Fire and explosion safety technology, is a door in order to prevent fire and explosion accident of the integrated technology, involving a variety of engineering disciplines, a wide range, complicated technology. Fire and explosion is the archenemy of safe production, once happen, extremely easy to cause heavy casualties and loss of property. Therefore, must carry out " give priority to in case, to eliminate supplement" the work principle of fire prevention and control, strict control and management of various hazards and fire source, eliminating the risk factors, the fire and explosion hazard control in a minimum range; fire accident, workers can quickly evacuate from the dangerous area, safety evacuation, while at the same time to timely and effectively the fire spread, prevention and disaster.
One, ignition, combustion point and flash point
Fire and explosion is formed, and the combustible ignition point and flash point, closely related to nature. To understand this aspect the knowledge, to help prevent the occurrence of fire and explosion.
( a ). Ignition of combustible material is heated to the occurrence of spontaneous combustion is the lowest temperature. At this temperature, combustible material in contact with air, without open fire role, to be able to burn.
( two) spontaneous ignition point. Material of spontaneous ignition point is lower, the fire risk is greater. However, the autoignition material is not fixed, but with the pressure, temperature and heat dissipation condition different have corresponding change. For example, gasoline combustion point at 0.1 MPa ( 1 kgf / cm2) to 480, 1 MPa ( 25 kgf / cm2) to 250. General pressure is higher, the lower combustion point. Combustible gas in the compressor is relatively easy explosion, is one of the reasons for the high pressure combustion point reduces.
Flash point ( three). The flash point of flammable and combustible liquid volatile vapor and air to form a mixture, when fire occurs the minimum temperature in internal combustion.
Flashover occurs usually blue sparks, but a death. This is because, in the flash point of flammable and combustible liquid evaporating at slow speed, evaporation from the vapor can only maintain a moment of combustion, too late to add new vapor, cannot continue to burn. From the viewpoint of flashover is fire, fire aura, in the fire codes of related substances in dangerous grade classification, is subject to flash.
Two, combustion and explosion
To prevent fire and explosion, fire and explosion technology correctly, need to understand the basic principles of formation of combustion and explosion.
( a ) burning. Combustion of combustible material with air or oxidizer to react exothermically, luminous phenomena. In production and life, often causes beyond effective range against the will of the people is the fire burning. Combustion must have the following three basic conditions.
1 all the oxygen in the air or other oxidant to produce severe reaction material, are referred to as fuel. Such as wood, paper, metal magnesium, sodium metal, gasoline, ethanol, hydrogen, acetylene and liquefied petroleum.
2 combustion. Who can help and support burning material, are referred to as oxidizer. Such as the oxidation of potassium chlorate, potassium permanganate, sodium peroxide as oxidant. Because the air contains about 21% oxygen, so the combustion of combustible material can persist in the air for.
3 fire. All that can be caused by the combustion of combustible material thermal energy, are known as the fire. Such as fire, electric spark, focusing sunlight, high temperature burning body, as well as chemical and mechanical impact energy.
To prevent the above three conditions exist at the same time, avoid the interaction, is the basic requirement of fire protection technology.
( two) explosion. Matter is composed of a state rapidly transformed into another state, and in a very short time to mechanical power in the form of emit huge amounts of energy, or gas in a very short time drastic expansion, pressure drops quickly to normal phenomenon, are known as the explosion. Explosion can be divided into chemical explosion and physical explosion two.
1 Chemical explosion. The material due to a chemical reaction occurs, producing large amounts of gas and heat and the formation of explosive. The explosion can directly cause fire. According to its chemical reactions can be divided into the following three types:
( 1) simple explosion. For example, the explosive acetylene copper and silver acetylide and suffered a slight vibration of explosion.
( 2) complex explosive decomposition. Belong to this type of explosives, explosives picric acid, nitrocellulose and nitroglycerin.
( 3) mixed explosive explosion. Here refers to the combustible gas, steam or dust and air ( or oxygen ) uniformly mixed in a certain proportion, reach a certain concentration, the formation of explosive mixtures encountered fire and explosion.
2 physical explosion. Usually refers to the boiler, pressure container or bottle material as heat, impact factor, causes the expansion of gases, a steep increase in pressure, over the equipment can withstand the mechanical strength of the explosion.
