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Flammable gasesHazardous properties of flammable gases
1, flammable and explosive
The main danger of flammable gases is the flammability and explosiveness of < strong>flammable gases, all in the combustion concentration range of flammable gases, ignition sources may occur in the fire or explosion, some flammable gases can be detonated when encountering the role of a very small energy ignition source. Flammable gas fire or explosion of the degree of difficulty, in addition to the size of the ignition source energy, mainly depends on its chemical composition, and its chemical composition determines the size of the range of gas combustion concentration, spontaneous ignition point of the high and low, the speed of combustion and the amount of heat.
2, diffusivity
Any substance in the gas state has no fixed shape and volume, and can spontaneously fill any container. Because the molecular spacing of the gas is large, the interaction force is small, so it is very easy to diffuse, flammable gases have the same properties. Lighter than air, flammable gases escaped in the air, can be unlimited diffusion, and air to form explosive mixtures, and can be drifted downwind, rapid spread and expansion. Heavier than air when the flammable gases leaked out, a long time to gather and not disperse, easy to form explosive gas mixtures with the air in the local area, when the ignition source of fire or explosion phenomenon.
3, electrically charged
Any object friction will produce static electricity, hydrogen, ethylene, acetylene and other flammable gases from the mouth or breakage of high-speed spray, but also can produce static electricity, the main reason for this is the gas itself is caused by violent movement of molecules friction between each other, the gas contains solid particles or liquid impurities in the pressure at high speed when sprayed with the nozzle of friction will produce static electricity. The main reason is that the gas itself violent movement caused by molecular friction. The static electricity generated by the harm is often incalculable, and sometimes even ignite flammable gases.
4, corrosive
Some hydrogen, sulfur-containing elements of flammable gases with corrosive, such as hydrogen sulfide, sulfur oxidation, ammonia, hydrogen and other gases can corrode the equipment, weakening the equipment's pressure-resistant strength, and in severe cases, can lead to equipment system fissures, leaks, causing fire and other accidents. At present, the greatest danger is hydrogen, hydrogen at high pressure can penetrate into the carbon, so that the metal container "hydrogen embrittlement". Therefore, the container of such gases, to take certain anti-corrosion measures.
5, toxicity
Many flammable gases in addition to flammable and explosive, there are considerable toxicity, therefore, in dealing with or fighting such toxic gases fire, special attention should be paid to prevent poisoning.
What are the common flammable gases
1, hydrogen
Hydrogen is a colorless, odorless, tasteless gas, at high pressure and low temperature is a colorless liquid, slightly soluble in water. Hydrogen is extremely flammable, and air mixed with fire can occur violent explosion. Hydrogen and chlorine mixed in the sunlight can be natural coal explosions, mixed with fluorine in the dark that can explode, installed in cylinders of hydrogen can also explode when heated. Hydrogen in the combustion flame colorless, temperature pole, about 2000 ℃.
2, methane
Methane is a colorless, odorless gas, boiling point of -161.4 ℃, lighter than air, is an extremely difficult to dissolve in water flammable gas. Methane and air into the appropriate proportion of the mixture, will explode when a spark. Methane is chemically quite stable and does not react with strong acids, strong bases or strong oxidizing agents. Under appropriate conditions, oxidation, pyrolysis and halogenation will occur.
3, propane
Propane is a colorless gas, pure odorless, mixed with air can form explosive mixtures, when the heat source and the risk of combustion and explosion of open flame. Propane has a simple asphyxiation and anesthesia effect, people briefly exposed to 1% propane, does not cause symptoms. 10% of the concentration, only cause mild dizziness. When exposed to high concentrations, anesthesia and loss of consciousness can occur, and extremely high concentrations can lead to asphyxiation.
4, ethylene
Ethylene is a colorless gas with a special sweet odor, soluble in ethanol, ether and water. Easy to polymerize, especially in concentrated sulfuric acid is very easy to polymerize into a resin. Easy to combust and explode, when the ethylene content in the air reaches 3%, that is, can explode and burn, the explosion limit of 3.0-34.0%.
5, ethane
Ethane is a colorless and odorless gas, insoluble in water, slightly soluble in ethanol, acetone, soluble in benzene. Ethane mixed with air can form explosive mixtures, there is a danger of combustion and explosion when exposed to heat and open flames, and fluorine, chlorine and other contact will be a violent chemical reaction.
