in the top half minutes reach. So in the event of a fire in a building during the complete withdrawal of the personnel is very difficult, such as tenants remain in high-rise construction, comprehensive fire safety system must be included on smoke and fire control, so that certain areas of smoke concentration always maintained in building consumer tolerable levels. These specific areas including the staircase and all users are easy to reach and to accommodate their floor space, etc.
Control of smoke "smoke" and "smoke". The "smoke" is to prevent the entry of smoke, is passive; on the contrary, the "smoke" is a positive change in the flow of smoke, so that the discharge is active outdoors, both of which complement each other. Currently smoke control measures taken are:
(1) to limit the amount of smoke. Smoke the best approach is to eliminate the source of the smoke. Therefore, in high-rise buildings, design of fire alarm system and automatic fire extinguishing system to provide an early warning of fire, in mass smoke generated before the fight fires or fire control. At the same time, the choice of housing, building materials and decoration materials, furniture, where possible, adopt smoke small material, so unfortunately there is a fire occurs when a small amount of smoke, smoke slowly, relatively more escape time, reduce the threat to life. Currently, Japan, the United States, France and other countries are provided in a number of important public buildings, ceiling, flooring, wall decoration to the use of combustible materials, fire officials frequently sent to the hotel to check there for furniture, curtains, carpet is not a flame of fire load, accounting.
(2) set the mechanical pressurization smoke control system. Its purpose is to fire in high-rise buildings to provide is not affected by the smoke evacuation routes and interference of the shelters. Setting the system's position should be considered as structures in the specific circumstances of the case, there are: does not have natural smoke conditions of smoke front staircase and; to open window natural smoke staircase but do not have the natural smoke exhaust conditions; former room does not have natural smoke condition the elevator room of fire; the fire by stairs and elevator shaft chimney effect of combined front room; closed room refuge. On the non-fire zone and evacuation channels should rapidly adopt mechanical pressurization for smoke control measures, to make the region's air pressure above the fire region air pressure, prevent the intrusion of flue gas, control the spread of fire. According to relevant materials, a well-designed mechanical smoke extraction system in the fire to 80 per cent of the amount of heat emitted to fire temperature significantly reduced, so the evacuation and fire play an important role. Using this way exhaust, in the design and use of the smoke should be divided, reasonable effective partition using the partition wall, smoke exhaust vertical wall, etc.
(3) make full use of the buildings constructed for natural gas. Natural gas is the role of the natural forces, the indoor and outdoor air exhaust stream. Generally use may open window and the window balcony or concave Gallery for natural gas.
Understand the hazards of fire and its flow pattern, but also to us in the event of a fire escape method when you select a theoretical basis. Building fire escape method is flexible, specific methods usually consists of onsite construction, fire protection equipment and trapped workers health,Psychological ability, and other factors. In the fire, were trapped workers should have good mental quality, keep calm, don't panic, don't blindly action to select the correct method of escape.
When building Setup refuge layer, escape masks, lifesaving decelerating, life-saving evacuation channels and other fire rescue equipment, activities in the building of personnel should always take the initiative to become familiar with and have the device performance and use methods, for emergencies. And much-needed escape in the event of fire, should try to actively use these fire rescue equipment, which will maximize the success rate of exit.
When trapped in a burning range also not big stairs or room to wet body, head wet cotton wool; from fire, not in the busy to get the thing to get out of danger. Escape way encounter smoke when squatting or belly, to breathe the residue on the surface is not yet contaminated fresh air. Floor below the ignition, and stairs have been fire and smoke all sealed, no hope of escape, you should promptly shut down and the fire room adjacent all doors, Windows, slow the spread of fire, and wet towel to cover their mouth, nose, the roof, balcony, safe and easy to be found. At night you can use shake flashlight, dropped a thing or something with eye-catching colors, such as moving to issue a distress signal. Despair is available on the rope, curtain fabric or surface tear into bars form a rope, firmly tied by a door or window of a frame with its decline.
Live fire smoke, mentally tend to fall into a terrorist and nervous breakdown, easily select reckless escape tools, or even choose to jump from escape. Jump from escape is very dangerous, in principle only while the firefighters are ready to jump from a life-saving cushion command can only be taken when jumping from a method. Even if there is no retreat, if life grave also has not been finally also to threat level, calmly waiting for firefighters arrived. Jumping out of the way is very skilled, you should try to jump from a life-saving cushion Central jump or select a pool, soft awning, direction. If possible, try to have some loose items. Open a big jump from the umbrella is also very scientific, this can slow down the attack force in.; If Freehand must hand jumping from the window or balcony with the body's natural hanging up and down, to minimize the vertical distance, hold down both hands before you head to reduce injuries.
4 conclusions
This article on building fire smoke generation, hazards, flow of discussions drew on smoke control in three effective methods, combined with practical, discussed several typical situations fire escape, the fire prevention and control will play a positive theory and practical significance.

Reference documents
[1] Yeoh, Liu Haibin. building fire smoke damage and fire escape method. Shandong, 2002 (1).
[2] the term East. high-rise construction fire smoke flow regulation and control measures. Anhui fire, 1994 (1).