【 Weak current College 】 smoke engineering basics

1. basics of flue gas

Smoke is a material product of combustion and pyrolysis. Fire gases produced by the process, the remaining suspended in the air and gas particles sum referred to as flue gas.

Influence of smoke constituents and properties of elements.

Flue gas composition and properties of first by the pyrolysis and combustion occurs in the chemical composition of the material itself, and to a lesser extent also and combustion conditions.

For normal combustion conditions, burning conditions are good that the burning was more fully, the generated gases are not combustion, the combustion is called full combustion, the combustion products as complete combustion products.

For non-normal combustion conditions, no good combustion, the combustion is not completely conducted, called incomplete combustion, the combustion products as products of incomplete combustion. Building a fire, this is the case. As a result of a fire in the burning material is more complex, especially in light of the fire environment, so the composition of smoke is complex.

The dangers of fire smoke

Fire smoke may cause serious harm to their hazards are poisonous, and terror. The dangers of fire and smoke can be summarized as to harm people's physical and psychological harm, smoke toxicity and reduced light is physical harm, and the terrorist is the psychological harm.

(A) fire smoke toxic

First of all, the oxygen content in the flue gas is often normal bottom in physiological needs, when the oxygen content in air decreased to 15%, the abilities of the muscle activity decline down to 10-14%, person flaccid, intellectual confusion, and unclear directions; down to 6-10%, the person will be collapsed. So in a burning room people died when the oxygen concentration of short as 6%. The actual burning room minimum concentration of oxygen in up to 3%, visible in the event of a fire if not timely when people fled the scene is very dangerous.

Secondly, smoke contains a variety of toxic gases and gas content has more than one physiological function allows the most high, causing people to poisoning deaths.

Third, the suspended particles in the flue gas is harmful. Against the biggest particle diameter is less than 10 microns of particulate matters, they are invisible to the naked eye, long-term floating in the air, a few hours, then few years particles smaller than 5 microns of scoop dust, gas diffusion effect, cannot enter the human pulmonary alveolar cell adhesion and aggregation in the wall, causing respiratory disease and increases heart disease mortality rates, direct harm to persons.

Fourth, the smoke has a high temperature, it is also a very harmful, in fire room, flue gas temperature can be as high as several hundred degrees in underground construction, fire flue gas temperatures up to 1000 degrees. The height of the smoke patience is limited. At 65 ° c, short-time stand; in 120 degrees c 15 minutes will result in a non-recoverable injury.

In short, the fire produces poisonous smoke can be summarized as eight words that hypoxia, poisoned, dust and damage, high temperature.

(Ii) fire light reduction

The wavelength of visible light waves 0.4-0.7 Micron, General fire smoke tobacco particles to a few microns to dozens microns, which is the smoke particle size greater than the wavelength of visible light, they smoke particles on visible light is not transparent, i.e. visible light has full mask effects, when MI vines, visible due to smoke particles of shelter decreased substantially, reduced visibility, this is smoke reduction of light.

(C) fire smoke terrorist

Fires, particularly in the event of deflagration, flame and smoke rushed out of doors and Windows, smoke, fire, flames, people had to evacuate the horror, often cause confusion, make some people lose their activities, some even lose control, panic. Therefore, the terror of harm is great.
The way to smoke

One way, smoke

How to sum up a smoke non-burning of smoke, smoke, smoke hampered the closed and pressurization smoke control in several ways.

(A) non-burning of smoke

The basic approach first smoke is ranhua. Design of smoke is fundamentally eliminate smoke source of smoke. On the design of countries have enacted specific regulations or standards, including building materials, interior furniture materials, as well as various pipes and insulation materials, materials are clearly ranhua, especially for those special buildings, large buildings, underground buildings and many other places, the requirements are very strict. Non-burning material characteristics are not likely to smoke, that is, not the amount of combustion and smoke, so very few non-burning material can make fire when substantially reduce flue gas quantification, optical concentration in flue gas.

(Ii) the way closed smoke

On fire room implement closed smoke is the smoke of a basic manner, the principle is to adopt good sealing performance and so will the room walls, closed, and the air in and out of the room. When room once a fire is generally put fresh air to flow, so the fire burning in the room itself off from lack of oxygen, thus the purpose of achieving smoke fire.