6, acetylene
Ethyne is a colorless gas, with ether odor, slightly soluble in water, soluble in ethanol, soluble in acetone. Acetylene touching phosphide or sulfide, very easy to burn and explode, the explosion limit of 2.5 ~ 80%.
What are the flammable gasesFlammable gases have a lot of flammable gases, such as flammable gases: hydrocarbon gases in the organic matter: alkanes (methane flammable gases, propane, etc.) flammable gases, flammable gases, flammable gases. Olefins (ethylene, etc.), alkynes (acetylene, etc.), hydrogen, carbon monoxide, hydrogen sulfide, the gaseous state of methanol ethanol also belongs to the flammable, oxygen is combustion-assisted, not flammable gases, ethane, acetylene and other hydrocarbons. Among them, methane is widely distributed in nature and is one of the main components of natural gas, methane, pit gas and coal gas. It can be used as a fuel and a raw material for the manufacture of hydrogen, carbon monoxide, carbon black, acetylene, hydrocyanic acid and formaldehyde.
What gases are flammable?Flammable and explosive hazardous materials can be divided into four categories: gases, liquids, solids and dusts.
One, combustible gases
Combustible gases refers to any fire, heat or contact with oxidizing agents can ignite the gas. Combustion of gases and liquids and solids are different, do not need evaporation, melting and other processes, faster, and easy to explode. (2)
The combustible gases whose lower explosive limit (volume %) is more than 10, such as ammonia, carbon monoxide, furnace gas, and a few other combustible gases belong to this category. In the production or storage of combustible gases, class 1 combustible gases are categorized as Class A fire hazards, and 2-pole combustible gases are categorized as Class B fire hazards.
2 - the main factors affecting the explosion limit of combustible gases are:
(1) temperature The higher the original temperature of the explosive mixture, the lower limit of the lower explosive limit, the upper limit of the upper limit of the upper limit of the explosive limit of the expansion of the range of explosive hazards increase;
(2) oxygen content of oxygen content in the mixture, the explosion limit of the expansion of the range of the explosive limit of the upper limit of the upper limit of the upper limit of the explosion in particular to increase more. Such as acetylene, the explosion limit in air 2.2 ~ 31%, in oxygen 2.8 ~ 93%;
(3) inert media If the explosive mixture mixed with non-combustible inert gases (such as nitrogen, carbon dioxide, argon, etc.), with the increase in the percentage of inert gases, the range of explosion limits narrowed. When the concentration of inert gases increased to a certain value, the explosive nature of the mixture can disappear. Usually inert gases on the upper limit of the explosion of the mixture than the lower limit of the impact is more significant;
(4) pressure The initial pressure of the mixture has a great impact on the explosion limit. Pressure increases, the explosion limit range is also expanded, in particular, the upper limit of the explosion increased significantly. When the pressure drops to a certain value, the lower limit and the upper limit of the re-synthesis of a point, the pressure is further reduced, the mixture will become non-explosive material. Explosive limit range is reduced to zero when the pressure is called the explosion of the critical pressure;
(5) container The smaller the diameter of the container, the smaller the explosive limit range of the mixture. When the container diameter or flame channel is small to a certain value, the explosion can be eliminated, the diameter is called the critical diameter or the maximum fire spacing;
(6) energy The higher the intensity of the energy, the greater the heating area, the longer the action, the wider the range of explosive limits.
(7) In addition, light also has an impact on the explosion limit.
Two, combustible liquids
Combustible liquids refers to fire, heat or contact with oxidizers can burn the liquid. Most of the liquid combustion form is the liquid is heated to form a flammable vapor, mixed with air according to the gas combustion mode. The flame on the surface of the liquid to the liquid within the heat transfer is mainly through convection and conduction two ways.
1-flash ignition and flash point of combustible liquids When the temperature of combustible liquids is not high, a small amount of combustible vapors on the surface of the liquid mixed with air, due to meet the ignition source and the occurrence of a flash that is extinguished (continuation of the time is less than 5 seconds) of the combustion phenomenon, known as flash ignition. The lowest temperature at which flash ignition occurs in a flammable liquid is called the flash point of the flammable liquid.