( three) the explosion limit. The combustible gas, steam and dust and air ( or oxygen ) mixture, in a certain concentration range of explosion. Explosive mixture can explode at the lowest concentration, known as the lower explosion limit explosion; to the highest concentration, known as the upper explosive limit. Between the lower explosive limit and range, called the explosion limit. The explosion limit of flammable gas or vapor in the mixture, usually expressed as a percentage of combustible dust; the explosion limit, to the mixture in the weight ratio of ( g / M ) said. For example, acetylene and air mixture explosion limit ( 2.281% aluminum method, lower explosion limit of 35 g / m. Apparently, the lower the combustible material explosion limit, explosion limit range is wide, the greater is the danger of explosion. Influence factors of explosion limit of lot. Explosive mixture temperature is high, the greater the pressure, the oxygen content is higher, and fire energy large, will make the explosion limit range expansion. Several kinds of combustible gas mixture of oxygen and air respectively, explosion limit. Combustible gas and oxygen mixture explosion is mixed with the air blast range. So it is more danger of explosion.
Three, dangerous chemical substances classification
Hazardous material variety, has its own physical, chemical reaction. There are many chemicals in the heat, friction, impact, vibration, exposure to fire, sunlight exposure, exposure to air and other conditions, can cause combustion, explosion, corrosion and poisoning accident. These chemical dangerous goods depending on their properties, morphology and accident risk degree, in our current law, roughly divided into the following ten categories:
The first category, explosive substances. Explosive substances subject to heat, friction, impact, vibration or the effects of certain substances stimulate action, can react vigorously, produce large amounts of gas and heat, gas volume increased sharply, pressure increases, causing the explosion.
Second, oxidizing agent. Oxidizing agent according to their chemical composition can be divided into inorganic oxidizer and organic oxidizer. Two kinds of oxidants in the oxidizability intensity is divided into a, level two two.
Third, combustible gas. Combustible gas explosion lower limit according to its concentration, is divided into a, level two two.
Fourth, spontaneous combustible substance. Spontaneous combustible substance, is divided into two two levels.
Fifth, water burning material. Water combustion substances according to their level of risk is divided into a, level two two.
Sixth, flammable and combustible liquids. Flammable and combustible liquids according to its flash point, is divided into two two levels.
Seventh, flammable and combustible solid. Flammable and combustible solid according to their level of risk is divided into a, level two two.
Eighth, toxic substances. Toxic substances according to their nature is divided into the following 4 types: ( 1) inorganic toxic substance; ( 2) the organic toxic substance; ( 3) inorganic toxic substances; ( 4) toxic organic substances.
Ninth, corrosive substances.
Tenth, radioactive substances.
Four, flammable and explosive substances
Fire and explosion prevention work has very strong specific aim, must have a definite object in view of, ability obtains result. A very important point, is to identify the features of a flammable and explosive substances.
( a ) the combustible gas. Refers to any fire, heat or when the oxidant exposure to fire, explosion gas. According to the lower explosive limit of different, divided into two levels. A combustible gas, explosion concentration limit for less than 10% of the combustible gas. For example, hydrogen, methane, ethylene, acetylene, ethylene oxide, vinyl chloride, hydrogen sulfide, water gas and natural gas, the vast majority of.
Class two flammable gas explosion lower limit is equal to the concentration and more than 10% of the combustible gas. For example, ammonia, carbon monoxide and producer gas and a small number of combustible gas. In the actual production, storage and use, will be a combustible gas to a fire hazard, two levels of combustible gas to class B fire hazards.
( two) the combustible dust. Those tiny particles, can occur in fire combustion, explosion of solid material, is called a combustible dust. For example, in the processing of hemp, tobacco, sugar, corn, sulfur, aluminum and other material process, crushing, grinding, screening and other operations by the dust, on its physicochemical properties, than the original generating material fire risk is much greater, under certain conditions to be able to explode. Combustible dust explosion must have three conditions: ( 1) the dust itself with explosive dust; ( 2 ) to be suspended in the air is mixed with the air reaches the explosion limit; ( 3) there is sufficient to cause the dust explosion heat energy.
( three) spontaneous combustible substance. Those who do not need an external source, and air oxidation or by outside temperature, humidity, heat and thermal dispersion can achieve spontaneous combustion caused by combustion of the material, are called spontaneous combustible substance. Spontaneous combustible substance according to the occurrence of spontaneous combustion of difficult easy degree is divided into two levels. The level of spontaneous physical, chemistry is more lively, easy oxidation in air decomposition, liable to spontaneous combustion, and combustion are violent, dangerous. Such as phosphorus, three tetraethyl lead, nitrocellulose and metal solvent. Two stage combustion material, oxidation in air is relatively slow, spontaneous ignition point is low, the heat accumulation is not scattered conditions to spontaneous combustion. Such as paper, linoleum and other articles containing oil. In the actual production, storage and use, will be a pyrophoric material into a fire hazard, two stage combustion material classified as class B fire hazards.