This approach is generally applicable to fire partitions easy finely residential, apartment, hotel, etc., and give priority to the use of fire-prone, such as the kitchen room room. The advantages of this approach is not required, but the effect is pretty good. The disadvantage is that doors and Windows, and so often is powered using the inconvenient, but also in case of fire, if a friend in the room, will still be evacuated due to leakage.

(3) impede smoke method

In flue gas diffusion flow routes set various obstacles to prevent the spread of smoke continued to hinder the smoke of the approach is called. This approach is often used in smoke control zone at the junction, sometimes also in the same area. Smoke curtain, fire doors, fire valveVertical wall, smoke, etc are all this kind of obstacle structure.

(Iv) pressurized smoke control mode

In building a fire, the fire areas outside the regions for pressurization, keep a positive pressure to prevent smoke intrusive way known as pressurized smoke smoke. Because the compression zone and the non-pressurized area has a number of conventional smoke, such as walls, doors, floors and], smoke from both sides of the pressure difference can effectively prevent flue gas through the cracks around doors and Windows and the envelope, if you seam seepage 4-10 shown below. The fire is, because of the need for evacuation and rescue, pressure range between doors always open, or in the evacuation period opens, or is open during the entire fire. If you open the door at the speed of air flow direction and the flue gas to the contrary, due to reach a certain value, you will still be able to effectively prevent flue gas, i.e. to prevent smoke from non-pressurized fire district flows.

Pressurization smoke control mode has the advantage that can effectively prevent flue gas into the control of the region, and since the fed a lot of fresh air, especially suitable as evacuation channels of stairs, elevator and the smoke before the Chamber.

II. exhaust system:

(A) the way of spontaneous combustion exhaust

Natural gas is the use of fire smoke air buoyancy and external wind effect of external by building the smoke exhaust openings to the outside of the exhaust gas of essence is hot flue gas and cold air convection movement. In natural gas, there must be cold air inlet and heat and smoke outlet. Flue gas discharge can be building exterior Windows, can also be specifically set in the side wall at the top of the exhaust port. On top of the building, was once used for the ventilation exhaust shaft, in the normal, because the building air temperature higher than outdoor, resulting in increased air buoyancy, making for easy room exhaust. Fires when the indoor temperature is rising sharply, indoor and outdoor temperature difference is large, the formation of chimney effect, become a dynamic smoke, abroad often called smoke Tower.

In this way because of the use of a shaft of the "stack effect", produces pumping wind, so the smoke effect is good, it is not affected by the impact of outdoor conditions, and equipment is simple, does not require power, if you consider the shaft of the heat problem, exclude the high temperature of the flue gas, get a certain application. The main disadvantage is the large footprint.

(B) mechanical smoke extraction methods

1. comprehensive smoke method

In the room using mechanical exhaust smoke machines, using blowers for mechanical ventilation, this way is called a comprehensive smoke. Because of this the way to smoke control areas into a lot of fresh air, for the avoidance of combustion, it does not apply to applications in fire zones, can be used for non-burning smoke zone system runtime allows the system air supply volume slightly larger than the amount of exhaust smoke, so that the control area micro positive pressure. The advantages of this approach is the smoke effect is good, but stable and free from any influence of weather conditions to ensure the safety of the control zone, the disadvantage is the need to be sent, exhaust two sets of machinery and equipment. Investment is high. Power consumption is also larger.

2. negative pressure mechanical smoke extraction methods

Use the fire smoke machine room smoke exhaust gas through the mouth to the outdoor exhaust approach is called negative pressure exhaust. Early in the development of fire, the fire smoke extraction mode enables the room pressure drops, caused negative pressure, gas does not like the other regional proliferation. But fire hit stage of development, as a result of flue gas exhaust mass produce, as did the machine completely excluded, smoke may spread to other regions. Additional requirements for smoke machine can withstand the high temperature flue gas, but also need to set fire dampers, over-temperature shutdown automatically when you stop the smoke. So, not only the initial investment and ongoing maintenance management costs are also higher.