2-Classification of flammable liquids: National standard GB6944-86 flammable liquids are divided into: low flash point liquids (-18 ℃); flash point liquids (-18 ℃ (23 ℃); high flash point liquids (23 ℃ ~ 61 ℃). The lower the flash point of a flammable liquid, the easier it is to catch fire and burn. The flash point of a mixture of two flammable liquids, generally located between the flash point of the original two liquids, and lower than the average of the flash point of the two.
3-liquid flame mainly boiling flame, spattering flame and jet flame.
Three, combustible solids
Combustible solids refers to fire, heat, moisture, impact, friction, or contact with oxidizing agents can burn the solid material. The combustion process of different solid substances are not the same. Low melting point of the solid combustion process is the first heat melting, and then evaporation of steam and decomposition of oxygen, such as asphalt, paraffin, rosin, sulfur, phosphorus, etc.; complex solid combustion process is the direct decomposition of the gaseous precipitation products, and then oxidized and burned, such as wood, paper, coal, plastics, man-made fibers, etc..
Four, explosive dust
Explosive dust refers to the uniform mixing with air to reach the explosion limit, when the ignition source can explode the dust.
1-Classification has been found in the following seven categories of explosive dust:
(1) metal such as magnesium powder, aluminum powder, manganese powder;
(2) coal such as activated charcoal, coal, etc.;
(3) grains such as starch, flour, etc.;
(4) synthetic materials such as dyes, plastics;
(5) feed such as fish meal, blood meal
(6) agricultural by-products, such as tobacco, cotton;
(7) forest products, such as paper meal, wood flour, and so on.
Common flammable and explosive gases whichOur daily common flammable gases are: natural gas, liquefied petroleum gas, methane, gas, gas
1, natural gas
Natural gas is the remains of ancient organisms long-term deposition of underground, slowly transformed and metamorphic cracking and the production of gaseous hydrocarbons, with flammability, more in the oilfield mining crude oil accompanied by out.
Natural gas is mainly composed of methane, but also contains a small amount of ethane, butane, pentane, carbon dioxide, carbon monoxide, hydrogen sulfide and so on. With a specific gravity of 0.65, it is lighter than air, colorless, odorless, and non-toxic. Natural gas companies follow government regulations to add odorants so that customers can smell it.
Lighter than air, the general way we install is 30-60cm above the ceiling, heavier than air, installed in the lower 30-60cm.
General applications of natural gas are:
Civilian fuel: natural gas is cheap, high calorific value, safety performance, environmental performance is good, is the first choice of civilian gas fuel.
Industrial fuel: natural gas is used instead of coal for factory heating, boilers for production and gas turbine boilers for thermal power plants.
(3) process production: such as baking paint production line, tobacco drying, asphalt heating insulation, etc.
2, liquefied petroleum gas
Liquefied petroleum gas is derived from petroleum processing or oil, natural gas extraction process, its main components are propane, propylene, butane and butene. Gaseous LPG is heavier than air, and its specific gravity is 1.5-2 times that of air.
LPG has an anesthetic effect on the human central nervous system when its concentration is high in the air, and produces toxic gases such as carbon monoxide if it is not burned completely. LPG plus has a special odor, once the leak can be detected. LPG mixed with air is flammable and explosive, when the concentration of LPG in the air reaches 1.5-9.5%, it will explode when it encounters a fire, so it must be prevented from leaking. When LPG burns completely, it requires a large amount of air to fuel the combustion.
3, biogas
Biogas is a combustible gas produced by the action of biogas bacteria in the isolation of organic matter in the air and a certain temperature, humidity, acidity, alkalinity and other conditions. Since this gas was first found in swamps, it is called biogas. The main component of biogas is methane, and the rest is carbon dioxide, oxygen, nitrogen and hydrogen sulfide. The methane content is about 55% to 70% and the carbon dioxide content is about 30% to 45%. Biogas is a mixture of gases.
4, gas
Methane, the main component of gas, is a flammable gas, colorless and odorless, insoluble in water, less dense than air, mixed with oxygen or air to a certain temperature in a certain space is prone to explosion.
5, gas
The main components of gas are carbon monoxide, hydrogen and alkanes, olefins, aromatics and so on. Gas is toxic because of the carbon monoxide, aromatics, etc. can be combined with hemoglobin in the human body, resulting in hypoxia, causing unconsciousness or even death, in low concentrations can also make people dizzy, nausea and dehydration. Therefore, the use of gas to be particularly careful, should always check the pipeline, stove and the valve, each time after the use of the valve should be closed tightly to prevent leakage.