( four) the water burning material. Who can produce severe reaction with water emit flammable gases, at the same time to release a large quantity of heat, so that the gas temperature soared to spontaneous ignition point, thus cause burning explosive substances, are known as the water burning material. Water burning material by water or moisture after the reaction intensity and damage size, divided into two levels.
A water burning material, with water or acid reaction speed, can release a large number of flammable gas, heat, extremely easy to cause spontaneous combustion or explosion. Such as lithium, sodium, potassium, rubidium, cesium, strontium, barium and metal hydride.
Two stage water burning material, with water or acid reaction at a relatively slow speed, heat is relatively small, the combustible gas, general need for water contact, can occur in the combustion or explosion. Calcium metal, such as aluminum hydride, potassium borohydride, such as zinc powder.
In the actual production, storage and use, the water burning material into a fire hazards.
( five) the burning of liquid. Any fire, heat or and oxidant exposure to combustion and explosion of liquid, are known as the combustion of liquid. Combustion of liquid according to its flash point size, divided into flammable and combustible liquid two.
1 of flammable liquids. Means the flash point is equal to and less than 45 of the burning liquid. The fluid is divided into two levels.
A flammable liquid, the flash point of flammable liquid that is less than 28. Such as gasoline, alcohol, acetone and benzene.
Class two flammable liquid, a flash point between 28 ~ 45 of the flammable liquid. Such as kerosene, turpentine. Acetic acid.
2 combustible liquids. Means the flash point is higher than the 45 combustion of liquid. Such as alcohol, diesel oil, ethylene glycol, such as benzene.
In the actual production, storage and use, will be a flammable liquid into a fire hazards; class two flammable and combustible liquid flash point below 60 classified as class B fire hazards; combustible liquids and flash point is equal to and above the 60 classified as class C fire hazards.
( six) the combustion of solid. Where the fire, heat, impact, friction and oxidant exposure to combustion of solid material, collectively referred to as the combustion of solid. The combustion of solid according to its melting point, ignition point or point of different height, divided into flammable and combustible solid two.
1 flammable solids. A high melting solid ( ignition point below 300 ), low melting solid ( flash point below 100 ), and as the chemical raw materials and products using the combustion of solid. According to its combustion easy degree is divided into two levels.
A flammable solid, low ignition, easy combustion or explosion, and the combustion speed, and can emit toxic gases. They generally are items : 1 phosphorus and phosphorus compounds, such as phosphorus, three phosphorus sulfide; the nitro compounds, such as the two TNT, two nitronaphthalene; the other, such as nitrogen in 12.5% following the nitrocellulose, sodium amide, diazo benzene ammonia base, flash powder.
Class two flammable solid, combustion performance than a flammable solid, slower burning, burning to produce less toxicity. They generally include the following items: a variety of metal powder, such as magnesium powder, aluminum powder, manganese powder. The alkali metal amides, such as lithium amide, amino - calcium. The nitro compounds, such as nitro aromatics, nitro propane two. The nitrocellulose products, such as nitrocellulose varnished, celluloid. The naphthalene and its derivatives, such as naphthalene, methylnaphthalene etc.. The other, such as sulfur, rosin, such as pom.
2 solid combustible. A high melting solid ( ignition in 300 above ), low melting solid ( flash point in more than 100 ), and as the chemical raw materials and products using the combustion of solid, and lighted in 300 following the natural fiber and its agricultural and sideline products.
In the actual production, storage and use, will be a flammable solid into a fire hazards, class two flammable solid classified as class B fire hazardous, flammable solid is classified as class C fire hazards.
In five, fire, explosion
In general, the fire, the cause of the explosion has the following nine aspects.
( a ) and improper management. Both the production of fire ( such as welding, forging, casting and heat treatment technology on fire ), still life ( such as smoking, use of stoves etc.), fire management.
( two) flammable materials management, warehouse does not conform to the standard, not according to the properties of substances classified storage. For example, the nature of conflicting chemicals together, fire fighting requirements of different substances are put together, the water burning material in wet locations.
( three) electrical equipment insulation failure, installation does not meet the standard requirement, short circuit, overload, excessive contact resistance etc..
( four) layout unreasonable, inflammable and explosive places without corresponding measures of explosion protection, lack of equipment maintenance, maintenance, repair or inferior quality.
( five) the violation of safety rules, so that the equipment of super Wen Chao press